Study on the mechanical performance of lightweight arched prefabricated structures in large-span cut-and-cover tunnels

Study on the mechanical performance of lightweight arched prefabricated structures in large-span cut-and-cover tunnels | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Study on the mechanical performance of lightweight arched prefabricated structures in large-span cut-and-cover tunnels Zhanglong Xu, Zhi Lin, Xiande Guo, Wanlin Feng, Xiaoying Gou This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7052054/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract An innovative composite-jointed arch structure is proposed to address construction challenges such as slow progress, high precision requirements, and elevated costs encountered in the large-span prefabricated cut-and-cover tunnel project of Xinsen Avenue in Chongqing. The study incorporates theoretical analyses, field tests, and nonlinear numerical simulations to examine the mechanical properties, deformation characteristics, load-bearing mechanisms, and failure modes of prefabricated hollow structures compared to solid structures. Results indicate the newly developed composite-jointed arch structure exhibits excellent load-bearing capacity. The structure forms a two-hinged arch system, where grout-keyed joints at the inverted arch and rubble-concrete sidewall backfills collectively ensure horizontal and vertical stability, maintaining overall structural integrity. Composite joints efficiently transfer internal forces, ensuring coordinated deformation of components. Although hollow structures experience increased stress and deformation due to reduced stiffness and sectional discontinuity-induced stress concentration, both solid and hollow structures exhibit typical four-hinged failure mechanisms under ultimate loading conditions without significant degradation of ultimate load-bearing capacity. Current thin-walled hollow components effectively balance weight reduction with structural safety, significantly enhance concrete temperature control efficiency, shorten lifting periods, optimize construction efficiency and economic indicators, and promote broader application and development of prefabricated techniques in underground engineering. Physical sciences/Engineering Physical sciences/Materials science Lightweight prefabricated arch cut-and-cover tunnel soil–structure interaction bearing characteristic failure mechanism Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 1. Introduction Prefabricated construction—widely regarded as a hallmark of industrialized building—has attracted intense attention in recent years and now shows remarkable growth potential across the construction sector [ 1 , 2 ]. Compared with cast-in-place structures, prefabrication offers clear advantages—including shorter schedules and lower labor intensity [ 3 , 4 ], reduced material waste [ 5 ], higher energy efficiency [ 6 ], and diminished air- and noise-borne pollution [ 7 ]—thereby boosting productivity and quality while cutting costs and environmental impact. These benefits have been confirmed in many projects. The method is also gaining traction in underground construction, where China’s rapid urbanization has further highlighted its value [ 8 ]. Internationally, Russia, the Netherlands, France, Japan and others have applied prefabrication to underground works and amassed considerable experience [ 9 – 11 ]. Notable examples include Minsk Metro’s large-span segmental arches (1985) [ 12 ], Tokyo’s precast-beam underground reservoir (1998) [ 13 ], Rotterdam Metro’s “shell tunnel” with high-precision waterproof joints (1986) [ 14 ], and France’s Obel Station, where prefabricated arches were placed under NATM conditions [ 15 , 16 ]. Within China, the approach is now advancing rapidly. The Yuanjiadian Station in Changchun—the nation’s first fully prefabricated metro station—has provided an influential benchmark [ 17 , 18 ]. Extensive domestic research on design, performance, and construction technology [ 19 – 22 ] has laid a solid theoretical foundation for further underground use. Coupling prefabrication with hollow components is an emerging trend. Hollow sections lighten dead weight, simplify transport and erection, and can even enhance ductility and hysteretic energy dissipation [ 23 , 24 ]. In recent years, the same concept has migrated underground. In industrial and residential buildings, Lee et al. [ 25 ] and Park et al. [ 26 ] showed that prestressed hollow slabs outperform conventional members in bending and shear while offering superior quality control, lower labor cost, and shorter build time. In recent years, the same concept has migrated underground. For the first large underground station in China built entirely from prefabrication—the Changchun Metro Line 2—Han et al. [ 27 ] and Yang et al. [ 28 ] analyzed stress distribution in novel twin-cell thin-walled components under various load states. Tao et al. [ 29 ] later clarified the bearing capacity and failure mechanisms of such thin-walled stations and confirmed their sound load-bearing and deformation performance. Qiu et al. [ 30 ] performed full-scale tests on stations using precast hollow components (PHC) and showed that optimized void-to-section ratios enable PHC to satisfy design demands. Although significant progress has been made—especially in marrying prefabrication with hollow-weight-reduction technology—reports on large-span, cut-and-cover highway tunnels featuring thin-walled closed cavities remain scarce. Key gaps include (1) limited understanding of load-bearing behavior in large-span hollow arches, (2) insufficient data on their mechanical and deformation characteristics, and (3) inadequate insight into failure mechanisms under ultimate loading. These challenges underscore the need for comprehensive studies on the mechanics and design optimization of prefabricated hollow structures in large tunnels. Priority topics include soil–structure interaction, joint mechanics, and real-world failure modes. Results will help unlock the energy-saving potential of lightweight prefabrication and provide actionable guidance for design and construction. Taking Chongqing’s large-span Xinsen Avenue cut-and-cover tunnel as a case study, this paper investigates the load-bearing behavior and failure mechanisms of its prefabricated arch. The remainder of the article is organized as follows: Section 2 describes the project and the experimental segment; Section 3 outlines the finite-element model and parameter sensitivity analysis, validated with field data; Section 4 compares hollow and solid arches in terms of mechanics, deformation, and failure; Section 5 presents conclusions, engineering recommendations, and future research directions. 2. Engineering background This study examines the application and innovation of prefabricated assembly technology in large-span cut-and-cover tunnel structures through a case study of the bi-directional eight-lane tunnel project on Xinsen Avenue in Chongqing’s Hi-Tech Zone. As the zone’s primary north-south arterial corridor, Xinsen Avenue spans 2.5 km, with 790 m constituting a tunnel section featuring a single-bore clear width of 16.5 m, vertical clearance of 9.8 m, and geotechnically challenging Class V surrounding rock conditions (Fig. 1(a)-(b)). A predominantly silty clay soil cover, 0.5 to 4.8 m thick, overlies the tunnel; beneath this cover, the bedrock consists of mudstone and sandstone. The construction methodology combines underground mining with open-cut techniques, the latter utilizing precast components along a 445 m assembly segment (K1+255 to K1+700). This segment exhibits backfill soil thicknesses varying between 7 m and 12 m. Excavation of the side slopes creates embankments with heights ranging from 4.6 to 17.2 m on the left and from 3.2 to 13.2 m on the right. Since excavation removes any pre-existing fissures, slope stability is governed primarily by the inherent strength of the rock mass. To enhance foundation adaptability and streamline construction processes, the open-cut segment incorporates a hybrid structural system integrating a cast-in-situ inverted arch with precast arch segments. The standardized ring system, divided into 2 m segments, consists of 417 rings (208 left-side and 209 right-side units). Each ring features two symmetrical precast elements (Blocks A and B) and a cast-in-situ inverted arch (Block C), as shown in Fig. 1(c)-(e). Precast components adopt a lightweight closed-cavity thin-walled design, substantially improving construction efficiency. Inter-element connections utilize grout-augmented mortise-tenon joints to eliminate gaps. The Block A-B interface incorporates dual prestressed tension-locking systems to guarantee structural load capacity and waterproofing performance, whereas Block A-C/B-C joints integrate externally anchored restraint systems compliant with arch mechanics principles (Fig. 2). Longitudinal joints employ continuous-seam assembly with sequentially tensioned prestressed steel bars using a relay-stressing method, ensuring structural continuity and watertight integrity (Fig. 3). Notably, the project pioneers a mortise-tenon joint system at the vault interface of precast arch rings, combined with comprehensive investigations into key design and construction parameters. Key parameters encompass joint topology optimization, high-precision mold fabrication, mass-reduction strategies for large-curvature components, logistics for oversized element transportation-assembly workflows, and waterproofing system design. Comparative analyses indicate that mortise-tenon joint-equipped precast tunnels exhibit enhanced construction quality, operational efficiency, and safety performance compared to cast-in-situ linings, thereby improving labor efficiency, material utilization, and carbon footprint reduction. However, unresolved challenges—including intricate production workflows, stringent assembly tolerances, and cost inflation—highlight the need for advancements in joint mechanical behavior and standardized construction protocols. To meet the demands of the ultra-large span and high loading conditions of the Xinsen Avenue prefabricated tunnel, our research team innovatively proposed a "prefabricated + cast-in-place" construction method for a "two-hinged arch" structural system, as shown in Fig. 4 (a). The crown sections A and B of the tunnel utilize prefabricated assembly technology to enhance construction efficiency, while the inverted arch section C retains the cast-in-place process to ensure deformation coordination with the foundation. The crown AB joint employs a composite wet joint, as shown in Fig. 4 (b), to form a rigid connection, while the arch-springing AC/BC joints adopt grouted keyed joints, as illustrated in Fig. 4 (c), to balance structural stiffness and construction tolerances. This solution integrates the high efficiency of prefabricated assembly with the overall integrity of cast-in-place joints, significantly enhancing the structure's high reliability under backfilling and loading conditions. Five key innovations distinguish the “composite joint” from classical mortise–tenon schemes: (1) tolerating ±10 mm of fabrication error, thus lowering mold precision by 30 % and eliminating custom trolleys; (2) replacing extended starter bars with indirect laps via ring bars, which simplifies transport; (3) shortening lap lengths and post-cast strip widths; (4) doubling steel at the joint plus transverse bars to raise load capacity; and (5) stiffening the vault so arch-foot loads fall, making simpler slot-type hinges feasible. 3. Numerical model 3.1 Finite element model Based on the assembly and backfilling construction process of the open-cut prefabricated tunnel with composite joints, a three-dimensional solid-contact computational model established according to the strata-structure interaction mode (Fig. 5 (a)) is used to focus on revealing the mechanical response of the composite joint system under progressive backfilling loads. The backfill height is determined based on the maximum design burial depth of 12 meters. The prefabricated structural model consists of three components—A, B, and C blocks—as well as the composite cast-in-place concrete and main reinforcement bars. (Fig. 5 (b)). To simplify the model and computational work, the calculation model is based on a single ring (with a ring width of 2 m). The overall dimensions of the model are 140 m × 50 m × 2 m; the mesh type is identical to that used in Section 4.1, resulting in 110 982 elements and 137 834 nodes. 3.1.1 Assumptions The assumptions for the computational model in this paper are as follows: 1) Longitudinal effects of the structure are not considered. 2) Assembly errors and precision of the structure are not taken into account. 3) Slippage of reinforcement bars is not considered. 4) Groundwater effects are not considered, due to the scarcity of groundwater within the drilling depth near the tunnel site. 3.1.2 Material properties 1. Surrounding soil Soils are commonly treated either as purely elastic media—appropriate for small-strain porous materials—or as elastic-plastic media when hydrostatic pressure sensitivity is significant. Accordingly, all soil layers were modelled with the Mohr–Coulomb elastic-plastic formulation. Parameters derived from site testing are shown in Table 1. Table 1 Related mechanical parameters of surrounding soil. stratum Young’s modulus E (MPa) Poisson’s ratio υ Unit weight γ (kN/m 3 ) Cohesion c (kPa) Internal-friction angle φ (◦) Backfill 12.6 0.4 19.5 10-40 22 Silty clay 8.68 0.3 22.7 12.8 12.8 Mudstone 783.3 0.34 24.56 299 28.91 2. Precast components and internal concrete All precast blocks and the post-cast concrete at composite joints were assigned C50 concrete governed by the Concrete-Damaged Plasticity (CDP) model. Rebars were modelled as HRB400 steel with an ideal elastic–plastic law, and bond–slip was neglected. Side-wall backfill behaves as a fluid with E = 1 Pa until set, after which it adopts C25 concrete properties. Relevant parameters appear in Table 2. Table 2 Material parameters of the concrete and the reinforcement steel Material Young’s modulus E (MPa) Poisson’s ratio υ Density (kg/m³) Rubble concrete 15000 0.2 2244 C50 concrete 34500 0.2 2420 Reinforcement steel 200000 0.3 7850 The joint material is defined as C50 concrete, with the parameters for its plastic damage constitutive model derived from the stress-strain relationships specified in Appendix C of the Code for Design of Concrete Structures (GB 50010-2010 [31]). Fig. 6 illustrates the corresponding uniaxial stress-strain curves and damage factors under tension and compression. In this paper, relevant research and applications of concrete damage parameters from previous studies [32–34] are referenced. Consequently, the adopted input parameters are provided in Table 3. 3.1.3 Contact properties The embedded element technique is adopted to simulate the interaction between concrete and reinforcement. Additionally, there are three types of contact interactions among the entity components in the model. The first type involves the connection between the backfill soil layers and the layered backfilled rubble concrete, which is achieved through bonded constraints. The second type involves the contact between soil and structure, as well as between prefabricated components, using a Coulomb friction model, where the normal direction of contact surfaces was modeled with "hard" contact and friction defined via the "penalty" method with a friction coefficient of 0.6 [35, 36]; the third type addressed the interface between newly cast and existing concrete in composite cast-in-place sections, utilizing a cohesion-friction hybrid model whose specific parameters were determined according to AASHTO [37] and validated test results [38]. Table 3 Concrete-damaged plastic model input parameters. Ψ (◦) ξ σ b0 / σ c0 K c μ (s -1 ) 38° 0.1 1.16 0.6667 0.0005 3.1.4 Boundary conditions and staged loading The model boundaries restrict normal horizontal displacements on all sides and vertical displacements at the base. During backfilling, manual compaction is applied after each layer to ensure density and flatness. The compaction effect is equivalently modeled as horizontal additional earth pressure (2 k₀γh ᵢ), (where k₀ = 1−sinφ, lateral earth pressure coefficient; γ is soil unit weight, and hᵢ is the activated layer thickness.). The Geo static Stress module in ABAQUS incrementally activates these stresses to simulate the staged backfilling and compaction process. After the design backfill thickness of 12 m had been placed, a uniformly distributed surcharge was applied to the ground surface to study the failure mechanism of the two-hinged arch. Four surcharge levels—200 kPa, 600 kPa, 1 000 kPa and 1 200 kPa—were considered, simulating additional overburden thicknesses of roughly 10 m, 30 m, 50 m and 60 m, respectively (unit weight of mixed fill = 20 kN m⁻³). 3.2 Sensitivity analysis of critical modeling parameters 3.2.1 Soil–arch interface modelling strategy To accurately simulate the interaction between the prefabricated structure and surrounding soil in ABAQUS, two common modeling approaches are typically used. The first involves defining contact pairs with the Coulomb friction model to represent the mechanical behavior in the normal and tangential directions. The normal behavior is modeled as "hard" contact, while the tangential behavior follows the "penalty" friction formulation. The second approach uses a tie constraint, which couples nodes to enforce identical deformation between the structure and soil. To realistically capture the interaction between the prefabricated structure and the backfill soil, this study compares the calculation results of two contact relationships: a contact pair with an empirical friction coefficient of 0.6 and a tied constraint. The results are shown in Fig. 7. From Fig. 7, the following observations can be made: 1. At the arch crown, both contact models—tied constraint and friction contact—produce similar trends in bending moment and axial force, with only minor numerical differences. This suggests that the contact modeling strategy has minimal impact on the mechanical response at the crown. 2. At the arch haunch, compared with the tied constraint model, the friction contact model shows a 39.6% decrease in bending moment (from -968 kN·m to -585 kN·m) and a 32.7% increase in axial force (from -1835 kN to -2435 kN). 3. With the tied constraint model, the axial force difference between the crown and haunch is within 6%, indicating relatively uniform force distribution. However, with the friction contact model, the crown axial force is 28% lower than that at the haunch, reflecting the actual stress distribution in cut-and-cover tunnels more accurately. In conclusion, the results between the tied and friction contact models differ significantly. The friction contact model better represents sliding and friction effects at the soil–structure interface, resulting in a more realistic internal force distribution. Therefore, the Coulomb friction model is adopted in this study. 3.2.2 Hardening behaviour of rubble concrete In the actual construction process, a layered backfill technique using hardening rubble concrete is adopted. Each new layer is poured only after the previous layer has hardened to the design strength. To reflect this process, two models were compared—one considering the hardening process of the footing concrete (from liquid to solid) and one without. The elastic modulus is set to 1 Pa in the liquid phase and adjusted to C20-grade values after hardening, with a layer height of 1.5 m. The results are presented in Fig. 8. The findings are as follows: 1. The final differences in bending moment and axial force are small. Variations are mainly due to cumulative internal forces during the layered backfill process, warranting further analysis of the hardening effect during backfilling. 2. Before reaching 9.2 m (shoulder level), the model considering concrete hardening shows a slight decrease in crown bending moment due to horizontal pressure from the liquid concrete. The haunch moment remains negative and increases with fill height. In contrast, the model without hardening mainly bears self-weight and footing constraint forces, resulting in a nearly constant crown moment and a haunch moment that shifts from negative to positive, then decreases. 3. For axial forces, both models follow similar trends. However, at 10.8 m (shoulder level), the model with hardening shows a 25% higher crown force and 12% lower haunch force compared to the non-hardening model. In summary, the hardening behavior of rubble concrete significantly affects the internal force distribution and should be incorporated into detailed numerical simulations. 3.2.3 Layered backfill compaction load effects To ensure proper compaction and surface uniformity, each backfill layer is manually compacted after placement. Based on actual construction procedures, this study compares models that include and exclude compaction load effects. To simulate this, the compaction force is modeled as an additional horizontal earth pressure acting on the structure, calculated as 2 k 0 γh i , where k 0 =1−sinϕ (earth pressure coefficient at rest), γ is the unit weight of the soil, and h i is the thickness of the active layer. These pressures are applied using the Geostatic Stress feature in ABAQUS. The results are shown in Fig. 9. The key findings are: 1. Compared to the model without compaction, the axial forces differ by up to 10% at the crown and 2% at the haunch—both occurring after crown backfilling. The overall trend remains consistent. 2. Final bending moment results at the crown differ significantly. Including compaction increases the moment from 745 kN·m to 902 kN·m, a 21% rise. 3. After reaching 6 m (end of rubble concrete backfill), the crown moment decreases due to lateral compaction forces. After 9.2 m (shoulder level), vertical soil loads cause the crown moment to increase. In contrast, the model without compaction shows a continuous increase in crown moment after 6 m, with an accelerating trend. 4. At the haunch, both models exhibit similar moment trends with a maximum deviation of 12%. In conclusion, backfill compaction significantly affects internal force distribution. It tends to increase bending moments and reduce axial forces, potentially compromising structural safety. Therefore, the effects of compaction must be considered in the simulation. 3.3 Model Validation Considering the contact behavior between the backfill soil and structure, the hardening process of rubble concrete, and the compaction load during construction, a refined geotechnical-structural model was developed. To validate the numerical simulation results, long-term on-site monitoring was conducted on the composite joint structure of the Xinsen Avenue Tunnel. The primary monitoring items included concrete strain and reinforcement stress, as illustrated in the sensor layout in Fig. 10. For ease of analysis, the concrete strain values have been converted to stress values. Fig. 11 presents a comparison between the simulated values and field measurements for concrete stress, reinforcement stress, and relative deformation at the tunnel crown joint. In Fig. 11 (a), a comparison of simulated and monitored concrete stress is shown. During construction, compressive stress was observed on the water-facing side and tensile stress on the opposite side, which aligns with the simulation results. For monitoring point C1 (close to the water-facing side), the compressive stress increased with the accumulation of backfill, reaching a maximum of 0.74 MPa, while the simulated value reached 0.94 MPa, showing an increase of 27%. For monitoring point C2 (near the non-water-facing side), the tensile stress similarly increased with the fill height, reaching 0.27 MPa, while the simulated value was 0.32 MPa, an 18% increase. In the long term after top-backfilling, the overall trend of changes was consistent with the simulation. Fig. 11 (b) compares simulated and monitored reinforcement stress. It can be observed that the trends in both datasets align well. After ring assembly, under self-weight and construction loads, the compressive stress at monitoring point R1 (main longitudinal reinforcement near the water-facing side) increased, while R2 (on the non-water-facing side) showed tensile stress with a relatively lower magnitude. As layered backfilling progressed, stress in all monitored points increased gradually and then stabilized, maintaining a stress state of compression in the upper part and tension in the lower part. The maximum compressive stress at R1 was 13.57 MPa, which closely matches the simulated peak of 14.08 MPa. For R2, the difference between measured and calculated compressive stresses was within 5%. These results confirm that the upper reinforcement mainly experienced compression, while the lower reinforcement primarily bore lower tensile stresses, demonstrating good agreement between simulation and field observations. Fig. 11 (c) shows the relative deformation of the joint. The simulation and monitoring results followed similar trends. As construction progressed, the relative deformation increased from the start of ring assembly, peaking after completion of top backfilling. The rate of increase was similar between monitoring and simulation. During sidewall and haunch backfilling, the deformation growth was more moderate. The maximum measured deformation was 4.7 mm, while the simulated value was 5.4 mm, about 14.8% higher—mainly due to compaction modeling in the simulation. As backfilling was completed and disturbance reduced, the structure stabilized, and both measured and simulated deformation slightly decreased. This suggests that although minor differences exist, the overall trends are consistent, and the simulation effectively replicates deformation behavior during actual construction. In conclusion, the numerical results at critical locations show good agreement with field measurements, verifying the reliability and accuracy of the refined model. 4. Analysis of the results To further investigate the influence of internal cavity formation on structural deformation and mechanical performance, both cavity-structured and solid (non-cavity) models were designed for comparative analysis, as detailed in Table 4. Working Condition 1 (Case 1) examines the structural performance under self-weight after the precast elements are assembled into a ring. Working Condition 2 (Case 2) focuses on the structural response to the progressive backfilling of 21 m of soil (from tunnel arch springing to the backfill surface). Working Condition 3 (Case 3) applies a vertical uniform load on the top surface of the backfill to simulate the failure mechanism of the precast arch structure under ultimate loading conditions. Table 4 Staged construction loading analysis for structural models Model Cavity volume /m 3 Cavity ratio/% Analysis step Case 1 Case 2 Case 3 Cavity structure 8.8m 3 14% Gravity Gravity + 21m layered backfill soil load Gravity + 21m layered backfill soil load + Vertical uniform load Solid structure 0 0 4.1 Mechanical properties 4.1.1 Stress During the analysis, the maximum and minimum principal stress values and their corresponding locations were extracted to evaluate the stress state of the structure. The maximum principal stress identifies zones subjected to the greatest tensile forces, while the minimum principal stress highlights compressive stress zones. The results show that high stress concentrations are mainly located at the haunch areas of the arch. The inner haunches (points P3 and P5) are primarily under compressive stress, while the outer haunches (points P4 and P6) are subjected to tensile stress. The stress contour under 12 m of design backfill is shown in Fig. 12. Fig. 13 presents the evolution of stress during the transition from assembly to the end of backfilling. Though different key points exhibit varying amplitudes of stress change under identical burial depths, the overall trends are consistent. The solid structure consistently shows lower stress values at all key points compared to the cavity structure. At the crown of the arch, the monitoring point near the water-facing side (P2) is under compressive stress, while the back-facing side (P1) experiences tensile stress. After blocks A and B are assembled into a ring, a new integral structure is formed, which undergoes self-adaptive internal force redistribution under gravity. This results in compressive stress in the upper joints and tensile stress in the lower part. In the early stages of sidewall backfilling (0–6 m), stress at all points decreases, attributed to the sidewall concrete providing enhanced constraint on the arch foot. Between 6 m and 9 m depth, the stress stabilizes, indicating minor influence from the added backfill. As the top backfill progresses, the increased vertical load causes stress to rise across all points. Due to the internal cavity, the hollow structure experiences notable stress concentration, resulting in a significantly higher overall stress level than the solid structure. At the haunches, stress follows a similar trend to that at the crown. The haunch is primarily subjected to compressive forces. On the outer haunch side (P4, P6), tensile stresses are eventually transformed into compressive stresses due to lateral confinement from sidewall fill, which acts as lateral thrust. The inner haunch sides (P3, P5) mainly bear compressive stress. 4.1.2 Internal forces A total of 24 critical cross-sections were selected based on cavity layout and structural characteristics. These sections cover the major load-bearing regions of the structure, with numbering shown in Fig. 14(a). Internal force data from each section were extracted for a systematic investigation of structural response, providing reliable data support for subsequent structural optimization and performance assessment. Fig. 14 (b)–14(d) show the axial force, shear force, and bending moment for both the solid and cavity structures. The results demonstrate that the introduction of internal cavities effectively reduces axial force and shear force at most cross-sections. Specifically, the maximum axial force in the cavity structure is reduced by 142 kN compared to the solid structure, and the maximum shear force is reduced by 168 kN. However, the maximum bending moment in the cavity structure increases by 160 kN·m. The analysis indicates that incorporating cavities reduces the structure’s self-weight and thereby decreases axial and shear forces—contributing positively to structural load optimization. However, because the bending stiffness of the cavity structure is lower, it results in higher bending moments under the same earth pressure. This is particularly notable at the crown and side regions of the arch, where the solid structure demonstrates more uniform and lower bending moment distribution. In summary, rational cavity design can optimize self-weight distribution and improve internal force profiles to some extent. However, special attention should be given to regions with increased bending moment (such as the crown and arch shoulders) by enhancing their flexural stiffness. Meanwhile, in regions subject to lower forces (such as sidewalls and springings), the cavity ratio can be optimized to ensure both structural safety and stability. 4.2 Deformation analysis 4.2.1 Integral deformation of the structure Fig.15 illustrates the deformation patterns of the hollow and solid structures under load. It can be observed that the horizontal convergence at the arch waist and the vertical displacement at the arch crown follow similar trends. After the assembly is completed, the solid structure exhibits greater deformation due to its larger self-weight, whereas the hollow structure shows smaller initial deformation. During the lateral backfilling stage, the lateral thrust exerted by the fill material causes the deformation of the hollow structure to gradually exceed that of the solid structure. This phenomenon is attributed to the higher stiffness of the solid structure, which better resists external forces. As backfilling progresses—especially at the arch crown—the structural deformation accelerates. The deformation magnitude increases linearly with the fill thickness, and the displacement of the hollow structure consistently remains greater than that of the solid structure. This indicates that the hollow structure, due to its lower stiffness, is more susceptible to larger deformations during the backfilling process, while the solid structure exhibits smaller displacements. When the backfill reaches the design height, the structure experiences maximum deformation. At this point, the horizontal convergence and vertical displacement at the crown of the hollow structure are 2.14 mm and 7.21 mm respectively, whereas those of the solid structure are 1.75 mm and 6.83 mm, all of which are within the limits specified by the design code and still retain a considerable safety margin. According to the Code for Design of Concrete Structures, for structures with a span greater than 9 m, the allowable deflection limit for bending structures is l/300. With a crown span of 20,100 mm, the deflection limit for the crown is 67 mm. Furthermore, the peak displacement of the hollow structure exceeds that of the solid structure. The introduction of internal cavities increased the peak displacement by approximately 5.56%, while also enhancing the ultimate deformation capacity of the structure by the same proportion. 4.2.2 The opening deformation of the joints Under load conditions, relative displacement occurs between the two end faces of the joints. As illustrated in Fig. 16, the rotational angle of joints was calculated based on the horizontal displacement at the upper and lower edges of the joint. The measurement principle involves: 1. Tracking horizontal displacements (X₁-X₄) at four predefined measurement points, 2. Using the fixed vertical spacing (L) between paired points to compute two component angles (θ₁, θ₂) through trigonometric relations, 3. Summing the components to obtain the total joint rotation angle (θ). The calculation follows these equations: where X denotes horizontal displacement and L is the vertical distance between measurement points. This dual-angle approach accounts for both shear and bending deformations at the joint interface. Fig. 17 (a) shows the change in the opening angle of the crown joint (A-B) for both solid and hollow structures. It can be seen that under self-weight, the upper side of the A-B joint is compressed, while the lower side shows a slight opening tendency. Due to the greater self-weight of the solid structure, the initial joint opening at the arch crown is slightly larger than that of the hollow structure. As the sidewalls are backfilled layer by layer, the lateral confinement increases, causing a continuous reduction in the rotation angle of the joint, gradually closing the gap. The closure angle exhibits a linear trend during the initial stage. Between backfill heights of 6 m and 9 m, changes in the joint rotation angle are relatively small, indicating a stable state. When backfilling begins at the top, the joint rotation angle for both models increases again, reflecting a decrease in structural stiffness. Because the hollow structure has lower overall stiffness, its joint opening is consistently greater than that of the solid structure. After backfilling is complete, the rotation angles of the crown joint are 0.0134 for the solid structure and 0.0124 for the hollow structure. Although these values remain small, the inclusion of internal cavities results in an increase of approximately 8.06% in joint deformation. This suggests that even with cavities, the joints maintain stable performance under load. The internal cavities reduce structural self-weight while enhancing deformation adaptability and design flexibility—crucial for maintaining overall stability and improving force transfer between components. Fig. 17 (b) shows the rotation angle variation of the footing joints (A–C and B–C) under different backfill heights. The initial relative rotation angle is 0° for both joints, as self-weight was not considered for the footing. The A–C and B–C joints exhibit symmetric but opposite trends: A–C becomes compressed while B–C opens. This asymmetry arises from the uneven lateral load induced by staged backfilling, leading to non-uniform deformation in the footing area. As the backfill approaches the top of the footing, the A–C joint rotation stabilizes, while the B–C joint reaches its maximum. In the final backfilling stage, the relative rotation of both joints begins to shrink (absolute values decrease), with A–C returning close to its initial state and B–C showing significantly reduced opening. These trends indicate that the uniformly distributed load from the top enhances the lateral constraint at the joints, stabilizing the overall structure. In addition, the rotation angle changes of the hollow structure joints are consistently greater than those of the solid structure, especially during sidewall backfilling. This indicates that due to its lower stiffness, the hollow structure experiences more pronounced deformation under asymmetric loads. Although the inclusion of cavities slightly increases joint rotation, it reduces the structure’s self-weight and improves the deformation coordination among components. The hollow structure maintains good stability under load and provides greater flexibility for spatial and mechanical design optimization. 4.3 Analysis of failure mechanism of single-ring structure 4.3.1 Damage evolution of single-ring structure Fig. 18 illustrates the evolution of damage in the precast hollow arch structure during staged backfill loading. Overall, the distribution of tensile damage is limited. In the early stage, stress concentration occurs in the invert region with a variable cross-section, as shown in Fig. 18 (b), where several nearly through-cracks appear early. With increasing load, Fig. 18 (c) and (d) show that damage first occurs at the boundary between the cavity and solid parts, particularly at the haunches and shoulders, where cavities are introduced. Additionally, visible tensile damage emerges below the crown joint and on the upper surface of the invert. At the ultimate stage, stress concentrations become widespread in the invert, haunches, and crown, indicating severe structural damage overall, as depicted in Fig. 18 (e). Similarly, for compressive damage, the hollow arch first shows damage on the outer surface of the haunches and at the invert variable section (Fig. 18 (g)). As the load increases, Fig. 18 (h) and (i) show that the invert first develops a plastic hinge, followed by additional hinges at the left haunch and right side of the crown joint. At failure, four plastic hinges are observed—at the crown, both haunches, and invert (Fig. 18 (j))—consistent with the compression-dominated behavior of arch structures. Under the same conditions, Fig. 19 presents the damage evolution of the precast solid arch during staged backfilling. Fig. 19 (a)– (e) display the tensile damage, and Fig. 19 (f)–(j) show the compressive damage. Similar to the hollow structure, the solid arch primarily undergoes compressive damage, and the failure pattern also involves four plastic hinges at the crown, haunches, and invert. However, the sequence of hinge formation differs: in the hollow structure, hinges form in the order invert → left haunch → crown → right haunch, whereas in the solid structure, the order is invert → right haunch → left haunch → crown. This variation is attributed to the presence of enclosed cavities in the hollow design, which reduce stiffness and lead to faster damage development at the crown. 4.3.2 Damage analysis of key parts The damage behavior at the composite joint of the crown is similar for both hollow and solid structures. The schematic in Fig. 20 shows that after deformation, the crown settles downward, causing the composite slab joint to open. As loading increases, cracks form in the tensile zone beneath the post-cast concrete at the interface with old concrete. Under ultimate conditions, the upper compressive zone of the post-cast concrete is crushed, leading to global structural failure. Fig. 21 shows the damage mechanism of precast arched component A(B). This component carries both vertical and horizontal loads, resulting in complex and significant stresses. As the load increases, the structure bends downward, compressing the outer side and stretching the inner side of the crown joint’s post-cast concrete. The presence of enclosed cavities accelerates stiffness degradation, causing rapid arch deformation and failure. Horizontally, the haunch exterior experiences tensile failure, while the interior is primarily compressed. Although the damage location in the solid structure is similar, its ultimate deformation capacity is greater and load-bearing performance is superior. 4.4 Damage mechanism of single-ring structure Fig. 22 illustrates the three-stage deterioration process of both hollow and solid arch structures featuring composite crown joints. The progression of damage in the hollow arch can be summarized as follows: 1. Stage I (O–A–B): Elastic Stage At the early stage, the arch below the crown is embedded in backfill, and the surrounding soil exerts lateral confinement that effectively restrains deformation. Consequently, crown settlement remains negligible before point A. Once the backfill surpasses the crown elevation (segment A–B), settlement begins to increase approximately linearly, though the structure still behaves elastically. 2. Stage II (B–C–D): Progressive Damage Stage Damage initiates at point B when crown settlement reaches about 37 mm, primarily manifesting as minor cracking at the crown joint, haunches, and invert. This substage (IIa) is characterized by slow damage development without significant loss of stiffness. As settlement increases beyond approximately 86 mm at point C, a plastic hinge forms at the left haunch, marking the onset of rapid stiffness degradation and structural instability—defining substage IIb. 3. Stage III (Beyond Point D): Structural Failure Stage When crown settlement exceeds approximately 278 mm (point D), plastic hinges have fully formed at the crown and both haunches. Crown deflection escalates sharply, indicating structural collapse and complete loss of load-bearing capacity. Compared with the solid structure, the hollow arch exhibits an approximately 18% reduction in ultimate load-bearing capacity. However, it demonstrates significantly enhanced deformation capacity in earlier stages: crown settlement in the elastic stage (Stage I) increases by 68%, and deformation tolerance in substage IIa improves by 72%. Accordingly, a crown settlement limit of 86 mm is recommended for the design of hollow structures. To ensure that damage remains within the controllable and repairable range (Stage IIa), it is advisable to reinforce the haunch regions, strictly regulate the backfilling thickness and compaction, and set an early-warning threshold when crown settlement reaches approximately 37 mm. 5. Conclusions This study, grounded in the context of the Chongqing Xinsen Avenue open-cut long-span precast tunnel project, developed a refined soil-structure interaction model via finite element analysis (FEA). Through sensitivity analysis of key parameters and validation against field monitoring data, the model's accuracy was confirmed. A systematic assessment was conducted on the mechanical behavior and failure mechanism of a long-span precast hollow arch structure with composite joints, yielding the following main conclusions: Soil-structure friction, riprap concrete hardening, and layered compaction significantly influence internal force distribution. Neglecting compaction load can lead to over 20% underestimation of crown bending moment, highlighting the necessity of fine-grained calculations synchronized with actual construction stages. The combination of composite crown joints and grouted toe key joints forms a stable two-hinged arch load-bearing system. The high consistency between on-site monitoring and FEA results validates both the mechanical model and the proposed construction method. A 14% cavity ratio in the arch cross-section reduces peak axial force and shear force by 142 kN and 168 kN, respectively. Although local bending moment increases by approximately 160 kN·m, overall stresses remain within allowable design limits. The final horizontal convergence (2.14 mm) and vertical crown deflection (7.21 mm) are well below the l/300 span limit, even with a ~ 6% increase in peak displacement due to the hollow design. This indicates the structure retains sufficient safety redundancy. The ultimate bearing capacity of the hollow arch is only 18% lower than that of the solid arch. Both structures fail through a four-hinge mechanism at the crown, haunches, and invert, confirming that weight reduction does not significantly compromise safety. A crown settlement of 86 mm is recommended as the limit control value, with 37 mm as a warning threshold. To maintain structural integrity, reinforcement should be enhanced at the haunch and joint regions, and backfill layer thickness and compaction quality must be strictly controlled. Future work will focus on the long-term durability and seismic performance of composite joints, multi-objective optimization of cavity parameters, large-scale ultimate load testing of full-ring structures, and incorporation of life-cycle low-carbon economic assessments, aiming to develop a standardized, resilient, and environmentally friendly design system for precast arch structures. Declarations CRediT authorship contribution statement Zhanglong Xu: Investigation, Methodology, Data curation, Validation, Writing - Original Draft, Visualization. Zhi Lin: Supervision, Methodology, Funding acquisition, Project administration, Writing - Review & Editing. Xiande Guo: Data Curation, Writing – review & editing. Wanlin Feng: Formal analysis, Writing - Review & Editing. Xiaoying Gou: Investigation, Writing - Review & Editing. Declaration of Competing Interest The authors declare that they have no conflicts of interest related to this work. Acknowledgements The authors would like to acknowledge the financial support received from the National Natural Science Foundation of China (Grant numbers 52078089 and 52274176), the Chongqing Natural Science Foundation Innovation and Development Joint Fund (CSTB2022NSCQ-LZX0079), and the China Construction Seventh Bureau Science and Technology R & D Project(CSCEC7B-2022-Z-19). Data availability Data will be made available on request. Data requests should be addressed to the first author: Zhanglong Xu, [email protected] , College of Civil Engineering, Chongqing Jiaotong University. References Liu, G., Gu, T., Xu, P., Hong, J., Shrestha, A., & Martek, I., 2019. A production line-based carbon emission assessment model for prefabricated components in China. J. Cleaner Prod. 209, 30–39. Zhao, C., Zhang, Z., Wang, J., & Wang, B., 2019. Numerical and theoretical analysis on the mechanical properties of improved CP-GFRP splice sleeve. Thin-Walled Struct. 137, 487–501. 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Hu, M., Han, Q., Wu, S., et al., 2021. Shear capacity of precast concrete shear keys with ultrahigh-performance concrete for connections. J. Bridge Eng. 26(7): 04021036. AASHTO, 2012. LRFD Bridge Design Specifications. American Association of State Highway and Transportation Officials, Washington, DC. Jia, J., Ren, Z., Bai, Y., et al., 2023. Tensile behavior of UHPC wet joints for precast bridge deck panels. Eng. Struct. 282: 115826. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7052054","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":484156811,"identity":"d220a295-118f-477b-a4c6-1f36c15bd9d7","order_by":0,"name":"Zhanglong Xu","email":"","orcid":"","institution":"Chongqing Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Zhanglong","middleName":"","lastName":"Xu","suffix":""},{"id":484156812,"identity":"0f9c8166-d515-425c-9456-dfe5e025c1d7","order_by":1,"name":"Zhi 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1","display":"","copyAsset":false,"role":"figure","size":881759,"visible":true,"origin":"","legend":"\u003cp\u003eConstruction of the Chongqing Xinsen Avenue prefabricated highway tunnel.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/c2f7b8b99c4f472a5ea28540.png"},{"id":86804035,"identity":"f9cdfdb3-7a81-4ddf-899b-cddc090eebe6","added_by":"auto","created_at":"2025-07-15 17:40:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":414596,"visible":true,"origin":"","legend":"\u003cp\u003eLayout schematic and detailed construction drawings of various joint types.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/12912ac397168269c1ada325.png"},{"id":86804540,"identity":"0d506d5a-fa50-46b2-a4bc-90d5dfaf2bb5","added_by":"auto","created_at":"2025-07-15 17:48:37","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":274204,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of longitudinal prestressing tensioning and locking for the tunnel.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/623d43f566348e43bca08c78.png"},{"id":86804064,"identity":"954a8e45-7314-4b3d-889f-fc8ec1861599","added_by":"auto","created_at":"2025-07-15 17:40:38","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":526789,"visible":true,"origin":"","legend":"\u003cp\u003eComposition of structural members and node distribution of composite joints in the test section (unit: mm)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/2f1116a370ce7827db3b8c84.png"},{"id":86804543,"identity":"5819441d-8c86-46e2-87cc-d9767d135e5b","added_by":"auto","created_at":"2025-07-15 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strain.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/49a94e8dfc78321de61b34be.png"},{"id":86804545,"identity":"1789302c-f037-4891-b810-bf2053365c78","added_by":"auto","created_at":"2025-07-15 17:48:37","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":156539,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of friction contact and binding constraint models.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/70a56632beffdbd05b51bd7e.png"},{"id":86804033,"identity":"b9bdd8f9-031d-4811-a17b-29ad58876a5a","added_by":"auto","created_at":"2025-07-15 17:40:37","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":156155,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of models with and without rubble concrete 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12","display":"","copyAsset":false,"role":"figure","size":365493,"visible":true,"origin":"","legend":"\u003cp\u003eStress contours under 12m design backfill thickness.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/9c7b2bfc8177df6900ea0e11.png"},{"id":86804080,"identity":"e69a2e7b-8ed9-44d1-b7b8-7c45bd2ef096","added_by":"auto","created_at":"2025-07-15 17:40:39","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":201224,"visible":true,"origin":"","legend":"\u003cp\u003eStress change curves: (a) Maximum principal stress; (b) Minimum principal stress.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/827cb4c0840f8b47ef6a0dd3.png"},{"id":86804560,"identity":"834a7872-de84-4c60-abe3-3adba2d8a5c2","added_by":"auto","created_at":"2025-07-15 17:48:38","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":362180,"visible":true,"origin":"","legend":"\u003cp\u003eInternal forces of critical crosssections of the tunnel structure: (a) Distribution of the critical crosssections; (b) Axial force; (c) Shear force;(d) Bending moment.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/96d094e5fbe53f06986a3761.png"},{"id":86804043,"identity":"31cce1b7-d6f6-485f-a5f9-151db6a57c3c","added_by":"auto","created_at":"2025-07-15 17:40:37","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":304846,"visible":true,"origin":"","legend":"\u003cp\u003eDeformation of the arch structures: (a) Deformation contours under Case 2; (b) deformation change curves.\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/dd21310749268af86ba64267.png"},{"id":86804556,"identity":"c260c17a-3c41-4c71-ba44-b3f24f081023","added_by":"auto","created_at":"2025-07-15 17:48:38","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":104435,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of posture of joint deformation\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/25b578468e01032b06f1efc3.png"},{"id":86804041,"identity":"18359dad-09ff-4608-8404-a46a73c7b134","added_by":"auto","created_at":"2025-07-15 17:40:37","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":241271,"visible":true,"origin":"","legend":"\u003cp\u003eChange curves of joints opening: (a) A-B joint; (b) A-C joint and B-C joint.\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/d621bd1d747d8a2f0c19aa48.png"},{"id":86804558,"identity":"29539401-c720-410c-a210-646f4fc99113","added_by":"auto","created_at":"2025-07-15 17:48:38","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":458507,"visible":true,"origin":"","legend":"\u003cp\u003eTensile and compressive damage evolution of cavity structure during staged backfilling: (a) 12 m, (b) 40 m, (c) 60 m, (d) 95 m, (e) 102 m; (f) 12 m, (g) 40 m, (h) 60 m, (i) 95 m, (j) 102 m of backfill.\u003c/p\u003e","description":"","filename":"18.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/aee1877c2c466eb21a3a3b9e.png"},{"id":86804055,"identity":"7c9b2174-ad33-4f57-86b7-9ffb7cb6ab4b","added_by":"auto","created_at":"2025-07-15 17:40:38","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":407085,"visible":true,"origin":"","legend":"\u003cp\u003eTensile and compressive damage evolution of solid structure during staged backfilling: (a) 12 m, (b) 45 m, (c) 65 m, (d) 113 m, (e) 125 m, (f) 12 m, (g) 45 m, (h) 65 m, (i) 113 m, (j) 125 m of backfill.\u003c/p\u003e","description":"","filename":"19.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/bc7821b39037129291ad69c3.png"},{"id":86804098,"identity":"fe61321d-04fa-4661-93ad-91fa8abf476e","added_by":"auto","created_at":"2025-07-15 17:40:39","extension":"png","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":159406,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of damage mechanism of crown composite joint.\u003c/p\u003e","description":"","filename":"20.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/0070215b0f8c3590c9c52abb.png"},{"id":86804095,"identity":"f29c634b-d7f0-44d7-a2ea-ceeeddcfcb25","added_by":"auto","created_at":"2025-07-15 17:40:39","extension":"png","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":234814,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of damage mechanism of the precast A/B.\u003c/p\u003e","description":"","filename":"21.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/1a6305b8438b0b2627a625ce.png"},{"id":86804101,"identity":"1700b788-79dd-4821-89bd-78a9d0b4ad77","added_by":"auto","created_at":"2025-07-15 17:40:39","extension":"png","order_by":22,"title":"Figure 22","display":"","copyAsset":false,"role":"figure","size":202251,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between crown settlement and backfill depth for the arch with a composite crown joint.\u003c/p\u003e","description":"","filename":"22.png","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/c2275d42a46410993a8a4307.png"},{"id":91972797,"identity":"c62ab197-842f-47bf-93ad-8fa89e1ff084","added_by":"auto","created_at":"2025-09-23 09:24:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7335170,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7052054/v1/795b2a70-7c3f-401f-bcc6-8bc065b6b39b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on the mechanical performance of lightweight arched prefabricated structures in large-span cut-and-cover tunnels","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePrefabricated construction\u0026mdash;widely regarded as a hallmark of industrialized building\u0026mdash;has attracted intense attention in recent years and now shows remarkable growth potential across the construction sector [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Compared with cast-in-place structures, prefabrication offers clear advantages\u0026mdash;including shorter schedules and lower labor intensity [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], reduced material waste [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], higher energy efficiency [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and diminished air- and noise-borne pollution [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u0026mdash;thereby boosting productivity and quality while cutting costs and environmental impact. These benefits have been confirmed in many projects.\u003c/p\u003e\u003cp\u003eThe method is also gaining traction in underground construction, where China\u0026rsquo;s rapid urbanization has further highlighted its value [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Internationally, Russia, the Netherlands, France, Japan and others have applied prefabrication to underground works and amassed considerable experience [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Notable examples include Minsk Metro\u0026rsquo;s large-span segmental arches (1985) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], Tokyo\u0026rsquo;s precast-beam underground reservoir (1998) [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], Rotterdam Metro\u0026rsquo;s \u0026ldquo;shell tunnel\u0026rdquo; with high-precision waterproof joints (1986) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], and France\u0026rsquo;s Obel Station, where prefabricated arches were placed under NATM conditions [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Within China, the approach is now advancing rapidly. The Yuanjiadian Station in Changchun\u0026mdash;the nation\u0026rsquo;s first fully prefabricated metro station\u0026mdash;has provided an influential benchmark [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Extensive domestic research on design, performance, and construction technology [\u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] has laid a solid theoretical foundation for further underground use.\u003c/p\u003e\u003cp\u003eCoupling prefabrication with hollow components is an emerging trend. Hollow sections lighten dead weight, simplify transport and erection, and can even enhance ductility and hysteretic energy dissipation [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In recent years, the same concept has migrated underground. In industrial and residential buildings, Lee et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] and Park et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] showed that prestressed hollow slabs outperform conventional members in bending and shear while offering superior quality control, lower labor cost, and shorter build time. In recent years, the same concept has migrated underground. For the first large underground station in China built entirely from prefabrication\u0026mdash;the Changchun Metro Line 2\u0026mdash;Han et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] and Yang et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] analyzed stress distribution in novel twin-cell thin-walled components under various load states. Tao et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] later clarified the bearing capacity and failure mechanisms of such thin-walled stations and confirmed their sound load-bearing and deformation performance. Qiu et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] performed full-scale tests on stations using precast hollow components (PHC) and showed that optimized void-to-section ratios enable PHC to satisfy design demands.\u003c/p\u003e\u003cp\u003eAlthough significant progress has been made\u0026mdash;especially in marrying prefabrication with hollow-weight-reduction technology\u0026mdash;reports on large-span, cut-and-cover highway tunnels featuring thin-walled closed cavities remain scarce. Key gaps include (1) limited understanding of load-bearing behavior in large-span hollow arches, (2) insufficient data on their mechanical and deformation characteristics, and (3) inadequate insight into failure mechanisms under ultimate loading. These challenges underscore the need for comprehensive studies on the mechanics and design optimization of prefabricated hollow structures in large tunnels. Priority topics include soil\u0026ndash;structure interaction, joint mechanics, and real-world failure modes. Results will help unlock the energy-saving potential of lightweight prefabrication and provide actionable guidance for design and construction.\u003c/p\u003e\u003cp\u003eTaking Chongqing\u0026rsquo;s large-span Xinsen Avenue cut-and-cover tunnel as a case study, this paper investigates the load-bearing behavior and failure mechanisms of its prefabricated arch. The remainder of the article is organized as follows: Section \u003cspan refid=\"Sec2\" class=\"InternalRef\"\u003e2\u003c/span\u003e describes the project and the experimental segment; Section \u003cspan refid=\"Sec3\" class=\"InternalRef\"\u003e3\u003c/span\u003e outlines the finite-element model and parameter sensitivity analysis, validated with field data; Section \u003cspan refid=\"Sec16\" class=\"InternalRef\"\u003e4\u003c/span\u003e compares hollow and solid arches in terms of mechanics, deformation, and failure; Section \u003cspan refid=\"Sec30\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents conclusions, engineering recommendations, and future research directions.\u003c/p\u003e"},{"header":"2. Engineering background","content":"\u003cp\u003eThis study examines the application and innovation of prefabricated assembly technology in large-span cut-and-cover tunnel structures through a case study of the bi-directional eight-lane tunnel project on Xinsen Avenue in Chongqing\u0026rsquo;s Hi-Tech Zone. As the zone\u0026rsquo;s primary north-south arterial corridor, Xinsen Avenue spans 2.5 km, with 790 m constituting a tunnel section featuring a single-bore clear width of 16.5 m, vertical clearance of 9.8 m, and geotechnically challenging Class V surrounding rock conditions (Fig. 1(a)-(b)). A predominantly silty clay soil cover, 0.5 to 4.8 m thick, overlies the tunnel; beneath this cover, the bedrock consists of mudstone and sandstone. The construction methodology combines underground mining with open-cut techniques, the latter utilizing precast components along a 445 m assembly segment (K1+255 to K1+700). This segment exhibits backfill soil thicknesses varying between 7 m and 12 m. Excavation of the side slopes creates embankments with heights ranging from 4.6 to 17.2 m on the left and from 3.2 to 13.2 m on the right. Since excavation removes any pre-existing fissures, slope stability is governed primarily by the inherent strength of the rock mass. To enhance foundation adaptability and streamline construction processes, the open-cut segment incorporates a hybrid structural system integrating a cast-in-situ inverted arch with precast arch segments.\u003c/p\u003e\n\u003cp\u003eThe standardized ring system, divided into 2 m segments, consists of 417 rings (208 left-side and 209 right-side units). Each ring features two symmetrical precast elements (Blocks A and B) and a cast-in-situ inverted arch (Block C), as shown in Fig. 1(c)-(e). Precast components adopt a lightweight closed-cavity thin-walled design, substantially improving construction efficiency. Inter-element connections utilize grout-augmented mortise-tenon joints to eliminate gaps. The Block A-B interface incorporates dual prestressed tension-locking systems to guarantee structural load capacity and waterproofing performance, whereas Block A-C/B-C joints integrate externally anchored restraint systems compliant with arch mechanics principles (Fig. 2). Longitudinal joints employ continuous-seam assembly with sequentially tensioned prestressed steel bars using a relay-stressing method, ensuring structural continuity and watertight integrity (Fig. 3).\u003c/p\u003e\n\u003cp\u003eNotably, the project pioneers a mortise-tenon joint system at the vault interface of precast arch rings, combined with comprehensive investigations into key design and construction parameters. Key parameters encompass joint topology optimization, high-precision mold fabrication, mass-reduction strategies for large-curvature components, logistics for oversized element transportation-assembly workflows, and waterproofing system design. Comparative analyses indicate that mortise-tenon joint-equipped precast tunnels exhibit enhanced construction quality, operational efficiency, and safety performance compared to cast-in-situ linings, thereby improving labor efficiency, material utilization, and carbon footprint reduction. However, unresolved challenges\u0026mdash;including intricate production workflows, stringent assembly tolerances, and cost inflation\u0026mdash;highlight the need for advancements in joint mechanical behavior and standardized construction protocols.\u003c/p\u003e\n\u003cp\u003eTo meet the demands of the ultra-large span and high loading conditions of the Xinsen Avenue prefabricated tunnel, our research team innovatively proposed a \u0026quot;prefabricated + cast-in-place\u0026quot; construction method for a \u0026quot;two-hinged arch\u0026quot; structural system, as shown in Fig. 4 (a). The crown sections A and B of the tunnel utilize prefabricated assembly technology to enhance construction efficiency, while the inverted arch section C retains the cast-in-place process to ensure deformation coordination with the foundation. The crown AB joint employs a composite wet joint, as shown in Fig. 4 (b), to form a rigid connection, while the arch-springing AC/BC joints adopt grouted keyed joints, as illustrated in Fig. 4 (c), to balance structural stiffness and construction tolerances. This solution integrates the high efficiency of prefabricated assembly with the overall integrity of cast-in-place joints, significantly enhancing the structure\u0026apos;s high reliability under backfilling and loading conditions.\u003c/p\u003e\n\u003cp\u003eFive key innovations distinguish the \u0026ldquo;composite joint\u0026rdquo; from classical mortise\u0026ndash;tenon schemes: (1) tolerating \u0026plusmn;10 mm of fabrication error, thus lowering mold precision by 30 % and eliminating custom trolleys; (2) replacing extended starter bars with indirect laps via ring bars, which simplifies transport; (3) shortening lap lengths and post-cast strip widths; (4) doubling steel at the joint plus transverse bars to raise load capacity; and (5) stiffening the vault so arch-foot loads fall, making simpler slot-type hinges feasible.\u003c/p\u003e"},{"header":"3. Numerical model","content":"\u003cp\u003e\u003cstrong\u003e3.1 Finite element model\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBased on the assembly and backfilling construction process of the open-cut prefabricated tunnel with composite joints, a three-dimensional solid-contact computational model established according to the strata-structure interaction mode (Fig. 5 (a)) is used to focus on revealing the mechanical response of the composite joint system under progressive backfilling loads. The backfill height is determined based on the maximum design burial depth of 12 meters. The prefabricated structural model consists of three components\u0026mdash;A, B, and C blocks\u0026mdash;as well as the composite cast-in-place concrete and main reinforcement bars. (Fig. 5 (b)). To simplify the model and computational work, the calculation model is based on a single ring (with a ring width of 2 m). The overall dimensions of the model are 140 m \u0026times; 50 m \u0026times; 2 m; the mesh type is identical to that used in Section 4.1, resulting in 110 982 elements and 137 834 nodes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.1 Assumptions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe assumptions for the computational model in this paper are as follows: 1) Longitudinal effects of the structure are not considered. 2) Assembly errors and precision of the structure are not taken into account. 3) Slippage of reinforcement bars is not considered. 4) Groundwater effects are not considered, due to the scarcity of groundwater within the drilling depth near the tunnel site.\u003c/p\u003e\n\u003cp\u003e3.1.2 Material properties\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e1. Surrounding soil\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSoils are commonly treated either as purely elastic media\u0026mdash;appropriate for small-strain porous materials\u0026mdash;or as elastic-plastic media when hydrostatic pressure sensitivity is significant. Accordingly, all soil layers were modelled with the Mohr\u0026ndash;Coulomb elastic-plastic formulation. Parameters derived from site testing are shown in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u0026nbsp;\u003c/strong\u003eRelated mechanical parameters of surrounding soil.\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003estratum\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003eYoung\u0026rsquo;s modulus \u003cem\u003eE\u0026nbsp;\u003c/em\u003e(MPa)\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003ePoisson\u0026rsquo;s ratio \u003cem\u003e\u0026upsilon;\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003eUnit weight \u003cem\u003e\u0026gamma;\u0026nbsp;\u003c/em\u003e(kN/m\u003csup\u003e3\u003c/sup\u003e)\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003eCohesion \u003cem\u003ec\u0026nbsp;\u003c/em\u003e(kPa)\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003eInternal-friction angle \u003cem\u003e\u0026phi;\u0026nbsp;\u003c/em\u003e(◦)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eBackfill\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e12.6\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e0.4\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e19.5\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e10-40\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e22\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eSilty clay\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e8.68\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e0.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e22.7\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e12.8\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e12.8\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eMudstone\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e783.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e0.34\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e24.56\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e299\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e28.91\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e2. Precast components and internal concrete\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll precast blocks and the post-cast concrete at composite joints were assigned C50 concrete governed by the Concrete-Damaged Plasticity (CDP) model. Rebars were modelled as HRB400 steel with an ideal elastic\u0026ndash;plastic law, and bond\u0026ndash;slip was neglected. Side-wall backfill behaves as a fluid with E = 1 Pa until set, after which it adopts C25 concrete properties. Relevant parameters appear in Table 2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eMaterial parameters of the concrete and the reinforcement steel\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 24px;\"\u003eMaterial\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 33px;\"\u003eYoung\u0026rsquo;s modulus \u003cem\u003eE\u0026nbsp;\u003c/em\u003e(MPa)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003ePoisson\u0026rsquo;s ratio \u003cem\u003e\u0026upsilon;\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003eDensity (kg/m\u0026sup3;)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 24px;\"\u003eRubble concrete\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 33px;\"\u003e15000\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e0.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e2244\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 24px;\"\u003eC50 concrete\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 33px;\"\u003e34500\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e0.2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e2420\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 24px;\"\u003eReinforcement steel\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 33px;\"\u003e200000\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 21px;\"\u003e0.3\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e7850\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe joint material is defined as C50 concrete, with the parameters for its plastic damage constitutive model derived from the stress-strain relationships specified in Appendix C of the Code for Design of Concrete Structures (GB 50010-2010 [31]). Fig. 6 illustrates the corresponding uniaxial stress-strain curves and damage factors under tension and compression. In this paper, relevant research and applications of concrete damage parameters from previous studies [32\u0026ndash;34] are referenced. Consequently, the adopted input parameters are provided in Table 3.\u003c/p\u003e\n\u003cp\u003e3.1.3 Contact properties\u003c/p\u003e\n\u003cp\u003eThe embedded element technique is adopted to simulate the interaction between concrete and reinforcement. Additionally, there are three types of contact interactions among the entity components in the model. The first type involves the connection between the backfill soil layers and the layered backfilled rubble concrete, which is achieved through bonded constraints. The second type involves the contact between soil and structure, as well as between prefabricated components, using a Coulomb friction model, where the normal direction of contact surfaces was modeled with \u0026quot;hard\u0026quot; contact and friction defined via the \u0026quot;penalty\u0026quot; method with a friction coefficient of 0.6 [35, 36]; the third type addressed the interface between newly cast and existing concrete in composite cast-in-place sections, utilizing a cohesion-friction hybrid model whose specific parameters were determined according to AASHTO [37] and validated test results [38].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u0026nbsp;\u003c/strong\u003eConcrete-damaged plastic model input parameters.\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 19px;\"\u003e\u003cem\u003e\u0026Psi;\u003c/em\u003e (◦)\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e\u003cem\u003e\u0026xi;\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\u003cem\u003e\u0026sigma;\u003csub\u003eb0\u003c/sub\u003e\u003c/em\u003e/\u003cem\u003e\u0026sigma;\u003csub\u003ec0\u003c/sub\u003e\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\u003cem\u003eK\u003c/em\u003e\u003cem\u003e\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e\u003cem\u003e\u0026mu;\u0026nbsp;\u003c/em\u003e(s\u003csup\u003e-1\u003c/sup\u003e)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 19px;\"\u003e38\u0026deg;\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 19px;\"\u003e0.1\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e1.16\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e0.6667\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003e0.0005\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e3.1.4 Boundary conditions and staged loading\u003c/p\u003e\n\u003cp\u003eThe model boundaries restrict normal horizontal displacements on all sides and vertical displacements at the base.\u003c/p\u003e\n\u003cp\u003eDuring backfilling, manual compaction is applied after each layer to ensure density and flatness. The compaction effect is equivalently modeled as horizontal additional earth pressure (2\u003cem\u003ek₀\u0026gamma;h\u003c/em\u003eᵢ), (where \u003cem\u003ek₀\u003c/em\u003e=\u003cem\u003e1\u0026minus;sin\u0026phi;,\u0026nbsp;\u003c/em\u003elateral earth pressure coefficient; \u003cem\u003e\u0026gamma;\u0026nbsp;\u003c/em\u003eis soil unit weight, and \u003cem\u003ehᵢ\u003c/em\u003e is the activated layer thickness.). The Geo static Stress module in ABAQUS incrementally activates these stresses to simulate the staged backfilling and compaction process.\u003c/p\u003e\n\u003cp\u003eAfter the design backfill thickness of 12 m had been placed, a uniformly distributed surcharge was applied to the ground surface to study the failure mechanism of the two-hinged arch. Four surcharge levels\u0026mdash;200 kPa, 600 kPa, 1 000 kPa and 1 200 kPa\u0026mdash;were considered, simulating additional overburden thicknesses of roughly 10 m, 30 m, 50 m and 60 m, respectively (unit weight of mixed fill = 20 kN m⁻\u0026sup3;).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Sensitivity analysis of critical modeling parameters\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e3.2.1 Soil\u0026ndash;arch interface modelling strategy\u003c/p\u003e\n\u003cp\u003eTo accurately simulate the interaction between the prefabricated structure and surrounding soil in ABAQUS, two common modeling approaches are typically used. The first involves defining contact pairs with the Coulomb friction model to represent the mechanical behavior in the normal and tangential directions. The normal behavior is modeled as \u0026quot;hard\u0026quot; contact, while the tangential behavior follows the \u0026quot;penalty\u0026quot; friction formulation. The second approach uses a tie constraint, which couples nodes to enforce identical deformation between the structure and soil.\u003c/p\u003e\n\u003cp\u003eTo realistically capture the interaction between the prefabricated structure and the backfill soil, this study compares the calculation results of two contact relationships: a contact pair with an empirical friction coefficient of 0.6 and a tied constraint. The results are shown in\u0026nbsp;Fig. 7.\u003c/p\u003e\n\u003cp\u003eFrom Fig. 7, the following observations can be made:\u003c/p\u003e\n\u003cp\u003e1. At the arch crown, both contact models\u0026mdash;tied constraint and friction contact\u0026mdash;produce similar trends in bending moment and axial force, with only minor numerical differences. This suggests that the contact modeling strategy has minimal impact on the mechanical response at the crown.\u003c/p\u003e\n\u003cp\u003e2. At the arch haunch, compared with the tied constraint model, the friction contact model shows a 39.6% decrease in bending moment (from -968 kN\u0026middot;m to -585 kN\u0026middot;m) and a 32.7% increase in axial force (from -1835 kN to -2435 kN).\u003c/p\u003e\n\u003cp\u003e3. With the tied constraint model, the axial force difference between the crown and haunch is within 6%, indicating relatively uniform force distribution. However, with the friction contact model, the crown axial force is 28% lower than that at the haunch, reflecting the actual stress distribution in cut-and-cover tunnels more accurately.\u003c/p\u003e\n\u003cp\u003eIn conclusion, the results between the tied and friction contact models differ significantly. The friction contact model better represents sliding and friction effects at the soil\u0026ndash;structure interface, resulting in a more realistic internal force distribution. Therefore, the Coulomb friction model is adopted in this study.\u003c/p\u003e\n\u003cp\u003e3.2.2 Hardening behaviour of rubble concrete\u003c/p\u003e\n\u003cp\u003eIn the actual construction process, a layered backfill technique using hardening rubble concrete is adopted. Each new layer is poured only after the previous layer has hardened to the design strength. To reflect this process, two models were compared\u0026mdash;one considering the hardening process of the footing concrete (from liquid to solid) and one without. The elastic modulus is set to 1 Pa in the liquid phase and adjusted to C20-grade values after hardening, with a layer height of 1.5 m. The results are presented in Fig. 8.\u003c/p\u003e\n\u003cp\u003eThe findings are as follows:\u003c/p\u003e\n\u003cp\u003e1. The final differences in bending moment and axial force are small. Variations are mainly due to cumulative internal forces during the layered backfill process, warranting further analysis of the hardening effect during backfilling.\u003c/p\u003e\n\u003cp\u003e2. Before reaching 9.2 m (shoulder level), the model considering concrete hardening shows a slight decrease in crown bending moment due to horizontal pressure from the liquid concrete. The haunch moment remains negative and increases with fill height. In contrast, the model without hardening mainly bears self-weight and footing constraint forces, resulting in a nearly constant crown moment and a haunch moment that shifts from negative to positive, then decreases.\u003c/p\u003e\n\u003cp\u003e3. For axial forces, both models follow similar trends. However, at 10.8 m (shoulder level), the model with hardening shows a 25% higher crown force and 12% lower haunch force compared to the non-hardening model.\u003c/p\u003e\n\u003cp\u003eIn summary, the hardening behavior of rubble concrete significantly affects the internal force distribution and should be incorporated into detailed numerical simulations.\u003c/p\u003e\n\u003cp\u003e3.2.3 Layered backfill compaction load effects\u003c/p\u003e\n\u003cp\u003eTo ensure proper compaction and surface uniformity, each backfill layer is manually compacted after placement. Based on actual construction procedures, this study compares models that include and exclude compaction load effects. To simulate this, the compaction force is modeled as an additional horizontal earth pressure acting on the structure, calculated as 2\u003cem\u003ek\u003csub\u003e0\u003c/sub\u003e\u0026gamma;h\u003csub\u003ei\u003c/sub\u003e\u003c/em\u003e, where \u003cem\u003ek\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e=1\u0026minus;sinϕ (earth pressure coefficient at rest), \u0026gamma; is the unit weight of the soil, and \u003cem\u003eh\u003csub\u003ei\u003c/sub\u003e\u003c/em\u003e is the thickness of the active layer. These pressures are applied using the Geostatic Stress feature in ABAQUS. The results are shown in Fig. 9.\u003c/p\u003e\n\u003cp\u003eThe key findings are:\u003c/p\u003e\n\u003cp\u003e1. Compared to the model without compaction, the axial forces differ by up to 10% at the crown and 2% at the haunch\u0026mdash;both occurring after crown backfilling. The overall trend remains consistent.\u003c/p\u003e\n\u003cp\u003e2. Final bending moment results at the crown differ significantly. Including compaction increases the moment from 745 kN\u0026middot;m to 902 kN\u0026middot;m, a 21% rise.\u003c/p\u003e\n\u003cp\u003e3. After reaching 6 m (end of rubble concrete backfill), the crown moment decreases due to lateral compaction forces. After 9.2 m (shoulder level), vertical soil loads cause the crown moment to increase. In contrast, the model without compaction shows a continuous increase in crown moment after 6 m, with an accelerating trend.\u003c/p\u003e\n\u003cp\u003e4. At the haunch, both models exhibit similar moment trends with a maximum deviation of 12%.\u003c/p\u003e\n\u003cp\u003eIn conclusion, backfill compaction significantly affects internal force distribution. It tends to increase bending moments and reduce axial forces, potentially compromising structural safety. Therefore, the effects of compaction must be considered in the simulation.\u003c/p\u003e\n\u003cp\u003e3.3 Model Validation\u003c/p\u003e\n\u003cp\u003eConsidering the contact behavior between the backfill soil and structure, the hardening process of rubble concrete, and the compaction load during construction, a refined geotechnical-structural model was developed. To validate the numerical simulation results, long-term on-site monitoring was conducted on the composite joint structure of the Xinsen Avenue Tunnel. The primary monitoring items included concrete strain and reinforcement stress, as illustrated in the sensor layout in Fig. 10.\u003c/p\u003e\n\u003cp\u003eFor ease of analysis, the concrete strain values have been converted to stress values. Fig. 11 presents a comparison between the simulated values and field measurements for concrete stress, reinforcement stress, and relative deformation at the tunnel crown joint.\u003c/p\u003e\n\u003cp\u003eIn Fig. 11 (a), a comparison of simulated and monitored concrete stress is shown. During construction, compressive stress was observed on the water-facing side and tensile stress on the opposite side, which aligns with the simulation results. For monitoring point C1 (close to the water-facing side), the compressive stress increased with the accumulation of backfill, reaching a maximum of 0.74 MPa, while the simulated value reached 0.94 MPa, showing an increase of 27%. For monitoring point C2 (near the non-water-facing side), the tensile stress similarly increased with the fill height, reaching 0.27 MPa, while the simulated value was 0.32 MPa, an 18% increase. In the long term after top-backfilling, the overall trend of changes was consistent with the simulation.\u003c/p\u003e\n\u003cp\u003eFig. 11 (b)\u0026nbsp;compares simulated and monitored reinforcement stress. It can be observed that the trends in both datasets align well. After ring assembly, under self-weight and construction loads, the compressive stress at monitoring point R1 (main longitudinal reinforcement near the water-facing side) increased, while R2 (on the non-water-facing side) showed tensile stress with a relatively lower magnitude. As layered backfilling progressed, stress in all monitored points increased gradually and then stabilized, maintaining a stress state of compression in the upper part and tension in the lower part. The maximum compressive stress at R1 was 13.57 MPa, which closely matches the simulated peak of 14.08 MPa. For R2, the difference between measured and calculated compressive stresses was within 5%. These results confirm that the upper reinforcement mainly experienced compression, while the lower reinforcement primarily bore lower tensile stresses, demonstrating good agreement between simulation and field observations.\u003c/p\u003e\n\u003cp\u003eFig. 11 (c)\u0026nbsp;shows the relative deformation of the joint. The simulation and monitoring results followed similar trends. As construction progressed, the relative deformation increased from the start of ring assembly, peaking after completion of top backfilling. The rate of increase was similar between monitoring and simulation. During sidewall and haunch backfilling, the deformation growth was more moderate. The maximum measured deformation was 4.7 mm, while the simulated value was 5.4 mm, about 14.8% higher\u0026mdash;mainly due to compaction modeling in the simulation. As backfilling was completed and disturbance reduced, the structure stabilized, and both measured and simulated deformation slightly decreased. This suggests that although minor differences exist, the overall trends are consistent, and the simulation effectively replicates deformation behavior during actual construction.\u003c/p\u003e\n\u003cp\u003eIn conclusion, the numerical results at critical locations show good agreement with field measurements, verifying the reliability and accuracy of the refined model.\u003c/p\u003e"},{"header":"4. Analysis of the results","content":"\u003cp\u003eTo further investigate the influence of internal cavity formation on structural deformation and mechanical performance, both cavity-structured and solid (non-cavity) models were designed for comparative analysis, as detailed in Table 4. Working Condition 1 (Case 1) examines the structural performance under self-weight after the precast elements are assembled into a ring. Working Condition 2 (Case 2) focuses on the structural response to the progressive backfilling of 21 m of soil (from tunnel arch springing to the backfill surface). Working Condition 3 (Case 3) applies a vertical uniform load on the top surface of the backfill to simulate the failure mechanism of the precast arch structure under ultimate loading conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eStaged construction loading analysis for structural models\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 17px;\"\u003eModel\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 12px;\"\u003eCavity volume /m\u003csup\u003e3\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 11px;\"\u003eCavity ratio/%\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 58px;\"\u003eAnalysis step\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 8px;\"\u003eCase 1\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 20px;\"\u003eCase 2\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 29px;\"\u003eCase 3\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003eCavity structure\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e8.8m\u003csup\u003e3\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e14%\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 8px;\"\u003eGravity\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 20px;\"\u003eGravity + 21m layered backfill soil load\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 29px;\"\u003eGravity + 21m layered backfill soil load + Vertical uniform load\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17px;\"\u003eSolid structure\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e0\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e0\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e4.1 Mechanical properties\u003c/p\u003e\n\u003cp\u003e4.1.1 Stress\u003c/p\u003e\n\u003cp\u003eDuring the analysis, the maximum and minimum principal stress values and their corresponding locations were extracted to evaluate the stress state of the structure. The maximum principal stress identifies zones subjected to the greatest tensile forces, while the minimum principal stress highlights compressive stress zones. The results show that high stress concentrations are mainly located at the haunch areas of the arch. The inner haunches (points P3 and P5) are primarily under compressive stress, while the outer haunches (points P4 and P6) are subjected to tensile stress. The stress contour under 12 m of design backfill is shown in Fig. 12.\u003c/p\u003e\n\u003cp\u003eFig. 13 presents the evolution of stress during the transition from assembly to the end of backfilling. Though different key points exhibit varying amplitudes of stress change under identical burial depths, the overall trends are consistent. The solid structure consistently shows lower stress values at all key points compared to the cavity structure.\u003c/p\u003e\n\u003cp\u003eAt the crown of the arch, the monitoring point near the water-facing side (P2) is under compressive stress, while the back-facing side (P1) experiences tensile stress. After blocks A and B are assembled into a ring, a new integral structure is formed, which undergoes self-adaptive internal force redistribution under gravity. This results in compressive stress in the upper joints and tensile stress in the lower part. In the early stages of sidewall backfilling (0\u0026ndash;6 m), stress at all points decreases, attributed to the sidewall concrete providing enhanced constraint on the arch foot. Between 6 m and 9 m depth, the stress stabilizes, indicating minor influence from the added backfill. As the top backfill progresses, the increased vertical load causes stress to rise across all points. Due to the internal cavity, the hollow structure experiences notable stress concentration, resulting in a significantly higher overall stress level than the solid structure.\u003c/p\u003e\n\u003cp\u003eAt the haunches, stress follows a similar trend to that at the crown. The haunch is primarily subjected to compressive forces. On the outer haunch side (P4, P6), tensile stresses are eventually transformed into compressive stresses due to lateral confinement from sidewall fill, which acts as lateral thrust. The inner haunch sides (P3, P5) mainly bear compressive stress.\u003c/p\u003e\n\u003cp\u003e4.1.2 Internal forces\u003c/p\u003e\n\u003cp\u003eA total of 24 critical cross-sections were selected based on cavity layout and structural characteristics. These sections cover the major load-bearing regions of the structure, with numbering shown in Fig. 14(a). Internal force data from each section were extracted for a systematic investigation of structural response, providing reliable data support for subsequent structural optimization and performance assessment.\u003c/p\u003e\n\u003cp\u003eFig. 14 (b)\u0026ndash;14(d) show the axial force, shear force, and bending moment for both the solid and cavity structures. The results demonstrate that the introduction of internal cavities effectively reduces axial force and shear force at most cross-sections. Specifically, the maximum axial force in the cavity structure is reduced by 142 kN compared to the solid structure, and the maximum shear force is reduced by 168 kN. However, the maximum bending moment in the cavity structure increases by 160 kN\u0026middot;m.\u003c/p\u003e\n\u003cp\u003eThe analysis indicates that incorporating cavities reduces the structure\u0026rsquo;s self-weight and thereby decreases axial and shear forces\u0026mdash;contributing positively to structural load optimization. However, because the bending stiffness of the cavity structure is lower, it results in higher bending moments under the same earth pressure. This is particularly notable at the crown and side regions of the arch, where the solid structure demonstrates more uniform and lower bending moment distribution.\u003c/p\u003e\n\u003cp\u003eIn summary, rational cavity design can optimize self-weight distribution and improve internal force profiles to some extent. However, special attention should be given to regions with increased bending moment (such as the crown and arch shoulders) by enhancing their flexural stiffness. Meanwhile, in regions subject to lower forces (such as sidewalls and springings), the cavity ratio can be optimized to ensure both structural safety and stability.\u003c/p\u003e\n\u003cp\u003e4.2 Deformation analysis\u003c/p\u003e\n\u003cp\u003e4.2.1 Integral deformation of the structure\u003c/p\u003e\n\u003cp\u003eFig.15 illustrates the deformation patterns of the hollow and solid structures under load. It can be observed that the horizontal convergence at the arch waist and the vertical displacement at the arch crown follow similar trends. After the assembly is completed, the solid structure exhibits greater deformation due to its larger self-weight, whereas the hollow structure shows smaller initial deformation. During the lateral backfilling stage, the lateral thrust exerted by the fill material causes the deformation of the hollow structure to gradually exceed that of the solid structure. This phenomenon is attributed to the higher stiffness of the solid structure, which better resists external forces.\u003c/p\u003e\n\u003cp\u003eAs backfilling progresses\u0026mdash;especially at the arch crown\u0026mdash;the structural deformation accelerates. The deformation magnitude increases linearly with the fill thickness, and the displacement of the hollow structure consistently remains greater than that of the solid structure. This indicates that the hollow structure, due to its lower stiffness, is more susceptible to larger deformations during the backfilling process, while the solid structure exhibits smaller displacements.\u003c/p\u003e\n\u003cp\u003eWhen the backfill reaches the design height, the structure experiences maximum deformation. At this point, the horizontal convergence and vertical displacement at the crown of the hollow structure are 2.14 mm and 7.21 mm respectively, whereas those of the solid structure are 1.75 mm and 6.83 mm, all of which are within the limits specified by the design code and still retain a considerable safety margin. According to the Code for Design of Concrete Structures, for structures with a span greater than 9 m, the allowable deflection limit for bending structures is l/300. With a crown span of 20,100 mm, the deflection limit for the crown is 67 mm.\u003c/p\u003e\n\u003cp\u003eFurthermore, the peak displacement of the hollow structure exceeds that of the solid structure. The introduction of internal cavities increased the peak displacement by approximately 5.56%, while also enhancing the ultimate deformation capacity of the structure by the same proportion.\u003c/p\u003e\n\u003cp\u003e4.2.2 The opening deformation of the joints\u003c/p\u003e\n\u003cp\u003eUnder load conditions, relative displacement occurs between the two end faces of the joints. As illustrated in Fig. 16, the rotational angle of joints was calculated based on the horizontal displacement at the upper and lower edges of the joint. The measurement principle involves:\u003c/p\u003e\n\u003cp\u003e1. Tracking horizontal displacements (X₁-X₄) at four predefined measurement points,\u003c/p\u003e\n\u003cp\u003e2. Using the fixed vertical spacing (L) between paired points to compute two component angles (\u0026theta;₁, \u0026theta;₂) through trigonometric relations,\u003c/p\u003e\n\u003cp\u003e3. Summing the components to obtain the total joint rotation angle (\u0026theta;).\u003c/p\u003e\n\u003cp\u003eThe calculation follows these equations:\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" width=\"636\" height=\"197\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eX\u003c/em\u003e denotes horizontal displacement and \u003cem\u003eL\u003c/em\u003e is the vertical distance between measurement points. This dual-angle approach accounts for both shear and bending deformations at the joint interface.\u003c/p\u003e\n\u003cp\u003eFig. 17 (a) shows the change in the opening angle of the crown joint (A-B) for both solid and hollow structures. It can be seen that under self-weight, the upper side of the A-B joint is compressed, while the lower side shows a slight opening tendency. Due to the greater self-weight of the solid structure, the initial joint opening at the arch crown is slightly larger than that of the hollow structure.\u003c/p\u003e\n\u003cp\u003eAs the sidewalls are backfilled layer by layer, the lateral confinement increases, causing a continuous reduction in the rotation angle of the joint, gradually closing the gap. The closure angle exhibits a linear trend during the initial stage. Between backfill heights of 6 m and 9 m, changes in the joint rotation angle are relatively small, indicating a stable state. When backfilling begins at the top, the joint rotation angle for both models increases again, reflecting a decrease in structural stiffness. Because the hollow structure has lower overall stiffness, its joint opening is consistently greater than that of the solid structure.\u003c/p\u003e\n\u003cp\u003eAfter backfilling is complete, the rotation angles of the crown joint are 0.0134 for the solid structure and 0.0124 for the hollow structure. Although these values remain small, the inclusion of internal cavities results in an increase of approximately 8.06% in joint deformation. This suggests that even with cavities, the joints maintain stable performance under load. The internal cavities reduce structural self-weight while enhancing deformation adaptability and design flexibility\u0026mdash;crucial for maintaining overall stability and improving force transfer between components.\u003c/p\u003e\n\u003cp\u003eFig. 17 (b) shows the rotation angle variation of the footing joints (A\u0026ndash;C and B\u0026ndash;C) under different backfill heights. The initial relative rotation angle is 0\u0026deg; for both joints, as self-weight was not considered for the footing. The A\u0026ndash;C and B\u0026ndash;C joints exhibit symmetric but opposite trends: A\u0026ndash;C becomes compressed while B\u0026ndash;C opens. This asymmetry arises from the uneven lateral load induced by staged backfilling, leading to non-uniform deformation in the footing area.\u003c/p\u003e\n\u003cp\u003eAs the backfill approaches the top of the footing, the A\u0026ndash;C joint rotation stabilizes, while the B\u0026ndash;C joint reaches its maximum. In the final backfilling stage, the relative rotation of both joints begins to shrink (absolute values decrease), with A\u0026ndash;C returning close to its initial state and B\u0026ndash;C showing significantly reduced opening. These trends indicate that the uniformly distributed load from the top enhances the lateral constraint at the joints, stabilizing the overall structure.\u003c/p\u003e\n\u003cp\u003eIn addition, the rotation angle changes of the hollow structure joints are consistently greater than those of the solid structure, especially during sidewall backfilling. This indicates that due to its lower stiffness, the hollow structure experiences more pronounced deformation under asymmetric loads. Although the inclusion of cavities slightly increases joint rotation, it reduces the structure\u0026rsquo;s self-weight and improves the deformation coordination among components. The hollow structure maintains good stability under load and provides greater flexibility for spatial and mechanical design optimization.\u003c/p\u003e\n\u003cp\u003e4.3 Analysis of failure mechanism of single-ring structure\u003c/p\u003e\n\u003cp\u003e4.3.1 Damage evolution of single-ring structure\u003c/p\u003e\n\u003cp\u003eFig. 18\u0026nbsp;illustrates the evolution of damage in the precast hollow arch structure during staged backfill loading. Overall, the distribution of tensile damage is limited. In the early stage, stress concentration occurs in the invert region with a variable cross-section, as shown in Fig. 18 (b), where several nearly through-cracks appear early. With increasing load, Fig. 18 (c) and (d) show that damage first occurs at the boundary between the cavity and solid parts, particularly at the haunches and shoulders, where cavities are introduced. Additionally, visible tensile damage emerges below the crown joint and on the upper surface of the invert. At the ultimate stage, stress concentrations become widespread in the invert, haunches, and crown, indicating severe structural damage overall, as depicted in Fig. 18 (e).\u003c/p\u003e\n\u003cp\u003eSimilarly, for compressive damage, the hollow arch first shows damage on the outer surface of the haunches and at the invert variable section (Fig. 18 (g)). As the load increases, Fig. 18 (h) and\u0026nbsp;(i) show that the invert first develops a plastic hinge, followed by additional hinges at the left haunch and right side of the crown joint. At failure, four plastic hinges are observed\u0026mdash;at the crown, both haunches, and invert (Fig. 18 (j))\u0026mdash;consistent with the compression-dominated behavior of arch structures.\u003c/p\u003e\n\u003cp\u003eUnder the same conditions, Fig. 19 presents the damage evolution of the precast solid arch during staged backfilling. Fig. 19 (a)\u0026ndash; (e) display the tensile damage, and Fig. 19 (f)\u0026ndash;(j) show the compressive damage. Similar to the hollow structure, the solid arch primarily undergoes compressive damage, and the failure pattern also involves four plastic hinges at the crown, haunches, and invert. However, the sequence of hinge formation differs: in the hollow structure, hinges form in the order invert \u0026rarr; left haunch \u0026rarr; crown \u0026rarr; right haunch, whereas in the solid structure, the order is invert \u0026rarr; right haunch \u0026rarr; left haunch \u0026rarr; crown. This variation is attributed to the presence of enclosed cavities in the hollow design, which reduce stiffness and lead to faster damage development at the crown.\u003c/p\u003e\n\u003cp\u003e4.3.2 Damage analysis of key parts\u003c/p\u003e\n\u003cp\u003eThe damage behavior at the composite joint of the crown is similar for both hollow and solid structures. The schematic in\u0026nbsp;Fig. 20\u0026nbsp;shows that after deformation, the crown settles downward, causing the composite slab joint to open. As loading increases, cracks form in the tensile zone beneath the post-cast concrete at the interface with old concrete. Under ultimate conditions, the upper compressive zone of the post-cast concrete is crushed, leading to global structural failure.\u003c/p\u003e\n\u003cp\u003eFig. 21\u0026nbsp;shows the damage mechanism of precast arched component A(B). This component carries both vertical and horizontal loads, resulting in complex and significant stresses. As the load increases, the structure bends downward, compressing the outer side and stretching the inner side of the crown joint\u0026rsquo;s post-cast concrete. The presence of enclosed cavities accelerates stiffness degradation, causing rapid arch deformation and failure. Horizontally, the haunch exterior experiences tensile failure, while the interior is primarily compressed. Although the damage location in the solid structure is similar, its ultimate deformation capacity is greater and load-bearing performance is superior.\u003c/p\u003e\n\u003cp\u003e4.4 Damage mechanism of single-ring structure\u003c/p\u003e\n\u003cp\u003eFig. 22\u0026nbsp;illustrates the three-stage deterioration process of both hollow and solid arch structures featuring composite crown joints. The progression of damage in the hollow arch can be summarized as follows:\u003c/p\u003e\n\u003cp\u003e1. Stage I (O\u0026ndash;A\u0026ndash;B): Elastic Stage\u003c/p\u003e\n\u003cp\u003eAt the early stage, the arch below the crown is embedded in backfill, and the surrounding soil exerts lateral confinement that effectively restrains deformation. Consequently, crown settlement remains negligible before point A. Once the backfill surpasses the crown elevation (segment A\u0026ndash;B), settlement begins to increase approximately linearly, though the structure still behaves elastically.\u003c/p\u003e\n\u003cp\u003e2. Stage II (B\u0026ndash;C\u0026ndash;D): Progressive Damage Stage\u003c/p\u003e\n\u003cp\u003eDamage initiates at point B when crown settlement reaches about 37 mm, primarily manifesting as minor cracking at the crown joint, haunches, and invert. This substage (IIa) is characterized by slow damage development without significant loss of stiffness. As settlement increases beyond approximately 86 mm at point C, a plastic hinge forms at the left haunch, marking the onset of rapid stiffness degradation and structural instability\u0026mdash;defining substage IIb.\u003c/p\u003e\n\u003cp\u003e3. Stage III (Beyond Point D): Structural Failure Stage\u003c/p\u003e\n\u003cp\u003eWhen crown settlement exceeds approximately 278 mm (point D), plastic hinges have fully formed at the crown and both haunches. Crown deflection escalates sharply, indicating structural collapse and complete loss of load-bearing capacity.\u003c/p\u003e\n\u003cp\u003eCompared with the solid structure, the hollow arch exhibits an approximately 18% reduction in ultimate load-bearing capacity. However, it demonstrates significantly enhanced deformation capacity in earlier stages: crown settlement in the elastic stage (Stage I) increases by 68%, and deformation tolerance in substage IIa improves by 72%.\u003c/p\u003e\n\u003cp\u003eAccordingly, a crown settlement limit of 86 mm is recommended for the design of hollow structures. To ensure that damage remains within the controllable and repairable range (Stage IIa), it is advisable to reinforce the haunch regions, strictly regulate the backfilling thickness and compaction, and set an early-warning threshold when crown settlement reaches approximately 37 mm.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study, grounded in the context of the Chongqing Xinsen Avenue open-cut long-span precast tunnel project, developed a refined soil-structure interaction model via finite element analysis (FEA). Through sensitivity analysis of key parameters and validation against field monitoring data, the model's accuracy was confirmed. A systematic assessment was conducted on the mechanical behavior and failure mechanism of a long-span precast hollow arch structure with composite joints, yielding the following main conclusions:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSoil-structure friction, riprap concrete hardening, and layered compaction significantly influence internal force distribution. Neglecting compaction load can lead to over 20% underestimation of crown bending moment, highlighting the necessity of fine-grained calculations synchronized with actual construction stages.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe combination of composite crown joints and grouted toe key joints forms a stable two-hinged arch load-bearing system. The high consistency between on-site monitoring and FEA results validates both the mechanical model and the proposed construction method.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eA 14% cavity ratio in the arch cross-section reduces peak axial force and shear force by 142 kN and 168 kN, respectively. Although local bending moment increases by approximately 160 kN\u0026middot;m, overall stresses remain within allowable design limits.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe final horizontal convergence (2.14 mm) and vertical crown deflection (7.21 mm) are well below the l/300 span limit, even with a\u0026thinsp;~\u0026thinsp;6% increase in peak displacement due to the hollow design. This indicates the structure retains sufficient safety redundancy.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe ultimate bearing capacity of the hollow arch is only 18% lower than that of the solid arch. Both structures fail through a four-hinge mechanism at the crown, haunches, and invert, confirming that weight reduction does not significantly compromise safety.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eA crown settlement of 86 mm is recommended as the limit control value, with 37 mm as a warning threshold. To maintain structural integrity, reinforcement should be enhanced at the haunch and joint regions, and backfill layer thickness and compaction quality must be strictly controlled.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eFuture work will focus on the long-term durability and seismic performance of composite joints, multi-objective optimization of cavity parameters, large-scale ultimate load testing of full-ring structures, and incorporation of life-cycle low-carbon economic assessments, aiming to develop a standardized, resilient, and environmentally friendly design system for precast arch structures.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZhanglong Xu: Investigation, Methodology, Data curation, Validation, Writing - Original Draft, Visualization. Zhi Lin: Supervision, Methodology, Funding acquisition, Project administration, Writing - Review \u0026amp; Editing. Xiande Guo: Data Curation, Writing \u0026ndash; review \u0026amp; editing. Wanlin Feng: Formal analysis, Writing - Review \u0026amp; Editing. Xiaoying Gou: Investigation, Writing - Review \u0026amp; Editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflicts of interest related to this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to acknowledge the financial support received from the National Natural Science Foundation of China (Grant numbers 52078089 and 52274176), the Chongqing Natural Science Foundation Innovation and Development Joint Fund (CSTB2022NSCQ-LZX0079), and the China Construction Seventh Bureau Science and Technology R \u0026amp; D Project(CSCEC7B-2022-Z-19).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003eData requests should be addressed to the \u0026nbsp;first author: Zhanglong Xu, [email protected], College of Civil Engineering, Chongqing Jiaotong University.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLiu, G., Gu, T., Xu, P., Hong, J., Shrestha, A., \u0026amp; Martek, I., 2019. 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Shear capacity of precast concrete shear keys with ultrahigh-performance concrete for connections. J. Bridge Eng. 26(7): 04021036.\u003c/li\u003e\n\u003cli\u003eAASHTO, 2012. LRFD Bridge Design Specifications. American Association of State Highway and Transportation Officials, Washington, DC.\u003c/li\u003e\n\u003cli\u003eJia, J., Ren, Z., Bai, Y., et al., 2023. Tensile behavior of UHPC wet joints for precast bridge deck panels. Eng. Struct. 282: 115826.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Lightweight prefabricated arch, cut-and-cover tunnel, soil–structure interaction, bearing characteristic, failure mechanism","lastPublishedDoi":"10.21203/rs.3.rs-7052054/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7052054/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAn innovative composite-jointed arch structure is proposed to address construction challenges such as slow progress, high precision requirements, and elevated costs encountered in the large-span prefabricated cut-and-cover tunnel project of Xinsen Avenue in Chongqing. The study incorporates theoretical analyses, field tests, and nonlinear numerical simulations to examine the mechanical properties, deformation characteristics, load-bearing mechanisms, and failure modes of prefabricated hollow structures compared to solid structures. Results indicate the newly developed composite-jointed arch structure exhibits excellent load-bearing capacity. The structure forms a two-hinged arch system, where grout-keyed joints at the inverted arch and rubble-concrete sidewall backfills collectively ensure horizontal and vertical stability, maintaining overall structural integrity. Composite joints efficiently transfer internal forces, ensuring coordinated deformation of components. Although hollow structures experience increased stress and deformation due to reduced stiffness and sectional discontinuity-induced stress concentration, both solid and hollow structures exhibit typical four-hinged failure mechanisms under ultimate loading conditions without significant degradation of ultimate load-bearing capacity. Current thin-walled hollow components effectively balance weight reduction with structural safety, significantly enhance concrete temperature control efficiency, shorten lifting periods, optimize construction efficiency and economic indicators, and promote broader application and development of prefabricated techniques in underground engineering.\u003c/p\u003e","manuscriptTitle":"Study on the mechanical performance of lightweight arched prefabricated structures in large-span cut-and-cover tunnels","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-15 17:40:32","doi":"10.21203/rs.3.rs-7052054/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ec1793c1-ca65-4752-898c-571f9cf38192","owner":[],"postedDate":"July 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":51409666,"name":"Physical sciences/Engineering"},{"id":51409667,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-09-23T09:24:30+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-15 17:40:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7052054","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7052054","identity":"rs-7052054","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}