Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei

Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei | 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 Method Article Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei Tai-Yi Liu, Chao-Pang Wang, Shih-Ping Ho, Sung-Fang Yeh, Kai-Chun Ten, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8333320/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Feb, 2026 Read the published version in Geotechnical and Geological Engineering → Version 1 posted 12 You are reading this latest preprint version Abstract This study examines advanced grouting techniques applied in the Taipei MRT Zhonghe–Wanda Line project, particularly the underground section between LG06 and Y11 stations. Dense underground utilities and challenging subsurface conditions—soft silty clay and a shallow groundwater table—made conventional diaphragm walls infeasible. Two methods were implemented: standard high-pressure jet grouting (JSG) and large-diameter super high-pressure jet grouting. Retaining piles were constructed by injecting cement grout (100–220 kg/cm²) via rotating drill rods, then inserting H-shaped steel beams to form high-strength, low-permeability composite elements. In critical areas beneath power lines and telecom conduits, 3.6 m super high-pressure grouting (up to 400 kg/cm²) was used to enhance soil uniformity and minimize impacts on adjacent infrastructure. Detailed construction records—grout pressure, flow rate, and lifting speed—were maintained. Post-construction coring and laboratory tests confirmed unconfined compressive strength ≥ 10 kg/cm² and permeability K ≤ 10⁻⁵ cm/sec. The results demonstrate that integrating standard and large-diameter jet grouting effectively addresses excavation challenges in dense urban environments and provides a practical reference for future MRT developments. Jet Grouting Soil Improvement Underground MRT Construction High-Density Urban Utilities Super High-Pressure Grouting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1 Introduction Urban mass rapid transit (MRT) construction in densely populated metropolitan areas presents significant engineering challenges, especially when it involves underground excavation in soft or unstable soil conditions. The Taipei MRT Zhonghe–Wanda Line project exemplifies these challenges, particularly the underground connecting passage between LG06 and Y11 stations, traversing complex geotechnical environments and densely built urban utilities, including 161KV power trench, telecommunication cables, gas supply pipes, water supply pipes, and sewage Pipes. The subsurface profile includes soft alluvial soils, silt and clay layers with high plasticity, and a relatively shallow groundwater table—conditions that demand robust excavation support and effective ground improvement strategies [ 1 ]. Figure 1 illustrates the geographical context of the Zhonghe–Wanda Line, delineating the positions of LG06 and Y11 stations and the alignment of the intervening underground connecting passage within the urban fabric. As shown in Fig. 2 , the cross-sectional schematic depicts the intricate arrangement of major subterranean utilities—including water, gas, sewage, and 161 kV electrical conduits—positioned directly above the proposed connecting passage, highlighting the complexity of the construction environment. Traditional retaining systems and soil improvement techniques for excavation often prove inadequate under such demanding conditions, especially in urban environments where vibration, noise, and settlement must be strictly controlled to protect adjacent utilities and structures [ 2 ]. The steel sheet piles, steel H beams, bored-hole RC piles, and diaphragm walls were widely adopted to serve as the retaining system for excavation [ 3 ]. To meet these requirements, this study focuses on two advanced geotechnical solutions: high-pressure jet grouting (JSG) and large-diameter super high-pressure jet grouting. These techniques are increasingly applied in urban tunnelling due to their ability to enhance soil strength, reduce permeability, and provide ground stability during deep excavation [ 4 ]. The retaining pile system adopted for this project involves a 0.8-meter-diameter jet grouted column formed using rotating drill rods equipped with high-pressure nozzles. Cementitious grout is injected at pressures of 100 ~ 220 kg/cm² to form Jet-grouted columns. Steel H-piles are then inserted into the freshly grouted mass to form composite elements capable of resisting earth pressure and groundwater intrusion [ 5 ]. This methodology reduces environmental disturbance and ensures construction safety even in the presence of nearby telecom ducts and power cables. Figure 3 presents a schematic representation of a high-pressure jet-grouted column incorporating an H-shaped steel pile, elucidating the interaction between the soilcrete mass, the reinforced element, and their proximity to adjacent underground works. To further strengthen the subsoil beneath critical utility corridors, the project employed a 3.6-meter-diameter super high-pressure jet grouting method. This technique uses dual symmetric nozzles delivering grout at 400 kg/cm² with high flow rates (up to 300 L/min), creating homogeneous jet-grouted columns of exceptional size and uniformity. The enhanced soil bodies significantly improve load-bearing capacity and reduce permeability, essential for safe excavation near vital infrastructures such as 161kV power lines and deep communication ducts [ 6 ]. This dual-method approach offers an adaptable solution for managing excavation-induced risks in urban transit systems. The objective of this paper is to document and assess the implementation of these innovative grouting methods, analysing their practical performance in the context of the CQ861 contract zone. The report outlines equipment specifications, grout mix designs, construction sequencing, and quality control protocols. Field coring and laboratory tests were conducted to verify the unconfined compressive strength and permeability of the soilcrete columns, ensuring compliance with the project’s technical specifications (≥ 10 kg/cm²; K ≤ 10⁻⁵ cm/sec) [ 7 ]. Through this case study, the paper demonstrates the feasibility, reliability, and engineering value of advanced jet grouting techniques for MRT projects in complex urban terrains. The findings contribute to improved geotechnical design practices and offer practical references for future underground construction endeavours in similar geological and infrastructural settings [ 8 ]. 2. Methodology To address the geotechnical complexities in the Taipei MRT Zhonghe–Wanda Line CQ861 project—especially the underpass between LG06 and Y11 stations—this study adopted a field-driven engineering methodology that combines high-pressure jet grouting (JSG) and large-diameter super high-pressure grouting. The methodology includes equipment selection, construction sequencing, grout material control, quality assurance, and performance validation. 2.1 Retaining Pile Construction with JSG The retaining piles were constructed using a jet mixing method, involving in-situ soil cutting and cement grout injection, followed by steel H-beam insertion. Jet grouting was carried out using both 30B crawler-type and CC-2L hydraulic drill rigs, selected based on site constraints and required penetration depth. Drill rods equipped with high-pressure nozzles rotated while injecting grout at 100–220 kg/cm² to form cylindrical silcrete columns approximately 0.8 m in diameter. After reaching the target depth of 18–19 meters, the rods were withdrawn at a controlled rate (e.g., 13 sec/5 cm), and H428*407*20*35 steel piles were placed into the fresh grout to form composite piles with high structural integrity and permeability. Figure 4 comprises a series of site photographs documenting the installation of H-Pile within a Jet-Grouted Column. The cement grout was mixed at 505 kg of cement and 840 L of water per cubic meter, targeting a specific gravity of 1.345 ± 5% [ 8 ]. 2.2 Large-Diameter Super High-Pressure Grouting for Soil Improvement In areas beneath critical infrastructure, such as 161kV power lines and major telecom conduits, traditional JSG was inadequate. A super high-pressure, large-diameter grouting method (3.6 m) was thus employed. This system used double-tube drilling rods with dual 2.6 mm nozzles that delivered cementitious slurry at 400 ± 40 kg/cm². The technique involved initial waterjet cutting at 300 kg/cm² to fracture and loosen the soil, followed by grout injection in alternating cycles. Figure 5 illustrates the sequential procedure for constructing a 3.6-meter super high-pressure jet-grouted column, encompassing double-tube drilling, waterjet pre-cutting, and subsequent grout injection required to generate a uniform large-diameter soilcrete body. Each column was formed incrementally from the bottom up, using lifting speeds of 51 sec/2.5 cm and rotation speeds of 2 ~ 3 rpm. The process ensured uniform mixing of in-situ soils with the grout, forming continuous cylindrical bodies with superior load-bearing and waterproofing performance [ 9 ]. The grouting sequence followed a leapfrog (jump pile) pattern to avoid interaction between adjacent piles and maintain column continuity. 2.3 Quality Control and Verification Comprehensive quality control protocols were applied during and after construction. Real-time monitoring systems recorded injection pressures, flow rates, grout volumes, and drill rod movements. Using NX casing, the central and peripheral coring locations were employed for post-construction verification of column integrity, strength uniformity, and material homogeneity, as shown in Fig. 6 . The unconfined compressive strength of the silcrete was tested in accordance with CNS 12384 A3282, targeting ≥ 10 kg/cm². Permeability was assessed through falling head tests, with the allowable coefficient set to ≤ 10⁻⁵ cm/sec, in line with project specifications [ 10 ]. The Recovery Quality Designation (RQD) of the core samples was required to exceed 90% for column acceptance. Figure 7 presents photographic records of on-site inspections, demonstrating both the grouting operations and the subsequent evaluation of extracted core samples for Recovery Quality Designation (RQD) compliance. (Inspected by the corresponding author) This integrated methodology ensured both structural performance and environmental compatibility in an urban MRT context, while offering a replicable model for future underground construction projects under similar geotechnical constraints. Figure 8 illustrates the spatial configuration of the jet-grouted H-piles and the adjacent super high-pressure grouting zones, emphasizing column overlap, geometric continuity, and their collective role in stabilizing the connecting passage. 3. Problems Faced and Solutions The construction of the Taipei MRT Zhonghe–Wanda Line between LG06 and Y11 stations encountered numerous technical and logistical challenges due to complex urban geologic conditions and highly congested utility corridors. This section outlines the major problems encountered during the retaining pile and soil improvement phases, and the engineered solutions implemented to ensure construction quality and safety. 3.1 Congested Underground Utilities One of the most critical problems was the high density of underground utilities, including 161kV power lines, major telecommunications ducts, water mains, and gas pipelines. Trial excavations revealed that some of these could not be relocated due to service continuity requirements and spatial limitations. As shown in Fig. 9 , trial excavation photographs reveal the density and complexity of underground utilities at the conflict zone, including multiple intersecting ducts and pipelines that impose significant constraints on excavation strategy. A traditional bored pile or diaphragm wall posed a high risk of damaging these installations through vibration or displacement. (Inspected by the corresponding author) Solution : A “jump pile” sequencing strategy was adopted in combination with small-diameter high-pressure jet grouting, which reduced construction-induced ground movement. For areas under sensitive facilities, large-diameter (3.6 m) super high-pressure jet grouting was implemented using a waterjet pre-cutting method to reduce lateral stress propagation. The use of symmetrical double-tube systems also minimized eccentric disturbance [ 11 ]. Real-time monitoring of displacement and settlement was employed to guide adjustments in pile layout and injection pressure during execution [ 12 ]. 3.2 Variable and Weak Soil Profiles The subsurface stratigraphy consisted of loose fill, soft silty clays, and interbedded sand seams. The strength and permeability characteristics varied significantly even within short lateral distances. These inconsistencies made it difficult to achieve uniform soil improvement, leading to potential seepage risks and excavation instability. Solution : The project team adjusted grouting parameters dynamically based on in-situ conditions. For example, in sandier zones, cement content was increased by 10–15% to enhance the binding effect. In cohesive layers, pre-cutting with waterjets was extended to increase grout penetration. This adaptive approach ensured that the resulting silcrete columns met the required unconfined compressive strength (≥ 10 kg/cm²) and permeability (K ≤ 10⁻⁵ cm/sec), as confirmed by post-construction coring and testing [ 13 ]. 3.3 Limited Construction Access and Urban Constraints The site was located at a major traffic intersection, with commercial buildings, residential towers, and public infrastructure on all sides. There was limited working space, strict noise and vibration restrictions, and constrained access for machinery mobilization and material delivery. Solution : Compact drilling equipment and modular grout batching systems were selected to reduce the construction footprint. Night-time deliveries and modular staging areas were arranged to reduce daytime traffic disruption. A detailed Environmental Protection Plan (EPP) was executed, incorporating acoustic barriers, sedimentation tanks, and vibration control protocols, in compliance with city construction regulations [ 14 ]. 3.4 Groundwater Control and Seepage Risk The shallow groundwater table (~ 2–3 m below the surface) posed a significant challenge during excavation. The risk of uplift pressure and seepage through untreated zones had to be minimized to ensure bottom stability of the cut. Solution : To mitigate the challenges posed by the shallow groundwater table (~ 2–3 m below ground level), a combination of large-diameter super high-pressure jet grouting columns was employed to enhance both seepage resistance and uplift stability. These grouting columns formed an impervious and reinforced subgrade, effectively minimizing seepage through untreated zones and counteracting potential uplift pressure. The effectiveness of this measure was verified through piezometric monitoring, which indicated stable hydraulic conditions and negligible groundwater intrusion during excavation [ 15 ]. 3.5 H-Pile Removal Difficulty Following the completion of jet grouting and excavation support, the removal of embedded steel H-piles posed significant engineering challenges. These piles, firmly bonded to the surrounding soilcrete, extended deep into stratified ground layers with varying stiffness. Extraction was further complicated by limited working space, stringent noise and vibration restrictions, and the presence of critical aboveground and underground infrastructure. In particular, the overhead steel girder of the Yellow Line MRT restricted the vertical clearance at the site to just 6 meters, severely limiting the allowable hoisting height for pile removal. This constraint rendered conventional full-length extraction methods infeasible, especially for standard H-piles exceeding 6 meters in length. Solution : To overcome these challenges, a segmented removal method was adopted. Each H-pile was cut into sections shorter than 4 meters to accommodate the constrained headroom beneath the Yellow Line MRT girder. High-torque vibratory drivers (e.g., PC400) were combined with waterjet perimeter cutting, which effectively weakened the bond between the steel and surrounding soilcrete. In shallower layers (GL: 0 to -2 m), waterjet cutting was omitted to avoid disturbing adjacent facilities. A leapfrog (jump extraction) sequence was also implemented to reduce ground reaction and facilitate safe removal. This modified approach ensured efficient pile recovery under severe spatial and structural constraints. Table 1 lists the summary of the Problems and Solutions in CQ861 Project. Table 1 The summary of the Problems and Solutions in CQ861 Project. Problem Description Engineered Solution Congested Underground Utilities High-density utility networks (161kV lines, telecom ducts, etc.) restricted conventional excavation. Used “jump pile” sequencing with small-diameter JSG; applied 3.6 m super high-pressure grouting in sensitive zones; real-time displacement monitoring guided adjustments. Variable and Weak Soil Profiles Soft silty clays and sand seams caused uneven grout behavior and seepage risks. Adjusted grout mix in situ; increased cement in sandy layers and extended waterjet pre-cutting in cohesive zones. Limited Construction Access Narrow work zones with strict noise and vibration limits hampered logistics. Used compact rigs and modular systems; arranged night-time deliveries; implemented EPP with acoustic/vibration controls. Groundwater and Seepage Risk Shallow water table (~ 2–3 m) created uplift and seepage hazards. Installed large-diameter super high-pressure grout columns as a bottom seal; confirmed performance via piezometric monitoring. H-Pile Removal under Height Limitation MRT Yellow Line steel girder limited headroom to 6 m, restricting full pile extraction. Cut H-piles into < 4 m segments; used vibratory drivers with waterjet pre-cutting and jump extraction sequence. 4. Findings Following the implementation of high-pressure and super high-pressure jet grouting techniques in the Taipei MRT Zhonghe–Wanda Line CQ861 project, comprehensive field testing and performance assessments were conducted. This section presents the key findings related to structural performance, ground improvement effectiveness, permeability control, and environmental impact mitigation. 4.1 Compressive Strength and Structural Integrity Core samples retrieved from both standard jet grouting and super high-pressure columns exhibited excellent strength development. Laboratory testing on unconfined compressive strength (UCS) samples, prepared following CNS 12384 A3282, showed that most silcrete specimens exceeded the project requirement of 10 kg/cm². The average UCS values were: 12.6 kg/cm² for 0.8 m standard JSG columns. 15.2 kg/cm² for 3.6 m super high-pressure columns. Edge and center samples indicated consistent distribution, with a coefficient of variation (COV) below 8%, demonstrating good homogeneity (Please see Fig. 6 ). The presence of H-piles in jet-mixed columns further enhanced load distribution and bending resistance, improving pile-wall performance during excavation stages [ 16 ]. 4.2 Permeability and Seepage Resistance Falling-head permeability tests on core samples and in-situ packer tests confirmed that permeability coefficients consistently fell below the target of 1×10⁻⁵ cm/sec. Most results ranged between 2.3×10⁻⁶ and 7.1×10⁻⁶ cm/sec. These values are indicative of near-impermeable behavior, especially critical in zones with shallow groundwater and flood-prone conditions [ 17 ]. Seepage monitoring using piezometers installed at the tunnel invert level showed negligible fluctuations during excavation, validating the efficacy of the impermeable grout curtain system. This minimized uplift pressure and water ingress, ensuring safe and dry excavation conditions throughout construction. 4.3 Geometric Accuracy and Column Continuity Non-destructive testing using borehole camera inspection and ground-penetrating radar (GPR) revealed good geometric conformity of the grout columns to design specifications. The deviation in column diameter was typically within ± 5% of target values. In areas where the double-tube super high-pressure method was employed, column overlap achieved over 95% continuity, with no significant voids or soft zones detected. The column grid installed beneath the connecting tunnel formed an effective load-transfer platform and groundwater barrier. The excavation progression of the underground connecting passage, documenting exposed soil strata, temporary structural supports, and field personnel operating within the confined subsurface workspace, as shown in Fig. 10 . (Inspected by the corresponding author) 4.4 Environmental and Construction Efficiency Outcomes The selected methods proved advantageous in reducing environmental impact. Ground vibration monitoring during drilling and injection phases showed peak particle velocities (PPV) below 2 mm/s at sensitive locations, well under regulatory limits. Noise levels remained under 75 dBA due to the use of low-noise batch mixing units and acoustically shielded drilling rigs [ 18 ]. In terms of productivity, the average installation rate reached: 12–15 m/day per rig for standard JSG piles. 5–7 m/day per rig for large-diameter super high-pressure columns. Despite the slower rate for larger columns, the method’s effectiveness near critical infrastructure justified its use. No utility damage or safety incidents were recorded during execution, underscoring the reliability of the applied technologies. These findings demonstrate that the combined approach of JSG and super high-pressure grouting not only met but exceeded the performance criteria of the CQ861 project [ 19 ], offering a validated model for future underground construction in constrained urban settings. 5. Conclusion and Recommendations This study presented the successful application of high-pressure jet grouting and large-diameter super high-pressure jet grouting techniques in the Taipei MRT Zhonghe–Wanda Line CQ861 contract, particularly in the geotechnically complex and urban-sensitive zone between LG06 and Y11 stations. The engineering challenges encountered—such as weak and heterogeneous soils, shallow groundwater, and dense utility networks—required advanced and adaptable ground improvement solutions. Through carefully designed grouting methodologies, quality control protocols, and field testing, the project achieved its technical and safety goals without compromising the surrounding urban environment. The use of standard high-pressure jet grouting in retaining pile construction enabled effective integration of structural elements (H-piles) into strengthened soilcrete bodies, resulting in a system that offered both load-bearing and impermeability functions. Meanwhile, the deployment of large-diameter super high-pressure jet grouting beneath sensitive facilities and the connecting tunnel provided enhanced strength and seepage resistance, even in variable soil conditions. The leapfrog sequencing and double-tube nozzle systems ensured uniform grout distribution while minimizing disturbance to nearby utilities and structures. Post-construction evaluations confirmed that both the unconfined compressive strength and permeability performance of the grouted bodies met or exceeded project specifications. Furthermore, geometric precision, column continuity, and environmental compliance were all verified through rigorous monitoring and inspection. These results demonstrate that the combined use of high-pressure and super high-pressure grouting can effectively address the multifaceted requirements of urban underground infrastructure development. Based on the experience and outcomes of this project, several recommendations are offered for similar future applications: Early Integration of Utility Mapping and Risk Assessment : Accurate utility surveys and proactive coordination with utility owners are essential. Risk zones should be identified early, and flexible grouting solutions should be planned accordingly. Adaptive Grouting Strategy : Grouting parameters should be dynamically adjusted based on soil variability encountered during execution. Real-time monitoring tools and soil classification logs are critical for guiding in-field decisions. Use of Super High-Pressure Grouting in Critical Areas : For sections beneath sensitive infrastructure or where conventional methods pose a risk, super high-pressure jet grouting should be considered. Though slower in installation, its benefits in strength, uniformity, and safety outweigh the longer execution time. Comprehensive Quality Assurance : Field sampling, lab testing, and non-destructive evaluation should be consistently applied to verify performance and minimize construction uncertainty. Environmental Mitigation Planning : Projects in urban environments must implement stringent vibration, noise, and groundwater management plans. Compact equipment, shielded systems, and staged work schedules can greatly reduce the project’s environmental footprint. In conclusion, this case study reinforces the effectiveness, adaptability, and reliability of advanced grouting methods for MRT projects in challenging urban contexts. It provides a valuable reference for engineers, planners, and contractors tasked with delivering safe, high-quality underground infrastructure amid complex site constraints. Declarations Data Availability Statement The datasets generated and/or analyzed during the current study include publicly accessible technical specifications and standards, while project-specific construction data are available from the corresponding author, T.-Y. Liu, upon reasonable request, subject to confidentiality restrictions of the Taipei MRT project. Author Contributions Statement T.-Y. Liu conceived the study, supervised the research, and led manuscript writing. C.-P. Wang contributed to methodology and data processing. S.-P. Ho provided academic guidance and technical review. S.-F. Yeh supported project information verification. K.-C. Ten assisted with field investigations and construction documentation. B.-C. Ciou prepared figures and contributed to data compilation. Acknowledgment The authors sincerely acknowledge the Department of Rapid Transit Systems, Taipei City Government, for their continuous guidance, coordination, and provision of essential project information throughout the execution of this work. The authors also extend their appreciation to New Asia Construction and Development Corporation for offering technical support, site access, and valuable professional insights during field investigations and construction activities. The dedicated efforts of the onsite engineers, project teams, and technical staff in assisting with data collection, documentation, and quality verification significantly strengthened the rigor and completeness of this study. Their collective contributions are gratefully recognized. Disclosure Statement The authors declare that they have no known financial, commercial, legal, or professional conflicts of interest that could have influenced the research, analyses, or conclusions presented in this manuscript. All work was conducted independently, and no external organization or individual provided support that could be perceived as creating a competing interest. The affiliations of the authors, including roles related to the project, did not influence the objectivity or integrity of the study. References Department of Rapid Transit Systems (DORTS). (2016). Project Geotechnical Report: Taipei MRT Zhonghe–Wanda Line, CQ861 Section (Internal Report). Taipei City Government. (In Chinese, unpublished document) Ni, J. C. (2005). Grouting techniques in urban underground engineering. Taipei: Department of Civil Engineering, National Taipei University of Technology. 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Chou, Po-Han Chen, and Ching-Lung Liao, (2020). “Soil Improvement and Inspection Techniques for the Base Course of Rigid Pavement for an Airport Runway.” ASCE Journal of Performance of Constructed Facilities. https://doi.org/10.1061/(ASCE)CF. 1943-5509.0001560. (SCI). CNS (Chinese National Standards). (2022). CNS 12384 A3282: Unconfined compressive strength test for soilcrete (in Chinese). Bureau of Standards, Metrology and Inspection, Ministry of Economic Affairs, Taiwan. Tai-Yi Liu. (2021) “Enhancing the Risk Management and Carbon Emission Reduction Using a Special Retaining Method for Excavation.” In: Eliva Press SRL, Available in Amazon 2022, https://www.amazon.com/dp/1636486428 ; https://www.elivapress.com/en/book/book-7890848335/ . New Asia Construction and Development Corporation. (2014). “Jet Grouting Method Statement for CQ861 – LG06 Station”. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document) New Asia Construction and Development Corporation. (2014). “Test Method Statement for Unconfined Compressive Strength of Grouting”. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document) Jines Construction (2025): “Double Tube Grouting to Stop Water In Saline-Alkali Area”, Jines Construction 2025, https://www.jines.com/en/grouting-edm11/ . Mandolini, A. & Viggiani, C. (1997). “Settlement of piled foundations”, Geo-technique 47, No. 4, 791–816. https://www.researchgate.net/publication/245410705_Settlement_of_piled_foundations#fullTextFileContent . New Asia Construction and Development Corporation. (2014). “Test Method Statement for Grouting Permeability”. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document). New Asia Construction and Development Corporation. (2014). “Environmental Protection Plan (EPP)”. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document).. Liu, TY., Chou, N.N.S., Lin, SJ. et al. (2021). “Challenges and Sustainability-Based Solutions of Diaphragm Wall Construction for LG06 Underground Station in Taipei MRT.” Transportation Infrastructure Geotechnology (ESCI). https://doi.org/10.1007/s40515-021-00208-0 . New Asia Construction and Development Corporation. (2014). “Test Method Statement for Retaining Grouting Column with the Steel H-Beams”, Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document). Geotech Data (2025) “Falling head permeability test”, Geotech Data 2025, https://www.geotechdata.info/geotest/falling-head-permeability-test . Chang, Y.S., Fan, J.Y., Liu, T.Y. (2021). “In-Situ Test Reports for noise and vibration monitoring.”, Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document). New Taipei City Government. (2025). “Climate action: Noise and Vibration Control Standards.”, New Taipei City Government Policies, https://foreigner.ntpc.gov.tw/home.jsp?id=0e5a1b2e43639bf0 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 25 Feb, 2026 Read the published version in Geotechnical and Geological Engineering → Version 1 posted Editorial decision: Revision requested 25 Jan, 2026 Reviews received at journal 24 Jan, 2026 Reviews received at journal 14 Jan, 2026 Reviews received at journal 31 Dec, 2025 Reviewers agreed at journal 26 Dec, 2025 Reviewers agreed at journal 26 Dec, 2025 Reviewers agreed at journal 25 Dec, 2025 Reviewers agreed at journal 24 Dec, 2025 Reviewers invited by journal 12 Dec, 2025 Editor assigned by journal 12 Dec, 2025 Submission checks completed at journal 12 Dec, 2025 First submitted to journal 11 Dec, 2025 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. 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2","display":"","copyAsset":false,"role":"figure","size":399871,"visible":true,"origin":"","legend":"\u003cp\u003eThe complicate urban utilities in the site.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/7cbfda1460f0a3fcd64c33fd.png"},{"id":100736903,"identity":"df4ab5cf-72c3-454d-b471-208b8f7f505d","added_by":"auto","created_at":"2026-01-20 22:46:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":366402,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of High-Pressure Jet Grouting Pile with H-Pile Insertion.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/2d8825d572ad7fb91e2f478f.png"},{"id":100737060,"identity":"928edcdf-0992-4d24-b35e-cf83fa18cfb2","added_by":"auto","created_at":"2026-01-20 22:48:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":566432,"visible":true,"origin":"","legend":"\u003cp\u003eSome site photos of H-Pile within Jet-Grouted Column.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/3f0146caf94671a7a738537a.png"},{"id":100737056,"identity":"dd0075f5-1d91-4109-9e73-6754f1118d06","added_by":"auto","created_at":"2026-01-20 22:48:45","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":72163,"visible":true,"origin":"","legend":"\u003cp\u003eThe Process Diagram of Super High-Pressure 3.6 m Grouting with Waterjet Pre-cutting.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/e290c670087e4b62fc8f0acc.png"},{"id":100737260,"identity":"767dd7f2-978a-4d68-beff-70c614eb203a","added_by":"auto","created_at":"2026-01-20 22:51:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":91447,"visible":true,"origin":"","legend":"\u003cp\u003eCoring and sample locations for grout column strength verification.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/e58fbd25ff3aea71e84f7c9c.png"},{"id":100737237,"identity":"a8c926b1-7837-4e9b-b93e-0bd2303b4543","added_by":"auto","created_at":"2026-01-20 22:51:11","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":546893,"visible":true,"origin":"","legend":"\u003cp\u003eThe site inspections of the grouting and the RQD verification after the core sampling.\u003c/p\u003e\n\u003cp\u003e(Inspected by the corresponding author)\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/c40d7c263b0863ab3ac6f538.png"},{"id":100737121,"identity":"f3a5eca0-7767-4d47-a6f5-ab6db7d1ffcc","added_by":"auto","created_at":"2026-01-20 22:49:09","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":516268,"visible":true,"origin":"","legend":"\u003cp\u003eThe plan layout of the JSG H-piles and the Super High-Pressure Jet Grouping.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/3e1ab6d231a987899c40cee4.png"},{"id":100736908,"identity":"b9df2c37-6cd8-44b7-b14b-78abff1eecaa","added_by":"auto","created_at":"2026-01-20 22:46:37","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":618493,"visible":true,"origin":"","legend":"\u003cp\u003eTrial Excavation Revealing high-density utility conflict zone. (Inspected by the corresponding author)\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/5f0c0baa20a005836121e374.png"},{"id":100737248,"identity":"81490c1c-ad3c-4b2f-98a2-51ec697edaa0","added_by":"auto","created_at":"2026-01-20 22:51:16","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":435334,"visible":true,"origin":"","legend":"\u003cp\u003eField excavation photos of the underground connecting passage. (Inspected by the corresponding author)\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/094bc9c0ad708747e60ae83f.png"},{"id":103765688,"identity":"3f8e6c97-245a-40fb-bfb2-d9e2a4e7208e","added_by":"auto","created_at":"2026-03-02 16:07:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4860933,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8333320/v1/38939a49-09e0-4230-a334-05d8dff66f66.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eUrban mass rapid transit (MRT) construction in densely populated metropolitan areas presents significant engineering challenges, especially when it involves underground excavation in soft or unstable soil conditions. The Taipei MRT Zhonghe\u0026ndash;Wanda Line project exemplifies these challenges, particularly the underground connecting passage between LG06 and Y11 stations, traversing complex geotechnical environments and densely built urban utilities, including 161KV power trench, telecommunication cables, gas supply pipes, water supply pipes, and sewage Pipes. The subsurface profile includes soft alluvial soils, silt and clay layers with high plasticity, and a relatively shallow groundwater table\u0026mdash;conditions that demand robust excavation support and effective ground improvement strategies [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the geographical context of the Zhonghe\u0026ndash;Wanda Line, delineating the positions of LG06 and Y11 stations and the alignment of the intervening underground connecting passage within the urban fabric. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the cross-sectional schematic depicts the intricate arrangement of major subterranean utilities\u0026mdash;including water, gas, sewage, and 161 kV electrical conduits\u0026mdash;positioned directly above the proposed connecting passage, highlighting the complexity of the construction environment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTraditional retaining systems and soil improvement techniques for excavation often prove inadequate under such demanding conditions, especially in urban environments where vibration, noise, and settlement must be strictly controlled to protect adjacent utilities and structures [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The steel sheet piles, steel H beams, bored-hole RC piles, and diaphragm walls were widely adopted to serve as the retaining system for excavation [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. To meet these requirements, this study focuses on two advanced geotechnical solutions: high-pressure jet grouting (JSG) and large-diameter super high-pressure jet grouting. These techniques are increasingly applied in urban tunnelling due to their ability to enhance soil strength, reduce permeability, and provide ground stability during deep excavation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe retaining pile system adopted for this project involves a 0.8-meter-diameter jet grouted column formed using rotating drill rods equipped with high-pressure nozzles. Cementitious grout is injected at pressures of 100\u0026thinsp;~\u0026thinsp;220 kg/cm\u0026sup2; to form Jet-grouted columns. Steel H-piles are then inserted into the freshly grouted mass to form composite elements capable of resisting earth pressure and groundwater intrusion [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This methodology reduces environmental disturbance and ensures construction safety even in the presence of nearby telecom ducts and power cables. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents a schematic representation of a high-pressure jet-grouted column incorporating an H-shaped steel pile, elucidating the interaction between the soilcrete mass, the reinforced element, and their proximity to adjacent underground works.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further strengthen the subsoil beneath critical utility corridors, the project employed a 3.6-meter-diameter super high-pressure jet grouting method. This technique uses dual symmetric nozzles delivering grout at 400 kg/cm\u0026sup2; with high flow rates (up to 300 L/min), creating homogeneous jet-grouted columns of exceptional size and uniformity. The enhanced soil bodies significantly improve load-bearing capacity and reduce permeability, essential for safe excavation near vital infrastructures such as 161kV power lines and deep communication ducts [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This dual-method approach offers an adaptable solution for managing excavation-induced risks in urban transit systems.\u003c/p\u003e \u003cp\u003eThe objective of this paper is to document and assess the implementation of these innovative grouting methods, analysing their practical performance in the context of the CQ861 contract zone. The report outlines equipment specifications, grout mix designs, construction sequencing, and quality control protocols. Field coring and laboratory tests were conducted to verify the unconfined compressive strength and permeability of the soilcrete columns, ensuring compliance with the project\u0026rsquo;s technical specifications (\u0026ge;\u0026thinsp;10 kg/cm\u0026sup2;; K\u0026thinsp;\u0026le;\u0026thinsp;10⁻⁵ cm/sec) [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThrough this case study, the paper demonstrates the feasibility, reliability, and engineering value of advanced jet grouting techniques for MRT projects in complex urban terrains. The findings contribute to improved geotechnical design practices and offer practical references for future underground construction endeavours in similar geological and infrastructural settings [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cp\u003eTo address the geotechnical complexities in the Taipei MRT Zhonghe\u0026ndash;Wanda Line CQ861 project\u0026mdash;especially the underpass between LG06 and Y11 stations\u0026mdash;this study adopted a field-driven engineering methodology that combines high-pressure jet grouting (JSG) and large-diameter super high-pressure grouting. The methodology includes equipment selection, construction sequencing, grout material control, quality assurance, and performance validation.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Retaining Pile Construction with JSG\u003c/h2\u003e \u003cp\u003eThe retaining piles were constructed using a jet mixing method, involving in-situ soil cutting and cement grout injection, followed by steel H-beam insertion. Jet grouting was carried out using both 30B crawler-type and CC-2L hydraulic drill rigs, selected based on site constraints and required penetration depth. Drill rods equipped with high-pressure nozzles rotated while injecting grout at 100\u0026ndash;220 kg/cm\u0026sup2; to form cylindrical silcrete columns approximately 0.8 m in diameter.\u003c/p\u003e \u003cp\u003eAfter reaching the target depth of 18\u0026ndash;19 meters, the rods were withdrawn at a controlled rate (e.g., 13 sec/5 cm), and H428*407*20*35 steel piles were placed into the fresh grout to form composite piles with high structural integrity and permeability. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e comprises a series of site photographs documenting the installation of H-Pile within a Jet-Grouted Column. The cement grout was mixed at 505 kg of cement and 840 L of water per cubic meter, targeting a specific gravity of 1.345\u0026thinsp;\u0026plusmn;\u0026thinsp;5% [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Large-Diameter Super High-Pressure Grouting for Soil Improvement\u003c/h2\u003e \u003cp\u003eIn areas beneath critical infrastructure, such as 161kV power lines and major telecom conduits, traditional JSG was inadequate. A super high-pressure, large-diameter grouting method (3.6 m) was thus employed. This system used double-tube drilling rods with dual 2.6 mm nozzles that delivered cementitious slurry at 400\u0026thinsp;\u0026plusmn;\u0026thinsp;40 kg/cm\u0026sup2;. The technique involved initial waterjet cutting at 300 kg/cm\u0026sup2; to fracture and loosen the soil, followed by grout injection in alternating cycles. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the sequential procedure for constructing a 3.6-meter super high-pressure jet-grouted column, encompassing double-tube drilling, waterjet pre-cutting, and subsequent grout injection required to generate a uniform large-diameter soilcrete body. Each column was formed incrementally from the bottom up, using lifting speeds of 51 sec/2.5 cm and rotation speeds of 2\u0026thinsp;~\u0026thinsp;3 rpm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe process ensured uniform mixing of in-situ soils with the grout, forming continuous cylindrical bodies with superior load-bearing and waterproofing performance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The grouting sequence followed a leapfrog (jump pile) pattern to avoid interaction between adjacent piles and maintain column continuity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Quality Control and Verification\u003c/h2\u003e \u003cp\u003eComprehensive quality control protocols were applied during and after construction. Real-time monitoring systems recorded injection pressures, flow rates, grout volumes, and drill rod movements. Using NX casing, the central and peripheral coring locations were employed for post-construction verification of column integrity, strength uniformity, and material homogeneity, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe unconfined compressive strength of the silcrete was tested in accordance with CNS 12384 A3282, targeting\u0026thinsp;\u0026ge;\u0026thinsp;10 kg/cm\u0026sup2;. Permeability was assessed through falling head tests, with the allowable coefficient set to \u0026le;\u0026thinsp;10⁻⁵ cm/sec, in line with project specifications [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The Recovery Quality Designation (RQD) of the core samples was required to exceed 90% for column acceptance. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents photographic records of on-site inspections, demonstrating both the grouting operations and the subsequent evaluation of extracted core samples for Recovery Quality Designation (RQD) compliance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Inspected by the corresponding author)\u003c/p\u003e \u003cp\u003eThis integrated methodology ensured both structural performance and environmental compatibility in an urban MRT context, while offering a replicable model for future underground construction projects under similar geotechnical constraints. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e illustrates the spatial configuration of the jet-grouted H-piles and the adjacent super high-pressure grouting zones, emphasizing column overlap, geometric continuity, and their collective role in stabilizing the connecting passage.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Problems Faced and Solutions","content":"\u003cp\u003eThe construction of the Taipei MRT Zhonghe\u0026ndash;Wanda Line between LG06 and Y11 stations encountered numerous technical and logistical challenges due to complex urban geologic conditions and highly congested utility corridors. This section outlines the major problems encountered during the retaining pile and soil improvement phases, and the engineered solutions implemented to ensure construction quality and safety.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Congested Underground Utilities\u003c/h2\u003e \u003cp\u003eOne of the most critical problems was the high density of underground utilities, including 161kV power lines, major telecommunications ducts, water mains, and gas pipelines. Trial excavations revealed that some of these could not be relocated due to service continuity requirements and spatial limitations. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, trial excavation photographs reveal the density and complexity of underground utilities at the conflict zone, including multiple intersecting ducts and pipelines that impose significant constraints on excavation strategy. A traditional bored pile or diaphragm wall posed a high risk of damaging these installations through vibration or displacement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Inspected by the corresponding author)\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eA \u0026ldquo;jump pile\u0026rdquo; sequencing strategy was adopted in combination with small-diameter high-pressure jet grouting, which reduced construction-induced ground movement. For areas under sensitive facilities, large-diameter (3.6 m) super high-pressure jet grouting was implemented using a waterjet pre-cutting method to reduce lateral stress propagation. The use of symmetrical double-tube systems also minimized eccentric disturbance [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Real-time monitoring of displacement and settlement was employed to guide adjustments in pile layout and injection pressure during execution [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Variable and Weak Soil Profiles\u003c/h2\u003e \u003cp\u003eThe subsurface stratigraphy consisted of loose fill, soft silty clays, and interbedded sand seams. The strength and permeability characteristics varied significantly even within short lateral distances. These inconsistencies made it difficult to achieve uniform soil improvement, leading to potential seepage risks and excavation instability.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eThe project team adjusted grouting parameters dynamically based on in-situ conditions. For example, in sandier zones, cement content was increased by 10\u0026ndash;15% to enhance the binding effect. In cohesive layers, pre-cutting with waterjets was extended to increase grout penetration. This adaptive approach ensured that the resulting silcrete columns met the required unconfined compressive strength (\u0026ge;\u0026thinsp;10 kg/cm\u0026sup2;) and permeability (K\u0026thinsp;\u0026le;\u0026thinsp;10⁻⁵ cm/sec), as confirmed by post-construction coring and testing [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Limited Construction Access and Urban Constraints\u003c/h2\u003e \u003cp\u003eThe site was located at a major traffic intersection, with commercial buildings, residential towers, and public infrastructure on all sides. There was limited working space, strict noise and vibration restrictions, and constrained access for machinery mobilization and material delivery.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eCompact drilling equipment and modular grout batching systems were selected to reduce the construction footprint. Night-time deliveries and modular staging areas were arranged to reduce daytime traffic disruption. A detailed Environmental Protection Plan (EPP) was executed, incorporating acoustic barriers, sedimentation tanks, and vibration control protocols, in compliance with city construction regulations [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Groundwater Control and Seepage Risk\u003c/h2\u003e \u003cp\u003eThe shallow groundwater table (~\u0026thinsp;2\u0026ndash;3 m below the surface) posed a significant challenge during excavation. The risk of uplift pressure and seepage through untreated zones had to be minimized to ensure bottom stability of the cut.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eTo mitigate the challenges posed by the shallow groundwater table (~\u0026thinsp;2\u0026ndash;3 m below ground level), a combination of large-diameter super high-pressure jet grouting columns was employed to enhance both seepage resistance and uplift stability. These grouting columns formed an impervious and reinforced subgrade, effectively minimizing seepage through untreated zones and counteracting potential uplift pressure. The effectiveness of this measure was verified through piezometric monitoring, which indicated stable hydraulic conditions and negligible groundwater intrusion during excavation [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5 H-Pile Removal Difficulty\u003c/h2\u003e \u003cp\u003eFollowing the completion of jet grouting and excavation support, the removal of embedded steel H-piles posed significant engineering challenges. These piles, firmly bonded to the surrounding soilcrete, extended deep into stratified ground layers with varying stiffness. Extraction was further complicated by limited working space, stringent noise and vibration restrictions, and the presence of critical aboveground and underground infrastructure.\u003c/p\u003e \u003cp\u003eIn particular, the overhead steel girder of the Yellow Line MRT restricted the vertical clearance at the site to just 6 meters, severely limiting the allowable hoisting height for pile removal. This constraint rendered conventional full-length extraction methods infeasible, especially for standard H-piles exceeding 6 meters in length.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSolution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eTo overcome these challenges, a segmented removal method was adopted. Each H-pile was cut into sections shorter than 4 meters to accommodate the constrained headroom beneath the Yellow Line MRT girder. High-torque vibratory drivers (e.g., PC400) were combined with waterjet perimeter cutting, which effectively weakened the bond between the steel and surrounding soilcrete. In shallower layers (GL: 0 to -2 m), waterjet cutting was omitted to avoid disturbing adjacent facilities. A leapfrog (jump extraction) sequence was also implemented to reduce ground reaction and facilitate safe removal. This modified approach ensured efficient pile recovery under severe spatial and structural constraints.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e lists the summary of the Problems and Solutions in CQ861 Project.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe summary of the Problems and Solutions in CQ861 Project.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProblem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEngineered Solution\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCongested Underground Utilities\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigh-density utility networks (161kV lines, telecom ducts, etc.) restricted conventional excavation.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUsed \u0026ldquo;jump pile\u0026rdquo; sequencing with small-diameter JSG; applied 3.6 m super high-pressure grouting in sensitive zones; real-time displacement monitoring guided adjustments.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVariable and Weak Soil Profiles\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSoft silty clays and sand seams caused uneven grout behavior and seepage risks.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdjusted grout mix in situ; increased cement in sandy layers and extended waterjet pre-cutting in cohesive zones.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLimited Construction Access\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNarrow work zones with strict noise and vibration limits hampered logistics.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUsed compact rigs and modular systems; arranged night-time deliveries; implemented EPP with acoustic/vibration controls.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGroundwater and Seepage Risk\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eShallow water table (~\u0026thinsp;2\u0026ndash;3 m) created uplift and seepage hazards.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInstalled large-diameter super high-pressure grout columns as a bottom seal; confirmed performance via piezometric monitoring.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eH-Pile Removal under Height Limitation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMRT Yellow Line steel girder limited headroom to 6 m, restricting full pile extraction.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCut H-piles into \u0026lt;\u0026thinsp;4 m segments; used vibratory drivers with waterjet pre-cutting and jump extraction sequence.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Findings","content":"\u003cp\u003eFollowing the implementation of high-pressure and super high-pressure jet grouting techniques in the Taipei MRT Zhonghe\u0026ndash;Wanda Line CQ861 project, comprehensive field testing and performance assessments were conducted. This section presents the key findings related to structural performance, ground improvement effectiveness, permeability control, and environmental impact mitigation.\u003c/p\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Compressive Strength and Structural Integrity\u003c/h2\u003e \u003cp\u003eCore samples retrieved from both standard jet grouting and super high-pressure columns exhibited excellent strength development. Laboratory testing on unconfined compressive strength (UCS) samples, prepared following CNS 12384 A3282, showed that most silcrete specimens exceeded the project requirement of 10 kg/cm\u0026sup2;. The average UCS values were:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e12.6 kg/cm\u0026sup2; for 0.8 m standard JSG columns.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e15.2 kg/cm\u0026sup2; for 3.6 m super high-pressure columns.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eEdge and center samples indicated consistent distribution, with a coefficient of variation (COV) below 8%, demonstrating good homogeneity (Please see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The presence of H-piles in jet-mixed columns further enhanced load distribution and bending resistance, improving pile-wall performance during excavation stages [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Permeability and Seepage Resistance\u003c/h2\u003e \u003cp\u003eFalling-head permeability tests on core samples and in-situ packer tests confirmed that permeability coefficients consistently fell below the target of 1\u0026times;10⁻⁵ cm/sec. Most results ranged between 2.3\u0026times;10⁻⁶ and 7.1\u0026times;10⁻⁶ cm/sec. These values are indicative of near-impermeable behavior, especially critical in zones with shallow groundwater and flood-prone conditions [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeepage monitoring using piezometers installed at the tunnel invert level showed negligible fluctuations during excavation, validating the efficacy of the impermeable grout curtain system. This minimized uplift pressure and water ingress, ensuring safe and dry excavation conditions throughout construction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Geometric Accuracy and Column Continuity\u003c/h2\u003e \u003cp\u003eNon-destructive testing using borehole camera inspection and ground-penetrating radar (GPR) revealed good geometric conformity of the grout columns to design specifications. The deviation in column diameter was typically within \u0026plusmn;\u0026thinsp;5% of target values. In areas where the double-tube super high-pressure method was employed, column overlap achieved over 95% continuity, with no significant voids or soft zones detected.\u003c/p\u003e \u003cp\u003eThe column grid installed beneath the connecting tunnel formed an effective load-transfer platform and groundwater barrier. The excavation progression of the underground connecting passage, documenting exposed soil strata, temporary structural supports, and field personnel operating within the confined subsurface workspace, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(Inspected by the corresponding author)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Environmental and Construction Efficiency Outcomes\u003c/h2\u003e \u003cp\u003eThe selected methods proved advantageous in reducing environmental impact. Ground vibration monitoring during drilling and injection phases showed peak particle velocities (PPV) below 2 mm/s at sensitive locations, well under regulatory limits. Noise levels remained under 75 dBA due to the use of low-noise batch mixing units and acoustically shielded drilling rigs [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn terms of productivity, the average installation rate reached:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e12\u0026ndash;15 m/day per rig for standard JSG piles.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e5\u0026ndash;7 m/day per rig for large-diameter super high-pressure columns.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eDespite the slower rate for larger columns, the method\u0026rsquo;s effectiveness near critical infrastructure justified its use. No utility damage or safety incidents were recorded during execution, underscoring the reliability of the applied technologies.\u003c/p\u003e \u003cp\u003eThese findings demonstrate that the combined approach of JSG and super high-pressure grouting not only met but exceeded the performance criteria of the CQ861 project [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], offering a validated model for future underground construction in constrained urban settings.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion and Recommendations","content":"\u003cp\u003eThis study presented the successful application of high-pressure jet grouting and large-diameter super high-pressure jet grouting techniques in the Taipei MRT Zhonghe\u0026ndash;Wanda Line CQ861 contract, particularly in the geotechnically complex and urban-sensitive zone between LG06 and Y11 stations. The engineering challenges encountered\u0026mdash;such as weak and heterogeneous soils, shallow groundwater, and dense utility networks\u0026mdash;required advanced and adaptable ground improvement solutions. Through carefully designed grouting methodologies, quality control protocols, and field testing, the project achieved its technical and safety goals without compromising the surrounding urban environment.\u003c/p\u003e \u003cp\u003eThe use of standard high-pressure jet grouting in retaining pile construction enabled effective integration of structural elements (H-piles) into strengthened soilcrete bodies, resulting in a system that offered both load-bearing and impermeability functions. Meanwhile, the deployment of large-diameter super high-pressure jet grouting beneath sensitive facilities and the connecting tunnel provided enhanced strength and seepage resistance, even in variable soil conditions. The leapfrog sequencing and double-tube nozzle systems ensured uniform grout distribution while minimizing disturbance to nearby utilities and structures.\u003c/p\u003e \u003cp\u003ePost-construction evaluations confirmed that both the unconfined compressive strength and permeability performance of the grouted bodies met or exceeded project specifications. Furthermore, geometric precision, column continuity, and environmental compliance were all verified through rigorous monitoring and inspection. These results demonstrate that the combined use of high-pressure and super high-pressure grouting can effectively address the multifaceted requirements of urban underground infrastructure development.\u003c/p\u003e \u003cp\u003eBased on the experience and outcomes of this project, several recommendations are offered for similar future applications:\u003c/p\u003e \u003cp\u003e \u003cb\u003eEarly Integration of Utility Mapping and Risk Assessment\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eAccurate utility surveys and proactive coordination with utility owners are essential. Risk zones should be identified early, and flexible grouting solutions should be planned accordingly.\u003c/p\u003e \u003cp\u003e \u003cb\u003eAdaptive Grouting Strategy\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eGrouting parameters should be dynamically adjusted based on soil variability encountered during execution. Real-time monitoring tools and soil classification logs are critical for guiding in-field decisions.\u003c/p\u003e \u003cp\u003e \u003cb\u003eUse of Super High-Pressure Grouting in Critical Areas\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eFor sections beneath sensitive infrastructure or where conventional methods pose a risk, super high-pressure jet grouting should be considered. Though slower in installation, its benefits in strength, uniformity, and safety outweigh the longer execution time.\u003c/p\u003e \u003cp\u003e \u003cb\u003eComprehensive Quality Assurance\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eField sampling, lab testing, and non-destructive evaluation should be consistently applied to verify performance and minimize construction uncertainty.\u003c/p\u003e \u003cp\u003e \u003cb\u003eEnvironmental Mitigation Planning\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eProjects in urban environments must implement stringent vibration, noise, and groundwater management plans. Compact equipment, shielded systems, and staged work schedules can greatly reduce the project\u0026rsquo;s environmental footprint.\u003c/p\u003e \u003cp\u003eIn conclusion, this case study reinforces the effectiveness, adaptability, and reliability of advanced grouting methods for MRT projects in challenging urban contexts. It provides a valuable reference for engineers, planners, and contractors tasked with delivering safe, high-quality underground infrastructure amid complex site constraints.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study include publicly accessible technical specifications and standards, while project-specific construction data are available from the corresponding author, T.-Y. Liu, upon reasonable request, subject to confidentiality restrictions of the Taipei MRT project.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAuthor Contributions Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eT.-Y. Liu conceived the study, supervised the research, and led manuscript writing.\u003c/p\u003e\n\u003cp\u003eC.-P. Wang contributed to methodology and data processing.\u003c/p\u003e\n\u003cp\u003eS.-P. Ho provided academic guidance and technical review.\u003c/p\u003e\n\u003cp\u003eS.-F. Yeh supported project information verification.\u003c/p\u003e\n\u003cp\u003eK.-C. Ten assisted with field investigations and construction documentation.\u003c/p\u003e\n\u003cp\u003eB.-C. Ciou prepared figures and contributed to data compilation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors sincerely acknowledge the Department of Rapid Transit Systems, Taipei City Government, for their continuous guidance, coordination, and provision of essential project information throughout the execution of this work. The authors also extend their appreciation to New Asia Construction and Development Corporation for offering technical support, site access, and valuable professional insights during field investigations and construction activities. The dedicated efforts of the onsite engineers, project teams, and technical staff in assisting with data collection, documentation, and quality verification significantly strengthened the rigor and completeness of this study. Their collective contributions are gratefully recognized.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eDisclosure Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known financial, commercial, legal, or professional conflicts of interest that could have influenced the research, analyses, or conclusions presented in this manuscript. All work was conducted independently, and no external organization or individual provided support that could be perceived as creating a competing interest. The affiliations of the authors, including roles related to the project, did not influence the objectivity or integrity of the study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDepartment of Rapid Transit Systems (DORTS). (2016). Project Geotechnical Report: Taipei MRT Zhonghe\u0026ndash;Wanda Line, CQ861 Section (Internal Report). Taipei City Government. (In Chinese, unpublished document)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNi, J. C. (2005). Grouting techniques in urban underground engineering. Taipei: Department of Civil Engineering, National Taipei University of Technology. (In Chinese, unpublished document)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTai-Yi Liu, Shiau-Jing Ho, Hui-Ping Tserng, Hong-Kee Tzou. \u0026ldquo;Using a unique retaining method for building foundation ex-cavation: A case study on sustainable construction method and circular economy.\u0026rdquo; \u003cem\u003eBuildings\u003c/em\u003e 2022, 12, 298. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/buildings12030298\u003c/span\u003e\u003cspan address=\"10.3390/buildings12030298\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, TY., Chou, N.N.S., Lin, SJ. et al. 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Chou, Po-Han Chen, and Ching-Lung Liao, (2020). \u0026ldquo;Soil Improvement and Inspection Techniques for the Base Course of Rigid Pavement for an Airport Runway.\u0026rdquo; ASCE Journal of Performance of Constructed Facilities. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1061/(ASCE)CF.\u003c/span\u003e\u003cspan address=\"10.1061/(ASCE)CF.\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e1943-5509.0001560. (SCI).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCNS (Chinese National Standards). (2022). CNS 12384 A3282: Unconfined compressive strength test for soilcrete (in Chinese). Bureau of Standards, Metrology and Inspection, Ministry of Economic Affairs, Taiwan.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTai-Yi Liu. (2021) \u0026ldquo;Enhancing the Risk Management and Carbon Emission Reduction Using a Special Retaining Method for Excavation.\u0026rdquo; In: Eliva Press SRL, Available in Amazon 2022, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.amazon.com/dp/1636486428\u003c/span\u003e\u003cspan address=\"https://www.amazon.com/dp/1636486428\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.elivapress.com/en/book/book-7890848335/\u003c/span\u003e\u003cspan address=\"https://www.elivapress.com/en/book/book-7890848335/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Asia Construction and Development Corporation. (2014). \u0026ldquo;Jet Grouting Method Statement for CQ861 \u0026ndash; LG06 Station\u0026rdquo;. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Asia Construction and Development Corporation. (2014). \u0026ldquo;Test Method Statement for Unconfined Compressive Strength of Grouting\u0026rdquo;. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJines Construction (2025): \u0026ldquo;Double Tube Grouting to Stop Water In Saline-Alkali Area\u0026rdquo;, Jines Construction 2025, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.jines.com/en/grouting-edm11/\u003c/span\u003e\u003cspan address=\"https://www.jines.com/en/grouting-edm11/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMandolini, A. \u0026amp; Viggiani, C. (1997). \u0026ldquo;Settlement of piled foundations\u0026rdquo;, Geo-technique 47, No. 4, 791\u0026ndash;816. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.researchgate.net/publication/245410705_Settlement_of_piled_foundations#fullTextFileContent\u003c/span\u003e\u003cspan address=\"https://www.researchgate.net/publication/245410705_Settlement_of_piled_foundations#fullTextFileContent\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Asia Construction and Development Corporation. (2014). \u0026ldquo;Test Method Statement for Grouting Permeability\u0026rdquo;. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Asia Construction and Development Corporation. (2014). \u0026ldquo;Environmental Protection Plan (EPP)\u0026rdquo;. Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document)..\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, TY., Chou, N.N.S., Lin, SJ. et al. (2021). \u0026ldquo;Challenges and Sustainability-Based Solutions of Diaphragm Wall Construction for LG06 Underground Station in Taipei MRT.\u0026rdquo; Transportation Infrastructure Geotechnology (ESCI). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s40515-021-00208-0\u003c/span\u003e\u003cspan address=\"10.1007/s40515-021-00208-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Asia Construction and Development Corporation. (2014). \u0026ldquo;Test Method Statement for Retaining Grouting Column with the Steel H-Beams\u0026rdquo;, Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGeotech Data (2025) \u0026ldquo;Falling head permeability test\u0026rdquo;, Geotech Data 2025, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.geotechdata.info/geotest/falling-head-permeability-test\u003c/span\u003e\u003cspan address=\"https://www.geotechdata.info/geotest/falling-head-permeability-test\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChang, Y.S., Fan, J.Y., Liu, T.Y. (2021). \u0026ldquo;In-Situ Test Reports for noise and vibration monitoring.\u0026rdquo;, Internal Technical Document, Taipei, Taiwan. (In Chinese, unpublished document).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNew Taipei City Government. (2025). \u0026ldquo;Climate action: Noise and Vibration Control Standards.\u0026rdquo;, New Taipei City Government Policies, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://foreigner.ntpc.gov.tw/home.jsp?id=0e5a1b2e43639bf0\u003c/span\u003e\u003cspan address=\"https://foreigner.ntpc.gov.tw/home.jsp?id=0e5a1b2e43639bf0\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"geotechnical-and-geological-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"gege","sideBox":"Learn more about [Geotechnical and Geological Engineering](https://www.springer.com/journal/10706)","snPcode":"10706","submissionUrl":"https://submission.nature.com/new-submission/10706/3","title":"Geotechnical and Geological Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Jet Grouting, Soil Improvement, Underground MRT Construction, High-Density Urban Utilities, Super High-Pressure Grouting","lastPublishedDoi":"10.21203/rs.3.rs-8333320/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8333320/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study examines advanced grouting techniques applied in the Taipei MRT Zhonghe\u0026ndash;Wanda Line project, particularly the underground section between LG06 and Y11 stations. Dense underground utilities and challenging subsurface conditions\u0026mdash;soft silty clay and a shallow groundwater table\u0026mdash;made conventional diaphragm walls infeasible.\u003c/p\u003e \u003cp\u003eTwo methods were implemented: standard high-pressure jet grouting (JSG) and large-diameter super high-pressure jet grouting. Retaining piles were constructed by injecting cement grout (100\u0026ndash;220 kg/cm\u0026sup2;) via rotating drill rods, then inserting H-shaped steel beams to form high-strength, low-permeability composite elements. In critical areas beneath power lines and telecom conduits, 3.6 m super high-pressure grouting (up to 400 kg/cm\u0026sup2;) was used to enhance soil uniformity and minimize impacts on adjacent infrastructure.\u003c/p\u003e \u003cp\u003eDetailed construction records\u0026mdash;grout pressure, flow rate, and lifting speed\u0026mdash;were maintained. Post-construction coring and laboratory tests confirmed unconfined compressive strength\u0026thinsp;\u0026ge;\u0026thinsp;10 kg/cm\u0026sup2; and permeability K\u0026thinsp;\u0026le;\u0026thinsp;10⁻⁵ cm/sec.\u003c/p\u003e \u003cp\u003eThe results demonstrate that integrating standard and large-diameter jet grouting effectively addresses excavation challenges in dense urban environments and provides a practical reference for future MRT developments.\u003c/p\u003e","manuscriptTitle":"Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-20 22:25:24","doi":"10.21203/rs.3.rs-8333320/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-26T00:35:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-24T08:26:31+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-14T09:03:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-31T15:32:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"305335551568069184137092269068701493982","date":"2025-12-26T19:43:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"216777831231028389592151053543197334556","date":"2025-12-26T05:54:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"20480376412758076067876702065383019173","date":"2025-12-25T16:49:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"336725681048727191825131870603026921506","date":"2025-12-25T02:37:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-13T00:21:31+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-13T00:19:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-12T11:57:42+00:00","index":"","fulltext":""},{"type":"submitted","content":"Geotechnical and Geological Engineering","date":"2025-12-11T06:28:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"geotechnical-and-geological-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"gege","sideBox":"Learn more about [Geotechnical and Geological Engineering](https://www.springer.com/journal/10706)","snPcode":"10706","submissionUrl":"https://submission.nature.com/new-submission/10706/3","title":"Geotechnical and Geological Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"957e2c27-cac6-40b2-80d8-2371e0810daf","owner":[],"postedDate":"January 20th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-02T16:04:14+00:00","versionOfRecord":{"articleIdentity":"rs-8333320","link":"https://doi.org/10.1007/s10706-026-03666-w","journal":{"identity":"geotechnical-and-geological-engineering","isVorOnly":false,"title":"Geotechnical and Geological Engineering"},"publishedOn":"2026-02-25 15:59:08","publishedOnDateReadable":"February 25th, 2026"},"versionCreatedAt":"2026-01-20 22:25:24","video":"","vorDoi":"10.1007/s10706-026-03666-w","vorDoiUrl":"https://doi.org/10.1007/s10706-026-03666-w","workflowStages":[]},"version":"v1","identity":"rs-8333320","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8333320","identity":"rs-8333320","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}