Research on Key Technologies of Thick Slurry Filling Chamber Method for Earth Pressure Balance Shield in Karst Areas

Research on Key Technologies of Thick Slurry Filling Chamber Method for Earth Pressure Balance Shield in Karst Areas | 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 Research on Key Technologies of Thick Slurry Filling Chamber Method for Earth Pressure Balance Shield in Karst Areas Kan Huang, Yiwei Sun, Xuesheng Qian, Xiangsheng Chen, Zhijian Luo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7824402/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Apr, 2026 Read the published version in Scientific Reports → Version 1 posted 14 You are reading this latest preprint version Abstract Due to the presence of numerous Karst cavities, fractures, and fissure water, Karst strata exhibit significant air leakage during pressurized chamber opening. This leads to a large gas replenishment volume, substantial formation water inflow, and the inability to conduct pressurized chamber opening operations normally. To address this issue, this study focuses on the shield tunneling project in the first standard section and second work area of the Shenzhen Metro Line 16 utility corridor. Based on the engineering characteristics of highly developed Karst strata, the technical mechanism of the thick-slurry filling method for pressurized chamber opening is analyzed. The slurry mix design parameters, filling parameters, grouting parameters, working pressure for pressurized chamber opening, construction technology, and control measures are systematically summarized. Consequently, a chamber-opening technology using the thick-slurry filling method for Earth Pressure Balance (EPB) shield tunneling in Karst formations is proposed. The results indicate that the thick-slurry filling method is an effective approach for chamber opening in EPB shield tunneling through Karst formations. It can successfully mitigate issues related to formation air leakage during chamber opening, thereby ensuring operational safety, enhancing efficiency, and reducing costs. Physical sciences/Energy science and technology Physical sciences/Engineering Earth and environmental sciences/Environmental sciences Keyword EPB Shield Karst Strata thick-slurry filling opening chamber under-pressure ground monitoring Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1 Introduction During the construction of shield tunnels, various issues are inevitable, such as the wear of cutterhead tools, the formation of mud cakes on the cutterhead, and the need to traverse important buildings and structures. Therefore, chamber-opening operations are necessary to inspect, replace, and clean the cutterhead tools. Based on the pressure maintenance condition within the pressure chamber, shield chamber-opening operations can be primarily classified into atmospheric-pressure chamber opening and pressurized chamber opening [1]. Currently, pressurized chamber opening mainly involves using pneumatic support for the excavation face. That is, operators enter the pressure chamber to carry out tasks under a specific air pressure environment. For strata with high permeability, the most commonly adopted approach to reducing soil permeability is to inject slurry in front of the excavation face, enabling the formation of a slurry film with excellent airtightness [2 - 3]. Zhu Wei and Min Fanlu have conducted extensive research and experiments on slurry, exploring the penetration patterns of slurry in strata and the formation mechanism of slurry films in slurry-pressure shield tunnels, and have put forward scientific theories and application techniques related to slurry [3 - 4]. Zhu Weibin, Kuang Shuhua, Li Maosong, et al. have carried out in-depth research on the auxiliary chamber-opening technology that utilizes "Hengdun mud" to form a slurry-film wall for protection. The characteristic of this method is that the "Hengdun mud" slurry fills, squeezes, and fractures into construction voids, stratum pores, and fractures, promptly sealing the water and gas leakage channels within the strata. Moreover, it forms a slurry film of a certain thickness on the excavation face, featuring a dense structure and good stability, thus overcoming the challenges of shield chamber-opening operations in unstable strata [5 - 6]. During the application of the pressurized chamber-opening method with slurry-film wall protection, due to the water-drainage effect of air pressure, the slurry skin starts to crack due to water loss after a certain period. Consequently, it is necessary to repeatedly inject high-viscosity slurry at regular intervals to repair the slurry skin. During the slurry-skin repair process, operations inside the chamber must be suspended. The slurry skin only serves the function of pressure maintenance and lacks reinforcement capabilities. Additionally, it is prone to cracking. Once the slurry skin cracks, it can easily lead to pressure loss and instability inside the chamber, posing significant safety risks [7]. Similar issues also exist in ordinary bentonite slurry, "Hengdun mud", and "Keneff". This study is based on the shield tunnel project in the second construction area of the first bid section of the shared pipe gallery of Shenzhen Metro Line 16. In response to the problems encountered in karst-developed strata, such as the instability of the filling materials within karst cavities at the excavation face, the well-developed and highly connected karst fissures, the large amount of air leakage during pressurized chamber opening, and the substantial water replenishment in the strata, which impede the normal implementation of atmospheric-pressure or pressurized chamber opening, this paper analyzes the technical mechanism of the thick-slurry chamber-filling method for pressurized chamber opening. It also examines the slurry proportioning parameters, chamber-filling parameters, grouting parameters, and the working pressure for pressurized chamber opening in the thick-slurry chamber-filling method. Furthermore, this paper summarizes the construction technology and control measures of the chamber-opening operations using the thick-slurry chamber-filling method, and proposes a chamber-opening technology for earth-pressure-balance shield tunnels in karst-developed strata based on the thick-slurry chamber-filling method. Finally, the effectiveness of the chamber-opening technology is verified through an analysis of the ground monitoring data during the actual chamber-opening process and the stability of the excavation face during the chamber-opening operation. 2 Project Overview The project of the first contract section and the second work area of the co-built pipe gallery of Shenzhen Metro Line 16 includes 4 shafts and 1 section, with a starting mileage of KA2+311.4 and an ending mileage of KA5+488.05. The total length of the section is 3176.65m. The route map is shown in Figure 1. The shield tunnel is divided into 3 sections, namely the 4→3 section, the 4→2→5 section, and the 6→5 section. The outer diameter of the shield tunnel segments is 8.8m, the ring width is 1.5m, and the thickness of the segments is 0.4m. The tunnel depth ranges from 11.06m to 34.95m, with a maximum longitudinal slope of 33.7‰ and a minimum turning radius of 500m. Two earth pressure balance shield machines with a cutting diameter of 8850mm are used for construction. The main strata that the shield tunnel passes through are gravelly silt clay, fully to strongly weathered sandstone, and slightly weathered limestone. The surrounding rock grades are III, IV, and V. The strata statistics are as follows: silt clay and gravelly silt clay about 768m, accounting for 24.8%; fully to strongly weathered sandstone about 680m, accounting for 21.9%; slightly weathered limestone and carbonaceous limestone about 1654m, accounting for 53.3%. It can be seen that the tunnel body is mainly in rock strata, accounting for three quarters of the entire shield tunnel. According to the geological investigation report and detailed investigation report, the adverse geological conditions of this tunnel are karst and faults. There were a total of 365 boreholes during the investigation stage, and 187 boreholes exposed karst caves. The total number of exposed karst caves was 389, with a height ranging from 0.10m to 23.80m and an average height of 2.7m. The karst cave exposure rate of the 3→4 section boreholes was 14.86%, with moderately developed karst; the karst cave exposure rate of the 4→2 section boreholes was 58.76%, with strongly developed karst; the karst cave exposure rate of the 2→5 section boreholes was 64.18%, with strongly developed karst; the karst cave exposure rate of the 5→6 section boreholes was 64.58%, with strongly developed karst. The filling conditions of the karst caves are irregular and the components are complex, with significant differences in physical and mechanical properties. The geological longitudinal section of the shield tunnel is shown in Figure 2 (the black-filled parts in the figure represent karst voids). The groundwater in this shield tunnel includes pore water in loose rock, fissure water in bedrock and karst fissure water. The fissure water in bedrock is stored in sandstone and limestone, with a relatively large thickness of aquifer and a moderate water volume. The karst fissure water is stored in fissures and karst caves in limestone, with a rich water volume. Its permeability and water-richness vary depending on the development degree, connectivity, topographic conditions and other factors of fissures and karst caves. It has confined pressure. The main factor affecting the opening of the tunnel is the strong development of karst in the limestone stratum, the development of karst fissures, and the abundance of confined karst groundwater. Due to the severe karst dissolution at the tunnel face, the fillings in karst cavities are unstable, the karst fissures are well developed and highly connected, the karst limestone stratum is highly permeable, the stratum is soft on top and hard at bottom, and the karst fissure water in the slightly weathered limestone stratum is abundant, the earth pressure chamber cannot maintain pressure, making it impossible to carry out normal atmospheric or pressurized opening. 3 Principle, Technology and Parameter Control of the Thick-slurry Bunker-filling Method for Chamber Opening 3.1 Principle of Chamber Opening Using the Thick-slurry Bunker-filling Method The thick slurry filling method for opening the chamber has no essential difference in principle from the general bentonite slurry wall pressure-supported opening of the chamber. The basic principle is to use air pressure to ensure the stability of the face during the opening process. However, due to the addition of a certain proportion of lime in the thick slurry, the slurry undergoes a hardening reaction similar to that of cement mortar. The formed mud film is thick and its strength increases over time, resulting in very little consolidation and shrinkage. Therefore, it can effectively fill karst cavities, seal karst fissures, and maintain pressure in the soil chamber. By taking advantage of the good stability of the thick slurry, its resistance to loss and dilution in water-rich strata, high later strength, and no cracking, thick slurry is injected into the soil chamber of the shield machine to fill the karst cavities at the face, seal the strata fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This solves the problems of air leakage in karst strata, ground slurry leakage, soil chamber pressure loss, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressure-supported opening in karst-developed strata. The mechanism diagram of the thick slurry filling method for opening the chamber is shown in Figure 3. 3.2 Process Flow of Opening the Bunker by Thick Slurry Filling Method The process flow of opening the bunker by thick slurry bunker filling method is presented in Figure 4. 3.2.1 Judgment of Whether to Open the Bunker Shield tunneling chamber opening is generally divided into active and passive chamber opening. In this project, the 4-2-5 section has more passive chamber openings. Whether the shield machine needs to open the chamber during the tunneling process is first determined by the geological profile of the shield tunnel to judge the basic situation of the stratum where the shield machine is currently located, and then combined with the specific tunneling parameters during the tunneling process for judgment. Generally, when the tunneling speed is lower than 5mm/min or the tunneling speed fluctuates greatly, the cutterhead torque fluctuates greatly, and the thrust abnormally increases, attention should be paid. At the same time, when there is a karst cave ahead, the earth pressure in the soil chamber will be unstable during tunneling, the pressure difference between the upper and lower parts of the soil chamber will increase, the soil chamber cannot maintain pressure, and the air compressor of the pressure maintenance system will frequently load. At the same time, the stratum conditions ahead of the face can also be judged by the debris samples and debris temperature. When the stone powder and fine particle content in the debris samples is very high (generally more than 60%) and the debris temperature exceeds 40°, it indicates that the rock-breaking ability of the cutter has decreased significantly, and chamber opening inspection should be carried out. 3.2.2 Shield machine shutdown and preparation for opening the chamber After deciding to carry out the opening operation, the shield machine is shut down to prepare for the opening. The main preparations include the layout of ground monitoring points in front of the face, the fabrication of the shield water-stop ring, and the determination of the working pressure for the pressurized opening. (1) Layout of Ground Monitoring Points To provide monitoring information for the pressurized opening operation and ensure the safety of the opening, the ground conditions corresponding to the cutterhead position are monitored during the opening. The monitoring points are densely arranged compared to the monitoring during the tunneling construction, following the first-level control (the monitoring level during tunneling construction is the second level). Specifically, a monitoring section is set up every 4 to 5 meters along the shield tunnel axis, totaling 5 sections, with 1 section in front of and 1 section behind the shield body, and 3 sections within the shield body range. Each monitoring section has 3 to 5 monitoring points, totaling 15 to 25 monitoring points. Within one section, the monitoring points are arranged on both sides of the tunnel axis, with a lateral spacing of approximately 3 to 4 meters. The specific layout can be adjusted locally based on the ground structures at the opening position and can be increased or decreased according to the feasibility of on-site measurement points. For example, the layout of the monitoring points for the opening at ring 309 is shown in Figure 5. When the shield stops, the initial values should be collected in a timely manner. During the process of opening the chamber for work, the monitoring frequency is twice a day until the excavation resumes. (2) Construction of the water-stop ring After the shield stops, a double-liquid grouting of cement and water glass is carried out on the entire ring of segments located 5 to 6 rings away from the shield tail (usually 2 rings of segments), forming a closed water-stop ring to prevent the soil chamber from connecting with the stratum through the gap at the shield tail, which could lead to air leakage and inability to maintain pressure. The double-liquid grout is injected through the reserved grouting holes on the segments. The ratio of the cement-water glass double-liquid grout is as follows: A liquid, cement slurry: cement: water = 1:1 (by weight); B liquid, water glass, with a specific gravity of 35 Be'; A liquid: B liquid = 1:0.5 (by volume). The setting time is controlled at around 20 seconds. To prevent segment displacement, the "diagonal injection" method is generally adopted, and the grouting pressure is controlled within 5 bar. (3) Determination of the pressure for opening the chamber The working pressure for opening the chamber is the soil chamber pressure that can ensure the stability of the face. It can be the soil chamber pressure during the excavation of the first few rings before opening the chamber and verified according to formula (1), while also taking into account the thickness of the overlying strata and the geological conditions for adjustment. According to the "Calculation Specifications for Chamber Opening and Pressure Work in Shield Tunneling" [8] (GJJ217-2014), the following formula is used for calculation: (1) Where P w represents the water head pressure calculated to the center of the tunnel excavation, and P r is the pressure adjustment value considering different geological conditions, ground environment and the position of the excavation face, which can be taken as 0 to 0.03 MPa. Taking the 734th ring of the 2-5 section as an example, the groundwater level at this position is approximately 3.68m, the depth of the tunnel bottom is about 32.48m, and the outer diameter of the shield machine is 8.85m. Then: (2) The pressure in the soil chamber during the tunnel boring is approximately 2.7 bar. The working pressure of 2.7 bar during tunnel boring can be adopted as the working pressure for the chamber opening operation. 3.2.3 Preparation, Transportation, and Filling of Thick Slurry (1) Thick slurry production Thick slurry is an inert slurry composed of hydrated lime, bentonite, fly ash, fine sand and water. Compared with ordinary bentonite slurry and cement mortar, its characteristics are: ① Good slurry stability, less prone to loss and dilution in water-rich strata; ② Good pressure retention effect (tail shield, radial holes, soil chamber), can quickly achieve pressure retention effect, and has better continuous grouting and settlement control; ③ Less likely to cause damage to the tail shield brush and entrapment of the shield body. This is the main reason for using the thick slurry filling method to open the chamber in karst strata. However, the thick slurry has a long curing time and requires less stability of the segments; the slurry has poor fluidity and high requirements for pumping equipment. These factors should be considered during application. The proportion of thick slurry is generally determined through on-site sampling of sand layers and indoor film-forming effect tests simulating the strata to be opened. However, due to the complexity of karst strata, the proportion is actually determined by referring to that of ordinary cement mortar and bentonite slurry and through multiple on-site filling tests. The actual proportion of thick slurry is shown in Table 1. Table1 Thick-slurry filling silo slurry ratio Raw materials（kg） sand coal fly ash lime water calcium bentonite Sodium-based high-viscosity bentonite Usage amount 1200 570 290 375 75 8 During the preparation of thick slurry, samples should be taken for consistency, spreadability tests, 4-hour water immersion test and 24-hour bleeding test. Only when the requirements are met can the slurry be prepared. The performance indicators of thick slurry mainly focus on initial setting time, consistency and spreadability, with bleeding rate and volume loss rate control as secondary. The performance indicators of the slurry are summarized as follows: ① Initial setting time ≤ 72 hours. ② Consistency ≈ 6.8mm, tested by a mortar consistency tester; spreadability ≤ 15cm, with 13-15cm being the best, measured by a mortar spreadability tester. The consistency and spreadability of the slurry are measured to test its fluidity. ③ After being sealed for 24 hours, there is water on the surface of the slurry, no segregation occurs, and the weight after bleeding is 762g when 770g is sampled. The bleeding rate of the slurry should be less than 2%. ④ The volume loss of the slurry in the 4-hour static water test is ≤ 10%, and in the 4-hour dynamic water test is ≤ 20%. The 4-hour static water test volume loss and 4-hour dynamic water test volume loss are mainly used as reference control indicators to judge the degree of erosion of thick slurry by karst fissure water during the filling process. The on-site measurement mainly uses standard mortar strength specimens with a side length of 70.7mm, placed in containers filled with still water or flowing water. The flow rate of dynamic water can be calculated based on the estimated water inflow at the excavation face of the opening position. After 4 hours of stillness, the volume of the specimen is measured, and the volume loss rate is obtained by comparison. ⑤ Fine sand with a fineness modulus of 1.6-2.2 must be used for slurry preparation. (2) Thick slurry transportation and filling of the storage tank ① Slurry pumping and transportation The slurry is pumped from the mortar mixing station to the slurry storage tank located on the middle plate of the shield shaft by the extrusion pump. The extrusion pipe of the extrusion pump should be inspected once for every 50 m³ of slurry mixed. After the slurry truck arrives, the slurry is discharged from the slurry storage tank to the slurry truck. The slurry truck is equipped with a self-stirring system to maintain the slurry state, and then transported to the grouting system of the shield car through the tunnel horizontal transport vehicle. ② Injection of thick slurry In karst strata, the full storage tank mode is rarely used for excavation. Generally, the local pneumatic mode is adopted, and the sludge in the soil storage tank accounts for about 2/3 of the storage tank. Before injecting thick slurry, the sludge and air should be replaced first. The sludge surface is lowered to about 1/2 of the storage tank by the screw conveyor, and the amount of sludge discharged is generally controlled at 10 to 15 m³. When the stratum is stable, due to the existence of rock layers and air pressure, and the time is short (about 1 hour), the collapse of the working face generally will not occur. However, when the stratum is unstable, thick slurry should be injected into the soil storage tank first before sludge replacement. After the thick slurry reaches the grouting system of the shield car, the shield machine's synchronous grouting system is used to connect two grouting pipes to the reserved valve on the soil storage tank partition. A test grouting is conducted first to determine the initial grouting pressure. The initial injection pressure should be 0.2 bar higher than the pressure at the top of the excavation storage tank to ensure that the slurry does not flow back and cause pipe blockage. If the pressure in the soil storage tank increases due to the grouting pressure during the grouting process, the grouting should be paused. Continue to inject thick slurry through the balance valve in the personnel lock chamber and the radial holes of the shield body. The injection pressure should be 0.5 bar higher than the pressure at the top of the soil chamber. Repeat the injection multiple times until the chamber is full. During the injection process, try not to start the cutter head to allow the thick slurry to diffuse into the gaps around the shield body and the face. Generally, the injection pressure will continuously increase until it reaches the termination pressure of 4.0 bar. After the thick slurry fills the soil chamber, the gap between the shield body and the stratum is usually filled with bentonite slurry or a chemical slurry composed of phosphoric acid solution and sodium silicate (in a ratio of 1:1) through the radial grouting holes of the shield body to fill the gaps behind the shield shell that the thick slurry cannot fill, forming a closed water-stop belt. 3.2.4 Air pressure displacement of thick slurry and pressure holding After the thick slurry fills the soil chamber, the pressure in the soil chamber drops from 4.0 bar to 3.0 bar (usually taking 3 to 4 hours), and when it remains at 3.0 bar for more than 2 hours without further pressure drop, the screw conveyor is activated to discharge the soil for gas-soil replacement. During the soil discharge process, the pressure fluctuation in the soil chamber is controlled within 0.3 bar. Finally, the pressure in the soil chamber is maintained at 2.7 bar (the working pressure for opening the chamber). During the soil discharge process, the pressure maintenance system (SAMSON system) continuously injects high-pressure gas into the soil chamber. When the thick slurry level reaches the center of the cutter head, the replacement is stopped and the pressure is maintained. 3.2.5 Condition judgment for Entering the Chamber under Pressure After the slurry-air replacement is completed, with the pressure maintenance system on, during the pressure maintenance process of the soil chamber, if the opening degree of the pressure maintenance system's air replenishment switch is less than 0.2, and the loading time of the air compressor is shorter than the unloading time, with a loading time of 10 seconds and an unloading time of 30 seconds being the optimal state, it is considered that the thick slurry mud film on the face can meet the conditions for opening the chamber. On-site, through detailed records of the opening degree of the pressure maintenance system's air replenishment switch, the slurry and air replacement, the specific depressurization time during the process, the loading and unloading time of the air compressor, and the injection volume of the thick slurry, a comprehensive analysis is conducted to determine whether the conditions for entering the chamber are met. 4 Analysis of the Opening Effect of the Thick-slurry Chamber-filling Method 4.1 Ground monitoring Ground monitoring during the opening of the warehouse is controlled at level one, using a Trimble DiNi03 precision level (with an accuracy of ±0.30mm) for measurement. The monitoring frequency is twice a day, with the cumulative settlement control value set at +10 to -20mm and the settlement rate control value at 3mm/d [9-10]. Through the analysis of a total of 27 opening operations in the 4-5 section of this project, the maximum cumulative settlement during the opening operation was -9.3mm, and the maximum settlement rate was -2.16mm/d, both of which were less than the specified values. Taking the longest-lasting 6th opening (309 rings) as an example, the settlement value changed from the first entry into the warehouse to the completion of the blade change and the resumption of advancement, which lasted for 28 days. Through the monitoring data, it was found that as the opening time increased, the cumulative settlement gradually increased. At the end of the opening operation, the cumulative settlement was -7.2mm, but the settlement rate during the opening operation was very stable, basically remaining at around -0.5mm/d. As the opening time increases, the settlement amount gradually increases, increasing the safety risk of the opening operation. The monitoring results of the 6th (309 rings) opening operation are shown in Figure 9. It can be known from the monitoring data that the thick slurry filling method for opening operations in karst strata can effectively control the stratum settlement. 4.2 Effect of opening the chamber Due to the complexity of the strata, the cutterhead of this project suffered significant wear during the excavation of karst-developed strata. Taking the 4-2-5 section as an example, it was necessary to open the chamber for inspection and blade replacement every 15 to 20 rings, with a very high frequency of chamber opening, and most of them were passive openings. From May 8, 2022 to January 7, 2024, a total of 27 chamber openings were carried out in this section. The longest opening operation was the 6th time (309 rings), with a total opening time of 28 days and a total of 150 chambers. No gas leakage or water leakage occurred during the opening period, and the face condition inside the chamber was very stable. The method of filling the chamber with thick slurry for opening has proven to be highly effective in ensuring the safety of the opening operation and improving its efficiency. 5 Conclusions (1) The thick slurry filling method for opening the chamber takes advantage of the good stability of thick slurry, its resistance to loss and dilution in water-rich strata, and its high later strength without cracking. It can fill karst cavities at the face, seal stratum fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This method solves the problems of air leakage, ground mud gushing, soil chamber depressurization in karst strata, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressurized opening in karst-developed strata. (2) The thick slurry filling method can form a good mud film, meeting the conditions for opening in karst-developed strata. The parameters such as the thick slurry grouting pressure, grouting method, grouting steps, slurry ratio, consistency, spreadability, and water loss rate during the opening process can provide references for similar projects. (3) During the shield tunneling in karst-developed strata, the thick slurry also plays a very important role in assisting the tunneling process, enabling the project to successfully complete the tunneling construction in the karst-developed strata of the 4-2-5 and 6-5 sections. Therefore, further research should be conducted on the use of thick slurry for slurry-assisted tunneling, and theoretical analysis and numerical simulation should also be carried out to form a complete construction method for thick slurry. (4) The research on the principle of the thick slurry's own slurry performance and the performance differences from ordinary cement mortar and bentonite slurry is still insufficient. Further analysis of the correlation between slurry parameters and specific opening parameters and tunneling parameters of the shield is needed in the future. Conclusions (1) The thick slurry filling method for opening the chamber takes advantage of the good stability of thick slurry, its resistance to loss and dilution in water-rich strata, and its high later strength without cracking. It can fill karst cavities at the face, seal stratum fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This method solves the problems of air leakage, ground mud gushing, soil chamber depressurization in karst strata, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressurized opening in karst-developed strata. (2) The thick slurry filling method can form a good mud film, meeting the conditions for opening in karst-developed strata. The parameters such as the thick slurry grouting pressure, grouting method, grouting steps, slurry ratio, consistency, spreadability, and water loss rate during the opening process can provide references for similar projects. (3) During the shield tunneling in karst-developed strata, the thick slurry also plays a very important role in assisting the tunneling process, enabling the project to successfully complete the tunneling construction in the karst-developed strata of the 4-2-5 and 6 − 5 sections. Therefore, further research should be conducted on the use of thick slurry for slurry-assisted tunneling, and theoretical analysis and numerical simulation should also be carried out to form a complete construction method for thick slurry. (4) The research on the principle of the thick slurry's own slurry performance and the performance differences from ordinary cement mortar and bentonite slurry is still insufficient. Further analysis of the correlation between slurry parameters and specific opening parameters and tunneling parameters of the shield is needed in the future. Declarations Funding This research was funded by Key Disciplines Research Enhancement Project of Guangdong Province, China (2024ZDJS053,2024ZDJS060);the National Key Research and Development Program of China (No. 2022YFC3800905)༛the National Natural Science Foundation of China (No. 52078060). Conflict of interest The authors declare no conflicts of interest. Author Contribution Y.S. and Z.L. wrote the main manuscript text and Y.S. prepared figures. All authors reviewed the manuscript. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. 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Practice application on technology of opening chamber and knife replacement underpressure aided by paste HDN[J]. Engineering Construction, 2020,52(10):55-60. Huang Hengru. Research on soil replacement reinforcement technique by unstable excavation face of shield[D]. South China University of Technology, 2017. Technical code for operation in excavation chamber of shield tunneling machine at atmospheric or compressed air: CJJ217-2014[S]. Beijing: China Architecture & Building Press, 2014. Code for monitoring measurement of urban rail transit engineering: GB50911-2013[S]. Beijing: China Architecture & Building Press, 2013. Code for construction and acceptance of metro engineering: GB50299-2018[S]. Beijing: China Architecture & Building Press, 2018. Chen Kui, Wang Jiangka, et al. Shied Machine Design And Tunneling Application[M]. China Communications Press Co.,Ltd, 2019. Zhang Huijian,Qiu Wenge,Hu Hui, et al. Changing Cutter Tools Technology of Earth Pressure Balance Shield in Water-rich Sandy Gravel Stratum Under Pressure[J], Construction Technology, 2010,39(01):55-58. XIA Guosong.Research on the Key Technology of Reinforcement of Shield Tunneling Face Under Pressure in Karst Zone[J]. Railway Construction Technology, 2010,39(01):55-58. Huang Kan, Yiwei Sun, Hongzhi Cui et al. Analysis of bearing capacity characteristics and resilience enhancement mechanism in shield tunnel segments based on fracture energy and modulus degradation. Tunnelling and Underground Space Technology 2026, 167: 106952. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 21 Apr, 2026 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 24 Dec, 2025 Reviews received at journal 23 Dec, 2025 Reviews received at journal 23 Dec, 2025 Reviewers agreed at journal 12 Dec, 2025 Reviewers agreed at journal 12 Dec, 2025 Reviews received at journal 16 Nov, 2025 Reviewers agreed at journal 16 Nov, 2025 Reviews received at journal 27 Oct, 2025 Reviewers agreed at journal 27 Oct, 2025 Reviewers invited by journal 13 Oct, 2025 Editor assigned by journal 13 Oct, 2025 Editor invited by journal 13 Oct, 2025 Submission checks completed at journal 10 Oct, 2025 First submitted to journal 10 Oct, 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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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-7824402","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":534049217,"identity":"d13c4311-ebc8-45b0-a4b2-cb8487b2520f","order_by":0,"name":"Kan Huang","email":"","orcid":"","institution":"Guangzhou Maritime College","correspondingAuthor":false,"prefix":"","firstName":"Kan","middleName":"","lastName":"Huang","suffix":""},{"id":534049218,"identity":"7280d426-d5ad-4256-9226-9f70217f9b08","order_by":1,"name":"Yiwei 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8","display":"","copyAsset":false,"role":"figure","size":234642,"visible":true,"origin":"","legend":"\u003cp\u003ePressure and air supply gauge of the pressure holding system\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7824402/v1/408d89fe0d9b881a6e85f82f.png"},{"id":94456969,"identity":"138a19a2-96f4-4556-8285-c1132f136f24","added_by":"auto","created_at":"2025-10-27 14:45:18","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":40842,"visible":true,"origin":"","legend":"\u003cp\u003eThe 6th (309 rings) settlement statistical chart\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7824402/v1/7d5b3e8a2acafc2a70d4549b.png"},{"id":107929001,"identity":"23f4cab7-8ec0-4054-8caa-06161a4376d7","added_by":"auto","created_at":"2026-04-27 16:13:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1840377,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7824402/v1/5f05a9e6-a614-4a74-8fbb-3034f9b71c9f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Research on Key Technologies of Thick Slurry Filling Chamber Method for Earth Pressure Balance Shield in Karst Areas","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eDuring the construction of shield tunnels, various issues are inevitable, such as the wear of cutterhead tools, the formation of mud cakes on the cutterhead, and the need to traverse important buildings and structures. Therefore, chamber-opening operations are necessary to inspect, replace, and clean the cutterhead tools.\u003c/p\u003e\n\u003cp\u003eBased on the pressure maintenance condition within the pressure chamber, shield chamber-opening operations can be primarily classified into atmospheric-pressure chamber opening and pressurized chamber opening [1]. Currently, pressurized chamber opening mainly involves using pneumatic support for the excavation face. That is, operators enter the pressure chamber to carry out tasks under a specific air pressure environment. For strata with high permeability, the most commonly adopted approach to reducing soil permeability is to inject slurry in front of the excavation face, enabling the formation of a slurry film with excellent airtightness [2 - 3].\u003c/p\u003e\n\u003cp\u003eZhu Wei and Min Fanlu have conducted extensive research and experiments on slurry, exploring the penetration patterns of slurry in strata and the formation mechanism of slurry films in slurry-pressure shield tunnels, and have put forward scientific theories and application techniques related to slurry [3 - 4]. Zhu Weibin, Kuang Shuhua, Li Maosong, et al. have carried out in-depth research on the auxiliary chamber-opening technology that utilizes \"Hengdun mud\" to form a slurry-film wall for protection. The characteristic of this method is that the \"Hengdun mud\" slurry fills, squeezes, and fractures into construction voids, stratum pores, and fractures, promptly sealing the water and gas leakage channels within the strata. Moreover, it forms a slurry film of a certain thickness on the excavation face, featuring a dense structure and good stability, thus overcoming the challenges of shield chamber-opening operations in unstable strata [5 - 6].\u003c/p\u003e\n\u003cp\u003eDuring the application of the pressurized chamber-opening method with slurry-film wall protection, due to the water-drainage effect of air pressure, the slurry skin starts to crack due to water loss after a certain period. Consequently, it is necessary to repeatedly inject high-viscosity slurry at regular intervals to repair the slurry skin. During the slurry-skin repair process, operations inside the chamber must be suspended. The slurry skin only serves the function of pressure maintenance and lacks reinforcement capabilities. Additionally, it is prone to cracking. Once the slurry skin cracks, it can easily lead to pressure loss and instability inside the chamber, posing significant safety risks [7]. Similar issues also exist in ordinary bentonite slurry, \"Hengdun mud\", and \"Keneff\".\u003c/p\u003e\n\u003cp\u003eThis study is based on the shield tunnel project in the second construction area of the first bid section of the shared pipe gallery of Shenzhen Metro Line 16. In response to the problems encountered in karst-developed strata, such as the instability of the filling materials within karst cavities at the excavation face, the well-developed and highly connected karst fissures, the large amount of air leakage during pressurized chamber opening, and the substantial water replenishment in the strata, which impede the normal implementation of atmospheric-pressure or pressurized chamber opening, this paper analyzes the technical mechanism of the thick-slurry chamber-filling method for pressurized chamber opening. It also examines the slurry proportioning parameters, chamber-filling parameters, grouting parameters, and the working pressure for pressurized chamber opening in the thick-slurry chamber-filling method. Furthermore, this paper summarizes the construction technology and control measures of the chamber-opening operations using the thick-slurry chamber-filling method, and proposes a chamber-opening technology for earth-pressure-balance shield tunnels in karst-developed strata based on the thick-slurry chamber-filling method. Finally, the effectiveness of the chamber-opening technology is verified through an analysis of the ground monitoring data during the actual chamber-opening process and the stability of the excavation face during the chamber-opening operation.\u003c/p\u003e"},{"header":"2 Project Overview","content":"\u003cp\u003eThe project of the first contract section and the second work area of the co-built pipe gallery of Shenzhen Metro Line 16 includes 4 shafts and 1 section, with a starting mileage of KA2+311.4 and an ending mileage of KA5+488.05. The total length of the section is 3176.65m. The route map is shown in Figure 1. The shield tunnel is divided into 3 sections, namely the 4\u0026rarr;3 section, the 4\u0026rarr;2\u0026rarr;5 section, and the 6\u0026rarr;5 section. The outer diameter of the shield tunnel segments is 8.8m, the ring width is 1.5m, and the thickness of the segments is 0.4m. The tunnel depth ranges from 11.06m to 34.95m, with a maximum longitudinal slope of 33.7\u0026permil; and a minimum turning radius of 500m. Two earth pressure balance shield machines with a cutting diameter of 8850mm are used for construction.\u003c/p\u003e\n\u003cp\u003eThe main strata that the shield tunnel passes through are gravelly silt clay, fully to strongly weathered sandstone, and slightly weathered limestone. The surrounding rock grades are III, IV, and V. The strata statistics are as follows: silt clay and gravelly silt clay about 768m, accounting for 24.8%; fully to strongly weathered sandstone about 680m, accounting for 21.9%; slightly weathered limestone and carbonaceous limestone about 1654m, accounting for 53.3%. It can be seen that the tunnel body is mainly in rock strata, accounting for three quarters of the entire shield tunnel.\u003c/p\u003e\n\u003cp\u003eAccording to the geological investigation report and detailed investigation report, the adverse geological conditions of this tunnel are karst and faults. There were a total of 365 boreholes during the investigation stage, and 187 boreholes exposed karst caves. The total number of exposed karst caves was 389, with a height ranging from 0.10m to 23.80m and an average height of 2.7m. The karst cave exposure rate of the 3\u0026rarr;4 section boreholes was 14.86%, with moderately developed karst; the karst cave exposure rate of the 4\u0026rarr;2 section boreholes was 58.76%, with strongly developed karst; the karst cave exposure rate of the 2\u0026rarr;5 section boreholes was 64.18%, with strongly developed karst; the karst cave exposure rate of the 5\u0026rarr;6 section boreholes was 64.58%, with strongly developed karst. The filling conditions of the karst caves are irregular and the components are complex, with significant differences in physical and mechanical properties. The geological longitudinal section of the shield tunnel is shown in Figure 2 (the black-filled parts in the figure represent karst voids).\u003c/p\u003e\n\u003cp\u003eThe groundwater in this shield tunnel includes pore water in loose rock, fissure water in bedrock and karst fissure water. The fissure water in bedrock is stored in sandstone and limestone, with a relatively large thickness of aquifer and a moderate water volume. The karst fissure water is stored in fissures and karst caves in limestone, with a rich water volume. Its permeability and water-richness vary depending on the development degree, connectivity, topographic conditions and other factors of fissures and karst caves. It has confined pressure. The main factor affecting the opening of the tunnel is the strong development of karst in the limestone stratum, the development of karst fissures, and the abundance of confined karst groundwater. Due to the severe karst dissolution at the tunnel face, the fillings in karst cavities are unstable, the karst fissures are well developed and highly connected, the karst limestone stratum is highly permeable, the stratum is soft on top and hard at bottom, and the karst fissure water in the slightly weathered limestone stratum is abundant, the earth pressure chamber cannot maintain pressure, making it impossible to carry out normal atmospheric or pressurized opening.\u003c/p\u003e"},{"header":"3 Principle, Technology and Parameter Control of the Thick-slurry Bunker-filling Method for Chamber Opening","content":"\u003cp\u003e3.1 Principle of Chamber Opening Using the Thick-slurry Bunker-filling Method\u003c/p\u003e\n\u003cp\u003eThe thick slurry filling method for opening the chamber has no essential difference in principle from the general bentonite slurry wall pressure-supported opening of the chamber. The basic principle is to use air pressure to ensure the stability of the face during the opening process. However, due to the addition of a certain proportion of lime in the thick slurry, the slurry undergoes a hardening reaction similar to that of cement mortar. The formed mud film is thick and its strength increases over time, resulting in very little consolidation and shrinkage. Therefore, it can effectively fill karst cavities, seal karst fissures, and maintain pressure in the soil chamber. By taking advantage of the good stability of the thick slurry, its resistance to loss and dilution in water-rich strata, high later strength, and no cracking, thick slurry is injected into the soil chamber of the shield machine to fill the karst cavities at the face, seal the strata fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This solves the problems of air leakage in karst strata, ground slurry leakage, soil chamber pressure loss, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressure-supported opening in karst-developed strata. The mechanism diagram of the thick slurry filling method for opening the chamber is shown in Figure 3.\u003c/p\u003e\n\u003cp\u003e3.2 Process Flow of Opening the Bunker by Thick Slurry Filling Method\u003c/p\u003e\n\u003cp\u003eThe process flow of opening the bunker by thick slurry bunker filling method is presented in Figure 4.\u003c/p\u003e\n\u003cp\u003e3.2.1\u0026nbsp; \u0026nbsp;Judgment of Whether to Open the Bunker\u003c/p\u003e\n\u003cp\u003eShield tunneling chamber opening is generally divided into active and passive chamber opening. In this project, the 4-2-5 section has more passive chamber openings. Whether the shield machine needs to open the chamber during the tunneling process is first determined by the geological profile of the shield tunnel to judge the basic situation of the stratum where the shield machine is currently located, and then combined with the specific tunneling parameters during the tunneling process for judgment. Generally, when the tunneling speed is lower than 5mm/min or the tunneling speed fluctuates greatly, the cutterhead torque fluctuates greatly, and the thrust abnormally increases, attention should be paid. At the same time, when there is a karst cave ahead, the earth pressure in the soil chamber will be unstable during tunneling, the pressure difference between the upper and lower parts of the soil chamber will increase, the soil chamber cannot maintain pressure, and the air compressor of the pressure maintenance system will frequently load. At the same time, the stratum conditions ahead of the face can also be judged by the debris samples and debris temperature. When the stone powder and fine particle content in the debris samples is very high (generally more than 60%) and the debris temperature exceeds 40\u0026deg;, it indicates that the rock-breaking ability of the cutter has decreased significantly, and chamber opening inspection should be carried out.\u003c/p\u003e\n\u003cp\u003e3.2.2\u0026nbsp; \u0026nbsp;Shield machine shutdown and preparation for opening the chamber\u003c/p\u003e\n\u003cp\u003eAfter deciding to carry out the opening operation, the shield machine is shut down to prepare for the opening. The main preparations include the layout of ground monitoring points in front of the face, the fabrication of the shield water-stop ring, and the determination of the working pressure for the pressurized opening.\u003c/p\u003e\n\u003cp\u003e(1) Layout of Ground Monitoring Points\u003c/p\u003e\n\u003cp\u003eTo provide monitoring information for the pressurized opening operation and ensure the safety of the opening, the ground conditions corresponding to the cutterhead position are monitored during the opening. The monitoring points are densely arranged compared to the monitoring during the tunneling construction, following the first-level control (the monitoring level during tunneling construction is the second level). Specifically, a monitoring section is set up every 4 to 5 meters along the shield tunnel axis, totaling 5 sections, with 1 section in front of and 1 section behind the shield body, and 3 sections within the shield body range. Each monitoring section has 3 to 5 monitoring points, totaling 15 to 25 monitoring points. Within one section, the monitoring points are arranged on both sides of the tunnel axis, with a lateral spacing of approximately 3 to 4 meters. The specific layout can be adjusted locally based on the ground structures at the opening position and can be increased or decreased according to the feasibility of on-site measurement points. For example, the layout of the monitoring points for the opening at ring 309 is shown in Figure 5.\u003c/p\u003e\n\u003cp\u003eWhen the shield stops, the initial values should be collected in a timely manner. During the process of opening the chamber for work, the monitoring frequency is twice a day until the excavation resumes.\u003c/p\u003e\n\u003cp\u003e(2) Construction of the water-stop ring\u003c/p\u003e\n\u003cp\u003eAfter the shield stops, a double-liquid grouting of cement and water glass is carried out on the entire ring of segments located 5 to 6 rings away from the shield tail (usually 2 rings of segments), forming a closed water-stop ring to prevent the soil chamber from connecting with the stratum through the gap at the shield tail, which could lead to air leakage and inability to maintain pressure.\u003c/p\u003e\n\u003cp\u003eThe double-liquid grout is injected through the reserved grouting holes on the segments. The ratio of the cement-water glass double-liquid grout is as follows: A liquid, cement slurry: cement: water = 1:1 (by weight); B liquid, water glass, with a specific gravity of 35 Be\u0026apos;; A liquid: B liquid = 1:0.5 (by volume). The setting time is controlled at around 20 seconds. To prevent segment displacement, the \u0026quot;diagonal injection\u0026quot; method is generally adopted, and the grouting pressure is controlled within 5 bar.\u003c/p\u003e\n\u003cp\u003e(3) Determination of the pressure for opening the chamber\u003c/p\u003e\n\u003cp\u003eThe working pressure for opening the chamber is the soil chamber pressure that can ensure the stability of the face. It can be the soil chamber pressure during the excavation of the first few rings before opening the chamber and verified according to formula (1), while also taking into account the thickness of the overlying strata and the geological conditions for adjustment. According to the \u0026quot;Calculation Specifications for Chamber Opening and Pressure Work in Shield Tunneling\u0026quot; [8] (GJJ217-2014), the following formula is used for calculation:\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"74\" height=\"24\" src=\"data:image/wmf;base64,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\" alt=\"image\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(1)\u003c/p\u003e\n\u003cp\u003eWhere \u003cem\u003eP\u003c/em\u003e\u003csub\u003ew\u003c/sub\u003e represents the water head pressure calculated to the center of the tunnel excavation, and \u003cem\u003eP\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e is the pressure adjustment value considering different geological conditions, ground environment and the position of the excavation face, which can be taken as 0 to 0.03 MPa. Taking the 734th ring of the 2-5 section as an example, the groundwater level at this position is approximately 3.68m, the depth of the tunnel bottom is about 32.48m, and the outer diameter of the shield machine is 8.85m. Then:\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"288\" height=\"24\" src=\"data:image/wmf;base64,R0lGODlhsAEkAHcAMSH+GlNvZnR3YXJlOiBNaWNyb3NvZnQgT2ZmaWNlACH5BAEAAAAALAMAAgCpARwAhgAAAAAAAB4AHh0AAAAAHR0dAAAdHR4eAB0AHRwcHB0AMh0dNAAAMwAdMgAdMwAcSB0dSR0dSB00HQAyMh0zWgAzWh0yWgAyWh4zRwA0SB1IWx1GbDMAADQdHTIdADMdADIAHTMAHTQdNDMeRzQ0HTMzSDVIWzNIWTNGbjVbbjVZbDNZfzNGbDNbgEgcAEkdHUgdAEgdHUceM0geNFszHVozAFszAEczHlozHUg0Hkg0AEgzM0YzRltIHUZGM1tINV1dRkhIW0hbbkhZf0ZGbltuSF1/f0Rqe1luf0huf113d0RubkRqalVqe1lublV3d2xGHW5IHW5bNW5GM25INW5bSH9uSH9/XX9uWW5uWWZ3d2Z/Zm5ugG6AbmaIiIBbM4BdM4BuboiIZgECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwf/gACCg4SFhoeIiYqLjI2Oj5CCUpGUlZaXmJmam5ydnp+goaKhU6Omp6ipmFSqra6vsJtfsbS1tpc0t7q7vJ9WvcDBtQLCxcbHABXIy8yZNsrN0dKmA9PWwrmQXwRH15ocAeHiAaokBJw34RSLBeELiO0BBpo1DIY4AwHnh/j6648uHhyKZyDFpn77HN3IZ4hgpwPh5iWSAlFeonH2FkEgRCMfAQuJOEC7lCMcSEXmOJlclPIigSGDBhBIMqoDAH2bOAgUtPNQQhczCyWUMmADJp2FXIwLMFKQUoyPyBkaWjTTU3FNLwIQUggKAYOCqmmiatSQV7AAxBbKJ64RTUEw/5ZmPDS3ElKeh351wJnpLoCehvYmPBQA8E3DoDgMtlRj8ICsgqQO4lBXrSCvmCRfLsT3cgNC4SAfymfYMgDMl6BwXmxIKaKqhFhHMo16bdlBi21E+nfaAegAFw7Z0BzJhuPgiBSPJTQA+SHlWglZGVA3FNC3l0xfL1TPkOQvAW4Lku0ISvhF5AcFqH4oxs1C4MUDSG+J/ntExL1ipxRfKOGu3AzyCyQiLLIeftkVAkOAiNjHiGkLdtNgIkq1wBl7nwCVSQ3nDcKhIZR5N5Jp3V1CnCE1AEaEIdQtMsthawFWIicpKsJUIgPIiCEkJGKYYyHV6YNBI6ot0iJhzkEyXP8hSyKyICbDyXfiIE++Vh2HonmiYSGTIIIWaF3dSEiIa3E2iBRBEdLlIV8CUGEmptn4nyQOenKkkwF8Nt4mkqEpoYJ54lYIOG0pMqCR0Q3CG0dzDhIFcInItugg2ZhJyKNJ+ofgWnVaJZsHkGEIjneGjbpWXR7oQ0IEiHiAInumHvIDAo1MiR9iqRKwqiezKmJeBgDEc8gHqrK6CbG6GosIsrsuG1omtt5U1wdZ2QDriYU5KRu1TF5LqraIKHXbDzJFstS5FKZZiKuE6AkiceBdKaZ6hHV4CLuDuDtmABZ6F85XiyBWCG/RhiNfZv+2CaYT6unrVDifGLxIXNEK8mj/tBsxInBk7I2k23PwHjjhsB4nRxwYIvv0GgESsGWACapseUhAbjq8r3fXajBIqlktQEI4G7spkAs2CxLrveH0ewitirinnsDvAO1Jqvw+t1hchvgs9SZaZ5tI10ED8KjALzRCzEXswSAQDEUDcDTH4Dq5dtvgrHBh3N7VIvPMXpscpsDpkMMVcQnlk6Wbfb+r9KbtLVIkvVPFNO9l5y51sKUgVmdeT9vQRNSUlY+jcliTD7KNJAwpAgN7Ly5Sto07Vvz22JEaqMjsiWvKXcWn7N1a7klhe3hMlTWVOt9Bu2agwI8nomxkpa3FOyXAu83enY8xN72Rxk+ZveSLsFfg/yJRMFJ9XEFjzVmmVNKHfiLqg4n3mDumsh0iQ9tOCIeX72+veVJKRP4QwaHFPecQzbtI6DICQMxxggO1k86PIgOf0kGigfJzIADAc7gECqJ/jqrVIWAwiKARJ0oRHGEJEyUIFI5Mg5YwT+ggFi7yeKAnNWgbBwnhO7OU7kQiMcQNPdS26XHgYJNyRO6AODxKHBGBJ1KLeUAELRBlBYOTaWIhMjYRJcrnAz2xQdFQlqQqjZA8YGwXfjKVHjMO4k206KEgslKDRMwoLY7LHXiiZwg6HmKHiqjOmgiRxEYJYo9l8kT9IEiI2txHQAMwoDZyF6dHxsRuiOCiICqFiEEqyv+QAPjAIYpmLeagZ1ijFE5lTrkaW7xNEIXEQUjeqK8JCsID5OEQb/BFSH48BzCKQUsC/IWusJjQMLrcmRZvBzBBDJM5gLHMCTXDLSgFgDeijElPqOkxApxgECWgXuVGWL9GMBIAbIPmvljQF2ikU5vrVA9UgmfAZTriKvrYTyVi0BlBTEcgHJLIRByiiSBFBGZqWqA/bZk3Q0iBoNA6aCH+uS4aHqIiBdkERSKSyEFgtE3EkofCAKDPhFZOVPZMxAv6CQCKRkYcnVIpS116E5g+oo548YYuKqnTniLjbD79hFF2EFRb4LSoSBWGB5O6iecxVRUgeKpUbxGCqWpiAi0qBQAQrKqKQnL1q6GQJFgdsZNzjvWsaI0GCtIaCbGy9RMjfatcFxHXrwYCADs=\" alt=\"image\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"150\" height=\"18\" src=\"data:image/wmf;base64,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\" alt=\"image\"\u003e\u0026nbsp;(2)\u003c/p\u003e\n\u003cp\u003eThe pressure in the soil chamber during the tunnel boring is approximately 2.7 bar. The working pressure of 2.7 bar during tunnel boring can be adopted as the working pressure for the chamber opening operation.\u003c/p\u003e\n\u003cp\u003e3.2.3\u0026nbsp; \u0026nbsp;Preparation, Transportation, and Filling of Thick Slurry\u003c/p\u003e\n\u003cp\u003e(1) Thick slurry production\u003c/p\u003e\n\u003cp\u003eThick slurry is an inert slurry composed of hydrated lime, bentonite, fly ash, fine sand and water. Compared with ordinary bentonite slurry and cement mortar, its characteristics are: ① Good slurry stability, less prone to loss and dilution in water-rich strata; ② Good pressure retention effect (tail shield, radial holes, soil chamber), can quickly achieve pressure retention effect, and has better continuous grouting and settlement control; ③ Less likely to cause damage to the tail shield brush and entrapment of the shield body. This is the main reason for using the thick slurry filling method to open the chamber in karst strata. However, the thick slurry has a long curing time and requires less stability of the segments; the slurry has poor fluidity and high requirements for pumping equipment. These factors should be considered during application.\u003c/p\u003e\n\u003cp\u003eThe proportion of thick slurry is generally determined through on-site sampling of sand layers and indoor film-forming effect tests simulating the strata to be opened. However, due to the complexity of karst strata, the proportion is actually determined by referring to that of ordinary cement mortar and bentonite slurry and through multiple on-site filling tests. The actual proportion of thick slurry is shown in Table 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable1 \u0026nbsp; Thick-slurry filling silo slurry ratio\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"586\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eRaw materials（kg）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003esand\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003ecoal fly ash\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003elime\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003ewater\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003ecalcium\u0026nbsp;\u003c/p\u003e\n \u003cp\u003ebentonite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003eSodium-based high-viscosity bentonite\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 106px;\"\u003e\n \u003cp\u003eUsage amount\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003e1200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e570\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e290\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e375\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDuring the preparation of thick slurry, samples should be taken for consistency, spreadability tests, 4-hour water immersion test and 24-hour bleeding test. Only when the requirements are met can the slurry be prepared. The performance indicators of thick slurry mainly focus on initial setting time, consistency and spreadability, with bleeding rate and volume loss rate control as secondary. The performance indicators of the slurry are summarized as follows:\u003c/p\u003e\n\u003cp\u003e① Initial setting time \u0026le; 72 hours.\u003c/p\u003e\n\u003cp\u003e② Consistency \u0026asymp; 6.8mm, tested by a mortar consistency tester; spreadability \u0026le; 15cm, with 13-15cm being the best, measured by a mortar spreadability tester. The consistency and spreadability of the slurry are measured to test its fluidity.\u003c/p\u003e\n\u003cp\u003e③ After being sealed for 24 hours, there is water on the surface of the slurry, no segregation occurs, and the weight after bleeding is 762g when 770g is sampled. The bleeding rate of the slurry should be less than 2%.\u003c/p\u003e\n\u003cp\u003e④ The volume loss of the slurry in the 4-hour static water test is \u0026le; 10%, and in the 4-hour dynamic water test is \u0026le; 20%. The 4-hour static water test volume loss and 4-hour dynamic water test volume loss are mainly used as reference control indicators to judge the degree of erosion of thick slurry by karst fissure water during the filling process. The on-site measurement mainly uses standard mortar strength specimens with a side length of 70.7mm, placed in containers filled with still water or flowing water. The flow rate of dynamic water can be calculated based on the estimated water inflow at the excavation face of the opening position. After 4 hours of stillness, the volume of the specimen is measured, and the volume loss rate is obtained by comparison.\u003c/p\u003e\n\u003cp\u003e⑤ Fine sand with a fineness modulus of 1.6-2.2 must be used for slurry preparation.\u003c/p\u003e\n\u003cp\u003e(2) Thick slurry transportation and filling of the storage tank\u003c/p\u003e\n\u003cp\u003e①\u0026nbsp;Slurry pumping and transportation\u003c/p\u003e\n\u003cp\u003eThe slurry is pumped from the mortar mixing station to the slurry storage tank located on the middle plate of the shield shaft by the extrusion pump. The extrusion pipe of the extrusion pump should be inspected once for every 50 m\u0026sup3; of slurry mixed. After the slurry truck arrives, the slurry is discharged from the slurry storage tank to the slurry truck. The slurry truck is equipped with a self-stirring system to maintain the slurry state, and then transported to the grouting system of the shield car through the tunnel horizontal transport vehicle.\u003c/p\u003e\n\u003cp\u003e②\u0026nbsp;Injection of thick slurry\u003c/p\u003e\n\u003cp\u003eIn karst strata, the full storage tank mode is rarely used for excavation. Generally, the local pneumatic mode is adopted, and the sludge in the soil storage tank accounts for about 2/3 of the storage tank. Before injecting thick slurry, the sludge and air should be replaced first. The sludge surface is lowered to about 1/2 of the storage tank by the screw conveyor, and the amount of sludge discharged is generally controlled at 10 to 15 m\u0026sup3;. When the stratum is stable, due to the existence of rock layers and air pressure, and the time is short (about 1 hour), the collapse of the working face generally will not occur. However, when the stratum is unstable, thick slurry should be injected into the soil storage tank first before sludge replacement.\u003c/p\u003e\n\u003cp\u003eAfter the thick slurry reaches the grouting system of the shield car, the shield machine\u0026apos;s synchronous grouting system is used to connect two grouting pipes to the reserved valve on the soil storage tank partition. A test grouting is conducted first to determine the initial grouting pressure. The initial injection pressure should be 0.2 bar higher than the pressure at the top of the excavation storage tank to ensure that the slurry does not flow back and cause pipe blockage. If the pressure in the soil storage tank increases due to the grouting pressure during the grouting process, the grouting should be paused.\u003c/p\u003e\n\u003cp\u003eContinue to inject thick slurry through the balance valve in the personnel lock chamber and the radial holes of the shield body. The injection pressure should be 0.5 bar higher than the pressure at the top of the soil chamber. Repeat the injection multiple times until the chamber is full. During the injection process, try not to start the cutter head to allow the thick slurry to diffuse into the gaps around the shield body and the face. Generally, the injection pressure will continuously increase until it reaches the termination pressure of 4.0 bar.\u003c/p\u003e\n\u003cp\u003eAfter the thick slurry fills the soil chamber, the gap between the shield body and the stratum is usually filled with bentonite slurry or a chemical slurry composed of phosphoric acid solution and sodium silicate (in a ratio of 1:1) through the radial grouting holes of the shield body to fill the gaps behind the shield shell that the thick slurry cannot fill, forming a closed water-stop belt.\u003c/p\u003e\n\u003cp\u003e3.2.4\u0026nbsp; Air pressure displacement of thick slurry and pressure holding\u003c/p\u003e\n\u003cp\u003eAfter the thick slurry fills the soil chamber, the pressure in the soil chamber drops from 4.0 bar to 3.0 bar (usually taking 3 to 4 hours), and when it remains at 3.0 bar for more than 2 hours without further pressure drop, the screw conveyor is activated to discharge the soil for gas-soil replacement. During the soil discharge process, the pressure fluctuation in the soil chamber is controlled within 0.3 bar. Finally, the pressure in the soil chamber is maintained at 2.7 bar (the working pressure for opening the chamber). During the soil discharge process, the pressure maintenance system (SAMSON system) continuously injects high-pressure gas into the soil chamber. When the thick slurry level reaches the center of the cutter head, the replacement is stopped and the pressure is maintained.\u003c/p\u003e\n\u003cp\u003e3.2.5\u0026nbsp; Condition judgment for Entering the Chamber under Pressure\u003c/p\u003e\n\u003cp\u003eAfter the slurry-air replacement is completed, with the pressure maintenance system on, during the pressure maintenance process of the soil chamber, if the opening degree of the pressure maintenance system\u0026apos;s air replenishment switch is less than 0.2, and the loading time of the air compressor is shorter than the unloading time, with a loading time of 10 seconds and an unloading time of 30 seconds being the optimal state, it is considered that the thick slurry mud film on the face can meet the conditions for opening the chamber. On-site, through detailed records of the opening degree of the pressure maintenance system\u0026apos;s air replenishment switch, the slurry and air replacement, the specific depressurization time during the process, the loading and unloading time of the air compressor, and the injection volume of the thick slurry, a comprehensive analysis is conducted to determine whether the conditions for entering the chamber are met.\u003c/p\u003e"},{"header":"4 Analysis of the Opening Effect of the Thick-slurry Chamber-filling Method","content":"\u003cp\u003e4.1 Ground monitoring\u003c/p\u003e\n\u003cp\u003eGround monitoring during the opening of the warehouse is controlled at level one, using a Trimble DiNi03 precision level (with an accuracy of \u0026plusmn;0.30mm) for measurement. The monitoring frequency is twice a day, with the cumulative settlement control value set at +10 to -20mm and the settlement rate control value at 3mm/d [9-10]. Through the analysis of a total of 27 opening operations in the 4-5 section of this project, the maximum cumulative settlement during the opening operation was -9.3mm, and the maximum settlement rate was -2.16mm/d, both of which were less than the specified values. Taking the longest-lasting 6th opening (309 rings) as an example, the settlement value changed from the first entry into the warehouse to the completion of the blade change and the resumption of advancement, which lasted for 28 days. Through the monitoring data, it was found that as the opening time increased, the cumulative settlement gradually increased. At the end of the opening operation, the cumulative settlement was -7.2mm, but the settlement rate during the opening operation was very stable, basically remaining at around -0.5mm/d. As the opening time increases, the settlement amount gradually increases, increasing the safety risk of the opening operation. The monitoring results of the 6th (309 rings) opening operation are shown in Figure 9.\u003c/p\u003e\n\u003cp\u003eIt can be known from the monitoring data that the thick slurry filling method for opening operations in karst strata can effectively control the stratum settlement.\u003c/p\u003e\n\u003cp\u003e4.2\u0026nbsp; Effect of opening the chamber\u003c/p\u003e\n\u003cp\u003eDue to the complexity of the strata, the cutterhead of this project suffered significant wear during the excavation of karst-developed strata. Taking the 4-2-5 section as an example, it was necessary to open the chamber for inspection and blade replacement every 15 to 20 rings, with a very high frequency of chamber opening, and most of them were passive openings. From May 8, 2022 to January 7, 2024, a total of 27 chamber openings were carried out in this section. The longest opening operation was the 6th time (309 rings), with a total opening time of 28 days and a total of 150 chambers. No gas leakage or water leakage occurred during the opening period, and the face condition inside the chamber was very stable. The method of filling the chamber with thick slurry for opening has proven to be highly effective in ensuring the safety of the opening operation and improving its efficiency.\u003c/p\u003e"},{"header":"5 Conclusions","content":"\u003cp\u003e(1) The thick slurry filling method for opening the chamber takes advantage of the good stability of thick slurry, its resistance to loss and dilution in water-rich strata, and its high later strength without cracking. It can fill karst cavities at the face, seal stratum fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This method solves the problems of air leakage, ground mud gushing, soil chamber depressurization in karst strata, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressurized opening in karst-developed strata.\u003c/p\u003e\n\u003cp\u003e(2) The thick slurry filling method can form a good mud film, meeting the conditions for opening in karst-developed strata. The parameters such as the thick slurry grouting pressure, grouting method, grouting steps, slurry ratio, consistency, spreadability, and water loss rate during the opening process can provide references for similar projects.\u003c/p\u003e\n\u003cp\u003e(3) During the shield tunneling in karst-developed strata, the thick slurry also plays a very important role in assisting the tunneling process, enabling the project to successfully complete the tunneling construction in the karst-developed strata of the 4-2-5 and 6-5 sections. Therefore, further research should be conducted on the use of thick slurry for slurry-assisted tunneling, and theoretical analysis and numerical simulation should also be carried out to form a complete construction method for thick slurry.\u003c/p\u003e\n\u003cp\u003e(4) The research on the principle of the thick slurry's own slurry performance and the performance differences from ordinary cement mortar and bentonite slurry is still insufficient. Further analysis of the correlation between slurry parameters and specific opening parameters and tunneling parameters of the shield is needed in the future.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003e(1) The thick slurry filling method for opening the chamber takes advantage of the good stability of thick slurry, its resistance to loss and dilution in water-rich strata, and its high later strength without cracking. It can fill karst cavities at the face, seal stratum fissures and form a mud film, preventing karst fissure water from entering the soil chamber. This method solves the problems of air leakage, ground mud gushing, soil chamber depressurization in karst strata, and the inability of ordinary bentonite to form a mud film, as well as the cracking of the mud film during the opening process. It can well establish the conditions required for pressurized opening in karst-developed strata.\u003c/p\u003e\u003cp\u003e(2) The thick slurry filling method can form a good mud film, meeting the conditions for opening in karst-developed strata. The parameters such as the thick slurry grouting pressure, grouting method, grouting steps, slurry ratio, consistency, spreadability, and water loss rate during the opening process can provide references for similar projects.\u003c/p\u003e\u003cp\u003e(3) During the shield tunneling in karst-developed strata, the thick slurry also plays a very important role in assisting the tunneling process, enabling the project to successfully complete the tunneling construction in the karst-developed strata of the 4-2-5 and 6\u0026thinsp;\u0026minus;\u0026thinsp;5 sections. Therefore, further research should be conducted on the use of thick slurry for slurry-assisted tunneling, and theoretical analysis and numerical simulation should also be carried out to form a complete construction method for thick slurry.\u003c/p\u003e\u003cp\u003e(4) The research on the principle of the thick slurry's own slurry performance and the performance differences from ordinary cement mortar and bentonite slurry is still insufficient. Further analysis of the correlation between slurry parameters and specific opening parameters and tunneling parameters of the shield is needed in the future.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis research was funded by Key Disciplines Research Enhancement Project of Guangdong Province, China (2024ZDJS053,2024ZDJS060);the National Key Research and Development Program of China (No. 2022YFC3800905)༛the National Natural Science Foundation of China (No. 52078060).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eY.S. and Z.L. wrote the main manuscript text and Y.S. prepared figures. All authors reviewed the manuscript.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZHU Wei ,MIN Fanlu,YAO Zhanhu,WANG Rui,WEI Daiwei,JIANG Teng. Technical status and case study on intervention in the shield chamber[J]. Modern Tunnelling Technology, 2015, 52(1): 9-18.\u003c/li\u003e\n\u003cli\u003eHOU Lei . Research on Technology of Replacing Cutting Tool with Pressure of EPB Shield in Water-Rich and Pebbly Sand Stratum[D]. Southwest Jiaotong University, 2009.\u003c/li\u003e\n\u003cli\u003eMIN Fanlu. Study on the Penetration Law of Slurry in Ground and Filter Cake Formation in Slurry Shield Tunnelling [D]. Nanjing:Hohai University, Doctoral Thesis, 2012\u003c/li\u003e\n\u003cli\u003eZhu W, Min F L, L\u0026uuml; Y Y, et al. Subject of\u0026quot; mud science and application technology\u0026quot; and its research progress[J]. Rock and Soil Mechanics, 2013, 34(11): 3041-3054.\u003c/li\u003e\n\u003cli\u003eZhu Weibin, Li Shijia, Fang Enquan, et al. On Pressurized Opening Technology with EPB Shield Mud Protection in Water-rich Sand Strata[J]. Municipal Engineering Technology, 2018,36(02):91-94.\u003c/li\u003e\n\u003cli\u003eKuang Shuhua. Practice application on technology of opening chamber and knife replacement underpressure aided by paste HDN[J]. Engineering Construction, 2020,52(10):55-60.\u003c/li\u003e\n\u003cli\u003eHuang Hengru. Research on soil replacement reinforcement technique by unstable excavation face of shield[D]. South China University of Technology, 2017.\u003c/li\u003e\n\u003cli\u003eTechnical code for operation in excavation chamber of shield tunneling machine at atmospheric or compressed air: CJJ217-2014[S]. Beijing: China Architecture \u0026amp; Building Press, 2014.\u003c/li\u003e\n\u003cli\u003eCode for monitoring measurement of urban rail transit engineering: GB50911-2013[S]. Beijing: China Architecture \u0026amp; Building Press, 2013.\u003c/li\u003e\n\u003cli\u003eCode for construction and acceptance of metro engineering: GB50299-2018[S]. Beijing: China Architecture \u0026amp; Building Press, 2018.\u003c/li\u003e\n\u003cli\u003eChen Kui, Wang Jiangka, et al. Shied Machine Design And Tunneling Application[M]. China Communications Press Co.,Ltd, 2019.\u003c/li\u003e\n\u003cli\u003eZhang Huijian,Qiu Wenge,Hu Hui, et al. Changing Cutter Tools Technology of Earth Pressure Balance Shield in Water-rich Sandy Gravel Stratum Under Pressure[J], Construction Technology, 2010,39(01):55-58.\u003c/li\u003e\n\u003cli\u003eXIA Guosong.Research on the Key Technology of Reinforcement of Shield Tunneling Face Under Pressure in Karst Zone[J]. Railway Construction Technology, 2010,39(01):55-58.\u003c/li\u003e\n\u003cli\u003eHuang Kan, Yiwei Sun, Hongzhi Cui et al. Analysis of bearing capacity characteristics and resilience enhancement mechanism in shield tunnel segments based on fracture energy and modulus degradation. Tunnelling and Underground Space Technology 2026, 167: 106952.\u003c/li\u003e\n\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Keyword, EPB Shield, Karst Strata, thick-slurry filling, opening chamber under-pressure, ground monitoring","lastPublishedDoi":"10.21203/rs.3.rs-7824402/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7824402/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDue to the presence of numerous Karst cavities, fractures, and fissure water, Karst strata exhibit significant air leakage during pressurized chamber opening. This leads to a large gas replenishment volume, substantial formation water inflow, and the inability to conduct pressurized chamber opening operations normally. To address this issue, this study focuses on the shield tunneling project in the first standard section and second work area of the Shenzhen Metro Line 16 utility corridor. Based on the engineering characteristics of highly developed Karst strata, the technical mechanism of the thick-slurry filling method for pressurized chamber opening is analyzed. The slurry mix design parameters, filling parameters, grouting parameters, working pressure for pressurized chamber opening, construction technology, and control measures are systematically summarized. Consequently, a chamber-opening technology using the thick-slurry filling method for Earth Pressure Balance (EPB) shield tunneling in Karst formations is proposed. The results indicate that the thick-slurry filling method is an effective approach for chamber opening in EPB shield tunneling through Karst formations. It can successfully mitigate issues related to formation air leakage during chamber opening, thereby ensuring operational safety, enhancing efficiency, and reducing costs.\u003c/p\u003e","manuscriptTitle":"Research on Key Technologies of Thick Slurry Filling Chamber Method for Earth Pressure Balance Shield in Karst Areas","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-27 11:42:08","doi":"10.21203/rs.3.rs-7824402/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-24T06:29:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-23T08:23:19+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-23T08:22:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"216365031849468488564865891326777704865","date":"2025-12-12T14:29:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"103858983149363272556776367479899367763","date":"2025-12-12T14:28:47+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-17T01:08:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"31520955119284381111751682464866035881","date":"2025-11-17T00:59:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-28T02:22:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"145456414833827608255015270161975904365","date":"2025-10-27T23:08:37+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-13T14:57:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-13T12:07:55+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-10-13T10:23:35+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-11T02:33:02+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-10-11T02:30:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"72b065e1-e1c6-42ea-8fbd-9650e85416f8","owner":[],"postedDate":"October 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":56785092,"name":"Physical sciences/Energy science and technology"},{"id":56785093,"name":"Physical sciences/Engineering"},{"id":56785094,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2026-04-27T16:10:57+00:00","versionOfRecord":{"articleIdentity":"rs-7824402","link":"https://doi.org/10.1038/s41598-026-47086-5","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-04-21 15:58:34","publishedOnDateReadable":"April 21st, 2026"},"versionCreatedAt":"2025-10-27 11:42:08","video":"","vorDoi":"10.1038/s41598-026-47086-5","vorDoiUrl":"https://doi.org/10.1038/s41598-026-47086-5","workflowStages":[]},"version":"v1","identity":"rs-7824402","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7824402","identity":"rs-7824402","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}