Large-scale model test study on the water pressure resistance of construction joints of karst tunnel linings

Abstract

Model tests and numerical calculations were adopted based on the New Yuanliangshan tunnel project to investigate the water pressure resistance of lining construction joints in high-pressure and water-rich karst tunnels. A large-scale model test was designed and conducted, innovatively transforming the external water pressure of the lining construction joint into internal water pressure. The effects of the embedded position and waterstop type on the water pressure resistance of the construction joint were analyzed, and the reliability of the model test was verified via numerical calculations. The results show that using waterstops can significantly improve the water pressure resistance of lining construction joints. The water pressure resistance of the lining construction joint is positively correlated with the lining thickness and embedded depth of the waterstop. In addition, the type of waterstop significantly influences the water pressure resistance of lining construction joints. The test results show that the water pressure resistance of the embedded transverse reinforced waterstop is similar to that of the steel plate waterstop, and both have more advantages than the rubber waterstop. The water pressure resistance of the construction joint determined via numerical calculations is similar to the model test results, indicating that the model test results have high accuracy and reliability. This study provides a reference for similar projects and has wide applications.

Graphical abstract

Keywords

karst tunnel / lining construction joint / water pressure resistance / large-scale model test / numerical calculations

1 Introduction

With the continuous promotion of the “Western Development” strategy (a policy of the People’s Republic of China. One of its aims is to make new breakthroughs in the construction of infrastructure and ecological environment in the western region), longer and deeper tunnels will inevitably be built in high-pressure and water-rich karst strata. Under high water pressure, lining construction joints are susceptible to disasters, such as fracture-caused water inrush and water leakage. For example, tunnel water inrush disasters are severe problems encountered during the construction of karst tunnels [1]. Water leakage, particularly joint leakage, is a major issue during the construction and operational stages of tunnels [2,3]. Similarly, circumferential joints and concrete cracks are common leakage points during the construction and operation of tunnels [4]. To substantiate, water leakages in tunnel linings and their construction joints are the most common defects in the tunnel drainage systems of the Renhua–Xinfeng and Yingde–Huaiji Expressways, accounting for 60% and 32% of the total defects, respectively [5]. The damage to the tunnel lining and water leakage at lining joints highlight the defects during the design and construction of tunnel linings [6], reducing the durability of the concrete lining, depreciating facilities, and worsening the tunnel surroundings [7]. Therefore, understanding the underlying processes of lining joint leakage is essential for predicting the waterproofing performance of lining joints, improving their design, and assessing their operational health in tunnels [8]. The water pressure resistance of the construction joint is closely related to that of the tunnel lining structure owing to the weak link of the tunnel lining structure. Therefore, the water pressure resistance and safety of lining construction joints are required during the construction of tunnels in high-pressure and water-rich karst strata. Moreover, it is necessary to further investigate the water pressure resistance of lining construction joints.

In terms of waterstop research, the main aims are determining waterproofing mechanism and the failure of waterstops for deformation joints and construction joints [9,10]. Other aims include the improvement, invention, and application of the back-attached waterstop of construction joints [11,12], mid-buried rubber waterstop [13], hydrophilic rubber waterstop [14], and double-sided tape with artificial adhesive [15]. In terms of model test research, Tan et al. [16] and Zhou et al. [17] conducted scaled-model tests using the loading mode of external water pressure on the tunnel lining based on the similarity theories to investigate the variation and distribution of water pressure and strain on lining construction joints. Gong et al. [18] proposed an experimental and computation-based design framework for joint waterproofing. Ding et al. [19] developed innovative apparatus that used the loading mode of internal water pressure to accurately monitor the water leakage pressure of segmental joints under various combinations of joint openings and offsets. Wu et al. [20] conducted full-scale waterproof tests on tunnel joints, providing a scientific reference for engineering applications and the design of a composite sealing rubber strip putty for underground post-tensioned concrete structures. In terms of numerical calculations, recent studies applied a water head on the outer boundary of the model or set seepage boundary conditions to induce water pressure on the outer surface of the tunnel lining to optimize the waterproofing and drainage modes [21] and to analyze the variation in the internal forces, deformation, and settlement of the tunnel and the surrounding soil during circumferential joint leakage [22].

Existing model tests on the water pressure resistance of lining construction joints generally adopt a scale test or full-scale model test under external water pressure. Additionally, experimental studies have been conducted on the water pressure resistance of lining construction joints of segmented tunnels. However, for the test conducted in this study on a large-scale model, water pressure was applied to the inner surface of the lining. For the high-pressure and water-rich karst tunnel excavated using the new Austrian tunneling method, the layout of the waterstops of the construction joints is different from that of the segment tunnel, and the test scale is relatively small compared with the full-scale test. In addition, the numerical calculation method adopted in this study was mainly used to determine the maximum water pressure resistance of construction joints by analyzing the failure process of lining construction joints under high water pressure, which is different from the focus of previous studies. A large-scale model test of the water pressure resistance capacity of a lining construction joint was conducted in this study based on the New Yuanliangshan Tunnel crossing the high-pressure and water-rich karst stratum. The reliability of the model test results was verified using numerical simulation calculations. The purpose of this study is to provide a theoretical basis for the water pressure resistance design of lining construction joints of tunnels crossing high-pressure and water-rich karst strata.

2 Materials and Methods

2.1 Test materials and mix proportion

P.O Type 42.5 Portland cement with a density of 3100 kg/m³ manufactured according to Common Portland Cement regulations (China National Standard GB 175-2007) was used in this study. The physical and mechanical properties of the cement are listed in Tab.1. Potable water conforming to Standards for Drinking Water Quality (China National Standard GB 5749-2022) was selected, and the water–cement ratio was 0.53. Because potable water contains a very low amount of impurities, it has no negative effect on the performance of concrete; therefore, the negative influence of water quality can be excluded when conducting model tests on the water pressure resistance capacity of construction joints of tunnel linings. The water quality of the water is listed in Tab.2. Continuously graded crushed gravel (5–31.5 mm) with a specific gravity of 2.56 was used as the coarse aggregate, and the gravel complied with the requirements of Pebble and Crushed Stone for Construction (China National Standard GB/T 14685-2011). Natural river sand (0.2–5 mm) with a specific gravity of 2.62 and fineness modulus of 2.59 was utilized as the fine aggregate. The sand satisfied the requirements of Sand for Construction (China National Standard GB/T 14684-2011). A high-range water reducer (HRWR) with a water reduction rate of 20%–35% and a solid content of 20% was used as the admixture, and it conformed to Concrete Admixtures requirements (China National Standard GB 8076-2008). Fig.1 shows the particle-size distribution of each aggregate, and Tab.3 lists the mix ratios of the concrete.

2.2 Engineering background

The New Yuanliangshan Tunnel (the new line) has a total length of 11.077 km. The construction scheme of fully utilizing the parallel pilot of the existing Yuanliangshan Tunnel of Yuhuai Line I (the existing line) for expanded excavation was adopted in constructing the New Yuanliangshan Tunnel, which is currently the longest tunnel using the parallel pilot for expanded excavation. The line spacing between the new and existing lines was approximately 30 m. The clearance dimension of the existing parallel pilot tunnel was 3.5 m × 3.8 m, and the section size of expanded excavation tunnel was 6.35 m × 9.06 m. The karst water surface in the drainage adit was approximately 8.17 and 6.67 m from the outer surfaces of the linings of the new and existing lines, respectively. The location relationship between the New Yuanliangshan Tunnel and the existing Yuanliangshan Tunnel is shown in Fig.2.

Approximately 70% of the length of the New Yuanliangshan Tunnel is located in limestone and argillaceous strata, passing through the Maoba Syncline and Tongmaling Anticline with complex geology. Three high-pressure and water-rich karst caves (#1, #2, and #3 karst caves) exist in the Maoba Syncline section, and the surveyed environmental water pressure reaches up to 3.0 MPa. In particular, #2 karst cave is filled with fine silty sand, which exhibits a self-stabilizing ability under the no-water condition but will collapse and gush out when water meets it. The geological profile of the New Yuanliangshan Tunnel is shown in Fig.3. During construction, a strong correlation was observed between water inflow and rainfall, indicating that the upper part of the #2 karst cave was connected to the surface. During the rainy season, the water pressure in the karst cave increases, and the water pressure in the karst cave might reach 3.0 MPa if the drainage channel is blocked. The extremely high water pressure severely threatens the safety of the lining structure of the New Yuanliangshan Tunnel. As the last line of defense for waterproofing and drainage systems for tunnels, the safety of the secondary lining under high water pressure must be guaranteed. Therefore, it is necessary to analyze the water pressure resistance of the lining structure, particularly the lining construction joints of the New Yuanliangshan Tunnel, to guide the design and construction of high-pressure and water-rich karst tunnels.

The New Yuanliangshan Tunnel was constructed by fully utilizing a parallel pilot of the existing Yuanliangshan Tunnel for expanded excavation. In contrast to the traditional completely randomized design method, the lining of the existing parallel pilot is regarded as a temporary load-bearing structure during excavation expansion. The temporary steel support was set on the lining of the existing parallel pilot, and the existing parallel pilot and temporary steel support were finally removed. The support structure design and expanded excavation process of the New Yuanliangshan Tunnel are depicted in Fig.4.

2.3 Large-scale model test

2.3.1 Model test principle

The construction joints of the tunnel lining are under external water pressure; however, it is difficult to perform a model test of the water pressure resistance of the lining construction joints under external loading. Therefore, the ultimate water pressure when the lining construction joint is completely damaged was analyzed in this study, and the external water pressure on the construction joints of the tunnel lining was converted into internal water pressure by applying water pressure inside the model. When external and internal water pressure loads are applied, the water pressure on the lining construction joint is the same [23]; that is, the two water pressure loading methods induce equivalent effects on the lining construction joint. Therefore, the internal water pressure load can be used instead of external water pressure load, which is conducive for conducting a model test of the water pressure resistance of lining construction joints. Fig.5 shows a schematic of the internal and external water pressure loads.

The innovation of the large-scale model test lies mainly in its ability to transform the water pressure at the construction joint on the outer lining surface into that acting on the inner lining surface. Based on the relationship between the water pressure resistance of the lining construction joint under the two water pressure loading modes obtained in previous studies, the water pressure resistance of the lining construction joint under internal water pressure was tested using large-scale model tests to determine the water pressure resistance of the lining construction joint under actual external water pressure. Because the large-scale model test adopts the water pressure loading method on the inner surface of the tunnel lining, the test is simple to implement, and the test process is easily operable.

2.3.2 Preparation of specimens

(1) Design of water-pressure-resistant lining of Yuanliangshan Tunnel

The secondary lining and construction joints were specially designed to improve the water pressure resistance of the secondary lining in the karst cave section of the New Yuanliangshan Tunnel. A circular reinforced concrete lining (K3.0) with a thickness of 120 cm, which can withstand water pressure of 3.0 MPa, was installed in the high-pressure and water-rich karst section of the tunnel. The circumferential construction joint was Type III, and the waterstop was arranged in the combined form of a back-attached rubber waterstop, middle-buried steel plate waterstop, and middle-buried corrugated steel waterstop. A schematic of the cross-section of the tunnel lining and the corresponding circumferential construction joint in the karst section are shown in Fig.6.

(2) Establishment of model

Six test models were constructed to determine the influence of different types of waterstops and their embedded positions on the water pressure resistance of lining construction joints (Tab.4). Fig.7 illustrates the process of building the test models. First, the casting mold was fabricated, and concrete was mixed using the mixing ratio listed in Tab.3. The upper and lower parts of the model were poured separately. The waterstop and pressure pipes were then fixed at specified positions. The concrete was first poured into the lower part of the model and then into the upper part of the model. Maintenance was carried out to obtain the model required for the tests. Fig.8 shows the test model. The buried depth of the waterstop was the distance between the waterstop and the free surface of the lining.

2.3.3 Model test of water pressure resistance of lining construction joints

(1) Design of pressurization system

A hydraulic pump station was used to pressurize the system. The hydraulic pump station comprised a power system, distribution system, and working system. The power system mainly consisted of a motor and a hydraulic pump, which converted mechanical energy into hydraulic energy. The distribution system was mainly used to regulate the direction, speed, and pressure of the hydraulic oil. The distribution system in this study was mainly used to control the pressure through the overflow valve. The working system mainly connected the oil outlet to the test piece, pressurized the test piece, and converted the hydraulic energy into osmotic force. The working principle diagrams of the hydraulic pump station and hydraulic pump are shown in Fig.9 and Fig.10, respectively.

(2) Construction of closed system

The waterstop was enclosed in a circle and poured into the concrete, and a pressurized pipe was inserted into the concrete. In addition, the waterstop disc was welded to extend the distance of the water seepage to the top such that the water started to leak from the construction joint and prevented the water from flowing out along the conduit. The diameter of the waterstop rolled into a cylinder was 30 cm, and the buried depths were 30, 60, and 80 cm. Fig.11 shows a schematic of the closed system used in the model test.

(3) Test pressurization

Test pressurization was conducted, as shown in Fig.12. The red circle in Fig.12 represents the permeable geotextile. Water entered the construction joint waterstop from the conduit and flowed along the red permeable cloth to the construction joint. The water-pressure resistance values of the waterstop at different buried depths were measured. During pressurization, the water pressure resistance of each construction joint was determined by holding the pressure for half an hour at every 0.5 MPa. The specific test rules are as follows.

1) The hydraulic pump station, pressure gauge, and other equipment were checked to ensure normal operation.

2) The hydraulic pump station and pressure pipe in the test model were connected through a high-pressure hose, a pressure gauge was installed, and the circuit was connected.

3) The pressurizing valve was closed, the pressure relief valve was opened, and the switch of the hydraulic pump station was turned on to determine whether the system could operate normally.

4) The pressure relief valve was closed, and the pressurizing valve was opened slowly; the pressure gradually increased. The high-pressure liquid flowed into the pressure pipe from the hydraulic pump station along the high-pressure hose and acted on the construction joint of the test model. The variations in the readings of pressure gauge were observed. When the pressure gauge was 0.5 MPa, the pressurizing valve was closed to stabilize the pressure at this value, and the pressure was maintained for 30 min. The model was checked to determine whether it leaked during this process.

5) After 30 min of pressure stabilization, the pressurizing valve was reopened. Pressurization was continued to 1.0 MPa, and the pressure was stabilized for 30 min. The readings were observed and recorded.

6) Pressure of 0.5 MPa was applied each time and maintained for 30 min until the test model had a large leakage area. The pressure at this time was considered the ultimate water pressure resistance of the test model. The values were recorded, and safety precautions were taken during the tests.

Large-scale model tests were performed following the above test rules to determine the ultimate water pressure resistance values of the test models under different working conditions.

2.4 Verification test of numerical simulation

Realistic failure process analysis (RFPA), a numerical calculation software, was used to analyze the water pressure resistance of the lining construction joints to verify the reliability of the model test results. RFPA is a software for analyzing the material fracture process based on finite element stress analysis and the statistical damage theory, which can simulate the entire damage process of a material from progressive failure to instability. Many scholars regard RFPA as an essential research tool and have obtained accurate results using it. For example, Tang and Zhang [24], Li et al. [25], and Men et al. [26] analyzed the interval fracture mechanism and hydraulic fracturing process of the rock mass and its impact on crack growth using RFPA. The research results are valuable and reliable, demonstrating that RFPA has high reliability and can predict the behavior of rock and soil masses subjected to fluid−solid interactions.

2.4.1 Establishment of numerical calculation model

The specific modeling process is depicted in Fig.13. Fig.13(a) shows a schematic of the karst water pressure on the back of the lining. The back of the lining under the karst external water pressure was converted into internal water pressure (Fig.13(b)) and subsequently transformed into a hydraulic test model in the lining (Fig.13(c)) to facilitate the water pressure resistance test of the lining construction joints [27]. The left portion of the central axis of the test model was used for further simplification to reduce the size and calculation unit of the numerical model and improve the calculation efficiency. Fig.13(d) shows a schematic of the numerical calculation model of the lining damage under the condition of the quality defect of the lining construction joint.

The numerical calculations were performed using a plane strain model according to the Mohr–Coulomb criterion. The length of the model was 1200 mm, and the width was selected based on the calculation conditions. For calculation accuracy, the model was divided into meshes of 5 mm × 5 mm. Because the spacing between the meshes was very narrow, the mesh lines are shown as gray faces. A cavity was excavated in the model, and an initial pressure head of 100 m was used for the cavity. The single-step loading head was set to 5 m to show the seepage process. The homogeneity of the contact interface between the simulated construction joint, waterstop, and concrete was 10 to achieve uniform permeability coefficient distribution inside the model uniform and minimize calculation errors, and the homogeneity of the concrete, rubber, and steel plate was set as 100. A drainage joint was set between the cavity and the construction joint to facilitate water flow into the construction joint from the cavity. The width of the drainage joint was set to three units to prevent water head reduction during the process of water pressure transferred from the cavity to the construction joint. The construction joint was simulated by one unit, and the construction joint parameters were adjusted based on the water pressure resistance capacity of the construction joint when no waterstop was used in the field test. The construction joint parameters were used as the parameters of other construction joints of the numerical calculation model. The numerical calculation model is shown in Fig.14. For the boundary conditions, the horizontal and vertical displacements were constrained to prevent the test piece from being jacked up during pressurization, and the flow boundary was set around the model.

The model test results of the tunnel lining without a waterstop and the lining construction joint waterstop with a buried depth of 30 cm were compared with the numerical results under the two conditions. This was performed to verify the reliability of the large-scale model test for the water pressure resistance capacity of the construction joint of the tunnel lining. The numerical calculation models under two working conditions are shown in Fig.15, and a schematic of numerical calculation model is shown in Fig.16.

The innovation of the numerical simulation method is that the external water pressure on the lining construction joint is first converted into internal water pressure on the lining construction joint. The numerical calculation model was then transformed into the model form of the large-scale model test, and half of the model was adopted as the numerical calculation model. This method has the advantages of simple modeling, high computing efficiency, and high accuracy.

2.4.2 Setting of numerical calculation parameters

The numerical calculation parameters were mainly selected according to the “Code for Design of Concrete Structures (GB 50010-2010)” and relevant test and inspection reports at the tunnel construction site. The mechanical and seepage parameters used for the numerical calculations are listed in Tab.5.

3 Results and discussion

3.1 Model test results

3.1.1 Test results for steel plate waterstop at embedded depth of 30 cm

In this test, the pressure was increased from 0 to 5 MPa, with an increase in intervals of 0.5 MPa, and the pressure was stabilized for 30 min at each level. The penetration rate (δ) was defined as the ratio of the penetration length around the specimen to the perimeter, as expressed by Eq. (1),

(1)\delta =\frac{l_{\mathrm{p}\mathrm{r}}}{l_{\mathrm{p}}}\times \text{100\%},

where l_pr is the penetration length around the specimen, and l_p is the perimeter of the specimen. Tab.6 lists the test process records.

The relationship between the applied pressure and permeability is shown in Fig.17. From the pressurization curve (Fig.17), the test specimen started to leak at 1.5 MPa, and the fracture seepage was approximately linear between 1.5 and 2.5 MPa, indicating that the test seepage failure rate was stable under this pressure. When the pressure was 2.5–4.0 MPa, the seepage failure of the specimen was accelerated, and it was in the accelerated failure stage. When the pressure was 4.0–4.5 MPa, the test specimen was in the complete penetration state, indicating that the construction joints of the test specimen was completely leaking. In addition, on pressurizing to 5.0 MPa, the permeability did not change significantly although the pressure increased; this indicated that when the pressure of the tunnel construction joint was lower than 5.0 MPa, seepage stabilized. Fig.18 shows the seepage of the test specimen at 1.5 MPa.

During pressurization, the penetration range increased within the first 10 min for each increase of 0.5 MPa and stabilized in the last 20 min, and the specimen leaked when the pressure reached 1.5 MPa. The reason was because the pressure was increased by 0.5 MPa each time and stabilized for 30 min in the model tests. The liquid searched for the seepage path under increased pressure and penetrated and diffused along the seepage path. This process lasted for approximately 10 min, and the penetration range did not increase over the next 20 min. However, this steady-state was disrupted when the pressure continued to increase, the penetration range continued to increase, finally reaching the next steady-state until the construction joint was fully penetrated by the high pressure. The inner radius of the circular lining of the New Yuanliangshan Tunnel is 4.17 m, and the outer radius is 5.37 m. The area behind the lining is large, and point leakage typically occurs at the weak point of the construction joint. When the water pressure continues to increase to a specific value, a broad range of linear leakage occurs, and the water pressure at the leakage point can be considered the water pressure resistance value. Therefore, the water pressure resistance of the steel waterstop at a buried depth of 30 cm was 1.5 MPa.

3.1.2 Pressurization results of other model tests

The seepages of other specimens after pressurization are shown in Fig.19. The other four groups of specimens were subjected to pressure tests, in which leakage occurred at a buried depth of 60 cm (no waterstop) and 1.0 MPa, a buried depth of 60 cm (rubber waterstop) and 2.1 MPa, and a buried depth of 60 cm (steel plate waterstop) and 4.0 MPa. However, leakage did not occur at a buried depth of 80 cm (steel plate waterstop) and 6.0 MPa, and its water pressure resistance capacity exceeded 6.0 MPa.

A summary of the model test results is listed in Tab.7. A comparison of the water pressure resistance values of the Nos. 1, 4, and 5 steel plate waterstops showed that the more extended the embedded depth of the waterstop, the higher the water pressure resistance of the construction joint. When the buried depth was increased from 30 to 60 cm, the water pressure resistance capacity increased from 1.5 to 4.0 MPa. When the buried depth was increased by 1.0 times, the water pressure resistance capacity increased by 1.67 times. When the buried depth was increased to 80 cm, the water pressure resistance capacity exceeded 6.0 MPa.

The water pressure resistance capacity of the lining construction joint with the embedded rubber and steel waterstops increased by 2.1 and 3 times, respectively, compared with that of the construction joint without an embedded waterstop. This indicates that a waterstop can significantly improve the water pressure resistance capacity of construction joints. A comparison of Nos. 1 and 2 specimens showed that the water pressure resistance capacity of the construction joint was 1.365 MPa when the steel waterstop was buried at a depth of 30 cm, which exceeded that without a waterstop.

A comparative analysis of Nos. 3 and 4 specimens showed that when the construction joint of the rubber waterstop lining at a buried depth of 60 cm was pressurized, the water pressure resistance of the construction joint was 2.1 MPa, lower than that of the steel waterstop (4.0 MPa). This indicates that the water pressure resistance of the lining construction joint with the steel plate waterstop was relatively stronger than that of the lining construction joint with the rubber waterstop. In addition, a comparison of Nos. 1 and 6 specimens showed that the water pressure resistance of the transverse reinforced waterstop was the same as that of the steel plate waterstop.

Different depths and types of waterstops indicate various water pressure resistance capacities because the type and buried depth of a waterstop are two critical parameters that influence the water pressure resistance of construction joints. For example, the water pressure resistance of a steel waterstop is generally higher than that of a rubber waterstop, and the greater the buried depth of a waterstop, the greater the thickness of the concrete involved in resisting the high water pressure. Thick concrete combined with an excellent waterstop can resist higher water pressures, thus exhibiting improved water pressure resistance.

The experimental research further clarified the waterstop mechanism. A waterstop changes the seepage path, and the water bypasses the waterstop to extend the seepage path and prevent water penetration. In addition, the stress field changes owing to the change in the seepage path, and the change in the stress field of the concrete structure causes the development of initial damage, such as micropores and microcracks in the concrete. This inevitably changes the permeability coefficient of the concrete structure, thus changing the seepage field and improving the water pressure resistance of the construction joints.

3.2 Verification of numerical calculation results

The numerical calculation results are presented in Fig.20 and Fig.21. The corresponding water pressure resistance capacities of the construction joints of the tunnel lining without waterstop and with a waterstop buried at a 30 cm depth were 1.0 and 1.4 MPa, respectively, whereas those under the two conditions obtained using the field model tests were 1.0 and 1.5 MPa, respectively, as listed in Tab.8. The numerical calculation results were similar to those of the large-scale field test. The numerical calculation results show that the large-scale model test method is highly reliable.

4 Conclusions

By comprehensively performing model tests and numerical calculations, the influence of the type and buried depth of waterstop on the water pressure resistance of lining construction joints was investigated. The main conclusions of this study are as follows.

1) A large-scale model test method for analyzing the water pressure resistance of construction joints of tunnel linings was developed to verify the water pressure resistance capacity of construction joints of tunnel linings. The proposed method converts the external water pressure load on the lining construction joints to internal water pressure load and reduces the difficulty of test implementation. This demonstrates that the lining construction joints of the New Yuanliangshan Tunnel crossing high-pressure and water-rich karst caves satisfies the design requirements of resisting water pressure of 3.0 MPa.

2) The results of the large-scale model test on water pressure resistance of lining construction joints show that the water pressure resistance can be improved by embedding waterstops and appropriately increasing the lining thickness or waterstop depth. At the same buried depth, the water pressure resistance of the steel waterstop is relatively higher than that of the rubber waterstop, indicating that the waterstop type significantly influences the water pressure resistance of construction joints. The test results can guide the design of construction joints for water pressure-resistant linings in similar tunnel projects.

3) A numerical calculation method is proposed to analyze the water pressure resistance capacity and deterioration process of construction joints to validate the large-scale model test method for analyzing the water pressure resistance of construction joints of tunnel linings. The numerical calculation results show that the large-scale model test method has high reliability and can be extended to similar projects to investigate the ultimate water pressure resistance capacity of construction joints of tunnel linings. The proposed calculation method can provide technical and theoretical guidance in designing and constructing tunnel linings for adequate water pressure resistance.

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