A tunnel surface area loading adaptive lining test device and test method

Abstract

The application discloses a tunnel face domain load adaptive lining test device and a test method. The test device comprises a pressure cylinder, a face domain load adaptive lining, surrounding rock, a loading cavity, monitoring instruments, a pressurizing system and a data acquisition instrument. The test method comprises pouring the face domain load adaptive lining, pouring the surrounding rock, loading the loading cavity and the pressure regulating cavity, and processing and analyzing test data. Compared with the existing test device and method, the application can accurately capture the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel with the face domain load adaptive lining and the conventional lining occurs long-term creep under large deformation of soft rock, and reflects the real running working properties and mechanism of the tunnel with the face domain load adaptive lining and the conventional lining when the tunnel occurs long-term creep under large deformation of soft rock.

Description

Technical Field

[0001] This invention relates to a surface-loaded adaptive lining test device and test method, specifically, to a surface-loaded adaptive lining test device and test method for tunnels, which is applied to the stability study of underground caverns in geotechnical engineering. Background Technology

[0002] Long, deeply buried tunnels are a major component of large and extra-large water conservancy, transportation, and mining projects, and a crucial control point in the entire project construction. Their construction progress and safety are directly related to the progress and safety of the entire project. Compared with other nonlinear engineering projects, long, deeply buried tunnels are typical linear projects. Although every effort is made to consider factors that threaten the safety of the project during the project layout phase, it is still difficult to completely avoid them due to technical, financial, and overall considerations. Unfavorable geological areas, which account for a small proportion of the entire tunnel section, have become the key and difficult areas that "bottleneck" the entire project. These include large deformations in high-stress areas, fault displacement, rock bursts, and altered rocks, which seriously affect the project progress and greatly increase the project cost. Large deformation in soft rock is unavoidable in long, deeply buried tunnels, such as the Jiazhujing Tunnel, Wushaoling Tunnel, Muzhailing Extra-Long Tunnel, and Baozhen Tunnel on the Yichang-Wanzhou Railway in my country, as well as the Tauen Tunnel and Alberg Tunnel in Austria, and the Enazan Tunnel in Japan. Due to the large magnitude and long duration of deformation, these tunnels pose significant threats to excavation and support design, surrounding rock stability, and the safety of permanent linings. Ultimately, the construction period, construction costs, and subsequent maintenance frequency and costs far exceeded expectations. It can be said that the problems of surrounding rock stability and lining safety caused by large deformation in soft rock have always been a global challenge.

[0003] In the support of soft rock caverns both domestically and internationally, various technologies are employed, including anchor-mesh-shotcrete, truss support, grouting reinforcement, and prestressed anchor cable support. From a stress perspective, these support methods can be categorized into strong and soft support, achieving the goal of controlling surrounding rock stability and ensuring support safety through the synergistic effect of the support system. With the development of the New Austrian Tunneling Method (NATM), the tunnel engineering community has recognized that rigid support methods cannot fully utilize the inherent stability of the surrounding rock and its self-stabilizing effect. Furthermore, as the burial depth of underground caverns increases, the deformation of the surrounding rock also increases, leading to frequent failures of existing support systems in tunnel engineering. Therefore, technologies such as grooved supports, retractable steel arches, and high-deformation anchor bolts under constant load have gradually developed and are being applied in numerous projects.

[0004] Although the above-mentioned methods of lining combined with excavation are effective in solving the stability of the surrounding rock during the large-scale excavation and rapid deformation stages, the following problems still exist: (1) Conventional support and lining need to be driven by the deformation of the surrounding rock to take effect, rather than actively applying support loads to the surrounding rock; (2) Existing anchor bolts and steel arch frames are basically linear supports, and the range of support loads is relatively small relative to the entire tunnel wall; (3) Existing support and lining do not have a large bearing capacity, and for soft rock tunnel sections with long-term creep properties, they face the risk of overload damage in the later stage.

[0005] To address the shortcomings of existing physical model testing techniques for conventional tunnel linings under large deformation in soft rock, this invention proposes a surface-load-supply adaptive lining technology. This lining can actively apply a constant surface load of a certain amount to the surrounding rock, providing support over a wide range. Furthermore, during the later stages of creep deformation in the surrounding rock, it can reduce pressure while maintaining the supplied load, achieving a stable readjustment between rock deformation and load. To verify this surface-load-supply adaptive lining technology, corresponding physical model tests were designed. These tests accurately capture the stress and displacement changes in the surrounding rock, the dynamic evolution of the contact state between the surrounding rock and the lining, and the stress on the lining structure during long-term creep in tunnels under large deformation in soft rock, using both surface-load-supply adaptive and conventional linings. This invention reflects the actual operational characteristics and mechanisms of surface-load-supply adaptive and conventional linings during long-term creep in tunnels under large deformation in soft rock. Summary of the Invention

[0006] To address the problems existing in the above-mentioned background technology, the purpose of this invention is to provide a test device and test method for adaptive lining of tunnel surface area under load.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A test device for adaptive lining of tunnel surface loading includes a pressure cylinder, an adaptive lining for surface loading, surrounding rock, a loading chamber, monitoring instruments, a pressurization system, and a data acquisition instrument. The pressure cylinder includes a front flange, a rear flange, a cylindrical body, nuts, bolts, a pressure regulating chamber loading joint, a pressure regulating chamber drainage joint, a loading chamber loading joint, a loading chamber drainage joint, a loading chamber pressure-bearing pipe, a cable outlet, and a base. The adaptive lining for surface loading includes a pressure regulating chamber, a pressure-bearing pipe, a concrete lining, and a pressure stabilizing control unit, formed by assembling the pressure regulating chamber, pressure-bearing pipe, and pressure stabilizing control unit after concrete pouring and curing. The surrounding rock is formed by pouring soft rock material. The loading chamber is laid between the inner wall of the pressure cylinder and the outer wall of the surrounding rock. The monitoring instruments include a single-point displacement gauge, a concrete circumferential strain gauge, and an earth pressure gauge. The pressurization system includes a pressurized water pump, a pressure stabilizing cylinder, and a servo control system.

[0009] Furthermore, the front flange is equipped with bolt holes, stiffening ribs, and cable outlet holes; the cylindrical body is equipped with bolt holes; and the rear flange is equipped with bolt holes and stiffening ribs. The bolt holes on the front and rear flanges are aligned with the bolt holes on the cylindrical body, and the flanges are secured to the cylindrical body with bolts and nuts. The sensor cable is led out through the cable outlet hole and connected to the data acquisition instrument for data collection.

[0010] Furthermore, the adaptive lining with surface load supply has an internal pressure regulating cavity and an external pressure-bearing pipe. It provides a constant surface load to the lining by injecting water and pressurizing it through a pressure stabilization control unit. In conventional linings, the pressure regulating cavity is not pressurized by injecting water through a pressure stabilization control unit.

[0011] Furthermore, the pressurized water pump is connected to the pressure regulating chamber loading joint and the loading chamber loading joint to pressurize the surrounding rock and the adaptive lining. The study analyzes the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock, using the surface-loaded adaptive lining and conventional lining. The study clarifies the mutual feedback process among the three and reveals the actual operating characteristics and mechanisms of the surface-loaded adaptive lining and conventional lining when the tunnel undergoes long-term creep under large deformation of soft rock.

[0012] The present invention also provides a test method for a tunnel surface-loaded adaptive lining test device, comprising the following test steps:

[0013] (1) Adaptive lining for load supply in the casting area;

[0014] (2) Casting the surrounding rock;

[0015] (3) Loading of the loading chamber and the pressure regulating chamber;

[0016] (4) The loading chamber is loaded and the pressure regulating chamber is not pressurized;

[0017] (5) Process and analyze experimental data.

[0018] The specific steps of step (1) include:

[0019] (1.1) Determine the layout plan for monitoring instruments;

[0020] This invention employs a surface-load adaptive lining technology to actively apply a constant surface load of a certain amount to the surrounding rock, providing support force over a large area. Furthermore, during the later stages of creep deformation in the surrounding rock, it maintains the applied load while reducing pressure, thus achieving a stable readjustment between the rock deformation and the load. By strategically deploying monitoring instruments such as single-point displacement gauges, concrete circumferential strain gauges, and earth pressure cells, the operational characteristics of the surrounding rock during the later stages of creep deformation can be accurately captured.

[0021] Furthermore, in order to obtain experimental data on the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock with adaptive lining and conventional lining, two monitoring sections were set up: 1-1 and 2-2. The monitoring instruments set up in the monitoring sections included single-point displacement gauges, concrete circumferential strain gauges, and earth pressure cells.

[0022] Furthermore, with the top of the pressure cylinder as the 0° direction, six single-point displacement gauges are arranged clockwise at positions of 0°, 120°, and 240° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2;

[0023] Furthermore, four of the ten concrete circumferential strain gauges are arranged clockwise at positions of 225°, 315°, 45°, and 165° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2; the other six are arranged clockwise at positions of 0°, 120°, 240°, 90°, 210°, and 330° inside the surface-load-supply adaptive lining in monitoring sections 1-1 and 2-2.

[0024] Furthermore, the six earth pressure cells are arranged clockwise at positions of 15°, 135°, 255°, 105°, 225°, and 345° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2.

[0025] (1.2) Fabricate the surface area load-adaptive lining casting mold and the fixing components for monitoring instruments;

[0026] Furthermore, in step (1.2), the inner and outer molds for the surface-loaded adaptive lining casting are made according to the inner and outer diameters of the surface-loaded adaptive lining in the tunnel model test scheme, respectively, and their two end faces are flush with the two end faces of the cylindrical body.

[0027] Furthermore, based on the installation profile position of the circumferential strain gauge in the concrete, a cable outlet hole is reserved on the inner steel cylinder for each concrete circumferential strain gauge.

[0028] Furthermore, based on the installation profile position of the concrete circumferential strain gauge in the adaptive lining layer, steel reinforcement supports are welded on the inner wall of the outer formwork of the lining layer, and polyester fibers are used to tie and fix the concrete circumferential strain gauge on the steel reinforcement supports.

[0029] Furthermore, based on the position of the pressure regulating chamber inlet and outlet water pipes in the concrete lining, steel pipes are fixed at the corresponding positions inside, and inlet and outlet water pipe holes for the pressure regulating chamber are reserved.

[0030] (1.3) Fixing components for the assembly area load-adaptive lining casting mold and monitoring instruments;

[0031] Furthermore, according to the arrangement plan of the monitoring instruments in step (1.1), the monitoring instrument fixing parts made in step (1.2) are respectively installed at the designated positions of the inner mold and outer mold of the surface area load-adaptive lining casting.

[0032] Furthermore, according to the arrangement scheme of the concrete circumferential strain gauges in step (1.1), the strain gauges are installed on the monitoring instrument fixing parts on the inner wall of the outer mold of the surface-load adaptive lining casting.

[0033] Furthermore, the cable of the concrete circumferential strain gauge is passed through the reserved cable outlet hole of the fixed steel pipe, and the cables are bundled together at the cable outlet position.

[0034] (1.4) Pouring concrete;

[0035] Furthermore, with the rear flange placed horizontally, the assembled surface area load-adaptive lining casting inner and outer molds are placed vertically on the rear flange, with their centers concentric with the center of the rear flange. Then, the surface area load-adaptive lining casting inner and outer molds are spot-welded to the rear flange for fixation.

[0036] Furthermore, a pouring funnel is placed between the outer wall of the inner mold and the inner wall of the outer mold for the adaptive lining with surface loading. Concrete of a set grade is poured into the funnel, and at regular intervals, it is vibrated evenly until grout appears on the surface. Pouring continues until the concrete is flush with the top surfaces of both the inner and outer molds, and the end faces are smoothed. Further, after pouring, concrete strain gauges are connected to a data acquisition instrument to check their readings and identify any malfunctioning monitoring instruments.

[0037] (1.5) Curing concrete;

[0038] Furthermore, concrete curing is carried out in accordance with the "Code for Acceptance of Construction Quality of Concrete Structures" (GB 50204-2015). After the concrete has reached the required curing age, the external formwork for the surface-mounted adaptive lining is removed.

[0039] (1.6) Install the pressure regulating chamber;

[0040] Furthermore, the steel pipes inside the concrete lining are removed, and three pressure regulating chambers of the same size are installed on the outer surface of the concrete. The inlet and outlet water pipes of the pressure regulating chambers are led out from the reserved positions on the steel pipes.

[0041] Furthermore, the thickness of the pressure regulating cavity in step (1.6) can be determined according to the following formula:

[0042]

[0043]

[0044]

[0045]

[0046]

[0047] ε r (t)+ε θ (t)=0 (6)

[0048]

[0049]

[0050] In the formula: represents the radial strain of the surrounding rock; represents the circumferential strain of the surrounding rock; represents the radial stress at the outer boundary of the plastic zone; represents the creep compliance; E1 represents the elastic modulus of the material; E2 represents the viscoelastic modulus; represents the viscoelastic coefficient in the transition creep stage; represents the viscosity coefficient in the constant strain rate creep stage; represents the yield stress; represents the initial ground stress; represents the excavation radius of the surrounding rock; represents the radius of the plastic zone of the surrounding rock; represents the support force; u(t) represents the creep deformation of the surrounding rock; represents the thickness of the pressure regulating cavity.

[0051] The specific steps of step (2) include:

[0052] (2.1) Install a single-point displacement meter;

[0053] Furthermore, according to the arrangement scheme of the single-point displacement gauge in step (1.1), the single-point displacement gauge is installed on the outer wall of the pressure cylinder;

[0054] (2.2) Laying the loading cavity;

[0055] Furthermore, by setting up a loading cavity of a certain thickness between the inner wall of the pressure cylinder and the outer wall of the surrounding rock, the surrounding rock is ensured to be subjected to a certain initial in-situ stress.

[0056] (2.3) Pouring concrete

[0057] Furthermore, the cylindrical body is placed upside down on the rear flange and secured with bolts and nuts. The cables for the concrete circumferential strain gauge and earth pressure cell are led out from the cable outlet hole of the top flange and sealed with silicone sealant.

[0058] Furthermore, a grouting funnel is placed between the inner wall of the pressure cylinder and the outer wall of the surface-load-supply adaptive lining. The surrounding rock material prepared with soft rock material is poured into the funnel, and a vibrator is used to vibrate it evenly every certain height. The process is stopped when grout appears on the surface. The pouring of soft rock material is stopped after the surrounding rock is poured to be flush with the top surface of the surface-load-supply adaptive lining, and the end face is smoothed.

[0059] (2.4) Curing the surrounding rock;

[0060] Furthermore, based on the characteristics of soft rock materials, surrounding rock curing is carried out. After the surrounding rock curing reaches the required age, the pressure cylinder is erected and the rear flange is removed.

[0061] (2.5) Install earth pressure box

[0062] Furthermore, according to the arrangement scheme of the earth pressure box in step (1.1), the earth pressure box is installed on the inner wall surface of the surrounding rock;

[0063] Furthermore, the earth pressure box cable is led out from the cable outlet hole of the front flange and sealed with silicone sealant.

[0064] The specific steps of step (3) include:

[0065] (3.1) Connect the pressurized water pump to the loading chamber and the pressure regulating chamber joint to gradually fill the surrounding rock and the adaptive lining with water. The number of steps with a water filling pressure equal to 0.2 MPa, the total number of water filling steps, and the total number of water filling and drainage steps are calculated using the following formula:

[0066]

[0067]

[0068] S t =S j (11)

[0069] P t =0.2 (12)

[0070] Where: is the number of steps with a water filling pressure equal to 0.2 MPa, is the total number of steps for filling the loading cavity with water; is the water filling pressure of 0.2 MPa, is the initial ground stress (MPa) of the simulated pressure tunnel in the loading cavity, with a value of 0.8 MPa, is the loading amplitude (MPa) of the progressively increasing water filling pressure, with a value of 0.2 MPa, is the total number of steps for filling the pressure regulating cavity with water, and is the water filling pressure (MPa) of the pressure regulating cavity;

[0071] Furthermore, in step (3.1), when the loading chamber and pressure regulating chamber are filled with water in stages, the duration of each stage of water filling and pressurization is calculated using the following formula:

[0072]

[0073] Where: is the duration of the first stage of water filling and pressurization, is the number of steps of water filling in each stage, and is the total number of steps of water filling in the loading chamber or pressure regulating chamber;

[0074] (3.2) During the process of gradually filling the loading chamber and the pressure regulating chamber with water, monitor the pressure gauge readings and record the changes in internal water pressure;

[0075] The specific steps of loading the loading chamber and not pressurizing the pressure regulating chamber in step (4) include:

[0076] (4.1) Connect the pressurized water pump to the loading chamber joint to gradually fill the surrounding rock with water. The number of steps with a water pressure equal to 0.2 MPa, the total number of water filling steps, and the total number of water filling and drainage steps are calculated using the following formula:

[0077]

[0078]

[0079] S t =S j (16)

[0080] P t =0 (17)

[0081] Where: is the number of steps with a water filling pressure equal to 0.2 MPa, is the total number of steps for filling the loading cavity with water; is the water filling pressure of 0.2 MPa, is the initial ground stress (MPa) of the simulated pressure tunnel in the loading cavity, with a value of 0.8 MPa, is the loading amplitude (MPa) of the progressively increasing water filling pressure, with a value of 0.2 MPa; is the total number of steps for filling the pressure regulating cavity with water, is the water filling pressure (MPa) of the pressure regulating cavity.

[0082] Furthermore, in step (4.1), the duration of each stage of water filling and pressurization during the progressive water filling of the loading cavity is calculated using the following formula:

[0083]

[0084] Where: is the duration of the first stage of water filling and pressurization, is the number of steps of water filling in each stage, and is the total number of steps of water filling in the loading chamber or pressure regulating chamber;

[0085] Step 4.2: During the gradual filling of the loading cavity with water, monitor the pressure gauge readings and record the changes in internal water pressure;

[0086] Step 5: Process and analyze experimental data

[0087] The specific steps are as follows:

[0088] Step 5.1: Save and import the test data of single-point displacement gauge, concrete circumferential strain gauge and earth pressure cell, and contact force between lining and surrounding rock collected by the data acquisition instrument during the filling and drainage process of the physical model of the tunnel surface under large deformation of soft rock into the computer for processing.

[0089] Step 5.2: Study and analyze the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock with adaptive lining and conventional lining. Clarify the mutual feedback process among the three and reveal the actual operating characteristics and mechanisms of adaptive lining and conventional lining under large deformation of soft rock when the tunnel undergoes long-term creep.

[0090] Compared with existing conventional physical model testing techniques for lining under large deformation of soft rock, the advantages of this invention are:

[0091] (1) This invention proposes a surface-load adaptive lining technology. The lining can actively apply a certain amount of constant surface load to the surrounding rock to provide support force over a large area of ​​the surrounding rock. In the later creep deformation process of the surrounding rock, it has the function of reducing pressure but keeping the load unchanged, so as to achieve a stable state of readjustment between the deformation of the surrounding rock and the load.

[0092] (2) The present invention designed a corresponding physical model test, which can accurately capture the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock, the adaptive lining and conventional lining with surface load supply are subjected to surface load.

[0093] (3) The present invention can reflect the actual operating characteristics and mechanism of surface-loaded adaptive lining and conventional lining when tunnels undergo long-term creep under large deformation of soft rock by correspondingly deploying monitoring instruments such as single-point displacement gauges, concrete circumferential strain gauges and earth pressure cells. Attached Figure Description

[0094] Figure 1(a) is a longitudinal cross-sectional view of the test device according to an embodiment of the present invention;

[0095] Figure 1(b) is a schematic cross-sectional view of the test device according to an embodiment of the present invention;

[0096] Figure 1(c) is a schematic cross-sectional view 2 of the test device according to an embodiment of the present invention;

[0097] Figure 2 This is a schematic diagram of the pressure cylinder according to an embodiment of the present invention;

[0098] Figure 3(a) is a schematic diagram of the outer side of the front flange in an embodiment of the present invention;

[0099] Figure 3(b) is a schematic diagram of the inner side of the front flange in an embodiment of the present invention;

[0100] Figure 4(a) is a schematic diagram of the outer side of the rear flange in an embodiment of the present invention;

[0101] Figure 4(b) is a schematic diagram of the inner side of the rear flange in an embodiment of the present invention;

[0102] Figure 5 This is a schematic diagram of the cylindrical body according to an embodiment of the present invention;

[0103] Figure 6(a) is a schematic diagram of the overall adaptive lining with surface region loading according to an embodiment of the present invention;

[0104] Figure 6(b) is a schematic diagram of the pressure regulating chamber and pressure bearing pipe in an embodiment of the present invention;

[0105] Figure 6(c) is a schematic diagram of the pressure regulating cavity in an embodiment of the present invention;

[0106] Figure 7(a) is a schematic diagram of the loading cavity and pressure-bearing pipe in an embodiment of the present invention;

[0107] Figure 7(b) is a schematic diagram of the loading cavity in an embodiment of the present invention;

[0108] Figure 8 This is a schematic diagram of the monitoring section of the monitoring instrument according to an embodiment of the present invention;

[0109] Figure 9(a) is a schematic diagram of the monitoring instrument arrangement at the monitoring section in Embodiment 1-1 of the present invention;

[0110] Figure 9(b) is a schematic diagram of the monitoring instrument arrangement at the monitoring section in Embodiment 2-2 of the present invention;

[0111] Figure 10(a) is a schematic diagram of the internal mold for adaptive lining casting with surface region loading according to an embodiment of the present invention;

[0112] Figure 10(b) is a schematic diagram of the external mold for adaptive lining casting in a surface region according to an embodiment of the present invention;

[0113] Figure 11 This is a schematic diagram of the adaptive lining casting device for surface-based load supply according to an embodiment of the present invention;

[0114] Among them, 1-pressure cylinder; 2-area-region-supply adaptive lining; 3-surrounding rock; 4-loading cavity; 101-front flange, 102-rear flange, 103-cylindrical cylinder, 104-nut, 105-bolt, 106-pressure regulating cavity loading joint, 107-pressure regulating cavity drainage joint, 108-loading cavity loading joint, 109-loading cavity drainage joint, 110-loading cavity pressure-bearing pipe, 111-base; 201-pressure regulating cavity; 202-pressure-bearing pipe; 203-concrete lining; 204- Pressure-bearing pipe joint; 501 Single-point displacement gauge; 502 Concrete circumferential strain gauge; 503 Earth pressure gauge; 1011 Bolt hole; 1012 Stiffening rib; 1013 Cable outlet hole; 1031 Bolt hole; 1101 Loading cavity pressure-bearing pipe joint hole; 1021 Bolt hole; 1022 Stiffening rib; 1102 Loading cavity pressure-bearing pipe joint hole; 7 Inner mold for area-based load-adaptive lining casting; 8 Outer mold for area-based load-adaptive lining casting; 701 Bolt; 702 Nut. Detailed Implementation

[0115] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0116] Example 1

[0117] As shown in Figure 1(a), a tunnel surface-loaded adaptive lining test device includes a pressure cylinder 1, surface-loaded adaptive lining 2, surrounding rock 3, loading cavity 4, monitoring instruments, pressurization system and data acquisition instrument. The pressure cylinder 1 includes a front flange 101, a rear flange 102, a cylindrical body 103, a nut 104, a bolt 105, a pressure regulating chamber loading joint 106, a pressure regulating chamber drainage joint 107, a loading chamber loading joint 108, a loading chamber drainage joint 109, a loading chamber pressure-bearing pipe 110, and a base 111; the surface-mounted adaptive lining 2 includes a pressure regulating chamber 201, a pressure-bearing pipe 202, a concrete lining 203, a pressure stabilizing control unit, and a pressure-bearing pipe joint 204, which are assembled from concrete after pouring and curing; the surrounding rock 3 is cast from a soft rock-like material, with the two end faces of the surrounding rock 3 flush with the two end faces of the cylindrical body 103; the loading chamber 4 is laid between the inner wall of the pressure cylinder 1 and the outer wall of the surrounding rock 3; the monitoring instruments include a single-point displacement gauge 501, a concrete circumferential strain gauge 502, and an earth pressure gauge 503; the pressurization system includes a pressurization water pump, a pressure-stabilizing cylinder, and a servo control system.

[0118] like Figures 3(a)-4(b)As shown, the front flange 101 is provided with bolt holes 1011, stiffening ribs 1012 and cable outlet holes 1013; the cylindrical body 103 is provided with bolt holes 1031 and loading chamber pressure-bearing pipe joint holes 1101; the rear flange 102 is provided with bolt holes 1021, stiffening ribs 1022 and loading chamber pressure-bearing pipe joint holes 1102.

[0119] As shown in Figures 6(a)-(c), the pressure regulating cavity 201 inside the adaptive lining 2 and the pressure bearing pipe 202 outside provide a constant surface load to the lining through water injection and pressurization via the pressure stabilization control unit; in conventional lining, the pressure regulating cavity 201 does not receive water injection and pressurization through the pressure stabilization control unit.

[0120] As shown in Figures 7(a)-(b), the pressurized water pump connects the pressure regulating chamber loading joint 106 and the loading chamber loading joint 108 to pressurize the surrounding rock and the adaptive lining with water. This study analyzes the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress on the lining structure of the surface-loaded adaptive lining and conventional lining during long-term creep of the tunnel under large deformation in soft rock. It clarifies the mutual feedback process among these three elements and reveals the actual operational characteristics and mechanisms of the surface-loaded adaptive lining and conventional lining during long-term creep of the tunnel under large deformation in soft rock.

[0121] A test method for adaptive lining of tunnel surface under large deformation in soft rock includes the following test steps:

[0122] Step 1: Casting the surface area for adaptive lining

[0123] The specific steps are as follows:

[0124] Step 1.1: Determine the monitoring instrument layout plan

[0125] This invention employs a surface-load adaptive lining technology to actively apply a constant surface load of a certain amount to the surrounding rock, providing support force over a large area. Furthermore, during the later stages of creep deformation in the surrounding rock, it maintains the applied load while reducing pressure, thus achieving a stable readjustment between the rock deformation and the load. By strategically deploying monitoring instruments such as single-point displacement gauges, concrete circumferential strain gauges, and earth pressure cells, the operational characteristics of the surrounding rock during the later stages of creep deformation can be accurately captured.

[0126] like Figure 8 As shown, in order to obtain experimental data on the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock with adaptive lining and conventional lining, two monitoring sections were set up: 1-1 and 2-2. The monitoring instruments arranged in the monitoring sections include single-point displacement gauges, concrete circumferential strain gauges and earth pressure cells.

[0127] As shown in Figures 9(a)-(b), with the top of the pressure cylinder as the 0° direction, six single-point displacement gauges are arranged clockwise at positions of 0°, 120°, and 240° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2.

[0128] As shown in Figures 9(a)-(b), four of the ten concrete circumferential strain gauges are arranged clockwise at positions of 225°, 315°, 45°, and 165° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2, respectively; the other six are arranged clockwise at positions of 0°, 120°, 240°, 45°, 210°, and 330° inside the surface-mounted adaptive lining in monitoring sections 1-1 and 2-2, respectively.

[0129] As shown in Figures 9(a)-(b), the six earth pressure cells are arranged in a clockwise direction at positions of 15°, 135°, 255°, 105°, 225°, and 345° inside the soft rock surrounding rock in monitoring sections 1-1 and 2-2, respectively.

[0130] Step 1.2: Fabricate the area-based adaptive lining casting mold and the fixing components for the monitoring instruments.

[0131] As shown in Figures 10(a)-(b), in step 1.2, the inner and outer molds for the surface-loaded adaptive lining are made according to the inner and outer diameters of the surface-loaded adaptive lining in the tunnel model test scheme, and their two end faces are flush with the two end faces of the cylindrical body.

[0132] Furthermore, based on the installation profile position of the circumferential strain gauge in the concrete, a cable outlet hole is reserved on the inner steel cylinder for each concrete circumferential strain gauge.

[0133] Furthermore, based on the installation profile position of the concrete circumferential strain gauge in the adaptive lining layer, steel reinforcement supports are welded on the inner wall of the outer formwork of the lining layer, and polyester fibers are used to tie and fix the concrete circumferential strain gauge on the steel reinforcement supports.

[0134] Furthermore, based on the position of the pressure regulating chamber inlet and outlet water pipes in the concrete, steel pipes are fixed at the corresponding positions inside the chamber, and inlet and outlet water pipe holes for the pressure regulating chamber are reserved.

[0135] Step 1.3: Assemble the fixtures for the adaptive lining casting mold and monitoring instruments for the area-based load supply.

[0136] like Figure 11 As shown, according to the arrangement scheme of the monitoring instruments in step 1.1, the monitoring instrument fixing parts made in step 1.2 are installed at the designated positions of the inner mold and outer mold of the surface area load-adaptive lining casting.

[0137] Furthermore, according to the arrangement scheme of the concrete circumferential strain gauges in step 1.1, the strain gauges are installed on the monitoring instrument fixing parts on the inner wall of the outer mold of the surface-load adaptive lining casting.

[0138] Furthermore, the cable of the concrete circumferential strain gauge is passed through the reserved cable outlet hole of the fixed steel pipe, and the cables are bundled together at the cable outlet position.

[0139] Step 1.4: Pouring concrete

[0140] like Figure 11 As shown, the rear flange is placed horizontally, and the assembled surface area load-adaptive lining casting inner and outer molds are placed vertically on the rear flange, with their centers concentric with the center of the rear flange. Then, the surface area load-adaptive lining casting inner and outer molds are spot welded to the rear flange.

[0141] Furthermore, a pouring funnel is placed between the outer wall of the inner mold of the adaptive lining casting and the inner wall of the outer mold of the adaptive lining casting. Concrete of a set grade is poured into the funnel, and a vibrator is used to vibrate it evenly every certain height. The pouring stops when grout appears on the surface. The concrete pouring stops when the concrete is level with the top surface of the inner and outer molds of the adaptive lining casting and the end face is smoothed.

[0142] Furthermore, after the concrete pouring is completed, the concrete strain gauges are connected to a data acquisition system to check their readings and to inspect for any malfunctioning monitoring instruments.

[0143] Step 1.5: Curing Concrete

[0144] Furthermore, concrete curing is carried out in accordance with the "Code for Acceptance of Construction Quality of Concrete Structures" (GB 50204-2015). After the concrete has reached the required curing age, the external formwork for the surface-mounted adaptive lining is removed.

[0145] Step 1.6: Install the pressure regulating chamber

[0146] Furthermore, the steel pipes were removed from the concrete, and three pressure regulating chambers of the same size were installed on the outer surface of the concrete. The inlet and outlet pipes of the pressure regulating chambers were led out from the reserved positions on the steel pipes.

[0147] Furthermore, the thickness of the pressure regulating cavity in step 1.6 can be determined according to the following formula:

[0148]

[0149]

[0150]

[0151]

[0152]

[0153] ε r (t)+ε θ (t)=0 (6)

[0154]

[0155]

[0156] In the formula: represents the radial strain of the surrounding rock; represents the circumferential strain of the surrounding rock; represents the radial stress at the outer boundary of the plastic zone; represents the creep compliance; E1 represents the elastic modulus of the material; E2 represents the viscoelastic modulus; represents the viscoelastic coefficient in the transition creep stage; represents the viscosity coefficient in the constant strain rate creep stage; represents the yield stress; represents the initial ground stress; represents the excavation radius of the surrounding rock; represents the radius of the plastic zone of the surrounding rock; represents the support force; u(t) represents the creep deformation of the surrounding rock; represents the thickness of the pressure regulating cavity.

[0157] The specific steps of step (2) include:

[0158] (2.1) Install a single-point displacement meter;

[0159] Furthermore, according to the arrangement scheme of the single-point displacement gauge in step (1.1), the single-point displacement gauge is installed on the outer wall of the pressure cylinder;

[0160] (2.2) Laying the loading cavity;

[0161] Furthermore, by setting up a loading cavity of a certain thickness between the inner wall of the pressure cylinder and the outer wall of the surrounding rock, the surrounding rock is ensured to be subjected to a certain initial in-situ stress.

[0162] (2.3) Pouring concrete

[0163] Furthermore, the cylindrical body is placed upside down on the rear flange and secured with bolts and nuts. The cables for the concrete circumferential strain gauge and earth pressure cell are led out from the cable outlet hole of the top flange and sealed with silicone sealant.

[0164] Furthermore, a grouting funnel is placed between the inner wall of the pressure cylinder and the outer wall of the surface-load-supply adaptive lining. The surrounding rock material prepared with soft rock material is poured into the funnel, and a vibrator is used to vibrate it evenly every certain height. The process is stopped when grout appears on the surface. The pouring of soft rock material is stopped after the surrounding rock is poured to be flush with the top surface of the surface-load-supply adaptive lining, and the end face is smoothed.

[0165] (2.4) Curing the surrounding rock;

[0166] Furthermore, based on the characteristics of soft rock materials, surrounding rock curing is carried out. After the surrounding rock curing reaches the required age, the pressure cylinder is erected and the rear flange is removed.

[0167] (2.5) Install earth pressure box

[0168] Furthermore, according to the arrangement scheme of the earth pressure box in step (1.1), the earth pressure box is installed on the inner wall surface of the surrounding rock;

[0169] Furthermore, the earth pressure box cable is led out from the cable outlet hole of the front flange and sealed with silicone sealant.

[0170] The specific steps of step (3) include:

[0171] (3.1) Connect the pressurized water pump to the loading chamber and the pressure regulating chamber joint to gradually fill the surrounding rock and the adaptive lining with water. The number of steps with a water filling pressure equal to 0.2 MPa, the total number of water filling steps, and the total number of water filling and drainage steps are calculated using the following formula:

[0172]

[0173]

[0174] S t =S j (11)

[0175] P t =0.2 (12)

[0176] Where: is the number of steps with a water filling pressure equal to 0.2 MPa, is the total number of steps for filling the loading cavity with water; is the water filling pressure of 0.2 MPa, is the initial ground stress (MPa) of the simulated pressure tunnel in the loading cavity, with a value of 0.8 MPa, is the loading amplitude (MPa) of the progressively increasing water filling pressure, with a value of 0.2 MPa, is the total number of steps for filling the pressure regulating cavity with water, and is the water filling pressure (MPa) of the pressure regulating cavity;

[0177] Furthermore, in step (3.1), when the loading chamber and pressure regulating chamber are filled with water in stages, the duration of each stage of water filling and pressurization is calculated using the following formula:

[0178]

[0179] Where: is the duration of the first stage of water filling and pressurization, is the number of steps of water filling in each stage, and is the total number of steps of water filling in the loading chamber or pressure regulating chamber;

[0180] (3.2) During the process of gradually filling the loading chamber and the pressure regulating chamber with water, monitor the pressure gauge readings and record the changes in internal water pressure;

[0181] The specific steps of loading the loading chamber and not pressurizing the pressure regulating chamber in step (4) include:

[0182] (4.1) Connect the pressurized water pump to the loading chamber joint to gradually fill the surrounding rock with water. The number of steps with a water pressure equal to 0.2 MPa, the total number of water filling steps, and the total number of water filling and drainage steps are calculated using the following formula:

[0183]

[0184]

[0185] S t =S j (16)

[0186] P t =0 (17)

[0187] Where: is the number of steps with a water filling pressure equal to 0.2 MPa, is the total number of steps for filling the loading cavity with water; is the water filling pressure of 0.2 MPa, is the initial ground stress (MPa) of the simulated pressure tunnel in the loading cavity, with a value of 0.8 MPa, is the loading amplitude (MPa) of the progressively increasing water filling pressure, with a value of 0.2 MPa; is the total number of steps for filling the pressure regulating cavity with water, is the water filling pressure (MPa) of the pressure regulating cavity.

[0188] Furthermore, in step (4.1), the duration of each stage of water filling and pressurization during the progressive water filling of the loading cavity is calculated using the following formula:

[0189]

[0190] Where: is the duration of the first stage of water filling and pressurization, is the number of steps of water filling in each stage, and is the total number of steps of water filling in the loading chamber or pressure regulating chamber;

[0191] Step 4.2: During the gradual filling of the loading cavity with water, monitor the pressure gauge readings and record the changes in internal water pressure;

[0192] Step 5: Process and analyze experimental data

[0193] The specific steps are as follows:

[0194] Step 5.1: Save and import the test data of single-point displacement gauge, concrete circumferential strain gauge and earth pressure cell, and contact force between lining and surrounding rock collected by the data acquisition instrument during the filling and drainage process of the physical model of the tunnel surface under large deformation of soft rock into the computer for processing.

[0195] Step 5.2: Study and analyze the experimental data of single-point displacement gauges, earth pressure cells, and concrete circumferential strain gauges in surface-loaded adaptive lining and conventional lining. Obtain the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel undergoes long-term creep under large deformation of soft rock in surface-loaded adaptive lining and conventional lining. Clarify the mutual feedback process among the three and reveal the actual operating characteristics and mechanisms of surface-loaded adaptive lining and conventional lining when the tunnel undergoes long-term creep under large deformation of soft rock.

Claims

1. A test device for adaptive lining of tunnel surface under load, characterized in that: The system includes a pressure cylinder (1), a surface-mounted adaptive lining (2), surrounding rock (3), a loading chamber (4), monitoring instruments, a pressurization system, and a data acquisition instrument. The pressure cylinder (1) includes a front flange (101), a rear flange (102), a cylindrical body (103), a nut (104), bolts (105), a pressure regulating chamber loading joint (106), a pressure regulating chamber drainage joint (107), a loading chamber loading joint (108), a loading chamber drainage joint (109), a loading chamber pressure-bearing pipe (110), and a base (111). The front flange (101) and the rear flange (102) are connected by bolts. The nuts are fixed to the cylindrical body (103) with a base. The pressure regulating chamber loading joint (106) and the pressure regulating chamber drainage joint (107) are internally connected to the area-based load-adaptive lining (2). The loading chamber loading joint (108), the loading chamber drainage joint (109), and the loading chamber pressure-bearing pipe (110) are connected to the loading chamber (4) to load and unload the surrounding rock (3). The area-based load-adaptive lining (2) includes a pressure regulating chamber (201), a pressure-bearing pipe (202), a concrete lining (203), a pressure stabilizing control unit, and a pressure-bearing pipe joint (204). The pressure-bearing pipe (202) passes through the concrete lining (203) and is connected to the pressure regulating chamber (201) via the pressure-bearing pipe joint (204). Its inlet and outlet ends are respectively connected to the loading chamber drainage joint (109) and the loading chamber loading joint (108). The pressure stabilizing control unit controls the pressure inside the pressure regulating chamber (201) by connecting to the other end of the loading chamber drainage joint (109). The area-based adaptive lining (2) is internally connected to the pressure regulating chamber (201) and externally connected to the pressure-bearing pipe (202). The pressure stabilizing control unit injects water to pressurize and provide a constant pressure to the lining. The surrounding rock (3) is cast from a soft rock material and the two end faces of the surrounding rock (3) are flush with the two end faces of the cylindrical body (103). The loading cavity (4) is laid between the inner wall of the pressure cylinder (1) and the outer wall of the surrounding rock (3). The monitoring instruments include a single-point displacement gauge (501), a concrete circumferential strain gauge (502), and an earth pressure gauge (503). The pressurization system includes a pressurization water pump, a pressure stabilizing cylinder and a servo control system. The pressurization water pump is connected to the pressure regulating cavity loading joint (106) and the loading cavity loading joint (108) to pressurize the surrounding rock and the adaptive lining with water.

2. The tunnel surface area load-adaptive lining test device according to claim 1, characterized in that: The front flange (101) is provided with bolt holes (1011), stiffening ribs (1012) and cable outlet holes (1013); the cylindrical body (103) is provided with bolt holes (1031) and loading chamber pressure pipe joint holes (1101); the rear flange (102) is provided with bolt holes (1021), stiffening ribs (1022) and loading chamber pressure pipe joint holes (1102).

3. A test method for the tunnel surface area load-adaptive lining test device as described in claim 1 or 2, comprising the following steps: (1) Adaptive lining for load supply in the casting area; (2) Casting the surrounding rock; (3) Loading the loading chamber and the pressure regulating chamber, the specific steps include: (3.1) Connect the pressurized water pump to the loading chamber and the pressure regulating chamber joints to gradually fill the surrounding rock and the adaptive lining with water. The number of steps with a water pressure equal to 0.2 MPa, the total number of steps of filling the loading chamber with water, and the total number of steps of filling the pressure regulating chamber with water are calculated using the following formulas: （9） （10） （11） （12） In the formula: The number of steps to achieve a water pressure of 0.2 MPa. The total number of steps for filling the loading cavity with water; The filling pressure is 0.2 MPa. The initial in-situ stress (MPa) of the loading cavity to simulate the pressure tunnel was taken as 0.8 MPa. The loading amplitude (MPa) for the progressively increasing water filling pressure is set to 0.2 MPa. The total number of steps for filling the pressure regulating chamber with water. The pressure of the pressure regulating chamber is (MPa). Furthermore, in step (3.1), when the loading chamber and pressure regulating chamber are filled with water in stages, the duration of each stage of water filling and pressurization is calculated using the following formula: （13） In the formula: For the first The duration of the first stage of water filling and pressurization. The number of steps for gradually filling with water. The total number of steps to fill the loading chamber or pressure regulating chamber with water; (3.2) During the process of gradually filling the loading chamber and the pressure regulating chamber with water, monitor the pressure gauge readings and record the changes in internal water pressure; (4) Loading the loading chamber and not pressurizing the pressure regulating chamber, the specific steps include: (4.1) Connect the pressurized water pump to the loading chamber joint to gradually fill the surrounding rock with water. The calculation formulas are as follows: the number of steps with a filling pressure of 0.2 MPa, the total number of steps for filling the loading chamber, and the total number of steps for filling the pressure regulating chamber. （14） （15） (16) (17) In the formula: The number of steps to achieve a water pressure of 0.2 MPa. The total number of steps for filling the loading cavity with water; The filling pressure is 0.2 MPa. The initial in-situ stress (MPa) of the loading cavity to simulate the pressure tunnel was taken as 0.8 MPa. The loading amplitude (MPa) for the progressive water filling pressure is set to 0.2MPa; The total number of steps for filling the pressure regulating chamber with water. The pressure of the pressure regulating chamber is (MPa). Furthermore, in step (4.1), the duration of each stage of water filling and pressurization during the progressive water filling of the loading cavity is calculated using the following formula: (18) In the formula: For the first The duration of the first stage of water filling and pressurization. The number of steps for gradually filling with water. The total number of steps to fill the loading chamber or pressure regulating chamber with water; (4.2) During the process of gradually filling the loading cavity with water, monitor the pressure gauge readings and record the changes in internal water pressure; (5) Process and analyze the experimental data from steps (3) and (4).

4. The test method for a tunnel surface area load-adaptive lining test device according to claim 3, characterized in that: The specific steps of step (1), namely, pouring the adaptive lining for the surface area, include: (1.1) Determine the layout plan for monitoring instruments; (1.2) Fabricate the surface area load-adaptive lining casting mold and the fixing components for monitoring instruments; (1.3) Fixing components for the assembly area load-adaptive lining casting mold and monitoring instruments; (1.4) Pouring concrete; (1.5) Curing concrete; (1.6) Install the pressure regulating chamber.

5. The test method for a tunnel surface area load-adaptive lining test device according to claim 4, characterized in that: The specific steps for pouring the surrounding rock in step (2) include: (2.1) Install a single-point displacement meter; (2.2) Laying the loading cavity; (2.3) Cast-in-place soft rock materials; (2.4) Curing the surrounding rock; (2.5) Install earth pressure gauge.

6. The test method for a tunnel surface area load-adaptive lining test device according to claim 3, characterized in that: The specific steps for processing and analyzing the experimental data in step (5) include: (5.1) The test data of single-point displacement gauge, concrete circumferential strain gauge and earth pressure gauge, and contact force between lining and surrounding rock collected by the data acquisition instrument during the filling and drainage process of the physical model of the tunnel surface under large deformation of soft rock will be saved and imported into the computer for processing. (5.2) The experimental data of single-point displacement gauges, earth pressure gauges and concrete circumferential strain gauges in the adaptive lining and conventional lining with surface load supply were studied and analyzed. The results were obtained on the stress and displacement changes of the surrounding rock, the dynamic evolution characteristics of the contact state between the surrounding rock and the lining, and the stress of the lining structure when the tunnel under large deformation of soft rock undergoes long-term creep. The mutual feedback process among the three was clarified, and the actual operating characteristics and mechanisms of the adaptive lining and conventional lining under large deformation of soft rock undergo long-term creep were revealed.

Images