Device and method for simulating influence of underground water seepage on existing tunnel and frozen wall

Abstract

The invention relates to a device and a method for simulating influence of underground water seepage on an existing tunnel and a freezing wall, the device comprises a test box body, a tunnel model, a seepage system, a data acquisition monitoring system, a saline water circulation cooling system and a saline water circulation heating system, the test box body is formed by splicing three box bodies with different structures; a formed space area is used for laying a test soil body and a broken stone hardcore; the tunnel model is arranged in the hollow area in the test box body; the seepage system is used for providing an underground water source for simulating seepage; the data acquisition monitoring system is used for monitoring and recording the soil pressure and displacement of the soil body around the tunnel model and the temperature change of the soil body near the freezing pipe; the saline water circulating cooling system is used for providing cooling capacity required by soil body freezing; and the saline water circulation heating system is used for providing heat required for pulling out the freezing pipe. The device can be used for simulating the influence of groundwater seepage on soil deformation and soil pressure around the existing tunnel, adjusting the seepage direction of groundwater and restoring more real groundwater seepage movement.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial ground freezing simulation test, and in particular relates to a device and a method for simulating the influence of groundwater seepage on an existing tunnel and a frozen wall. Background Art

[0002] Artificial ground freezing is a method developed to temporarily reinforce soil by taking advantage of the high volumetric water content of water-rich soft strata. This method uses low-temperature refrigerants (such as brine, dry ice, liquid nitrogen, etc.) in freezing tubes to freeze the water-containing rock and soil within a certain range of the underground space into a frozen wall with high strength and the ability to block water flow, in order to resist soil pressure and pore water pressure, and provide a safe and reliable environment for construction within the frozen wall. With the development of urban tunnel construction, the artificial ground freezing method has become increasingly mature, and is currently widely used in water-rich soft soil areas such as Beijing, Shanghai, Nanjing, and Wuhan.

[0003] At present, there are still two safety risks when using the vertical artificial freezing method to construct the tunnel above the water-rich and soft strata near the river. First, the groundwater with a faster flow rate may take away the coldness of the soil near the freezing pipe, increase the energy consumption and time of cooling the unit volume of soil, expand the cooling area, delay the circle time of the frozen soil column, and even fail to form a frozen wall. In severe cases, water and sand may surge; in addition, if the freezing time is too long and the temperature of the freezing liquid is too low, the soil volume will expand excessively, and serious subsidence problems may occur after the freezing is lifted, and the strength of the soil will be greatly reduced. Second, when the vertical artificial freezing method is used for the soil above the existing tunnel, the soil above the existing tunnel will expand in volume due to freezing, which will cause complex deformations such as extrusion, shearing, and sliding of the soil above the existing tunnel, which will lead to significant changes in the soil pressure of the existing tunnel lining segments, and ultimately bring safety hazards to the normal operation of the existing tunnel.

[0004] Model tests based on similarity theory have the advantages of low cost, short cycle, and accurate data, and are widely used in the field of experimental research. At present, there are some model test devices for simulating freezing construction and groundwater seepage in the field of experimental research, but there are some shortcomings. For example, the public document of application number CN202410144611.7 has developed a test device that simulates the entire process of excavation of frozen walls in highly permeable strata, but the groundwater flow direction simulated by the device is limited to the "bottom-up" flow direction, while the actual groundwater flow direction is the result of the superposition of multi-directional water flows, and the device cannot control the rise and fall of the groundwater level. For example, the public document of application number CN202021275390.0 has developed a device that simulates the impact of groundwater level rise and fall on farmland nitrogen. The device simulates the rise and fall of the groundwater level by controlling the water inlet valve and the drain valve and observing the water level observation pipe at the same time, but the groundwater inside the device does not flow, and the actual farmland groundwater is in a turbulent state, not a static state.

[0005] Therefore, currently in the field of vertical artificial ground freezing experimental research, there is no simulation device and method that can be used to simulate the speed and direction of groundwater seepage as well as the impact of the height of the groundwater level on the existing tunnel and frozen wall. Summary of the invention

[0006] The technical problem to be solved by the present invention is to propose a device and method for simulating the influence of groundwater seepage on existing tunnels and frozen walls in view of the above-mentioned deficiencies in the existing experimental research field, which can multifunctionally simulate the influence of groundwater seepage velocity, direction and groundwater level on existing tunnels and frozen walls.

[0007] In order to solve the above problems, the present invention adopts the following technical solutions: A device for simulating the influence of groundwater seepage on existing tunnels and frozen walls, comprising a test box, a tunnel model, a seepage system, a data acquisition and monitoring system, a salt water circulation cooling system, and a salt water circulation heating system; The test box includes a first box, a second box, and a third box arranged from bottom to top, the lower parts of the four corners of the first box are connected to four rigid foot supports, and a first box hollow area is reserved in the upper middle part of the first box; the second box is divided into an upper part and a lower part, the lower part of the second box is placed in the hollow area of ​​the first box, and second box holes are opened all around the lower part of the second box, the upper and lower parts of the second box are separated by the second box upper and lower area partition plates with holes in the middle area, a left water stop baffle, a front water stop baffle and a rear water stop baffle are arranged between the upper part of the second box and the third box, and a second water stop baffle slot wall is fixed on the inner wall of the second box. The third box body has third box body holes all around the main body part, and the flange part extending on the right side of the third box body is not provided with holes, but two groups of third water-stop baffle slot walls are fixed on its inner wall; the left water-stop baffle is inserted into the slot in the second water-stop baffle slot wall, and fits tightly with the third box body; the left water-stop baffle is provided with two groups of left water-stop baffle slot walls opposite to the third water-stop baffle slot walls, and the front water-stop baffle and the rear water-stop baffle are respectively inserted into the slots formed by one group of the left water-stop baffle slot walls, the third water-stop baffle slot walls and the third box body, and fit tightly with the third box body; a hollow area is provided inside the third box body; The tunnel model is placed in the inner hollow area of ​​the third box, and the other hollow areas after the tunnel model is placed are the areas to be filled; The seepage system includes a water storage tank for providing a seepage water source, a first water pump for providing power transportation, a water inlet pipe connecting the first water pump and the test box, a series of second box outlet pipes at different heights installed on the right side of the second box, a number of flow meters and valve switches (by controlling the valve switches on the second box outlet pipes at different heights, the fluctuation of the groundwater level is simulated); The brine circulation cooling system includes a U-shaped freezing pipe, a water inlet conduit, a water outlet conduit, a normal temperature brine tank, a second water pump, a brine cooling device, a third water pump, and a plurality of valve switches; the U-shaped freezing pipe is inserted into the test box, and the brine cooling device is used to provide a sufficient cold source for the soil freezing test soil; the brine in the normal temperature brine tank is connected to one end of the second water pump through a conduit, and the other end of the second water pump is connected to one end of the brine cooling device through a conduit, and the other end of the brine cooling device is connected to one end of the third water pump through a conduit, and finally one end of the third water pump and one end of the normal temperature brine tank are connected to the two ends of the U-shaped freezing pipe through the water inlet conduit and the water outlet conduit respectively, and the whole loop forms a brine circulation cooling system; The connection mode and components of the brine circulation heating system are similar to those of the brine circulation cooling system, except that the brine cooling device is replaced by a brine heating device, which is used to provide a sufficient heat source for pulling out the U-shaped freezing pipe; The data acquisition monitoring system includes a temperature sensor, a PC terminal, a data acquisition instrument, an earth pressure sensor and a displacement sensor. The temperature sensor is arranged near the U-shaped freezing pipe, and the earth pressure sensor and the displacement sensor are arranged close to the tunnel model. The temperature sensor, the earth pressure sensor and the displacement sensor are connected to the data acquisition instrument and then to the PC terminal.

[0008] Preferably, a first box water outlet pipe is installed at the bottom of the first box for relieving pressure and emptying the moisture inside the test box; the first box is filled with a gravel cushion layer as a buffer area except for the middle first box hollow area.

[0009] Preferably, the first box body, the second box body, the third box body, the left water stop baffle, the front water stop baffle, and the rear water stop baffle are all made of high-strength transparent acrylic plates; the tops of the second box body and the third box body are flush and sealed with transparent insulating glass; and a plurality of pressure relief holes are arranged on the outside of the first box body and the second box body.

[0010] Preferably, the upper height of the second box is consistent with the height of the third box, and the third box is placed inside the second box; the bottom of the third box and the partition with holes in the middle area are connected with silicone sealant, and the flange part extending on the right side of the third box is connected with the inner wall of the second box with silicone sealant; the lower size of the second box is consistent with the size of the hollow area of ​​the first box, the lower part of the second box is embedded in the hollow area of ​​the first box, and the connection is sealed with silicone sealant.

[0011] Preferably, filter gauze is provided at the openings of the first box, the second box and the third box; except for the internal hollow area of ​​the third box which is the area to be filled with soil, the rest of the space is filled with gravel cushion layers for buffering water flow; the tunnel model is made of PVC pipe material, and both ends are sealed.

[0012] Preferably, the water storage tank is connected to one end of the first water pump through a pipe, and the other end of the first water pump is connected to the left side of the first box body and the second box body through the water inlet pipe; a series of second box body water outlet pipes of different heights installed on the right side of the second box body are arranged at equal intervals.

[0013] Preferably, a plurality of temperature sensors are provided, and each temperature sensor is evenly distributed in three rows, three columns and two layers in the space near the U-shaped freezing tube, and the temperature sensors are all located above the tunnel model.

[0014] Preferably, a plurality of soil pressure sensors are provided, and the plurality of soil pressure sensors are evenly distributed in four directions of “up, down, left, and right” close to the tunnel model, and the plurality of soil pressure sensors are arranged in three circles along the length direction of the tunnel model.

[0015] Preferably, a plurality of displacement sensors are provided, each displacement sensor is evenly distributed in close proximity to the four directions of “up, down, left, and right” of the tunnel model, and a plurality of displacement sensors are arranged in three circles along the length direction of the tunnel model.

[0016] The present invention also proposes a simulation method of the device for simulating the influence of groundwater seepage on existing tunnels and frozen walls, comprising the following steps: Step 1: Install the various components of the device for simulating the effect of groundwater seepage on the existing tunnel and frozen wall, and check whether the various components can work normally; Step 2: Determine the distance between the tunnel model and the U-shaped freezing pipe, as well as the type of soil based on the on-site investigation data and similarity theory; Step 3: First, fill the test soil according to the physical indicators of the on-site soil, then bury the tunnel model and temperature sensor, soil pressure sensor, and displacement sensor in the test soil, and finally cover it with transparent insulation glass and insert the U-shaped freezing tube; Step 4: Open the seepage system, simulate the seepage speed of different groundwater by controlling the valve switches on the water inlet pipe and the water outlet pipe and combining the pointer reading of the flow meter; simulate the height of different groundwater levels by controlling the valve switches of the water outlet pipes at different heights on the right side of the second box; simulate the seepage direction of groundwater by controlling the valve switches of the water inlet pipes connected to the first box and the second box, and the water stop baffles in the internal area of ​​the second box and the third box; Step 5: After the seepage inside the soil body reaches stability, start the second water pump to allow the brine to enter the brine cooling equipment. When the brine reaches the temperature required for the test, start the third water pump to allow the brine to enter the U-shaped freezing tube; record the closing time of the freezing wall outside the U-shaped freezing tube under different seepage conditions and brine temperatures, and collect data from the temperature sensor, displacement sensor, and soil pressure sensor in real time; after the freezing wall closes, close the brine circulation cooling system, open the pressure relief hole, and start the brine circulation heating system to pull out the U-shaped freezing tube; at the same time, open the valve switch installed on the water outlet pipe of the first box, and use a bucket to collect the test water; Step 6: After the test, the collected data is analyzed and processed, and various data analysis curves are drawn, including curves of temperature, displacement and soil pressure changing with time under different seepage conditions; the influence of different groundwater seepage conditions on the soil pressure and displacement around the existing tunnel is analyzed; the critical time and critical temperature required for the freezing wall to be closed under different groundwater seepage conditions are studied; thus, the influence of groundwater seepage on the existing tunnel and the freezing wall is analyzed and judged.

[0017] Compared with the traditional model test device, the beneficial effects of the present invention are mainly manifested in: 1. The test box of the present invention is assembled from three boxes of different structures, and the space area formed is used to lay the test soil and set the gravel cushion layer; the seepage system is used to provide a groundwater source for simulating seepage; the data acquisition monitoring system is used to monitor and record the soil pressure and displacement of the soil around the tunnel model and the temperature change of the soil near the freezing pipe; the salt water circulation cooling system is used to provide the cold required for freezing the soil; the salt water circulation heating system is used to provide the heat required for pulling out the freezing pipe. The device strictly controls the height of the groundwater level through a series of water outlet pipes uniformly fixed on the test box at different heights, thereby simulating the fluctuation of the groundwater level; compared with the traditional method of manually adjusting the height of the water tank to control the height of the groundwater level, the device of the present invention is not only simple and convenient to operate, but also can simulate the turbulent state of groundwater inside the soil; 2. The device of the present invention cleverly changes the seepage direction of groundwater by setting various water-stop baffles, and can realize horizontal seepage, vertical seepage, and mixed flow in horizontal and vertical directions, thus overcoming the singleness of the seepage direction of the traditional model test device; 3. The device of the present invention has the function of simulating a variety of seepage conditions, such as different groundwater levels, groundwater seepage velocities, and groundwater seepage directions, which changes the single function of traditional seepage model test devices and restores more realistic groundwater seepage movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The overall structure diagram of the device for simulating the influence of groundwater seepage on the existing tunnel and frozen wall of the present invention; Figure 2 This is a schematic diagram of the main structure of the device of the present invention; Figure 3 This is a front view of the main structure of the device of the present invention; Figure 4 It is a top view cross-sectional view of the main structure of the device of the present invention; Figure 5 It is a schematic diagram of the appearance of the first box of the main structure of the device of the present invention; Figure 6 It is a schematic diagram of the appearance of the second box of the main structure of the device of the present invention; Figure 7 A schematic diagram of the appearance of a third box body of the main structure of the device of the present invention; Figure 8 It is a plan view of the upper and lower partitions of the second box of the device of the present invention; Fig. 9 A schematic diagram of a U-shaped freezing tube of the device of the present invention; In the figure: 1-first box, 2-second box, 3-third box, 4-U-shaped freezing pipe, 5-left water stop baffle, 2.6-second water stop baffle slot wall, 3.6-third water stop baffle slot wall, 5.6-left water stop baffle slot wall, 7-foot support, 8-valve switch, 9-flow meter, 10-second box outlet pipe, 2.11-second box hole, 3.11-third box hole, 12-lead hole, 13-soil filling area, 14-gravel cushion, 15-temperature sensor, 16-test soil, 17-front water stop baffle, 18-rear water stop baffle, 19-transparent insulation glass, 20 -filter gauze, 21-water storage tank, 22.1-first water pump, 22.2-second water pump, 22.3-third water pump, 23-water bucket, 24-conduit, 24.1-water inlet conduit, 24.2-water outlet conduit, 25-brine cooling equipment, 26-brine heating equipment, 27-normal temperature brine tank, 28-hollow area of ​​the first box, 29-lower part of the second box, 30-water inlet pipe, 31-tunnel model, 32-PC terminal, 33-data acquisition instrument, 34-earth pressure sensor, 35-displacement sensor, 36-water outlet pipe of the first box, 37-upper and lower partitions of the second box, 38-pressure relief hole. DETAILED DESCRIPTION

[0019] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown, a device for simulating the influence of groundwater seepage on existing tunnels and frozen walls includes a test box, a tunnel model, a seepage system, a data acquisition and monitoring system, a salt water circulation cooling system, and a salt water circulation heating system; like Figure 2 As shown, the main body of the test box includes a first box 1, a second box 2, and a third box 3 arranged from bottom to top. Figure 2-Figure 5 As shown, the lower parts of the four corners of the first box body 1 are connected to four rigid foot supports 7, and a first box body hollow area 28 is reserved in the upper middle part of the first box body 1; a first box body water outlet pipe 36 is installed at the bottom of the first box body 1 for pressure relief and emptying the moisture inside the test box body; except for the middle hollow area 28, the first box body 1 is filled with a gravel cushion layer 14 as a buffer area.

[0021] like Figure 3-4 , Figure 5-6As shown, the second box body 2 is divided into two parts, an upper part and a lower part, and the second box body lower part 29 is completely surrounded by second box body holes 2.11; the upper and lower parts of the second box body 2 are separated by a second box body upper and lower area partition 37 with holes in the middle area; a left water stop baffle 5, a front water stop baffle 17 and a rear water stop baffle 18 are arranged between the upper part of the second box body 2 and the third box body 3, and a second water stop baffle card groove wall 2.6 is fixed on the inner wall of the second box body 2; as shown Figure 7 As shown, the third box body holes 3.11 are all formed around the main body of the third box body 3, and the flange part extending on the right side of the third box body 3 is not provided with holes, but two sets of third water stop baffle slot walls 3.6 are fixed on its inner wall; The left water-stop baffle plate slot wall 5.6 and the left water-stop baffle plate 5 are integrally formed; the left water-stop baffle plate 5 is inserted into the slot in the second water-stop baffle plate slot wall 2.6, and fits tightly with the third box body 3; the front water-stop baffle plate 17 is inserted into the slot formed by the third water-stop baffle plate slot wall 3.6, the left water-stop baffle plate slot wall 5.6 and the third box body, and fits tightly with the third box body; the fixing method of the rear water-stop baffle plate is consistent with the fixing method of the front water-stop baffle plate; water-stop baffle plates are provided on the inner walls of the second box body 2 and the third box body 3 to change the seepage direction of groundwater; like Figure 2-Figure 3 As shown, the tops of the second box body 2 and the third box body 3 are flush and sealed with a transparent insulating glass 19; and a plurality of pressure relief holes 38 are arranged on the outside of the first box body 1 and the second box body 2; the first box body 1, the second box body 2, the third box body 3, the left water stop baffle 5, the front water stop baffle 17, and the rear water stop baffle 18 are all made of high-strength transparent acrylic plates, in order to facilitate the observation of the freezing condition of the soil in the model box.

[0022] like Figure 3 As shown, the upper height of the second box body 2 is consistent with the height of the third box body 3, and the third box body 3 is placed inside the second box body 2; the bottom of the third box body 3 is connected to the upper and lower partitions 37 of the second box body with silicone sealant, and the flange part extending on the right side of the third box body 3 is also connected to the inner wall of the second box body 2 with silicone sealant; the lower size of the second box body 2 is consistent with the size of the hollow area 28 of the first box body, and the lower part of the second box body 2 is inserted into the hollow area 28 of the first box body, and the connection is sealed with silicone sealant.

[0023] Filter gauze 20 is provided at the openings of the first box 1, the second box 2, and the third box 3; a hollow area is provided inside the third box 3, and the remaining area after the tunnel model 31 is provided in the hollow area is the area to be filled 13, and the tunnel model 31 is made of PVC pipe material, and both ends are sealed; the space formed by the second box 2 and the third box 3 is filled with a gravel cushion layer for buffering water flow; The seepage system includes a water storage tank 21 for providing a seepage water source, a first water pump 22.1 for providing power transportation, an inlet pipe 30 connecting the first water pump 22.1 and the test box, a series of second box outlet pipes 10 at different heights installed on the right side of the second box 2, a number of flow meters 9 and a valve switch 8; the water storage tank 21 is connected to one end of the first water pump 22.1 through a pipeline, and the other end of the first water pump 22.1 is connected to the first box 1 and the left side of the second box 2 through the inlet pipe 30; a series of second box outlet pipes 10 with equal spacing are installed on the right side of the second box 2, and the rise and fall of the groundwater level can be simulated by controlling the valve switches 8 on the second box outlet pipes 10 at different heights.

[0024] The brine circulation cooling system includes a U-shaped freezing pipe 4, an inlet conduit 24.1, an outlet conduit 24.2, a normal temperature brine tank 27, a second water pump 22.2, a brine cooling device 25, a third water pump 22.3 and a number of valve switches; the brine cooling device 25 is used to provide a sufficient cold source for the soil 16 of the soil freezing test; the brine in the normal temperature brine tank 27 is connected to one end of the second water pump 22.2 through a conduit, and the other end of the second water pump 22.2 is connected to one end of the brine cooling device 25 through a conduit 24, and the other end of the brine cooling device 25 is connected to one end of the third water pump 22.3 through a conduit, and finally one end of the third water pump 22.3 and one end of the normal temperature brine tank 27 are connected to both ends of the U-shaped freezing pipe 4 through the inlet conduit 24.1 and the outlet conduit 24.2 respectively to form a brine circulation cooling system.

[0025] The connection method and component structure of the brine circulation heating system are similar to those of the brine circulation cooling system. It is only necessary to replace the brine cooling device 25 with the brine heating device 26. The brine heating device 26 is used to provide sufficient heat source for pulling out the U-shaped freezing tube 4.

[0026] The data acquisition monitoring system includes a temperature sensor 15, a PC terminal 32, a data acquisition instrument 33, an earth pressure sensor 34 and a displacement sensor 35; a plurality of temperature sensors 15 are provided, and each temperature sensor 15 is evenly distributed in the space near the U-shaped freezing pipe 4 in three rows, three columns and two layers, and each temperature sensor 15 is located above the tunnel model 31. A plurality of earth pressure sensors 34 are provided, and a plurality of earth pressure sensors 34 are evenly distributed in the four directions of "up, down, left and right" of the tunnel model 31; a plurality of earth pressure sensors 34 are arranged in three circles along the length direction of the tunnel model 31. A plurality of displacement sensors 35 are provided, and each displacement sensor 35 is evenly distributed in the four directions of "up, down, left and right" of the tunnel model 31; a plurality of displacement sensors 35 are arranged in three circles along the length direction of the tunnel model 31. The data lines of the temperature sensor 15, the earth pressure sensor 34 and the displacement sensor 35 are all led out from the lead hole 12 and connected to the data acquisition instrument 33; the data acquisition instrument 33 is then connected to the PC terminal 32 to collect data.

[0027] The simulation method of the device for simulating the influence of groundwater seepage on the existing tunnel and frozen wall of the present invention comprises the following steps: Step 1: Install the various components of the device that simulates the impact of groundwater seepage on the existing tunnel and frozen wall, and check whether the various components can work properly; Step 2: Determine the distance between the tunnel model 31 and the U-shaped freezing pipe 4, and the type of soil based on the on-site investigation data and similarity theory; Step 3: First, fill the test soil 16 according to the physical indicators of the on-site soil, then pre-embed the tunnel model 31 and the temperature sensor 15, the soil pressure sensor 34, and the displacement sensor 35 in the test soil 16, and finally cover it with transparent insulation glass 19 and insert the U-shaped freezing pipe 4; Step 4: Open the seepage system, simulate the seepage speed of different groundwater by controlling the valve switch 8 on the water inlet pipe and the water outlet pipe and combining the pointer reading of the flow meter 8; simulate the height of different groundwater levels by controlling the valve switch 8 of the water outlet pipe 10 at different heights on the right side of the second box; simulate the seepage direction of groundwater by controlling the valve switch of the water inlet pipe connected to the first box and the second box, and the water stop baffle in the internal area of ​​the second box and the third box; Step 5: After the internal seepage of the soil body reaches stability, start the second water pump 22.2 to allow the brine to enter the brine cooling device 25. When the brine reaches the temperature required for the test, start the third water pump 22.3 to allow the brine to enter the U-shaped freezing tube 4. Record the time of the outer freezing wall of the U-shaped freezing tube 4 under different seepage conditions and brine temperatures, and collect data from the temperature sensor 15, displacement sensor 35, and soil pressure sensor 34 in real time. After the freezing wall is closed, close the brine circulation cooling system, open the pressure relief hole 38, and start the brine circulation heating system to remove the U-shaped freezing tube 4. At the same time, open the valve switch 8 installed on the first box water outlet pipe 36, and use the bucket 23 to collect test water. Step 6: After the test, analyze and process the collected data, and draw various data analysis curves, such as the curves of temperature, displacement and soil pressure changing with time under different seepage conditions; analyze the influence of different groundwater seepage conditions on the soil pressure and displacement around the existing tunnel; study the critical time and critical temperature required for the freezing wall to close under different groundwater seepage conditions; thus analyze and judge the influence of groundwater seepage on the existing tunnel and freezing wall.

[0028] The above only describes the preferred examples applicable to the present invention, but the present invention is not limited to the above examples. Various changes can be made within the knowledge scope of those skilled in the art without departing from the purpose of the present invention, and various changes should be included in the protection scope of the present invention.

Claims

1. A device for simulating the effect of groundwater seepage on existing tunnels and frozen walls, characterized in that: Including test box, tunnel model, seepage system, data acquisition and monitoring system, brine circulation cooling system, brine circulation heating system; The test box includes a first box, a second box, and a third box arranged from bottom to top, the lower parts of the four corners of the first box are connected to four rigid foot supports, and a first box hollow area is reserved in the upper middle part of the first box; the second box is divided into an upper part and a lower part, the lower part of the second box is placed in the hollow area of ​​the first box, and second box holes are opened all around the lower part of the second box, the upper and lower parts of the second box are separated by the second box upper and lower area partition plates with holes in the middle area, a left water stop baffle, a front water stop baffle and a rear water stop baffle are arranged between the upper part of the second box and the third box, and a second water stop baffle slot wall is fixed on the inner wall of the second box. The third box body has third box body holes all around the main body part, and the flange part extending on the right side of the third box body is not provided with holes, but two groups of third water-stop baffle slot walls are fixed on its inner wall; the left water-stop baffle is inserted into the slot in the second water-stop baffle slot wall, and fits tightly with the third box body; the left water-stop baffle is provided with two groups of left water-stop baffle slot walls opposite to the third water-stop baffle slot walls, and the front water-stop baffle and the rear water-stop baffle are respectively inserted into the slots formed by one group of the left water-stop baffle slot walls, the third water-stop baffle slot walls and the third box body, and fit tightly with the third box body; a hollow area is provided inside the third box body; The tunnel model is placed in the inner hollow area of ​​the third box, and the other hollow areas after the tunnel model is placed are the areas to be filled; The seepage system includes a water storage tank for providing a seepage water source, a first water pump for providing power transportation, a water inlet pipe connecting the first water pump and the test box, a series of second box outlet pipes at different heights installed on the right side of the second box, a number of flow meters and valve switches; The brine circulation cooling system includes a U-shaped freezing pipe, a water inlet conduit, a water outlet conduit, a normal temperature brine tank, a second water pump, a brine cooling device, a third water pump, and a plurality of valve switches; the U-shaped freezing pipe is inserted into the test box, and the brine cooling device is used to provide a sufficient cold source for the soil freezing test soil; the brine in the normal temperature brine tank is connected to one end of the second water pump through a conduit, and the other end of the second water pump is connected to one end of the brine cooling device through a conduit, and the other end of the brine cooling device is connected to one end of the third water pump through a conduit, and finally one end of the third water pump and one end of the normal temperature brine tank are connected to the two ends of the U-shaped freezing pipe through the water inlet conduit and the water outlet conduit respectively, and the whole loop forms a brine circulation cooling system; The connection mode and components of the brine circulation heating system are similar to those of the brine circulation cooling system, except that the brine cooling device is replaced by a brine heating device, which is used to provide a sufficient heat source for pulling out the U-shaped freezing pipe; The data acquisition monitoring system includes a temperature sensor, a PC terminal, a data acquisition instrument, an earth pressure sensor and a displacement sensor. The temperature sensor is arranged near the U-shaped freezing pipe, and the earth pressure sensor and the displacement sensor are arranged close to the tunnel model. The temperature sensor, the earth pressure sensor and the displacement sensor are connected to the data acquisition instrument and then to the PC terminal.

2. A device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: A first box water outlet pipe is installed at the bottom of the first box for relieving pressure and emptying the moisture inside the test box; except for the hollow area of ​​the first box in the middle, the first box is filled with a gravel cushion layer as a buffer area.

3. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: The first box body, the second box body, the third box body, the left water stop baffle, the front water stop baffle, and the rear water stop baffle are all made of high-strength transparent acrylic plates; the tops of the second box body and the third box body are flush and sealed with transparent thermal insulation glass; and a plurality of pressure relief holes are arranged on the outside of the first box body and the second box body.

4. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: The upper height of the second box is consistent with the height of the third box, and the third box is placed inside the second box; the bottom of the third box and the partition with holes in the middle area are connected with silicone sealant, and the flange part extending on the right side of the third box is connected with the inner wall of the second box with silicone sealant; the lower size of the second box is consistent with the size of the hollow area of ​​the first box, the lower part of the second box is embedded in the hollow area of ​​the first box, and the connection is sealed with silicone sealant.

5. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: Filter gauze is set at the openings of the first box, the second box and the third box; except for the internal hollow area of ​​the third box which is the area to be filled with soil, the rest of the space is filled with gravel cushion layers for buffering water flow; the tunnel model is made of PVC pipe material, and both ends are sealed.

6. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: The water storage tank is connected to one end of the first water pump through a pipe, and the other end of the first water pump is connected to the left side of the first box body and the second box body through the water inlet pipe; a series of second box body water outlet pipes of different heights installed on the right side of the second box body are arranged at equal intervals.

7. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: A plurality of temperature sensors are provided, and each temperature sensor is evenly distributed in the space near the U-shaped freezing pipe in three rows, three columns and two layers, and the temperature sensors are all located above the tunnel model.

8. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: A plurality of soil pressure sensors are provided, and the plurality of soil pressure sensors are evenly distributed in four directions of "up, down, left, and right" close to the tunnel model. The plurality of soil pressure sensors are arranged in three circles along the length direction of the tunnel model.

9. The device for simulating the effect of groundwater seepage on existing tunnels and frozen walls according to claim 1, characterized in that: A plurality of displacement sensors are provided, each displacement sensor is evenly distributed in four directions of "up, down, left, and right" of the tunnel model, and a plurality of displacement sensors are arranged in three circles along the length direction of the tunnel model.

10. The simulation method of the device for simulating the influence of groundwater seepage on existing tunnels and frozen walls as described in claims 1 to 9, characterized in that: The following steps are involved: Step 1: Install the various components of the device for simulating the influence of groundwater seepage on the existing tunnel and frozen wall, and check whether the various components can work normally; Step 2: Determine the distance between the tunnel model and the U-shaped freezing pipe, as well as the type of soil based on the on-site survey data and similarity theory; Step 3: First, fill the test soil according to the physical indicators of the on-site soil, then bury the tunnel model and temperature sensor, soil pressure sensor, and displacement sensor in the test soil, and finally cover it with transparent insulation glass and insert the U-shaped freezing tube; Step 4: Open the seepage system, and simulate the seepage speed of different groundwater by controlling the valve switches on the water inlet pipe and the water outlet pipe and combining the pointer reading of the flow meter; simulate the height of different groundwater levels by opening the valve switches of the water outlet pipe of the second box arranged at equal intervals on the right side of the second box; simulate the seepage direction of groundwater by controlling the valve switches of the water inlet pipes connected to the first box and the second box, and the water stop baffles in the internal areas of the second box and the third box; Step 5: After the seepage inside the soil body reaches stability, start the second water pump to allow the brine to enter the brine cooling equipment. When the brine reaches the temperature required for the test, start the third water pump to allow the brine to enter the U-shaped freezing tube; record the closing time of the freezing wall outside the U-shaped freezing tube under different seepage conditions and brine temperatures, and collect data from the temperature sensor, displacement sensor, and soil pressure sensor in real time; after the freezing wall closes, close the brine circulation cooling system, open the pressure relief hole, and start the brine circulation heating system to pull out the U-shaped freezing tube; at the same time, open the valve switch installed on the water outlet pipe of the first box, and use a bucket to collect the test water; Step 6: After the test, the collected data is analyzed and processed, and various data analysis curves are drawn, including curves of temperature, displacement and soil pressure changing with time under different seepage conditions; the influence of different groundwater seepage conditions on the soil pressure and displacement around the existing tunnel is analyzed; the critical time and critical temperature required for the freezing wall to be closed under different groundwater seepage conditions are studied; thus, the influence of groundwater seepage on the existing tunnel and the freezing wall is analyzed and judged.

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