Model test device capable of simulating foundation pit excavation under action of confined water

Abstract

The utility model discloses a model test device capable of simulating foundation pit excavation under the action of confined water. The device comprises a model box, a water tank, a foundation pit supporting structure, a confined water head adjusting and monitoring system and a measuring system. The model box is a box body with an opening in the upper end, four side walls are marked as side walls I, II, III and IV, a through hole I and a plurality of through holes II which are communicated with the pressure-bearing layer are formed in the side walls, the through hole I is communicated with the water tank, the through holes II are communicated with the pressure-bearing water head adjusting and monitoring system, and the model box is filled with a sand soil layer and a clay layer. The foundation pit supporting structure comprises an underground baffle and a supporting unit, the underground baffle is of a plate-shaped structure, is embedded in a soil layer in the model box and is parallel to the side wall I, the supporting unit is of a rod-shaped structure, one end of the supporting unit is connected through a supporting positioning hole in the underground baffle, and the other end of the supporting unit abuts against the side wall I. And the measuring system records data in real time, so that the rules of bending moment, deformation and aquitard pore water pressure of the enclosure wall under the conditions of different excavation depths and water heads are obtained.

Description

Technical Field

[0001] The utility model relates to the technical field of geotechnical engineering, and specifically relates to a model test device for simulating the excavation of a foundation pit under the action of confined water. Background Technique

[0002] In coastal areas near rivers, the occurrence of groundwater is often complex, and the geological sedimentary conditions are diverse. In these areas, there are often characteristics of alternating weak and strong permeable layers, forming many confined aquifers. Therefore, during the excavation of deep foundation pits in coastal areas near rivers, groundwater engineering problems are often faced. When there are situations such as seasonal changes in rivers, tidal effects, and human activities, the water head of the confined aquifer will also change accordingly, thereby affecting the distribution of water and soil pressure and the stability during the excavation of the foundation pit. During the construction of deep foundation pit projects, a large number of safety accidents will also be caused by the change of the water head of confined water or phreatic water, such as damage situations like piping, bursting, and soil flow, bringing great risks to construction safety.

[0003] Currently, in the existing research on the bursting of foundation pits, less consideration is given to the influence of the permeability of the weak permeable layer and the dynamic change of confined water on the stability of the foundation pit properties. And in the existing model test research, less consideration is given to the alternating distribution of weak and strong permeable layers and the actual rising and falling process of the confined water head, and almost no research on the dewatering and pressure relief process during the excavation of the foundation pit in the confined water-bearing site is involved.

[0004] Therefore, there is an urgent need to develop a model test device and test method for the excavation and dewatering of a foundation pit under the action of dynamic confined water that can monitor the change of the confined aquifer water head, which is used for experimental research on the influence of factors such as the change of the confined water head and whether the diaphragm wall is embedded in the impermeable layer on the excess pore pressure distribution and earth pressure of the weak permeable soil layer. Analyze the bending moment, deformation of the retaining wall and the anti-bursting stability of the foundation pit under different excavation depths and water head conditions. Summarize the deformation of the retaining wall, the bursting conditions and failure mechanisms of the weak permeable layer of cohesive soil in combination with actual projects. Content of the Utility Model

[0005] The purpose of the utility model is to provide a model test device for simulating the excavation of a foundation pit under the action of confined water, including a model box, a water tank, a foundation pit support structure, a confined water head adjustment and monitoring system, and a measurement system.

[0006] The model box is a box with an open upper end, and the four side walls are denoted as side wall I, side wall II, side wall III, and side wall IV.

[0007] The inside of the model box is filled with a sand layer and a clay layer.

[0008] The sand layer is located below the clay layer.

[0009] The sand layer is a confined aquifer.

[0010] Through hole Ⅰ communicating with the pressure-bearing layer and several through holes Ⅱ are formed in the side wall of the model box.

[0011] The through hole Ⅰ is connected to the water tank through a connecting hose Ⅰ.

[0012] The through hole Ⅱ is connected to the confined water head adjustment and monitoring system through a connecting hose Ⅱ.

[0013] A foundation pit support structure is arranged inside the model box.

[0014] The foundation pit support structure includes an underground baffle and a support unit.

[0015] The underground baffle is a plate-like structure, buried in the soil layer inside the model box, arranged parallel to side wall Ⅰ, and dividing the soil body inside the model box into the soil body behind the wall and the soil body in front of the wall.

[0016] In the use state, the underground baffle can move along the height direction of the model box.

[0017] An observation window is arranged on the side wall of the model box at the position where the underground baffle is buried.

[0018] A water stop rubber strip is arranged between the underground baffle and the observation window.

[0019] A number of support positioning holes are formed on the plate surface of the underground baffle.

[0020] The support unit is a rod-like structure, located in the soil body behind the wall, connected at one end through the support positioning hole, and the other end abuts against side wall Ⅰ of the model box.

[0021] The measurement system includes a pore water pressure sensor, an earth pressure cell, a displacement sensor, a stress-strain gauge, a data collector and a digital camera.

[0022] One ends of the pore water pressure sensor, the earth pressure cell and the stress-strain gauge are fixedly pasted on the plate surface of the underground baffle, and the other ends are connected to the data collector.

[0023] The displacement sensor is buried in the soil outside the foundation pit and connected to the data collector.

[0024] Furthermore, the model box is welded by stainless steel bars and stainless steel plates.

[0025] Furthermore, the observation window is a toughened glass observation window, fixed on the side wall of the model box through bolts, and the connection gap between the bolts and the toughened glass is sealed with water stop glue.

[0026] Furthermore, the water tank includes an organic glass base and an organic glass cylinder fixed on the organic glass base.

[0027] The side wall of the plexiglass cylinder is vertically provided with scale lines, and a through hole III is provided at the bottom.

[0028] A connecting hose I is connected between the through hole III and the through hole I.

[0029] Water passing valves are provided on the through hole III and the through hole I.

[0030] Furthermore, a permeable geotextile is provided between the sandy soil layer and the clay layer; permeable geotextiles are provided on the through hole I and the through hole II of the model box.

[0031] Furthermore, the underground baffle is a stainless steel plate.

[0032] The underground baffle is always perpendicular to the observation window in the moving state.

[0033] Furthermore, the observation window is arranged on the contact surface between the underground baffle and the model box.

[0034] The observation window is provided with a groove, and the underground baffle is clamped into the groove.

[0035] U-shaped rubber waterstop strips are installed on both sides of the underground baffle in contact with the observation window, and waterstop glue is applied.

[0036] Furthermore, the support unit includes a nut and a hollow aluminum rod. The two ends of the nut are respectively connected to the threaded hollow aluminum rods, and the other ends of the two aluminum rods are respectively fixed on the support positioning holes of the underground baffle and the side plate of the model box.

[0037] Furthermore, the confined water head adjustment and monitoring system includes an observation board, a piezometer tube and a connecting hose II.

[0038] An observation board is arranged on the outer side wall of the model box; the observation board is provided with a scale bar; a number of piezometer tubes are fixedly installed on the observation board; a red floating ball with a density smaller than that of water is placed in the piezometer tube.

[0039] The two ends of the connecting hose II are respectively communicated with the piezometer tube and the through hole II to form a communicating vessel device.

[0040] The technical effect of the present utility model is beyond doubt. The beneficial effects of the present utility model are as follows:

[0041] 1. The main structure of the model box is enclosed by steel plates, which has excellent sealing performance, effectively preventing water leakage and ensuring the reliability and accuracy of test results. This design can not only avoid the adverse effects of water leakage on test results, but also provide a stable test environment, providing reliable data support for researchers. In addition, in order to facilitate the observation of water level changes and excavation processes during the test, tempered glass windows are specially added to the model box. These windows not only have good transparency, but also excellent water resistance and corrosion resistance, and can withstand water pressure and changes in the test environment, providing researchers with clear and accurate observation perspectives. Through these designs, data collection and observation during the test process become more convenient and reliable, helping to deeply understand test phenomena and improve the scientific nature and credibility of the test.

[0042] 2. The embedding depth, position of the retaining wall structure model, and the water head of the confined aquifer can all be adjusted according to the research needs. Such flexibility enables the experimental device to simulate a variety of different working conditions, thus better understanding and analyzing the behavior and performance of the retaining wall structure under different conditions. By adjusting these parameters, retaining wall projects under different geological conditions can be simulated, providing a more reliable basis for engineering design and construction.

[0043] 3. The device system is reasonably set up, considering various possible operation scenarios and requirements, ensuring the comprehensiveness and comparability of the experiment. The test operation is convenient, adopting a simple and intuitive control interface and operation process, enabling users to easily conduct experimental operations and reducing the possibility of misoperations during the operation process.

[0044] 4. This device can simulate the interaction between pore water pressure, earth pressure, and the support structure of the weak permeable layer under the condition of water head variation in the confined aquifer of the foundation pit, providing an ideal test platform for studying the response laws of water and soil pressure and the deformation laws of the support structure and the foundation pit. By simulating scenarios under different water head variation conditions, the behavior characteristics of the soil around the foundation pit and the support structure under different water pressure actions can be deeply understood, providing important references for engineering design and construction. In addition, the applicability of this device is relatively strong. It can not only be used for studying foundation pit engineering, but also be applied to the research of other underground engineering and groundwater dynamics problems, with broad application prospects and scientific research value. Description of the Drawings

[0045] Figure 1 is a model test device for foundation pit excavation under the action of confined water;

[0046] Figure 2 is a schematic diagram of the model box structure;

[0047] Figure 3 is a schematic diagram of the diaphragm wall support structure;

[0048] Figure 4 Schematic diagram of the support and retaining structure

[0049] In the figure: 1 - model box; 101 - model box frame; 102 - observation window; 103 - main body of the model box; 2 - water tank; 3 - foundation pit support structure; 301 - underground baffle structure; 302 - support unit; 4 - confined water head adjustment and monitoring system; 401 - observation board, 402 - piezometer tube, 403 - connecting hose II; 5 - connecting hose I. Specific implementation mode

[0050] The present utility model will be further described below in conjunction with embodiments, but it should not be understood that the above-mentioned theme scope of the present utility model is limited to the following embodiments. Without departing from the above-mentioned technical idea of the present utility model, various substitutions and changes made according to ordinary technical knowledge and customary means in the art should be included within the protection scope of the present utility model.

[0051] Embodiment 1:

[0052] See Figure 1 、 Figure 2 , a model test device capable of simulating the excavation of a foundation pit under the action of confined water, comprising a model box 1, a water tank 2, a foundation pit support structure 3, a confined water head adjustment and monitoring system 4 and a measurement system.

[0053] The model box 1 is a box with an open upper end, and the four side walls are denoted as side wall I, side wall II, side wall III and side wall IV.

[0054] The inside of the model box 1 is filled with a sand layer and a clay layer.

[0055] The sand layer is located below the clay layer.

[0056] The sand layer is a confined aquifer.

[0057] Through holes I communicating with the confined layer and several through holes II are provided on the side wall of the model box, and a water passing valve is provided on the through hole I.

[0058] The through hole I is connected to the water tank 2 through the connecting hose I 5, and water is injected into the model box 1 through the water tank 2 to form a seepage field of the confined water aquifer.

[0059] The through hole II is connected to the confined water head adjustment and monitoring system 4 through the connecting hose II 403, and the confined water head of the confined aquifer is monitored through the confined water head adjustment and monitoring system 4.

[0060] The foundation pit support structure 3 is arranged inside the model box 1.

[0061] The foundation pit support structure 3 includes an underground baffle 301 and a support unit 302.

[0062] The underground baffle 301 is in a plate-like structure and is buried in the soil layer inside the model box 1, arranged parallel to the side wall I, dividing the soil mass inside the model box 1 into the soil mass behind the wall and the soil mass in front of the wall. Among them, the permeable geotextile arranged between the sand layer and the clay layer is laid in sections without affecting the embedding of the underground baffle;

[0063] The underground baffle 301 can move along the height direction of the model box 1.

[0064] At the position where the underground baffle 301 is buried, an observation window 102 is provided on the side wall of the model box 1 for observing the embedding depth of the underground baffle 301.

[0065] A hole is opened at the position where the model box 1 installs the observation window 102 for installing the observation window 102.

[0066] A water-stop rubber strip is arranged between the underground baffle 301 and the observation window 102 to ensure that there is no water leakage at the contact surface between the underground baffle 301 and the observation window 102 during the movement process.

[0067] See Figure 3 , a number of support positioning holes are opened on the plate surface of the underground baffle 301.

[0068] The support unit 302 is in a rod-like structure, located in the soil mass behind the wall, connected at one end through the support positioning hole, and the other end abuts against the side wall I of the model box 1.

[0069] The confined water head adjustment and monitoring system 4 includes an observation board 401, a piezometer tube 402, and a connecting hose II 403.

[0070] An observation board 401 is arranged on the outer side wall of the model box 1, and a number of piezometer tubes 402 are fixedly installed on the observation board 401. The two ends of the connecting hose II 403 are respectively connected to the piezometer tube 402 and the through hole II to form a communicating vessel device for measuring the water head height of the confined aquifer.

[0071] The measurement system includes a pore water pressure sensor, an earth pressure cell, a displacement sensor, a stress-strain gauge, a data acquisition instrument, and a digital camera.

[0072] One ends of the pore water pressure sensor, the earth pressure cell, and the stress-strain gauge are fixedly pasted on the plate surface of the underground baffle, and the other ends are connected to the data acquisition instrument.

[0073] The displacement sensor is buried in the soil outside the foundation pit and is connected to the data acquisition instrument.

[0074] The digital camera is placed directly in front of the side wall II of the model box.

[0075] Example 2:

[0076] The main structure of this embodiment is the same as that of Embodiment 1. Further, the model box 1 is welded by stainless steel bars and stainless steel plates.

[0077] Embodiment 3:

[0078] The main structure of this embodiment is the same as any one of Embodiments 1 - 2. Further, the observation window 102 is a toughened glass observation window, which is fixed on the side wall of the model box 1 by bolts, and the connection gap between the bolts and the toughened glass is sealed with water-stop glue.

[0079] Embodiment 4:

[0080] The main structure of this embodiment is the same as any one of Embodiments 1 - 3. Further, the water tank 2 includes a plexiglass base 202 and a plexiglass cylinder 201 fixed on the plexiglass base 202.

[0081] Scale lines are vertically arranged on the side wall of the plexiglass cylinder 201, and a through-hole III is provided at the bottom.

[0082] A connecting hose I 5 is connected between the through-hole III and the through-hole I.

[0083] Water flow valves are provided on the through-hole III and the through-hole I.

[0084] Embodiment 5:

[0085] The main structure of this embodiment is the same as any one of Embodiments 1 - 4. Further, a permeable geotextile is provided between the sand layer and the clay layer, and permeable geotextiles are provided on the through-hole I and the through-hole II of the model box 1.

[0086] Embodiment 6:

[0087] The main structure of this embodiment is the same as any one of Embodiments 1 - 5. Further, the underground baffle 301 is a stainless steel plate, and its thickness is obtained by similarity ratio conversion according to the stiffness of the retaining wall simulated in the test.

[0088] The underground baffle 301 always remains perpendicular to the observation window 102 during the movement process.

[0089] Embodiment 7:

[0090] The main structure of this embodiment is the same as any one of Embodiments 1 - 6. Further, the observation window 102 is arranged on the contact surface between the underground baffle 301 and the model box 1.

[0091] The observation window 102 is provided with a groove. When the underground baffle 301 is buried in the soil, the underground baffle 301 is clamped into the groove.

[0092] U-shaped rubber water-stop strips are installed on both sides of the underground baffle 301 in contact with the observation window 102, and water-stop glue is applied.

[0093] Example 8:

[0094] The main structure of this embodiment is the same as any one of Embodiments 1 to 7. Further, referring to Figure 4 , the support unit 302 includes a nut and a hollow aluminum rod. The two ends of the nut are respectively connected to the threaded hollow aluminum rods, and the other ends of the two aluminum rods are respectively fixed on the support positioning holes of the underground baffle 301 and the side plate of the model box.

[0095] The thickness and diameter of the support unit 302 are obtained by similarity ratio conversion based on the support stiffness simulated by the test.

[0096] Example 9:

[0097] The main structure of this embodiment is the same as any one of Embodiments 1 to 8. Further, the confined water head adjustment and monitoring system 4 includes an observation board 401, a piezometer tube 402, and a connecting hose II 403.

[0098] An observation board 401 is arranged on the outer side wall of the model box 1, and the observation board 401 is provided with a scale bar.

[0099] A number of piezometer tubes 402 are fixedly installed on the observation board 401, and red floating balls with a density smaller than that of water are placed in the piezometer tubes 402 to facilitate observing the water head height in the piezometer tubes.

[0100] The two ends of the connecting hose II 403 are respectively communicated with the piezometer tube 402 and the through hole II to form a communicating vessel device for measuring the water head height of the confined aquifer.

[0101] Example 10:

[0102] A test method for a model test device capable of simulating the excavation of a foundation pit under the action of confined water according to any one of Embodiments 1 to 9 includes the following steps:

[0103] 1) Determine the designed heights of the sand layer and the clay layer, the position and depth of the foundation pit excavation, the buried depth of the underground baffle 301, the installation position of the support unit 302, and the designed water head height of the confined aquifer;

[0104] 2) Paste permeable geotextiles at the through hole I and the through hole II of the model box 1 to prevent sand from flowing into the water injection holes and causing blockage;

[0105] 3) Fill the sand layer and the clay layer into the model box 1 in sequence to the designed height, and lay a permeable geotextile between the sand layer and the clay layer;

[0106] 4) Paste stress-strain gauges, earth pressure sensors, and pore water pressure sensors on the underground baffle 301;

[0107] 5) Install the waterstop rubber strip on the underground baffle 301 and bury it to a corresponding depth in the soil layer. Then, press the waterstop putty on both sides where the underground baffle 301 contacts the model box.

[0108] 6) After the soil is fully consolidated, arrange displacement sensors at fixed points outside the foundation pit and record the initial readings of all sensors.

[0109] 7) Inject water into the model box 1 through the water tank 2 to fully saturate the bottom confined sand layer and let it stand for one day.

[0110] 8) Keep the water level in the water tank 2 at a certain height. At the same time, open the water passing valve and observe the water head height in the piezometer tube 402 in real time until the designed water head height is reached.

[0111] 9) Excavate the foundation pit at the designed water head height, excavate in layers and install the support unit 302 at the corresponding fixed points.

[0112] 10) Analyze and sort out the collected data to obtain the interaction between the pore water pressure, earth pressure of the weakly permeable layer and the supporting structure under the condition of water head change.

[0113] Example 11:

[0114] The main structure of this example is the same as any one of Examples 1 - 10. Further, it includes a model box 1, a water tank 2, a foundation pit support structure 3, a confined water head adjustment and monitoring system 4, and a measurement system.

[0115] The model box 1 is a rectangular box with an open top, which consists of a model box frame 101, a tempered glass observation window 102, a model box main body 103, and a water passing valve to form the model box.

[0116] Two tempered glass observation windows are respectively fixed on the front and back sides of the model box. The tempered glass observation window 102 is connected to the model box main body by bolts.

[0117] A water passing valve connecting to the confined layer is installed at the left bottom of the model box for connecting the model box and the water tank.

[0118] The four side walls of this rectangular box are successively side plate Ⅰ, side plate Ⅱ, side plate Ⅲ, and side plate Ⅳ.

[0119] The model box 1 is successively filled with sandy soil, clay, etc.

[0120] The water tank 2 includes a plexiglass cylinder 201, a plexiglass base 202, scale lines, and a water passing valve.

[0121] The plexiglass cylinder 201 is fixed on the plexiglass base 202, scale lines are vertically arranged on the side wall, and a water passing valve is arranged at the bottom.

[0122] The foundation pit support structure 3 includes an underground retaining wall 301 and a support unit 302.

[0123] The underground retaining wall 301 is a plate-like structure.

[0124] The underground retaining wall 301 is movably arranged in the model box 1 through a U-shaped rubber strip and a water-stop rubber, and the water-stop rubber strip ensures that there is no water leakage at the contact surface between the underground retaining wall 301 and the model box 1 during the movement process.

[0125] The underground retaining wall 301 divides the soil mass in the box into the soil mass behind the wall and the soil mass in front of the wall.

[0126] The plate surface of the underground retaining wall 301 is parallel to the side plate I.

[0127] A hole for the high-head water connecting hose II 403 to pass through is provided on the side plate II.

[0128] A hole communicating with the plexiglass cylinder 201 is provided on the side plate III.

[0129] The water inlet end of the connecting hose of the hole on the side plate III is connected to the water head generating device water tank, and the water outlet end is connected to the soil mass behind the wall in the model box.

[0130] A support positioning hole is provided in the middle of the underground retaining wall 301, and the support unit 302 is connected and installed through the positioning hole.

[0131] The middle part of the support unit 302 is a nut, which is respectively connected to the hollow aluminum rods with threads at both ends. During the installation process, the two hollow aluminum rods are respectively screwed outwards, one end is fixed to the retaining wall positioning hole, and one end is fixed to the side plate I of the model box to complete the installation of the support unit 302.

[0132] The confined water head adjustment and monitoring system 4 includes a confined water head monitoring system composed of a PVC observation board 401, a piezometer tube 402, and a connecting hose II 403. The PVC observation board is provided with a scale bar and is installed on one side of the model box.

[0133] The connecting hose II 403 is respectively connected to the hole on the side plate II of the model box and the piezometer tube 402 to form a similar communicating vessel device, and the water head height in the glass tube is the water head height of the confined aquifer.

[0134] The piezometer tube 402 is fixed on the PVC observation board 401, and the real-time water head of the confined aquifer is read through the scale on the observation board.

[0135] The measurement system 5 includes a micro pore water pressure sensor, a micro earth pressure cell, a displacement sensor, a waterproof strain gauge, a multi-channel data acquisition instrument, and a digital camera;

[0136] The micro pore water pressure sensor, micro earth pressure cell, displacement sensor, and waterproof strain gauge are connected to a multi-channel data acquisition instrument through signal transmission lines;

[0137] The digital camera is placed directly in front of the model box.

[0138] Furthermore, the model box frame 101 and the model box body 103 are welded by 8-mm-thick stainless steel bars and stainless steel plates, and the toughened glass observation window 102 is installed on the side plate II and the fourth side plate IV of the model box body 103 by bolt connection.

[0139] Furthermore, the underground baffle 301 is a stainless steel plate, and its thickness is obtained by similarity ratio conversion based on the stiffness of the retaining wall simulated in the test. The underground baffle 301 always remains perpendicular to the toughened glass observation window 102 during the movement process.

[0140] Furthermore, the middle part of the support unit 302 is a nut, which is respectively connected to the hollow aluminum rods with threads at both ends. During the installation process, the two hollow aluminum rods are respectively screwed outwards, one end is fixed to the retaining wall positioning hole, and the other end is fixed to the side plate I of the model box to realize the installation of the support unit 302; the thickness and diameter of the support unit 302 are obtained by similarity ratio conversion based on the support stiffness simulated in the test.

[0141] Furthermore, the overlying impervious layer is clay with relatively low permeability.

[0142] Furthermore, the signal transmission lines of the micro pore water pressure sensor, micro earth pressure cell, displacement sensor, and waterproof strain gauge are all connected to the same signal acquisition instrument to ensure synchronous acquisition of all signals during the test.

[0143] Furthermore, red floating balls with a density smaller than that of water are placed in the piezometer tubes to facilitate the observation of the water head height in the piezometer tubes.

[0144] Example 12:

[0145] The main structure of this example is the same as any one of Examples 1 to 11. Furthermore, the device includes a model box, a water tank, a foundation pit support structure, a confined water head adjustment and monitoring system, and a measurement system. During the test, water is injected through the water inlet hole at the bottom of the model box connected to an external water tank to form a seepage field simulating a confined aquifer. By using the water injection function of the water tank device and the confined water head monitoring system, the water head change in the confined sand layer in the model box can be accurately regulated and monitored. The measurement system can record data in real time, so as to obtain the response laws of the bending moment, deformation of the retaining wall, and pore water pressure in the weakly permeable layer under different excavation depths and water head conditions. These data can be used to analyze the deformation of the retaining wall, the sudden gushing conditions and failure mechanisms of the weakly permeable layer in cohesive soil in actual projects.

[0146] This device can truly simulate the rising and falling process of the confined water head, and accurately monitor the changes in the water and soil pressure of the weak permeable layer and the displacement changes of the soil outside the foundation pit during the excavation process of the foundation pit. This test has the advantage of low cost and has a wide application prospect in actual engineering. Through this test method, the influence of foundation pit excavation on the surrounding soil and structure can be deeply understood, the design scheme can be optimized, and the construction safety and engineering quality can be improved.

[0147] Example 13:

[0148] The main structure of this example is the same as any one of Examples 1 to 12. Further, during operation, the external water tank is connected to the water inlet hole at the bottom of the model box to inject water, forming a seepage field of the confined water aquifer. Through the water injection of the water tank device and the confined water head monitoring system, the water head of the confined sand layer in the model box changes quantitatively. The measurement system measures and records data in real time: the earth pressure cell measures the earth pressure along the depth of the diaphragm wall; the pore water pressure sensor measures the pore water pressure of the weak permeable layer at different depths; the resistance stress and strain gauge measures the stress and strain of the diaphragm wall steel plate to obtain the bending moment value; the displacement sensor measures the displacement generated on the ground surface during the water head change process.

[0149] Example 14:

[0150] The main structure of this example is the same as any one of Examples 1 to 13. Further, the present utility model proposes a model test device and its test method for simulating the excavation of a foundation pit under the action of confined water, which can simulate the excavation of a foundation pit under the action of confined water. This device solves the problem of quantitative monitoring during the rising and falling process of the confined water head in the test, can simulate the influence of the change of the confined water head on the interaction between groundwater and the foundation pit soil, and measures the water and soil pressure distribution and the deformation law of the soil and structure of the foundation pit under the action of confined water. This provides reliable test data support for studying the engineering groundwater problems caused by the rising and falling of the confined water head and provides a basis for future theoretical analysis.

[0151] The model test device includes a water pressure control system that can simulate the change of the groundwater level and a high-precision sensor network for real-time monitoring of the water head change, earth pressure and deformation conditions. By precisely controlling and adjusting the water pressure, researchers can reproduce the excavation scenarios of the foundation pit under different working conditions and observe and record the responses of the foundation pit under different water pressure conditions. The data acquisition system in the device can synchronously record multiple parameters and provide comprehensive experimental data.

[0152] The test method includes a variety of operation steps, from the preparation before the test, equipment calibration to the dynamic monitoring and data acquisition during the test, and finally to the data analysis and summary after the test. Before the test, the researchers need to set the simulation parameters according to the actual working conditions to ensure that the test device can accurately reproduce the on-site environment. During the test, the water pressure control system automatically adjusts the head change according to the preset program, and the sensor network captures the stress and deformation of the foundation pit soil mass and structure in real time.

[0153] Through this device and method, the researchers can not only better understand the influence of the confined water head change on the foundation pit excavation, but also provide guiding suggestions for the actual project, which helps to improve the safety and reliability of the foundation pit excavation. At the same time, these test results can also provide verification data for relevant numerical simulations and theoretical analyses, promoting the research progress in the field of groundwater and foundation pit engineering.

Claims

1. A model test device capable of simulating the excavation of a foundation pit under the action of confined water, characterized in that: It includes a model box (1), a water tank (2), a foundation pit support structure (3), a confined water head regulation and monitoring system (4), and a measurement system; The model box (1) is a box with an open upper end, and its four side walls are denoted as side wall I, side wall II, side wall III, and side wall IV; The interior of the model box (1) is filled with a sandy soil layer and a clay layer; The sandy soil layer is located below the clay layer; The sandy soil layer is a confined aquifer; Through holes I communicating with the confined layer and several through holes II are provided on the side wall of the model box (1); The through hole I is connected to the water tank (2) through a connecting hose I (5); The through hole II is connected to the confined water head regulation and monitoring system (4) through a connecting hose II (403); A foundation pit support structure (3) is arranged inside the model box (1); The foundation pit support structure (3) includes an underground baffle (301) and a support unit (302); The underground baffle (301) is a plate-like structure, buried in the soil layer inside the model box (1), arranged parallel to side wall I, and divides the soil inside the model box (1) into soil behind the wall and soil in front of the wall; In the use state, the underground baffle (301) can move along the height direction of the model box (1); An observation window (102) is provided on the side wall of the model box (1) at the position where the underground baffle (301) is buried; A water stop rubber strip is arranged between the underground baffle (301) and the observation window (102); A number of support positioning holes are provided on the plate surface of the underground baffle (301); The support unit (302) is a rod-like structure, located in the soil behind the wall, connected at one end through the support positioning holes, and the other end abuts against side wall I of the model box (1); The measurement system includes a pore water pressure sensor, an earth pressure cell, a displacement sensor, a stress and strain gauge, a data acquisition instrument, and a digital camera; One end of the pore water pressure sensor, the earth pressure cell, and the stress and strain gauge is fixedly pasted on the plate surface of the underground baffle (301), and the other end is connected to the data acquisition instrument; The displacement sensor is buried in the soil outside the foundation pit and is connected to the data acquisition instrument.

2. The model test device for simulating the excavation of foundation pits under the action of confined water according to claim 1, characterized in that: The model box (1) is welded by stainless steel bars and stainless steel plates; 3. A model test device capable of simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The observation window is a toughened glass observation window (102), fixed on the side wall of the model box (1) through bolts, and the connection gap between the bolts and the toughened glass is sealed with water stop glue; 4. A model test device capable of simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The water tank (2) includes a plexiglass base (202) and a plexiglass cylinder (201) fixed on the plexiglass base (202); Scale lines are vertically arranged on the side wall of the plexiglass cylinder (201), and a through hole III is provided at the bottom; A connecting hose I (5) is connected between the through hole III and the through hole I; Water passing valves are provided on the through hole III and the through hole I; 5. A model test device for simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: A permeable geotextile is provided between the sandy soil layer and the clay layer; permeable geotextiles are provided on the through hole I and the through hole II of the model box (1); 6. A model test device for simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The underground baffle (301) is made of stainless steel plate; The underground baffle (301) always remains perpendicular to the observation window (102) in the moving state; 7. A model test device for simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The observation window (102) is arranged on the contact surface between the underground baffle (301) and the model box (1); The observation window (102) is provided with a groove, and the underground baffle (301) is snapped into the groove; U-shaped rubber water stop strips are installed on both sides of the underground baffle (301) in contact with the observation window (102), and water stop glue is applied.

8. A model test device for simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The support unit (302) includes nuts and hollow aluminum rods. The two ends of the nut are respectively connected to the threaded hollow aluminum rods, and the other ends of the two aluminum rods are respectively fixed on the support positioning holes of the underground baffle (301) and the side plate of the model box.

9. A model test device for simulating the excavation of a foundation pit under the action of confined water according to claim 1, characterized in that: The confined water head adjustment and monitoring system (4) includes an observation board (401), a piezometer tube (402) and a connecting hose II (403); An observation board (401) is arranged on the outer side wall of the model box (1); the observation board (401) is provided with a scale bar; a number of piezometer tubes (402) are fixedly installed on the observation board (401); red suspension balls with a density smaller than that of water are placed in the piezometer tubes (402); The two ends of the connecting hose II (403) are respectively communicated with the piezometer tube (402) and the through hole II to form a communicating vessel device.

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