A simulation method for the vertical leakage and failure process of water-sand in foundation pits supported by ground-connected walls

Abstract

The present invention discloses a simulation method for the vertical leakage and damage process of water and sand in a ground-connected wall supporting foundation pit, comprising the following steps: embedding a defective card plate into a transparent outlet pipe, loading sand samples in layers in a transparent experimental box and compacting them in layers, installing a piezometer, and calculating the critical head difference of each layer of sand sample after the sand sample is saturated and consolidated; starting a simulation experiment, obtaining experimental data of the piezometer and the water and sand leakage quality, and determining the leakage and damage state of each layer of sand sample; calculating the additional unbearable head difference and the measured leakage and damage thickness of the critical layer sand sample, and then obtaining the time-varying data of the total leakage height of the sand layer during the simulation process; and using a visualization tool to establish a time-varying graph of pore water pressure, water and sand leakage quality, and the total leakage height of the sand layer. The simulation method established by the present invention can realize the simulation and data visualization of the leakage process, is helpful to explore the law and time of vertical leakage and damage of water and sand, can reflect the complexity of actual leakage, and is conducive to the development of research and teaching experiments.

Description

Technical Field

[0001] The invention relates to a method for simulating a water-sand vertical leakage failure process of a ground-connected wall supporting foundation pit, and belongs to the technical field of geotechnical testing. Background Art

[0002] Diaphragm walls are a commonly used retaining structure in foundation pit construction, combining soil retaining and water-stopping functions. Because they form a continuous wall, diaphragm walls effectively resist groundwater and soil erosion. Leakage damage caused by improper groundwater treatment is one of the most common accidents in diaphragm wall construction. Leakage from the water-stop curtains in deep pits, piping, and sudden inrush from the pit bottom are the main manifestations of this damage. Especially in areas with water-rich sand layers, foundation pit construction may involve defects in the retaining structure. When the openings of these defects are too large, they can easily lead to water and sand leakage. Water and sand mixtures can flow into the pit through these defects, potentially causing road collapse and traffic disruptions. According to statistics, in my country's water-rich sand layers, due to complex hydrogeological conditions such as high groundwater levels, thick sand layers, and poor stability, foundation pit leakage is common. By studying the development of sand layer leakage, soil flow patterns, and the impact range, we can more accurately assess disaster risks and provide a scientific basis for early warning and prevention of engineering disasters. Indoor experiments are an effective and feasible way to carry out the above research.

[0003] Chinese invention patent application CN107884325A discloses a test device and test method for simulating the development process of seepage damage in a pile-supported foundation pit. This technical solution can effectively simulate the development and evolution of soil particle force chains during the development process of seepage deformation in a pile-supported foundation pit, and has the characteristics of a simple model, easy assembly and disassembly, and strong feasibility. However, the device can only provide image analysis results for the soil seepage deformation damage process, and cannot automatically and continuously measure data and time series graphs to analyze the soil seepage deformation characteristics. In addition, in the absence of a constant pressure system, it cannot guarantee the impact of changes in inlet water pressure on the experiment. Although the patent application provides a seepage damage test method, it is only applicable to the pile support mode, not the ground-connected wall support mode, and even more so, it cannot be used to simulate vertical water-sand leakage damage. At present, the simulation of vertical water-sand leakage damage in a ground-connected wall support foundation pit still has the problem of a simple experimental model, which makes it difficult to reflect the complexity of real projects and difficult to meet the test requirements of simulating leakage gaps of different sizes and shapes, which is not conducive to the development of research-based experiments and teaching-based experiments. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a method for simulating the vertical leakage and damage process of water and sand in a ground-connected wall support foundation pit, and realize the simulation of the vertical leakage and damage of water and sand in a ground-connected wall support foundation pit under different defect sizes, soil gradations, and water pressure levels through an experimental device; this simulation method can realize real-time discrimination of the damage mode of the whole stage of vertical leakage development, and calculate the corresponding damage interval length, and realize digital simulation of the vertical leakage damage process, which not only helps researchers to further explore the damage law and damage time of vertical leakage of water and sand, but also helps students understand the vertical leakage and damage process of water and sand in a ground-connected wall support foundation pit through model experiments.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for simulating the vertical water-sand leakage failure process of a foundation pit supported by a ground-connected wall, comprising the following steps:

[0007] Step 1: Insert the defective card into the transparent outlet pipe installed outside the transparent test box, and close the outlet valve downstream of the transparent outlet pipe; load the sand samples into the transparent test box in layers and compact them layer by layer. While loading the samples, piezometers are placed in the sand layer in front of the transparent outlet pipe and at the boundary of the sand layer above the transparent outlet pipe. The particle specific gravity and porosity ratio of each layer of sand sample are obtained based on geotechnical tests; starting from the height of the center of the defective card, the sand layers are marked from bottom to top as i = 1, 2, 3, ..., n layers;

[0008] Step 2: Seal the transparent experimental box and fill it with water. After the sand sample is saturated and consolidated, measure the thickness of the i-th layer of sand sample.

[0009] Step 3: According to the particle density and porosity of the i-th layer of sand sample, its critical hydraulic gradient is obtained. According to the thickness and critical hydraulic gradient of the i-th layer of sand sample, its critical head difference is obtained. ;

[0010] Step 4: Open the outlet valve downstream of the transparent outlet pipe to maintain the water level in the transparent experimental box unchanged, and obtain the experimental data of the piezometer at different times in real time. The water and sand collection device collects the water and sand discharged from the transparent outlet pipe respectively, and measures the leakage quality of water and sand at different times in real time;

[0011] Step 5:

[0012] 5.1 Calculation of the total leakage damage height of the sand layer at any time :

[0013] According to the difference between the piezometer data at the top and bottom of the i-th layer of sand sample at any time, the measured water head difference of the i-th layer of sand sample is obtained. , according to the measured head difference Difference from critical head The leakage damage state of the i-th layer of sand sample is determined by the relationship between the size of the two layers. The bottom layer of sand sample without leakage damage is recorded as the j-th layer of sand sample, and the j-1-th layer of sand sample is measured to bear the water head difference. Subtract its critical head difference , get the extra head difference of the j-th layer sand sample Then, according to Darcy's law, the actual leakage damage thickness L of the jth layer of sand sample is calculated. rj , and the total leakage damage height of the sand layer at the corresponding moment is obtained , j = 1, 2, 3, ..., n;

[0014] 5.2 Repeat the process of 5.1 to obtain the total leakage damage height of the sand layer at different times during the whole simulation test. ;

[0015] Step 6: The leakage mass of water and sand collected by the water-sand collection device at different times and the total leakage height of the sand layer at different times obtained in step 4 are calculated. Import the data into the visualization tool to create a time-varying graph of pore water pressure, water-sand leakage quality, and total leakage height of the sand layer to complete the simulation of the leakage process and data visualization.

[0016] Furthermore, the water-sand leakage simulation test device includes a pressurized water inlet device, a water-sand collecting device, and a transparent experimental box;

[0017] A vertical sieve plate is provided in the transparent experimental box, which divides the internal space of the transparent experimental box into a water flow buffer area and a sand sample filling area, and the pressurized water inlet device is connected to the water flow buffer area;

[0018] A transparent water outlet pipe is provided outside the transparent experimental box, an embedded defect card plate is provided upstream of the transparent water outlet pipe, a vertically arranged rectangular hole is provided in the center of the defect card plate, and a water outlet valve is further provided downstream of the transparent water outlet pipe. The water inlet end of the transparent water outlet pipe is connected to the sand sample filling area, and the water outlet end is connected to the water-sand collection device;

[0019] The pressurized water inlet device includes a water storage tank, a water pump, a water inlet flow meter, and a pressure gauge; the water storage tank is connected to the water pump and the water flow buffer zone provided in the transparent experimental box in sequence through an inlet pipe; the water inlet flow meter and the pressure gauge are provided on the inlet pipe between the water pump and the transparent experimental box;

[0020] The water-sand collecting device comprises a water-sand collecting box, a broken-line water inlet pipe, a porous sand isolation plate, a weighing sensor, a transparent connecting pipe, a water outlet flow meter, and a wastewater collecting box;

[0021] The water and sand collection box is an open transparent box, a porous sand isolation plate is provided in the middle of the water and sand collection box, and the water and sand collection box is provided on a weighing sensor; the water inlet end of the zigzag water inlet pipe is connected to the water outlet end of a transparent water outlet pipe provided on the transparent experimental box, and the water outlet end of the zigzag water inlet pipe is horizontally arranged at the bottom of the water and sand collection box; a transparent connecting pipe is provided on the side wall of the water and sand collection box to communicate with the wastewater collection box, the transparent connecting pipe is located above the porous sand isolation plate, and a water outlet flow meter is provided on the transparent connecting pipe. According to the experimental data of the water outlet flow meter and the weighing sensor, the leakage mass of water and sand is calculated respectively.

[0022] Furthermore, in step 3, the critical head difference of the i-th layer of sand sample is According to formula (3.1), we can get:

[0023]

[0024] Where, is the critical head difference of the i-th layer of sand sample; is the critical hydraulic slope of the i-th layer of sand sample; is the thickness of the i-th layer of sand sample;

[0025] in, According to formula (3.2), we can get:

[0026]

[0027] Where G si is the specific gravity of sand particles in the i-th layer of sand sample; e i is the porosity ratio of the i-th layer of sand sample.

[0028] Furthermore, in step 5, the water head difference is measured for the i-th layer of sand sample. Calculate according to formula (5.1):

[0029]

[0030] Where, The measured water head difference for the sand sample of layer i; is the piezometer reading at the bottom boundary of the i-th layer of sand sample; It is the piezometer reading at the bottom boundary of the i+1th layer of sand sample.

[0031] Furthermore, in step 5, the leakage damage state of the i-th layer of sand sample is determined by the following method:

[0032] (1) When When , the i-th layer of sand sample is in a stable state and no seepage damage occurs;

[0033] (2) When When , the i-th layer of sand sample is in an unstable state and seepage damage occurs.

[0034] Furthermore, in step 5, the i-th layer does not bear the additional head difference Calculate according to formula (5.2):

[0035]

[0036] Where, The i-th layer of sand sample does not bear the additional head difference, The measured water head difference for the j-1 layer sand sample is is the critical head difference of the j-1th layer of sand sample.

[0037] Furthermore, in step 5, the total leakage damage height of the sand layer Calculate according to formula (5.3):

[0038]

[0039] Where, is the total leakage damage height of the sand layer; is the thickness of the i-th layer of sand sample; L rj is the actual leakage damage thickness of the jth layer of sand sample;

[0040] Among them, L ri According to formula (5.4) and (5.5), we can obtain:

[0041]

[0042]

[0043] Where, The jth layer of sand sample does not bear the additional head difference, is the critical hydraulic slope of the jth layer of sand sample, The measured water head difference for the j-th layer of sand sample is: is the measured hydraulic gradient of the jth layer of sand sample, L rj is the actual leakage damage thickness of the jth sand layer; is the thickness of the jth layer of sand sample.

[0044] Furthermore, the water inlet pressure of the pressurized water inlet device is 0-15 kPa, preferably 5-10 kPa.

[0045] Furthermore, the transparent experimental box and the transparent water outlet pipe are both made of transparent organic glass.

[0046] Furthermore, the sand sample filling area occupies 55%-60% of the volume of the transparent experimental box.

[0047] Furthermore, the distance between the transparent water outlet pipe and the bottom of the transparent experimental box is 1 / 8-3 / 8 of the clear height of the transparent experimental box.

[0048] The advantages and positive effects of the present invention are:

[0049] A defect plate is mounted on a transparent outlet pipe on the side of the transparent experimental box. The rectangular notch in the plate serves as a water and sand leakage opening, corresponding to the engineering limits for water and sand loss from defects in foundation pit diaphragm walls and cracks in shield tunnel sidewall segments. The rectangular notch can also be adjusted based on the size of cracks in actual projects. The system automatically monitors and displays piezometer readings, providing real-time readings of the hydraulic head difference between sand layers. The system can determine the seepage damage state of the sand layer in front of the leaking defect without measuring the permeability of sand samples, and can accurately calculate the seepage damage height of the sand layer in front of the leaking defect. This provides valuable insights into the evolution mechanism and prevention measures for vertical water and sand leakage in foundation pits supported by diaphragm walls, as well as experimental simulation teaching.

[0050] The present invention adopts an automated test device that can simulate the vertical leakage of water and sand in the ground-connected wall supporting foundation pit under conditions of different defect sizes, soil gradations, and water pressure levels. Through digital visualization simulation, the damage mode of the entire development process of the vertical leakage of water and sand in the ground-connected wall supporting foundation pit can be judged in real time, which will help researchers further explore the damage laws and damage time of the vertical leakage of water and sand, and also help students understand the damage process of the vertical leakage of water and sand in the ground-connected wall supporting foundation pit, further promoting the close integration of teaching and scientific research, and providing an innovative solution for the foundation pit seepage damage simulation experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the simulation method of the present invention;

[0052] Figure 2 It is the overall test system diagram of the present invention;

[0053] Figure 3 The main experimental box of the present invention;

[0054] Figure 4 Diagram of the pressurized water inlet system of the present invention;

[0055] Figure 5 This is a diagram of the water-sand collection system of the present invention;

[0056] Figure 6 Schematic diagram of a defective card board of the present invention.

[0057] In the figure: a water storage tank (1), a water inlet valve (2), a water pump (3), a water inlet flow meter (4), a pressure gauge (5), an organic glass experimental box (6), an organic glass cover (7), bolts (8), a screen plate (9), a defective card plate (10), a piezometer (11), a bottom frame (12), a pulley (13), an organic glass outlet pipe (14), an outlet valve (15), a broken line organic glass inlet pipe (16), a porous sand isolation plate (17), a weighing sensor (18), a water sand collection box (19), an organic glass connecting pipe (20), an outlet flow meter (21), and a wastewater collection box (22). DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0059] like Figures 1 to 6 As shown, the present invention uses a water-sand leakage simulation test device to simulate the vertical leakage and damage process of water and sand in the ground-connected wall support foundation pit. The water-sand leakage simulation test device includes: a pressurized water inlet device, a water-sand collection device, and a transparent test box;

[0060] A vertical sieve plate 9 is provided in the transparent experimental box, which divides the internal space of the transparent experimental box into a water flow buffer area on the left and a sand sample filling area on the right. The pressurized water inlet device is connected to the water flow buffer area;

[0061] A transparent water outlet pipe is provided outside the transparent experimental box. An embedded defect card plate is provided upstream of the transparent water outlet pipe. A vertically arranged rectangular hole is provided in the center of the defect card plate. A water outlet valve is also provided downstream of the transparent water outlet pipe. The water inlet end of the transparent water outlet pipe is connected to the sand sample filling area, and the water outlet end is connected to the water-sand collection device.

[0062] The transparent experimental box is mainly made of transparent organic glass, including an organic glass experimental box body 6, an organic glass cover 7, bolts 8, a sieve plate 9, a defect card plate 10, a bottom frame 12, a pulley 13, an organic glass water outlet pipe 14, and an outlet valve 15; the left side of the sieve plate 9 is a water flow buffer zone, and the right side of the sieve plate 9 is a sand sample filling area; the organic glass experimental box body 6 is made of 5 pieces of organic glass, distributed at the bottom and four sides of the organic glass experimental box body 6, the top of the organic glass experimental box body 6 is open, the organic glass cover 7 can be covered on the top of the organic glass experimental box body 6, the organic glass cover 7 and the organic glass experimental box body 6 are connected with bolts 8, and a layer of rubber water stop is placed between the organic glass cover 7 and the organic glass experimental box body 6 to enhance the sealing of the transparent experimental box; the transparent water outlet pipe passes through the right side wall of the organic glass experimental box body 6 and is connected to the sand sample filling area, and the transparent outlet The water pipe adopts an organic glass outlet pipe 14, which is located in the middle of the right side wall of the organic glass experimental box 6 in the horizontal direction, and the distance between the transparent water outlet pipe and the bottom of the transparent experimental box is 1 / 8-3 / 8 of the clear height of the transparent experimental box; the transparent experimental box is placed as a whole on the bottom frame 12, and a pulley 13 is provided at the four corners of the bottom frame 12 to realize the movement and fixation of the transparent experimental box; the defect card plate 10 is a circular glass plate with a rectangular hole, and the defect card plate 10 can be embedded in the organic glass outlet pipe 14, and the defect card plate 10 is located before the water outlet valve 15; when the experimental sand sample is filled into the transparent experimental box, a pore pressure gauge is arranged in the sand layer in front of the organic glass outlet pipe 14 and at each sand layer boundary position above the organic glass outlet pipe 14 to measure the pore water pressure change during the water-sand leakage simulation experiment, and the number of pore pressure gauges is basically consistent with the number of filled sand layers.

[0063] The pressurized water inlet device includes a water tank 1, a water inlet valve 2, a water pump 3, a water inlet flowmeter 4, and a pressure gauge 5. The water tank 1 is connected to the water pump 3 and the water flow buffer zone set in the transparent experimental box in sequence through the water inlet pipe. The water inlet valve 2 is arranged on the water inlet pipe between the water tank 1 and the water pump 3. The water inlet flowmeter 4 and the pressure gauge 5 are arranged on the water inlet pipe between the water pump 3 and the transparent experimental box; the water tank 1 is supplied with water by an external water source, and the water tank 1 provides the transparent experimental box with a stable water source required for the experiment. The water inlet flowmeter 4 measures the water inlet flow of the transparent experimental box, and the pressure gauge 5 measures the water inlet pressure of the transparent experimental box. The water pump 3 adjusts the water inlet pressure to ensure that the water inlet pressure of the transparent experimental box is constant.

[0064] The water and sand collection device includes a broken line organic glass water inlet pipe 16, a porous sand isolation plate 17, a weighing sensor 18, a water and sand collection box 19, an organic glass connecting pipe 20, a water flow meter 21, and a wastewater collection box 22; the water and sand collection box 19 is an open organic glass box body, which is arranged on the weighing sensor 18, and the porous sand isolation plate 17 is in the middle of the water and sand collection box 19; the water inlet end of the broken line organic glass water inlet pipe 16 is connected to the water outlet end of the organic glass water outlet pipe 14, and the water outlet end of the broken line organic glass water inlet pipe 16 extends to the bottom of the water and sand collection box 19, and the organic glass water outlet pipe 14 and the broken line organic glass water inlet pipe 1 6 is spliced ​​into a water and sand loss pipeline, and the ends of the broken-line organic glass water inlet pipe 16 are all arranged horizontally; an organic glass connecting pipe 20 is provided on the side wall of the water and sand collection box 19, which is higher than the porous sand isolation plate 17 but lower than the open top of the water and sand collection box 19. The end of the organic glass connecting pipe 20 is connected to the wastewater collection box 22. The organic glass connecting pipe 20 is provided with a water outlet flow meter 21 to obtain the mass of the leaked water during the water and sand leakage experiment; the weighing sensor 18 measures the mass of the water and sand collection box 19 and the water and sand therein in real time. According to the difference in the specific gravity of water and sand, the mass of the leaked sand can be converted. The aperture of the organic glass connecting pipe 20 is large enough to keep the water level in the water and sand collection box 19 constant; before the experiment, the water and sand collection box 19 must be filled with water, and the water level is flush with the pipe mouth of the organic glass connecting pipe 20.

[0065] The data acquisition device includes a pore pressure acquisition instrument and a pore pressure gauge 11. All pore pressure gauges 11 are connected to the pore pressure acquisition instrument. The pore pressure acquisition instrument, the weighing sensor 18, and the water inlet flow meter 4 are connected to the computer via a data line. The computer (24) can automatically obtain the amount of water and sand leakage and the pore water pressure reading.

[0066] Now Figure 1 As shown, taking the visualization model test of soil movement caused by water leakage and sand leakage in a foundation pit project with rectangular defects in the retaining structure as an example, the specific implementation method of the experimental device and the judgment method for simulating water leakage and sand leakage disasters in underground projects provided by the present invention is explained, and the steps are as follows.

[0067] Step 1: Assemble the water-sand leakage simulation test device, insert the defective card into the transparent outlet pipe, and close the outlet valve downstream of the transparent outlet pipe; load the sand samples into the transparent test box in layers and compact them layer by layer. At the same time, piezometers are placed in the sand layer in front of the transparent outlet pipe and at the boundary of the sand layer above the transparent outlet pipe. The particle density and porosity ratio of each sand layer are obtained based on geotechnical tests; starting from the height of the center of the defective card, the sand layers are marked from bottom to top as layer i = 1, 2, 3, ..., n;

[0068] Before loading the sample, correctly connect all parts of the water-sand leakage simulation test device, confirm that there is no leakage in any part of the water supply path, and ensure that the air inside the water inlet flow meter 4 and the water outlet flow meter 21 has been exhausted; embed the defective card plate 10 in the organic glass outlet pipe 14; divide the sand sample into 5 layers in the sand sample filling area and evenly load and tamp it. During the loading process, install a piezometer at the boundary of the sand layer, and determine the sand particle specific gravity G of each sand layer based on the geotechnical test. si and porosity ratio e i , and measure the thickness of each sand layer L i When installing the piezometer 11 , a 200-mesh screen is pasted and wrapped around the probe of the piezometer 11 to prevent fine sand from flowing into the piezometer 11 and causing damage to the piezometer 11 .

[0069] Step 2: Cover and seal the transparent experimental box, fill it with water through the pressurized water inlet device, and measure the thickness of the i-th layer of sand sample after the sand sample is saturated and consolidated;

[0070] After the sand sample filling area is filled with sand samples, cover it with the organic glass cover 7, open the water inlet valve 2, pump water from the water tank 1 through the water pump 3 and inject low-flow water into the water buffer zone of the transparent experimental box. The water slowly flows into the sand sample filling area through the vertical screen plate 9. When the water submerges the sand sample, stop injecting water. Let it stand for 8 hours to allow the water and sand in the sand sample filling area to be fully saturated and consolidated. Use a ruler to measure the thickness of each layer of sand sample outside the organic glass experimental box 6, and take the average of multiple measurements.

[0071] Step 3: According to the particle density and porosity of the i-th layer of sand sample, its critical hydraulic gradient is obtained. According to the thickness and critical hydraulic gradient of the i-th layer of sand sample, its critical head difference is obtained. ;

[0072] According to the critical hydraulic slope i of each sand layer cri Calculate its critical head difference Δh cri , the critical head difference of each layer of sand sample is obtained according to formula (3.1):

[0073]

[0074] Where, is the critical head difference of the i-th layer of sand sample; is the critical hydraulic slope of the i-th layer of sand sample; is the thickness of the i-th layer of sand sample;

[0075] in, According to formula (3.2), we can get:

[0076]

[0077] Where G si is the specific gravity of sand particles in the i-th layer of sand sample; e iis the porosity ratio of the i-th layer of sand sample.

[0078] Step 4: After the sand sample is saturated and consolidated, the outlet valve downstream of the transparent outlet pipe is opened to maintain the water level in the transparent experimental box unchanged, simulating the vertical leakage and damage process of water and sand in the foundation pit of the ground-connected wall support. The water and sand in the transparent experimental box flow into the water and sand collection device through the transparent outlet pipe and the defective card embedded therein. The pore pressure collector obtains the experimental data of the pore pressure gauge at different times in real time. The water and sand collection device collects the water and sand discharged from the transparent outlet pipe respectively, and measures the leakage quality of water and sand at different times in real time.

[0079] Step 5:

[0080] 5.1 Calculation of the total leakage damage height of the sand layer at any time :

[0081] According to the difference between the piezometer data at the top and bottom of the i-th layer of sand sample at any time, the measured water head difference of the i-th layer of sand sample is obtained. , according to the measured head difference Difference from critical head The leakage damage state of the i-th layer of sand sample is determined by the relationship between the size of the two layers. The bottom layer of sand sample without leakage damage is recorded as the j-th layer of sand sample, and the j-1-th layer of sand sample is measured to bear the water head difference. Subtract the critical head difference of the j-1th layer of sand sample , get the extra head difference of the j-th layer sand sample Then, according to Darcy's law, the actual leakage damage thickness L of the jth layer of sand sample is calculated. rj , and the total leakage damage height of the sand layer at the corresponding moment is obtained , j = 1, 2, 3, ..., n;

[0082] 5.2 Repeat the process of 5.1 to obtain the total leakage damage height of the sand layer at different times during the whole simulation test. ;

[0083] Open the water inlet valve 2, the water pump 3, and the water outlet valve 15, and the seepage test begins. During the seepage destruction stage, the dominant leakage path in the area in front of the defect is vertical, and the water head is lowest at the defect. It can be considered that the direction of the seepage force in this area is vertically pointing to the defect. Starting from the sand layer closest to the defect, read the piezometer readings 11 at both ends of the sand layer in the upward and downward directions layer by layer. i and h i+1 , the measured water head difference ΔH of the i-th layer of sand sample i Calculate according to formula (5.1):

[0084]

[0085] Where, The measured water head difference for the sand sample of layer i; is the piezometer reading at the bottom boundary of the i-th layer of sand sample; It is the piezometer reading at the bottom boundary of the i+1th layer of sand sample.

[0086] Comparison of critical water head difference Δh in sand layer cri The measured water head difference ΔH between the sand layer and the i , the leakage damage state of the i-th layer of sand sample is determined according to the following two situations:

[0087] (1) When When the sand layer is measured to bear the head difference ΔH i Does not exceed the critical head difference Δh cri , the sand layer is in a stable state and will not be damaged by seepage;

[0088] (2) When , then the measured water head difference ΔH of the sand layer is i Does not exceed the critical head difference Δh cri At this time, the sand layer is in an unstable state, and seepage damage occurs as the seepage force gushes out from the defect mouth.

[0089] When ΔH appears for the first time from the leakage defect i ≤Δh cri When the sand layer is unstable, the bottom sand sample without leakage damage is recorded as the jth sand sample. This sand layer also bears the head difference of the adjacent unstable sand layer. Difference from critical head

[0090] The difference is defined as the additional unaccounted head difference , the jth layer of sand sample does not bear the additional head difference Calculate according to formula (5.2):

[0091]

[0092] Where, The i-th layer of sand sample does not bear the additional head difference, The measured water head difference for the j-1 layer sand sample is is the critical head difference of the j-1th layer of sand sample.

[0093] According to the principle of water flow continuity and Darcy's law, the water head difference is borne by the sand layer. Calculate the average hydraulic gradient i of the sand layer a , and combined with the additional unburdened head difference of the adjacent unstable sand layer Determine the actual leakage damage thickness L of the jth layer of sand sample rj , L rj According to formula (5.4) and (5.5), we can obtain:

[0094]

[0095]

[0096] Where, The jth layer of sand sample does not bear the additional head difference, is the critical hydraulic slope of the jth layer of sand sample, The measured water head difference for the j-th layer of sand sample is: is the measured hydraulic gradient of the jth layer of sand sample, L rj is the actual leakage damage thickness of the jth layer of sand sample; is the thickness of the jth layer of sand sample;

[0097] Therefore, the total leakage damage height of the sand layer is Calculate according to formula (5.3):

[0098]

[0099] Where, is the total leakage damage height of the sand layer; is the thickness of the i-th layer of sand sample; L rj is the actual leakage damage thickness of the jth layer of sand sample;

[0100] Step 6: The mass of water and sand collected by the water-sand collection device at different times and the total leakage height of the sand layer at different times obtained in step 4 are calculated. Import the data into a visualization tool (such as MATLAB) to create a time-varying graph of pore water pressure, water-sand leakage quality, and total leakage height of the sand layer to complete the simulation of the leakage process and data visualization.

[0101] The pumping frequency of the water inlet pump is adjusted based on the water inlet pressure gauge reading to achieve stable, constant-pressure lateral water inlet testing conditions under varying levels of conditions, ensuring piezometer measurement quality. By adjusting and replacing defect holders with varying shapes and opening sizes, the seepage damage of sand layers under varying defect sizes can be simulated, facilitating the study of crack development and accurately reflecting the complexity of actual leakage. By placing piezometers at the boundaries of each sand layer, the hydraulic head difference between each sand layer can be read in real time, facilitating the assessment of its damage state. Through this determination cycle, the state of each sand layer in the area in front of the defect opening is determined, allowing for the determination of whether seepage damage has occurred. This determination cycle can also be used to calculate the unstable sand layer thickness (actual seepage damage thickness) in the area in front of the defect opening, thereby determining the extent of sand layer leakage and loosening under this state. Through a multi-stage determination cycle, the state of sand layer damage can be determined in real time throughout all stages of seepage damage, allowing the calculation of the total seepage damage height at different moments. The temporal relationship between the total seepage height and sand layer seepage can be used to predict when sand layer seepage damage will lead to ground collapse near the foundation pit in actual projects, thereby facilitating the development of technical countermeasures for engineering personnel. Based on the time-varying graphs of pore water pressure, water-sand leakage quality, and total leakage height of the sand layer, researchers can further explore the laws of vertical leakage and damage of water and sand. Students can more intuitively observe the vertical leakage and damage process of water and sand, thereby increasing their perceptual understanding.

[0102] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any modifications or replacements made to the technical solution by other technicians in this professional field should be included in the scope of the claims of the present invention as long as they do not depart from the connotation of the technical solution of the present invention.

Claims

1. A method for simulating the vertical water-sand leakage failure process of a foundation pit supported by a ground-connected wall, characterized by: The steps include: Step 1: Insert the defective card into the transparent outlet pipe installed outside the transparent test box, and close the outlet valve downstream of the transparent outlet pipe; load the sand samples into the sand sample filling area of ​​the transparent test box in layers and compact them layer by layer. While loading the samples, piezometers are placed in the sand layer in front of the transparent outlet pipe and at the boundary of the sand layer above the transparent outlet pipe; starting from the height of the center of the defective card, mark the sand layers from bottom to top as i = 1, 2, 3, ..., n layers, and obtain the particle density and porosity of the sand sample in layer i based on geotechnical tests; Step 2: Seal the transparent experimental box and fill it with water. After the sand sample is saturated and consolidated, measure the thickness of the i-th layer of sand sample. Step 3: According to the particle density and porosity of the i-th layer of sand sample, its critical hydraulic gradient is obtained. According to the thickness and critical hydraulic gradient of the i-th layer of sand sample, its critical head difference is obtained. ; Step 4: Open the outlet valve downstream of the transparent outlet pipe to maintain the water level in the transparent experimental box unchanged, and obtain the experimental data of the piezometer at different times in real time; the water and sand collection device collects the water and sand discharged from the transparent outlet pipe respectively, and measures the leakage quality of water and sand at different times in real time; Step 5: 5.1 Calculation of the total leakage damage height of the sand layer at any time : According to the difference between the piezometer data at the top and bottom of the i-th layer of sand sample at any time, the measured water head difference of the i-th layer of sand sample is obtained. , according to the measured head difference Difference from critical head The size relationship is used to determine the leakage damage state of the i-th layer of sand sample; The bottom sand sample without leakage damage is recorded as the jth layer sand sample, and the j-1th layer sand sample is measured to bear the water head difference. Subtract its critical head difference , get the extra head difference of the j-th layer sand sample , then according to Calculate the measured leakage damage thickness L of the jth layer of sand sample according to Darcy's law rj , and the total leakage damage height of the sand layer at the corresponding moment is obtained , j = 1, 2, 3, ..., n; 5.2 Repeat the process of 5.1 to obtain the total leakage damage height of the sand layer at different times during the whole simulation test ; Step 6: The leakage mass of water and sand collected by the water-sand collection device at different times and the total leakage height of the sand layer at different times obtained in step 4 are calculated. Import the data into the visualization tool to create a time-varying graph of pore water pressure, water-sand leakage quality, and total leakage height of the sand layer to complete the simulation of the leakage process and data visualization.

2. The simulation method according to claim 1, wherein: In step 3, the critical head difference of the i-th layer of sand sample is According to formula (3.1), we can get: ； Where, is the critical head difference of the i-th layer of sand sample; is the critical hydraulic slope of the i-th layer of sand sample; is the thickness of the i-th layer of sand sample; in, According to formula (3.2), we can get: ； Where G si is the specific gravity of sand particles in the i-th layer of sand sample; e i is the porosity ratio of the i-th layer of sand sample.

3. The simulation method according to claim 1, wherein: In step 5, the sand sample of layer i is measured to bear the water head difference Calculate according to formula (5.1): ； Where, The measured water head difference for the sand sample of layer i; is the piezometer reading at the bottom boundary of the i-th layer of sand sample; It is the piezometer reading at the bottom boundary of the i+1th layer of sand sample.

4. The simulation method according to claim 1, wherein: In step 5, the leakage damage state of the i-th layer of sand sample is determined by the following method: (1) When When , the i-th layer of sand sample is in a stable state and no seepage damage occurs; (2) When When , the i-th layer of sand sample is in an unstable state and seepage damage occurs.

5. The simulation method according to claim 1, wherein: In step 5, the i-th layer does not bear the additional head difference Calculate according to formula (5.2): ； Where, The i-th layer of sand sample does not bear the additional head difference, The measured water head difference for the j-1 layer sand sample is is the critical head difference of the j-1th layer of sand sample.

6. The simulation method according to claim 1, wherein: In step 5, the total leakage damage height of the sand layer Calculate according to formula (5.3): ； Where, is the total leakage damage height of the sand layer; is the thickness of the i-th layer of sand sample; is the measured leakage damage thickness of the jth layer of sand sample; Among them, L ri According to formula (5.4) and (5.5), we can obtain: ； ； Where, The jth layer of sand sample does not bear the additional head difference, is the critical hydraulic slope of the jth layer of sand sample, The measured water head difference for the j-th layer of sand sample is: is the measured hydraulic gradient of the jth layer of sand sample, L rj is the actual leakage damage thickness of the jth sand layer; is the thickness of the jth layer of sand sample.

7. The simulation method according to claim 1, wherein: The water inlet pressure of the pressurized water inlet device is 0-15kPa.

8. The simulation method according to claim 1, wherein: The sand sample filling area occupies 55%-60% of the volume of the transparent experimental box.

9. The simulation method according to claim 1, wherein: The distance between the transparent water outlet pipe and the bottom of the transparent experimental box is 1 / 8-3 / 8 of the clear height of the transparent experimental box.

10. The simulation method according to claim 1, wherein: The transparent experimental box and the transparent water outlet pipe are both made of transparent organic glass.

Images