Simulation method for water-sand vertical leakage damage process of underground diaphragm wall support foundation pit

Abstract

The invention discloses a method for simulating a water-sand vertical leakage damage process of an underground diaphragm wall support foundation pit, which comprises the following steps of: embedding a defect clamping plate into a transparent water outlet pipe, loading sand samples into a transparent experiment box in a layered manner, tamping in a layered manner, mounting a pore pressure meter, and calculating a critical water head difference of each layer of sand samples after the sand samples are saturated and solidified; starting a simulation experiment, obtaining experimental data and water-sand leakage quality of a pore pressure meter, and judging a leakage damage state of each layer of sand sample; calculating the extra unborne water head difference and the actually measured leakage damage thickness of the critical layer sand sample, and further obtaining time-varying data of the total leakage height of the sand layer in the simulation process; and establishing a time-varying graph of the pore water pressure, the water sand leakage quality and the total leakage height of the sand layer by adopting a visual tool. According to the simulation method established by the invention, the simulation and data visualization of the leakage process can be realized, the water-sand vertical leakage failure law and failure time can be explored, the complexity of actual leakage can be reflected, and the development of research type and teaching type experiments is facilitated.

Description

Technical Field

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

[0002] Ground-connected wall support is a commonly used retaining structure in foundation pit construction. It combines the functions of retaining and stopping water. Ground-connected wall foundation pit support can form a complete continuous wall, which can effectively resist groundwater and soil erosion. Leakage damage caused by improper groundwater treatment is one of the most common types of accidents in ground-connected wall foundation pit construction. Leakage of deep foundation pit water-stopping curtain, pipe burst and sudden burst at the bottom of the pit are the main manifestations of leakage damage. Especially in the water-rich sand layer area, there may be defects in the retaining structure during the foundation pit construction process. When the defect opening is too large, it is very easy to cause water leakage and sand leakage disaster accidents. The mixture of water and sand flows into the inner surface of the foundation pit through the defect opening, which may cause road collapse and traffic obstruction. According to statistics, in my country's water-rich sand layer area, due to the complex hydrogeological conditions such as high groundwater level, large sand layer thickness and poor stability, foundation pit leakage and sand leakage are relatively common. By studying the development process of sand layer leakage, the flow law of soil and its impact range, it is possible to more accurately assess the disaster risk and provide a scientific basis for the early warning and prevention and control 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 support foundation pit. The technical solution can effectively simulate the development and evolution of soil particle force chain in the process of seepage deformation development in a pile support foundation pit, and has the characteristics of simple model, convenient disassembly and assembly, and strong feasibility. However, the device can only provide image analysis results for the seepage deformation damage process of the soil, and cannot automatically and continuously measure data and time series graphs to analyze the seepage deformation characteristics of the soil. And in the absence of a constant pressure system, it is impossible to 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 to the ground-connected wall support mode, and even more so to the simulation of vertical water-sand seepage damage. At present, the simulation of vertical water-sand seepage damage in the ground-connected wall support foundation pit still has the problem of simple experimental model, which is difficult to reflect the complexity in the real project, and it is difficult to meet the test requirements of simulating leakage gaps of different sizes and shapes, which is not conducive to the development of research experiments and teaching experiments. Summary of the invention

[0004] To solve the above problems, the purpose of the present invention is to provide a simulation method for the vertical leakage damage process of water and sand in a ground-anchored wall supporting foundation pit, and realize the simulation of vertical leakage damage of water and sand in a ground-anchored wall supporting foundation pit under different defect sizes, soil gradings and water pressure levels through an experimental device; the 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, to realize digital simulation of the vertical leakage damage process, which is helpful for researchers to further explore the damage law and damage time of vertical leakage of water and sand, and also helps students to understand the vertical leakage damage process of water and sand in the ground-anchored wall supporting 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 leakage and damage process of water and sand in a foundation pit supported by a ground-connected wall, comprising the following steps:

[0007] Step 1: embed 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 in layers. While loading the samples, piezometers are arranged in the sand layer in front of the transparent outlet pipe and at the boundary of the sand layer above the transparent outlet pipe, and the particle specific gravity and porosity ratio of each layer of sand sample are obtained according to geotechnical tests; take the height of the center of the defective card as the starting point, and mark the sand layers from bottom to top as i=1, 2, 3, ..., n layers in sequence;

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

[0009] Step 3: According to the particle specific gravity and porosity of the i-th layer of sand sample, its critical hydraulic slope is obtained; according to the thickness and critical hydraulic slope 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, maintain the water level in the transparent experimental box unchanged, obtain the experimental data of the piezometer at different times in real time, and 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 the 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 size relationship; 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 , get the additional head difference of the j-th layer of 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 time is obtained , j = 1, 2, 3, ..., n;

[0014] 5.2 Repeat the process in 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 it into the visualization tool to establish the time-varying graphs 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 test box;

[0017] A vertical sieve plate is provided in the transparent test box, and the sieve plate divides the internal space of the transparent test 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, 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;

[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 a water flow buffer zone arranged in the transparent experimental box in sequence through a water inlet pipe; the water inlet flow meter and the pressure gauge are arranged on the water 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-sand collection box is an open transparent box, a porous sand isolation plate is provided in the middle of the water-sand collection box, and the water-sand collection box is arranged 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 arranged 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-sand collection box; a transparent connecting pipe is provided on the side wall of the water-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, and the leakage mass of water and sand is calculated respectively according to the experimental data of the water outlet flow meter and the weighing sensor.

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

[0023]

[0024] In the formula, 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 get:

[0026]

[0027] In the formula, 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 of the i-th layer of sand sample is measured Calculate according to formula (5.1):

[0029]

[0030] In the formula, The measured water head difference for the i-th layer of sand sample; is the reading of the piezometer at the bottom boundary of the i-th layer of sand sample; It is the pore pressure gauge 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] In the formula, 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] In the formula, 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 j-th layer of sand sample;

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

[0041]

[0042]

[0043] In the formula, The j-th 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 j-th 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 experiment box and the transparent water outlet pipe are both made of transparent plexiglass.

[0046] Furthermore, the sand sample filling area occupies 55%-60% of the volume of the transparent test 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] The defect card is set on the transparent outlet pipe on the side of the transparent experimental box. The rectangular gap in the defect card is used as a water and sand leakage port, which is consistent with the engineering limit of water and sand loss in the foundation pit ground-connected wall defects and shield tunnel side wall segment cracks. The rectangular gap can also be adjusted according to the size of the cracks in the actual project; the piezometer readings can be automatically monitored and displayed, and the water head difference of each sand layer can be read in real time; the seepage damage state of the sand layer in the area in front of the leakage defect can be determined without measuring the permeability coefficient of the sand sample; the leakage damage height of the sand layer in front of the leakage defect can be calculated more accurately. It has a reference significance for the evolution mechanism and prevention and control measures of vertical leakage damage of water and sand in the foundation pit supported by the ground-connected wall, as well as experimental simulation teaching.

[0050] The present invention adopts an automated test device that can realize simulated water-sand vertical leakage damage of ground-connected wall supporting foundation pits 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 water-sand vertical leakage of ground-connected wall supporting foundation pits can be judged in real time, which is helpful for researchers to further explore the damage laws and damage time of water-sand vertical leakage, and also helps students understand the damage process of water-sand vertical leakage of ground-connected wall supporting foundation pits, 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 is a 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 It is a diagram of the water-sand collection system of the present invention;

[0056] Figure 6 It is a schematic diagram of a defective pallet 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 defect card plate (10), a piezometer (11), a bottom frame (12), a pulley (13), an organic glass water outlet pipe (14), a water outlet valve (15), a broken line organic glass water 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), a water 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 in conjunction with 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 test box, and the sieve plate 9 divides the internal space of the transparent test 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 12 is a water flow buffer zone, and the right side of the sieve plate 12 is a sand sample filling area; the organic glass experimental box body 6 is made of 5 pieces of organic glass, distributed on 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 by bolts 8, and a layer of rubber water stop is padded 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 The water outlet pipe adopts an organic glass water 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 on the bottom frame 12 as a whole, 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 water 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 water outlet pipe 14 and at each sand layer boundary position above the organic glass water outlet pipe 14 to measure the change of pore water pressure 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 flow meter 4, and a pressure gauge 5. The water tank 1 is connected to the water pump 3 and a water flow buffer zone arranged in the transparent experiment box in sequence through an inlet pipe. The water inlet valve 2 is arranged on the inlet pipe between the water tank 1 and the water pump 3. The water inlet flow meter 4 and the pressure gauge 5 are arranged on the inlet pipe between the water pump 3 and the transparent experiment box. The water tank 1 is supplied with water from an external water source. The water tank 1 provides the transparent experiment box with a stable water source required for the experiment. The water inlet flow meter 4 measures the water inlet flow of the transparent experiment box. The pressure gauge 5 measures the water inlet pressure of the transparent experiment box. The water pump 3 adjusts the water inlet pressure to ensure that the water inlet pressure of the transparent experiment box is a constant pressure.

[0064] The water-sand collecting device comprises a zigzag organic glass water inlet pipe 16, a porous sand isolation plate 17, a weighing sensor 18, a water-sand collecting box 19, an organic glass connecting pipe 20, a water outlet flow meter 21, and a wastewater collecting box 22; the water-sand collecting box 19 is an open organic glass box body, which is arranged on the weighing sensor 18, and a porous sand isolation plate 17 is arranged in the middle of the water-sand collecting box 19; the water inlet end of the zigzag 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 zigzag organic glass water inlet pipe 16 extends to the bottom of the water-sand collecting box 19, and the organic glass water outlet pipe 14 and the zigzag organic glass water inlet pipe 1 6 are 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, and the organic glass connecting pipe 20 is higher than the porous sand isolation plate 17, but lower than the top opening 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, and the organic glass connecting pipe 20 is provided with a water outlet flow meter 21 to obtain the mass of the leaking 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, and the mass of the leaking sand can be converted according to the difference in the specific gravity of water and sand. The aperture of the organic glass connecting pipe 20 is large enough to keep the water level of the water and sand collection box 19 constant; before the experiment, the water and sand collection box 19 needs to 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, and 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 through a data line, and the water leakage and sand leakage amount and pore water pressure indication can be automatically obtained on the computer (24).

[0066] Now Figure 1 As shown, taking the visualized 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 discrimination 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, embed the defective cardboard into the transparent outlet pipe, and close the outlet valve downstream of the transparent outlet pipe; load the sand samples into the transparent experimental box in layers and compact them in layers, and at the same time, arrange piezometers in the sand layer in front of the transparent outlet pipe and at the boundary of the sand layer above the transparent outlet pipe, and obtain the particle specific gravity and porosity ratio of each layer of sand sample according to geotechnical tests; take the height of the center of the defective cardboard as the starting point, and mark the sand layers from bottom to top as i=1, 2, 3, ..., n layers in sequence;

[0068] Before loading, correctly connect all parts of the water-sand leakage simulation test device, confirm that there is no leakage in all parts 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 load them evenly and tamp them. 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 according to 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-grained sand from flowing into the piezometer 11 and causing damage to the piezometer 11 .

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

[0070] After the sand sample filling area is filled with sand, cover it with the organic glass cover 7, open the water inlet valve 2, pump water from the water storage tank 1 through the water pump 3 and inject low-flow water into the water flow 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 specific gravity 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] In the formula, 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 get:

[0076]

[0077] In the formula, 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 saturation consolidation of the sand sample is completed, the outlet valve downstream of the transparent outlet pipe is opened to maintain the water level in the transparent test 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 test box flow into the water and sand collection device through the transparent outlet pipe and the defective card plate 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 respectively;

[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 the 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 size relationship; 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 water head difference of the j-1th layer of sand sample , get the additional head difference of the j-th layer of 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 time is obtained , j = 1, 2, 3, ..., n;

[0082] 5.2 Repeat the process in 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. In the seepage damage stage, the dominant leakage path in the area in front of the defect is in the vertical direction, and the water head is the 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 readings of the pore pressure gauges 11 at both ends of the sand layer layer by layer in the upward and downward directions. 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] In the formula, The measured water head difference for the i-th layer of sand sample; is the reading of the piezometer at the bottom boundary of the i-th layer of sand sample; It is the pore pressure gauge reading at the bottom boundary of the i+1th layer of sand sample.

[0086] Comparison of critical water head difference of sand layer Δh 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 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] In the formula, 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 , 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] In the formula, The j-th 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 j-th layer of sand sample, L rj is the actual leakage damage thickness of the j-th layer of sand sample; is the thickness of the j-th layer of sand sample;

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

[0098]

[0099] In the formula, 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 j-th 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 it into a visualization tool (such as MATLAB) to establish 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] According to the reading of the water inlet pressure gauge, the pumping frequency of the water inlet pump is adjusted to achieve the test conditions of lateral stable constant pressure water inlet under different levels of conditions, and the measurement quality of the piezometer is ensured. By adjusting and replacing defect card plates of different shapes and opening sizes, the seepage damage of sand layers under different defect sizes can be simulated, which is helpful to study the crack development process and can truly reflect the complexity of actual leakage. By setting piezometers at the boundaries of each sand layer, the head difference borne by each sand layer can be read in real time, which is convenient for judging its damage state. Through the above judgment cycle, the state of each sand layer in the area in front of the defect mouth is obtained to determine whether seepage damage occurs. Through the above judgment cycle, the thickness of the unstable state sand layer in the area in front of the defect mouth (actual leakage damage thickness) can be calculated, and the leakage and loosening range of the sand layer in this state can be obtained. Through multi-stage cyclic judgment, the real-time judgment of the sand layer damage state in all stages of leakage damage can be realized, and the total leakage damage height of the sand layer at different times can be calculated. According to the relationship between the total leakage height of the sand layer and time, the time when the surface collapse near the foundation pit is caused by the leakage damage of the sand layer in the actual project can be realized, so as to facilitate the engineering and technical personnel to take corresponding technical measures. Based on the time-varying graphs of pore water pressure, water-sand leakage mass and total leakage height of sand layers, researchers can further explore the laws of vertical water-sand leakage damage, and students can more intuitively observe the vertical water-sand leakage damage process and increase 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 modification or replacement of the technical solution made by other technicians in this professional field should be included in the scope of the claims of the present invention as long as it does not deviate from the connotation of the technical solution of the present invention.

Claims

1. A method for simulating the vertical leakage and damage process of water and sand in a foundation pit supported by a ground-connected wall, characterized in that: The steps include: Step 1: embed the defective card plate 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 in layers. While loading the samples, piezometers are arranged 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 plate, mark the sand layers from bottom to top as i=1, 2, 3, ..., n layers in sequence, and obtain the particle specific gravity and porosity of the i-th layer of sand sample according to geotechnical tests; Step 2: Seal the transparent test box, fill it with water, and measure the thickness of the i-th layer of sand sample after the sand sample is saturated and consolidated; Step 3: According to the particle specific gravity 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, 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 the 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 of is used to determine the leakage damage state of the i-th layer of sand sample; The bottom layer of sand sample without leakage damage is recorded as the jth layer of sand sample, and the j-1th layer of sand sample is measured to bear the water head difference. Subtract the critical head difference , get the additional head difference of the j-th layer of 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 time 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 it into the visualization tool to establish the time-varying graphs 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, characterized in that: In step 3, the critical head difference of the i-th layer of sand sample is According to formula (3.1), we get: ； In the formula, 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 get: ； In the formula, 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, characterized in that: In step 5, the water head difference is measured for the i-th layer of sand sample Calculate according to formula (5.1): ； In the formula, The measured water head difference for the i-th layer of sand sample; is the reading of the piezometer at the bottom boundary of the i-th layer of sand sample; It is the pore pressure gauge reading at the bottom boundary of the i+1th layer of sand sample.

4. The simulation method according to claim 1, characterized in that: 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, characterized in that: In step 5, the i-th layer does not bear the additional head difference Calculate according to formula (5.2): ； In the formula, 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, characterized in that: In step 5, the total leakage damage height of the sand layer Calculate according to formula (5.3): ； In the formula, 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 j-th layer of sand sample; Among them, L ri According to formula (5.4) and (5.5), we can obtain: ； ； In the formula, The j-th 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 j-th 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, characterized in that: The water inlet pressure of the pressurized water inlet device is 0-15kPa.

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

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

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