A model test apparatus and test method for simulating road surface collapse caused by rainfall infiltration.

Abstract

This invention discloses a model test device and method for simulating road collapse caused by rainfall infiltration. The device includes a load-bearing module, a rainfall control module, a particle collection module, and a parameter monitoring module to ensure the operability and accuracy of the experiment. The rainfall control module controls the rainfall flow rate through a booster pump, an inlet valve, and a flow meter to trigger piping. The particle collection module collects lost particles in layers according to depth. Combined with pre-treatment of the foundation soil particles with staining, the particle loss patterns at different depths and sizes can be accurately analyzed. This invention has a simple structure and is easy to operate. It can effectively simulate the entire process of rainfall infiltration leading to piping and subsequent road collapse. By laying reinforced sections at different heights on the embankment, it can be used to study the piping mechanism and the reinforcement effect of reinforced embankments.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering model testing technology, and specifically relates to a model testing device and method for simulating road collapse caused by rainfall infiltration. Background Technology

[0002] In the rainy regions of southern my country, the fine particles within highway and railway embankments are easily carried away by the seepage under the long-term infiltration of heavy rainfall, forming piping and leading to soil structural damage, causing road surface collapses and other disasters, seriously threatening the safe operation of transportation infrastructure. Currently, the microscopic mechanisms by which rainfall infiltration causes embankment erosion and piping development are still insufficiently understood.

[0003] Existing model testing devices are mostly focused on studying soil arching effects or pile-soil load transfer. There is a lack of devices for simulating the loss patterns of particles of different depths and sizes within embankment fill material under simulated rainfall infiltration conditions, as well as the reinforcement effect of multi-layered reinforced structures. Furthermore, traditional devices struggle to precisely control rainfall intensity to trigger piping, and lack effective means to collect and differentiate particles lost at different depths, making it impossible to quantitatively analyze the development process of piping.

[0004] Therefore, there is an urgent need to provide a simple and easy-to-operate model test device that can accurately simulate the rainfall infiltration process, monitor the embankment response in real time, and effectively collect and analyze lost particles, thereby conducting in-depth research on the piping and collapse mechanisms caused by rainfall. Summary of the Invention

[0005] The purpose of this invention is to provide a model test device and test method for simulating road collapse caused by rainfall infiltration. The device can accurately control the rainfall intensity, simulate the conditions for piping, and collect and analyze particles lost at different depths in layers. At the same time, it can study the reinforcement effect of multi-layered reinforced bodies on embankments.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A model test device for simulating road collapse caused by rainfall infiltration includes a load-bearing module, a rainfall control module, a particle collection module, and a parameter monitoring module.

[0008] The supporting module includes a cuboid model box, inside which a foundation and embankment are filled from bottom to top, and a scale for observing deformation is set vertically along the top of the box.

[0009] The rainfall control module is used to provide simulated rainfall of controllable intensity into the model box. It includes a water tank, an inlet pipe, an inlet valve, a flow meter, a booster pump, and rainfall nozzles. One end of the inlet pipe is connected to the water tank, and the other end is connected in series with the inlet valve, the booster pump, and the flow meter, and then connected to the rainfall nozzles arranged on the top of the model box. The rainfall control module adjusts the rainfall amount through the coordinated control of the booster pump and the flow meter to ensure that the foundation triggers piping.

[0010] The particle collection module is used to collect lost soil particles in layers, and includes collection pipes arranged at different depths along the side wall of the model box and filter boxes connected to the collection pipes.

[0011] The parameter monitoring module is used to monitor changes in the physical and mechanical parameters of the soil during the test. It includes a pressure box, a pore water pressure sensor and a settlement plate buried between the embankment and the foundation, as well as an external control terminal. The pressure box, pore water pressure sensor and settlement plate are electrically connected to the control terminal.

[0012] Further optimization involves the foundation being composed of soil with a specific gradation. The particle size distribution, calculated by mass ratio, satisfies the following: 100% <10mm, 75% <8mm, 30% <4mm, 22% <2mm, 20% <1mm, and 20% 0.25mm to 0.5mm.

[0013] Further optimization involves the parameter monitoring module achieving precise measurement of soil physical and mechanical parameters in the following manner: the monitoring points for the foundation are arranged as follows: a monitoring section is set every 15cm along the depth direction of the foundation, and each section is simultaneously equipped with an earth pressure cell, a pore water pressure sensor, and a settlement plate, covering the entire 90cm high foundation to form a complete monitoring chain from the top surface to the bottom of the foundation.

[0014] The monitoring points for the embankment are arranged as follows: a monitoring section is set up every 10cm along the height of the embankment, and an earth pressure cell and settlement plate are buried in each section. The layout covers the entire 60cm high embankment, and the focus is on monitoring the stress changes at the upper and lower interfaces of the reinforced body.

[0015] A vibrating wire earth pressure cell was used for measurement, employing a pre-calibrated frequency-pressure conversion relationship. The earth pressure cell was installed with its pressure surface horizontal and in close contact with the surrounding soil to avoid localized stress concentration. The measurement frequency was once every 5 minutes, increasing to once every 1 minute during the initial stages of rainfall. The data acquisition instrument recorded frequency changes in real time, and the earth pressure value was calculated using the formula P=K1(f0²-f²), where K1 is the calibration coefficient, f0 is the initial frequency, and f is the measurement frequency.

[0016] A full stainless steel pore water pressure sensor is used, with the permeable stone of the sensor facing the water flow direction. Air is released before installation to ensure no air bubbles are present in the sensor cavity. The sensor diaphragm deformation caused by water pressure is monitored and converted into a voltage signal output. The actual pore water pressure value u=K is calculated using the following formula: p (U-U0), where K p U is the pressure coefficient, U is the measuring voltage, and U0 is the initial voltage.

[0017] The settling plate is a 10cm diameter circular steel plate connected to a stainless steel measuring rod on the embankment surface. Measurements are taken using a dial indicator or laser displacement sensor, achieving an accuracy of 0.01mm. The measurement reference point is set on a stable external structure of the model box to avoid interference from box deformation. The settlement is calculated as the difference in readings at different times, s = H. t -H0, where H t H is the reading at time t, and H0 is the initial reading.

[0018] Further optimization involves using a dyeing agent made by mixing acrylic pigment with a matte acrylic gel medium for the soil particle staining treatment of the foundation. The weight ratio of dry gravel, medium, and pigment is 100:5:(1-3).

[0019] Further optimization involves laying at least one layer of reinforcement within the embankment. The reinforcement is arranged in layers along the embankment height, with the reinforcement positions from bottom to top being 4cm, 8cm, 12cm, 16cm, 28cm, 40cm, 51cm, 54cm, and 57cm.

[0020] Further optimization involves using an arc-shaped pipe with a diameter of 50mm, arranged at 22.5cm intervals along the side wall of the model box. The arc-shaped structure is designed to prevent soil particles from clogging the pipe.

[0021] Further optimizations were made, with the model box dimensions set at 180cm*100cm*200cm; the foundation height at 90cm; the embankment height at 60cm; and the scale ratio between the simulation device and the actual embankment at 1:10.

[0022] The test method based on the above-mentioned model test device for simulating road surface collapse caused by rainfall infiltration includes the following steps:

[0023] Step S1: Device pretreatment: Place the model box on a level site, clean the impurities inside the box, and set the embankment height, foundation particle size distribution, and rainfall flow parameters according to the test requirements;

[0024] Step S2: Foundation filling and monitoring layout: After dyeing the soil particles for the foundation, the foundation is filled in layers according to the design gradation, and pressure cells, pore water pressure sensors and settlement plates are simultaneously installed in the embankment and foundation.

[0025] Step S3: Embankment construction: Fill the embankment material in layers according to the design height. If it is necessary to study the reinforcement effect, lay the reinforcement body at the same time.

[0026] Step S4: Module installation: Install the collection pipes at preset intervals on the side wall of the model box and connect them to the filter box. Then connect each component of the rainfall control module in sequence and check the pipe connectivity.

[0027] Step S5: Test run: Start the rainfall control module, adjust the rainfall intensity through the booster pump and flow meter, and collect particles through the collection pipe; continuously monitor the parameter data and observe the embankment surface condition until piping occurs in the foundation;

[0028] Step S6: Data Processing: After the experiment, stop the rainfall, analyze the weight, color and gradation of the collected particles, and combine the parameter monitoring data to study the piping pattern and embankment collapse characteristics or the reinforcement effect of the reinforced body.

[0029] To further optimize the process, during the layered filling of the embankment, each layer must be compacted. When laying the reinforcement, ensure that the reinforcement is flat and in close contact with the embankment fill to guarantee effective load transfer.

[0030] In the aforementioned steps, the collected particle samples need to be filtered and dried first, and then sieved to distinguish particles of different sizes. Combined with staining color to trace the original depth of the particles, quantitative analysis of the piping process can be achieved.

[0031] Further optimization involves adjusting the rainfall in step S5 to ensure the triggering of piping. The specific process is as follows:

[0032] Step S5.1: Extract the following parameters from the particle size distribution curve of the foundation soil for the calculation of the critical hydraulic gradient: relative density of soil particles Gs, void ratio e, permeability coefficient k, and characteristic particle sizes d5 and d6. 20 Where d5 is the particle size corresponding to a cumulative content of 5% in the particle size distribution curve, d 20 The particle size corresponding to a cumulative content of 20% is obtained from the curve.

[0033] Step S5.2: Based on the parameters obtained in step S5.1, calculate the critical hydraulic slope (icr) of the piping soil in the foundation according to the following formula: .

[0034] Step S5.3: Adjust the hydraulic gradient by controlling the rainfall and the infiltration rate:

[0035] First, calculate the seepage flow rate using the following formula: Q 渗=k×A×i, where i is the hydraulic gradient, i=h / L, h is the head difference of the seepage path, L is the length of the seepage path, i.e. the foundation height, and A is the cross-sectional area through which the water flows.

[0036] Secondly, determine the matching relationship between rainfall and infiltration rate: the rainfall at the top of the model box should be equal to or slightly greater than the infiltration rate, ignoring evaporation loss, i.e., the rainfall rate Q. 雨 ≈Q 渗 .

[0037] Third, calculate the critical seepage flow rate Q. cr When i = icr, Q 雨 =Q 渗 =Q cr =k×A×i cr .

[0038] Step S5.4: Adjustment operation of the rainfall control module:

[0039] Start the booster pump and gradually open the inlet valve, monitoring the rainfall flow rate in real time using a flow meter;

[0040] In the initial stage, the flow rate is set to the lower limit. The pore water pressure sensor data is continuously monitored. If there is no sudden increase in pore water pressure within 30 minutes (no signs of seepage breakthrough), the pressure is gradually increased by a booster pump, with each stage increasing by 0.5 L / min.

[0041] When the pore water pressure at a certain depth is detected to be close to the effective stress of the soil, i.e., i≥icr, and micro-cracks appear on the embankment surface or fine particles flow out of the collection pipe, the current rainfall flow rate is locked and maintained at this intensity until piping stabilizes.

[0042] The following methods were used to ensure that piping continued to occur during the test:

[0043] 1) Compare the pore water pressure data with the calculated value in real time. If the pore water pressure coefficient is consistently less than 0.5, it indicates that the hydraulic gradient is insufficient and the rainfall flow needs to be increased by using a booster pump.

[0044] 2) If a large amount of particles are lost from the collection pipeline, causing a sudden increase in flow, the power of the booster pump should be appropriately reduced to maintain the flow within the target range and avoid the soil from collapsing too quickly and affecting the test observation.

[0045] 3) Based on particle collection data, if the particle loss at a certain depth is significantly lower than expected, the rainfall flow rate can be fine-tuned to ensure the hydraulic gradient is within the range of i. cr ~1.2i cr Within the specified range, it can trigger piping without damaging the test system.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1) Precise rainfall control: Through the coordinated control of booster pumps and flow meters, combined with specific graded foundations, piping can be stably triggered, and the test reproducibility is high.

[0048] 2) Precise particle analysis: The combination of stratified collection system and staining technology can quantitatively analyze the loss patterns of particles at different depths and sizes, providing direct data for mechanism research.

[0049] 3) Comprehensive functions: Supports research on the reinforcement effect of reinforced bodies and provides reference for the design of reinforced embankments.

[0050] 4) High practicality: It has a simple structure, is easy to operate and has low cost. It can completely simulate the entire process of rainwater infiltration causing disasters, which is of great significance to the research on embankment disaster prevention technology. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0052] Figure 2 This is a particle size distribution curve of the foundation of the present invention;

[0053] The components are: 1-model box, 2-foundation, 3-embankment, 4-reinforcement, 5-sensor system, 6-rain spray nozzle, 7-support frame, 8-flow meter, 9-booster pump, 10-inlet valve, 11-inlet pipe, 12-water tank, 13-collection pipe, 14-filter box. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1:

[0055] As attached Figure 1 As shown, a model test device for simulating road collapse caused by rainfall infiltration includes a load-bearing module, a rainfall control module, a particle collection module, and a parameter monitoring module.

[0056] The bearing module in this embodiment includes a cuboid model box 1 with dimensions of 180cm*100cm*200cm. The interior of the box is filled with two parts, foundation 2 and embankment 3, from bottom to top. A scale for observing deformation is vertically set on the top of the box.

[0057] Foundation 2 is constructed using soil with the aforementioned specific gradation. Calculated by mass ratio, its particle size distribution satisfies the following: <10mm 100%, <8mm 75%, <4mm 30%, <2mm 22%, <1mm 20%, and 0.25mm~0.5mm 20%. This gradation design aims to simulate soil conditions prone to piping in actual engineering projects. The foundation particle size distribution curve is shown below. Figure 2 As shown.

[0058] Embankment 3 uses conventional embankment fill material with a filling height of 60cm.

[0059] The rainfall control module is used to provide controlled-intensity simulated rainfall into the model box 1. It includes a water tank 12, an inlet pipe 11, an inlet valve 10, a flow meter 8, a booster pump 9, and rainfall nozzles 6. The water tank 12 is placed on a level surface and is connected sequentially to the inlet valve 10, booster pump 9, and flow meter 8 via the inlet pipe 11. Finally, it is connected to the rainfall nozzles 6 on the top of the model box via a support frame 7, forming uniform rainfall. By adjusting the inlet valve 10 and booster pump 9, the rainfall intensity is controlled within a specific range, causing piping.

[0060] In this embodiment, the following parameters are extracted from the particle size distribution curve of the foundation soil for calculating the critical hydraulic gradient: the relative density of soil particles Gs is 2.65, the void ratio e is 0.81, and the permeability coefficient k is estimated to be within the range of 3.2 × 10⁻⁶ based on the particle size distribution curve. -2 cm / s ~5×10 -2 cm / s, and characteristic particle size d5 is 0.31 mm, d 20 It is 1mm.

[0061] This is based on the formula for calculating the critical hydraulic gradient of piping soil. Calculate i cr =0.33.

[0062] Then, according to the flow rate formula Q=kAi cr Let A be the cross-sectional area through which the water flows. Based on the dimensions of the model box and the foundation, A = 90 * 100 = 9000 cm². 2 The calculated flow rate range is approximately 5.7 L / min to 8.9 L / min. Therefore, in this embodiment, the rainfall control device slightly expands the rainfall flow rate range to 5.5 L / min to 9 L / min.

[0063] The particle collection module is used for stratified collection of lost soil particles. To quantitatively study the loss characteristics of soil particles at different depths, this device has a series of arc-shaped collection pipes 13 with a diameter of 50 mm buried at different heights (at equal intervals of 22.5 cm) on one side wall of the model box. The arc-shaped pipes facilitate particle flow and are not prone to clogging. Each collection pipe is connected to an external filter box 14, which contains a screen to collect lost particles.

[0064] Before the experiment begins, the foundation soil particles need to be dyed to distinguish different particle sizes. Acrylic pigments and matte acrylic gel mediums are used to dye the foundation soil particles of different sizes. The weight ratio of dry gravel, medium and pigment is 100:5:(1~3) to ensure that the particles are dyed evenly. After drying, the foundation is filled according to the design height.

[0065] The parameter monitoring module is used to monitor the changes in the physical and mechanical parameters of the soil during the test. It includes a pressure box 5, a pore water pressure sensor and a settlement plate buried between the embankment 3 and the foundation 2, as well as an external control terminal. The pressure box, pore water pressure sensor and settlement plate are electrically connected to the control terminal.

[0066] The specific steps of operating the three-dimensional soil arching effect research experimental device (excluding reinforced structures) in this embodiment are as follows:

[0067] (1) Place the model box on a level ground, clean the inside of the box, and set the embankment height, the number and arrangement height of the reinforcement, the particle size distribution of the foundation and the rainfall flow according to the specific requirements of the test.

[0068] (2) Foundation filling: The soil particles are dyed with acrylic paint and matte acrylic gel medium in advance, and the foundation soil is prepared and filled according to the designed particle size distribution. At the same time, the sensor system is installed: soil pressure cell, pore water pressure sensor and settlement plate.

[0069] (3) Embankment construction: The embankment fill material is filled in layers according to the design height and compacted layer by layer.

[0070] (4) Install the particle collection system: The collection pipes are arranged at intervals of 22.5cm, with one end connected to the model box and the other end connected to the filter box.

[0071] (5) Install and start the rainfall control device: One end of the inlet pipe is connected to the water tank, and the other end passes through the inlet valve, booster pump, and flow meter in sequence, and then connects to the rainfall nozzle arranged on the top of the model box through the support frame. After checking the connectivity of each pipeline, start the rainfall system and use the flow meter and booster pump to stably control the rainfall intensity within the preset range;

[0072] (6) Trial operation: Start the rainfall control module, adjust the rainfall intensity through the booster pump and flow meter, and collect particles through the collection pipe; continuously monitor the parameter data and observe the embankment surface condition until piping occurs in the foundation;

[0073] (7) After the experiment, rainfall was stopped. The collected mud-water mixture was filtered, dried, and the particles of different colors were sieved, weighed, and the particle loss and gradation were analyzed. Based on the sensor data, the occurrence and development mechanism of piping and the collapse of the embankment were systematically analyzed. Example 2:

[0074] In this embodiment, the model test device for simulating road surface collapse caused by rainfall infiltration differs from that in Embodiment 1 in that the reinforcing body 4 is laid in layers in the embankment 3, while the other parts are the same as in Embodiment 1.

[0075] In embankment 3, the reinforcement body 4 is laid in layers according to the following scheme. To further study the impact of reinforcement on the stability of the embankment, the reinforcement body 4 is laid in layers according to the height mentioned above in embankment 3, divided into three parts: upper, middle and lower. The middle part is sparse, and the upper and lower parts are dense. The lower part is laid with four layers, located at heights of 4cm, 8cm, 12cm and 16cm respectively, mainly used to transfer and distribute the load and provide support for the embankment. The middle part is laid with two layers, located at heights of 28cm and 40cm respectively, which play an overall reinforcement role and improve the overall rigidity of the embankment. The upper part is laid with three layers, located at heights of 51cm, 54cm and 57cm respectively, mainly used to resist road surface deformation, reduce the impact of traffic load, prevent collapse and deterioration, and provide a buffer for vehicles.

[0076] The specific steps of operating the three-dimensional soil arching effect research experimental device (including the reinforced body) in this embodiment are as follows:

[0077] (1) Place the model box on a level ground, clean the inside of the box, and set the embankment height, the number and arrangement height of the reinforcement, the particle size distribution of the foundation and the rainfall flow according to the specific requirements of the test.

[0078] (2) Foundation filling: The soil particles are dyed with acrylic paint and matte acrylic gel medium in advance, and the foundation soil is prepared and filled according to the designed particle size distribution. At the same time, the sensor system is installed: soil pressure cell, pore water pressure sensor and settlement plate.

[0079] (3) Embankment construction and reinforcement laying: Embankment fill material is laid in layers according to the design height and reinforcement is laid. Each layer is compacted to ensure that the reinforcement material is flat and in good contact with the soil.

[0080] (4) Install the particle collection system: The collection pipes are arranged at intervals of 22.5cm, with one end connected to the model box and the other end connected to the filter box.

[0081] (5) Install and start the rainfall control device: One end of the inlet pipe is connected to the water tank, and the other end passes through the inlet valve, booster pump, and flow meter in sequence, and then connects to the rainfall nozzle arranged on the top of the model box through the support frame. After checking the connectivity of each pipeline, start the rainfall system and use the flow meter and booster pump to stably control the rainfall intensity within the preset range;

[0082] (6) Trial operation: Start the rainfall control module, adjust the rainfall intensity through the booster pump and flow meter, and collect particles through the collection pipe; continuously monitor the parameter data and observe the embankment surface condition until piping occurs in the foundation;

[0083] (7) After the experiment, rainfall was stopped. The collected mud-water mixture was filtered, dried, and the particles of different colors were sieved, weighed, and the particle loss and gradation were analyzed. Based on the sensor data, the occurrence and development mechanism of piping was systematically analyzed, as well as the actual effect of the reinforcement on improving the embankment's resistance to collapse.

[0084] As described above, although the invention has been illustrated and described with reference to specific embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A model test device for simulating road surface collapse caused by rainfall infiltration, characterized in that, It includes a load-bearing module, a rainfall control module, a particle collection module, and a parameter monitoring module; The bearing module includes a rectangular model box (1), inside which a foundation (2) and an embankment (3) are filled from bottom to top. A scale for observing deformation is set vertically on the top of the model box. The rainfall control module is used to provide controlled simulated rainfall to the model box (1). It includes a water tank (12), an inlet pipe (11), an inlet valve (10), a flow meter (8), a booster pump (9), and a rainfall nozzle (6). One end of the inlet pipe (11) is connected to the water tank (12), and the other end is connected in series with the inlet valve (10), the booster pump (9), and the flow meter (8) to the rainfall nozzle (6) arranged on the top of the model box (1). The rainfall control module adjusts the rainfall through the coordinated control of the booster pump (9) and the flow meter (8) to ensure that the foundation triggers piping. The particle collection module is used to collect lost soil particles in layers, including collection pipes (13) set at different depths along the side wall of the model box (1) and filter boxes (14) connected to the collection pipes (13). The parameter monitoring module is used to monitor the changes in the physical and mechanical parameters of the soil during the test. It includes a pressure box, a pore water pressure sensor and a settlement plate buried in the embankment (3) and the foundation (2), as well as an external control terminal. The pressure box, the pore water pressure sensor and the settlement plate are electrically connected to the control terminal. The parameter monitoring module achieves accurate measurement of soil physical and mechanical parameters in the following way: the monitoring points in the foundation are arranged as follows: a monitoring section is set every 15cm along the foundation depth direction, and each section is simultaneously equipped with an earth pressure cell, a pore water pressure sensor and a settlement plate, and the layout range covers the entire foundation height. The collection pipe (13) is an arc-shaped pipe with a diameter of 50 mm, and is arranged at 22.5 cm intervals along the side wall of the model box (1).

2. The model test device for simulating road surface collapse caused by rainfall infiltration according to claim 1, characterized in that, The foundation (2) is composed of soil with a specific gradation. According to the mass ratio, the particle gradation satisfies the following: 100% of the particles are <10mm, 75% are <8mm, 30% are <4mm, 22% are <2mm, and 20% are <1mm. The monitoring points for the embankment are arranged as follows: a monitoring section is set up every 10cm along the height of the embankment, and each section is equipped with an earth pressure cell and a settlement plate, covering the entire height of the embankment.

3. The model test device for simulating road surface collapse caused by rainfall infiltration according to claim 2, characterized in that, The soil particle staining treatment of the foundation (2) uses a dyeing agent made by mixing acrylic pigment and matte acrylic gel medium. The weight ratio of dry gravel, medium and pigment is 100:5:(1~3).

4. The model test apparatus for simulating road surface collapse caused by rainfall infiltration according to any one of claims 1-3, characterized in that, At least one layer of reinforced body (4) is laid inside the embankment (3). The reinforced body (4) is arranged in layers along the height of the embankment (3), and the laying positions from bottom to top are 4cm, 8cm, 12cm, 16cm, 28cm, 40cm, 51cm, 54cm and 57cm respectively.

5. The model test device for simulating road surface collapse caused by rainfall infiltration according to claim 1, characterized in that, The dimensions of the model box are set to 180cm*100cm*200cm; The foundation (2) is 90cm high, the embankment (3) is 60cm high, and the scale ratio of the simulation device to the actual embankment is 1:

10.

6. A test method for a model test apparatus based on any one of claims 1-5 simulating road surface collapse caused by rainfall infiltration, characterized in that, Includes the following steps: Step S1: Device pretreatment: Place the model box (1) on a level field, clean the impurities inside the box, and set the height of the embankment (3), as well as the particle size distribution and rainfall flow parameters of the foundation (2) according to the test requirements; Step S2: Foundation filling and monitoring layout: After the foundation (2) is dyed with soil particles, the foundation (2) is filled in layers according to the design gradation. At the same time, pressure cells, pore water pressure sensors and settlement plates are buried in the embankment (3) and the foundation (2). Step S3: Embankment construction: Fill the embankment in layers according to the design height (3) fill material. If it is necessary to study the reinforcement effect, lay the reinforcement body (4) at the same time. Step S4: Module installation: Install the collection pipe (13) on the side wall of the model box (1) at preset intervals and connect it to the filter box (14). Then connect each component of the rainfall control module in sequence and check the pipeline connectivity. Step S5: Test run: Start the rainfall control module, adjust the rainfall intensity through the booster pump (9) and flow meter (8), and collect particles through the collection pipe (13); continuously monitor parameter data and observe the surface condition of the embankment (3) until piping occurs in the foundation; Step S6: Data processing: After the experiment, stop the rainfall, analyze the weight, color and gradation of the collected particles, and study the piping pattern and embankment collapse characteristics or reinforcement effect of the reinforced body (4) in combination with the parameter monitoring data.

7. The test method according to claim 6, characterized in that, In step S3, when filling the embankment (3) fill material in layers, it is necessary to compact each layer. When laying the reinforcement body (4), it is necessary to ensure that the reinforcement body (4) is flat and in close contact with the embankment (3) fill material to ensure effective load transfer. In step S6, the collected particle samples need to be filtered and dried first, and then the particles of different sizes are distinguished by sieving. Combined with the color of the dye to trace the original depth of the particles, the quantitative analysis of the piping process is realized.

8. The test method according to claim 6, characterized in that, In step S5, the rainfall is adjusted to ensure that piping is triggered. The specific process is as follows: Step S5.1: Extract the following parameters from the particle size distribution curve of the foundation soil for the calculation of the critical hydraulic gradient: relative density of soil particles Gs, void ratio e, permeability coefficient k, and characteristic particle sizes d5 and d6. 20 ; Where d5 is the particle size corresponding to 5% cumulative content in the particle size distribution curve, d 20 The particle size corresponding to a cumulative content of 20% was obtained from the curve; Step S5.2: Based on the parameters obtained in step S5.1, calculate the critical hydraulic gradient (icr) of the piping soil corresponding to the foundation according to the following formula. ; Step S5.3: Adjust the hydraulic gradient by controlling the rainfall and the infiltration rate: First, calculate the seepage flow rate using the following formula: Q 渗 =k×A×i, where i is the hydraulic gradient, i=h / L, h is the head difference of the seepage path, L is the length of the seepage path, i.e. the foundation height; A is the cross-sectional area through which the water flows. Secondly, determine the matching relationship between rainfall and infiltration rate: the rainfall at the top of the model box should be equal to or slightly greater than the infiltration rate, ignoring evaporation loss, i.e., the rainfall rate Q. 雨 ≈Q 渗 ; Third, calculate the critical seepage rate Qcr: when i = icr, Q 雨 =Q 渗 =Qcr=k×A×icr; Step S5.4: Adjustment operation of the rainfall control module: Start the booster pump and gradually open the inlet valve, monitoring the rainfall flow rate in real time using a flow meter; In the initial stage, the flow rate is adjusted to the lower limit, and the data of the pore water pressure sensor is continuously monitored. If there is no sudden increase in pore water pressure within 30 minutes, the pressure is gradually increased by the booster pump, so that the rainfall flow rate increases by 0.5 L / min per stage. When the pore water pressure at a certain depth is detected to be close to the effective stress of the soil, i.e., i≥icr, and micro-cracks appear on the embankment surface or fine particles flow out of the collection pipe, the current rainfall flow rate is locked and maintained at this intensity until piping stabilizes.

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