A loose soil particle dynamic migration test method based on solid-liquid gradual phase change

Abstract

The present application relates to the field of geotechnical simulation test, disclose a kind of loose soil particle dynamic migration test method based on solid-liquid gradual phase change, the test device used includes pressurized water supply system, test box system and water pressure monitoring system, test box system includes visual test box, the bottom of box has the water inlet of porous water-permeable plate, variable cross-section size ice column is placed on the plate, loose soil sample is layered and filled around ice column according to set density, and different layer height position of sample is divided into pressure measuring hole, overflow port is arranged above the position of loose soil sample surface;Water pressure monitoring system is used to measure the water pressure parameter at each pressure measuring hole;When testing, pressurized water supply system supplies water to test box system through the water inlet, the migration of loose soil sample is observed, the dynamic evolution process simulation of loose soil sample piping is carried out, and the water pressure change of different parts of loose soil sample in the test process is recorded, which can be used to intuitively reflect and study the piping instability mechanism of loose soil.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geotechnical simulation test, and particularly to a test method applied to a sand pebble progressive piping process. BACKGROUND

[0002] Among the many dangerous situations endangering the safety of embankments in major river basins in China, piping is one of the most widely distributed and most dangerous situations. Piping is subdivided into backward erosion piping and piping erosion. Backward erosion piping refers to the phenomenon that soil particles migrate away from the unprotected seepage outlet downstream or on the leeside of the embankment under the action of seepage and gradually form a concentrated seepage channel developing from the downstream or leeside to the upstream or water side. Piping erosion refers to the phenomenon that fine particles in the internal unstable soil are transported and lost in the skeleton pores of coarse particles under the action of seepage, gradually forming a locally hollowed and filled phenomenon in the foundation.

[0003] The mechanism of embankment piping collapse is complex, and has been the focus of research by scholars at home and abroad. Physical model test is one of the most important research methods. According to the simulated embankment soil layer structure, the physical model test of embankment piping can be roughly divided into single-layer, double-layer and multi-layer embankment piping physical model test. In the aspect of single-layer embankment piping test research, Liu Changjun et al. studied the failure mechanism of embankment piping erosion process, Yao Zhi xiong et al. studied the influence of particle size distribution on piping development, Robbins et al. measured the hydraulic conditions such as the horizontal critical hydraulic gradient of reverse erosion piping and the relationship between piping development speed and seepage velocity, Ni Xiaodong et al. studied the development law of erosion piping and the influence of external factors or seepage stability factors on the development process of erosion piping, Van den Boer et al. studied the influence of critical and supercritical hydraulic load on piping channel and eroded particles in small piping experiment. The single-layer embankment piping test better simulates the erosion and migration process of fine particles in the piping soil layer, and reveals the relationship between the properties of piping soil and the critical hydraulic conditions of piping. In the aspect of double-layer embankment piping test research, Mao Zhangxi et al. proposed that the horizontal average critical hydraulic slope of piping channel in double-layer embankment fine sand layer is about 0.1, which affects the safety of embankment, Li Guangxin et al. verified the seepage failure mode of binary structure embankment and the quantitative relationship between the depth of suspended impervious wall, embankment soil density and piping development, Liu Jie et al. studied the influence of the ratio of seepage coefficient of upper and lower soil layers on the seepage failure of embankment. In the aspect of multi-layer embankment piping test research, Ding Liqian et al. showed that the existence of strong permeable sand and gravel layer can reduce the horizontal average critical slope of embankment piping failure, Chen Jian sheng et al. studied the influence of different embankment soil layer structure and fine sand layer depth on the development of embankment piping and critical hydraulic gradient, Wang Fang et al. studied the influence of fine sand layer thickness on the critical hydraulic gradient, piping sand volume and channel development speed of piping.

[0004] The current piping simulation test cannot truly reflect the progressive failure process of piping difference, and cannot dynamically capture the evolution law of the flow field in the piping process. SUMMARY

[0005] In order to more fully and deeply study the piping instability mechanism of loose soil, better study the piping formation mechanism and flow field evolution law of loose soil under seepage action, the technical problem to be solved by the present application is to provide a loose soil particle dynamic migration test method based on solid-liquid gradual phase change.

[0006] The technical scheme adopted by the present application to solve its technical problem is: a loose soil particle dynamic migration test method based on solid-liquid gradual phase change, the test device used includes a pressurized water supply system, a test box system and a water pressure monitoring system.

[0007] The pressurized water supply system includes a water valve and a booster pump connected with a normal pressure water supply interface pipeline;

[0008] The test box system includes a visual test box enclosed by side plates and a bottom plate, the bottom plate of the test box is provided with a water inlet arranged with a porous water permeable plate, a single change variable cross-section size ice column is vertically arranged corresponding to the water inlet position, the large diameter end of the ice column is located on the porous water permeable plate, a loose soil sample is laid around the ice column on the bottom plate in the box, the loose soil sample is layered and filled according to the set density, and pressure measuring holes are arranged at different layer height positions, and an overflow port is arranged on the side plate higher than the surface of the loose soil sample;

[0009] The water pressure monitoring system includes pressure measuring pipes, connecting pipes and a scale, the pressure measuring pipes are connected with the pressure measuring holes one by one through the connecting pipes, and the scale is used to measure the liquid level of each pressure measuring pipe;

[0010] The pressurized water supply system supplies water to the test box system through the water inlet;

[0011] It includes the following steps:

[0012] (a) Install the simulation test device on a flat experimental site;

[0013] (b) Water is injected into the box through the top opening of the test box until the water level reaches the height of the overflow port;

[0014] (c) Adjust the scale and the pressure measuring pipe to keep them vertical;

[0015] (d) Open the water valve, adjust the pressure of the booster pump, observe and confirm that there is no water leakage phenomenon in the test box, and then close the water valve;

[0016] (e) Open the water valve, adjust the booster pump after the flow rate is stable, observe the migration of the loose soil sample, simulate the dynamic evolution process of the loose soil sample piping, and record the water pressure changes at different positions of the loose soil sample during the test.

[0017] The application has the beneficial effects that: by the progressive phase change of the ice column with variable cross-sectional size, the real process that the soil body at the water outlet is preferentially damaged and gradually evolves to the water inlet in the piping process is reflected, technical support can be provided for revealing dam foundation failure and reservoir bank slope instability caused by loose soil piping damage, and the application can be used for reflecting and studying the piping instability mechanism of loose soil. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic view of a loose soil particle dynamic migration test device based on solid-liquid progressive phase change adopted by the application.

[0019] Figure 2 is the water level evolution process of a loose soil sample piping process recorded by the test method of the application.

[0020] In the figure, 1 is a pressure measuring pipe, 2 is a scale, 3 is a connecting pipe, 4 is an overflow port, 5 is a test box, 6 is a control water level line, 7 is an ice column, 8 is a pressure measuring hole, 9 is a loose soil sample, 10 is a water inlet, 11 is a booster pump, 12 is a porous water permeable plate, 13 is a normal pressure water supply interface, 14 is a water valve, 15 is a piping channel, 16 is a flow direction, 51 is a bottom plate, and 52 is a side plate. DETAILED DESCRIPTION

[0021] The application will be further described below in combination with the drawings and examples.

[0022] Example:

[0023] As Figure 1As shown, the application is a kind of loose soil particle dynamic migration test method based on solid-liquid gradual phase change, and the loose soil particle dynamic migration test device based on solid-liquid gradual phase change comprises a pressurized water supply system, a test box system and a water pressure monitoring system. The pressurized water supply system comprises a water valve 14 and a booster pump 11 connected with a normal pressure water supply interface 13 pipeline. The test box system comprises a visual test box 5 enclosed by a side plate 52 and a bottom plate 51. The bottom plate 51 of the test box 5 is provided with a water inlet 10 arranged with a porous water permeable plate 12. A single change variable cross-section size ice column 7 is vertically arranged corresponding to the position of the water inlet 10. The large diameter end of the ice column 7 is located on the porous water permeable plate 12. A loose soil sample is laid around the ice column 7 on the bottom plate 51 in the box. The loose soil sample is layered and filled according to the set density, and pressure measuring holes 8 are arranged at different layer heights. An overflow port 4 is arranged on the side plate 52 above the surface of the loose soil sample. The water pressure monitoring system comprises a pressure measuring pipe 1, a connecting pipe 3 and a scale 2. The pressure measuring pipe 1 is connected with each pressure measuring hole 8 through the connecting pipe 3. The scale 2 is used to measure the liquid level of each pressure measuring pipe 1. The pressurized water supply system supplies water to the test box system through the water inlet 10. The connecting pipe 3 is recommended to be a plastic hose. In the water pressure monitoring system composed of the pressure measuring pipe 1, the connecting pipe 3 and the pressure measuring hole 8, the pressure measuring hole 8 can be made as small as possible, which has little effect on the loose soil sample and can obtain more accurate data. The sensor probe size of the digital water pressure monitoring device is large, which has great effect on the loose soil and may affect the accuracy of the test.

[0024] External normal pressure water is supplied to the test box 5 through the booster pump 11. The water supply system and the test box system adopt a porous water permeable plate 12 at the junction to ensure the normal flow of water. The test is controlled by opening / closing the water valve 14. Conventionally, the side plate 52 and the bottom plate 51 of the test box 5 are made of transparent tempered glass plates to ensure direct observation during the test. The variable cross-section size ice column 7 can be prefabricated by freezing the mixture of water and loose soil particles through a mold in the laboratory. The size changes at different heights. At the same temperature, the phase change is completed at the smaller diameter first, thereby simulating the phenomenon that the upper part is damaged first in the piping flow process. The water pressure monitoring system captures the water pressure of different parts of the sample in real time during the test process, reveals the flow field change law in the piping flow process, and simulates the dynamic migration process of loose soil particles.

[0025] The specific implementation steps of applying the above device to complete the test are as follows:

[0026] (1) Choose a flat experimental site, install the pressurized water supply system on the prefabricated test box 5, and ensure that the pipeline and the box body connection position has good sealing performance;

[0027] (ii) According to the geological conditions to be tested, the loose soil is laid in the test box 5 layer by layer according to the specified density to form a loose soil sample, and when the sample is prepared, the variable cross-section size ice column 7 is placed on the porous water permeable plate 12 in advance, and the ice column 7 is kept vertical, and the pressure measuring hole 8 is buried at different heights, and after the height reaches the required height, the top surface is trimmed to keep it flat;

[0028] (iii) Water is injected into the box through the top of the model box, so that the sand in the box is saturated, and the water level reaches the height of the overflow port 4, that is, the position of the control water level line 6;

[0029] (iv) The connecting pipe 3 is connected to each pressure measuring hole 8 and each pressure measuring pipe 1 of the water pressure testing device one by one, and the pressure measuring pipe 1 and the scale 2 are kept vertical;

[0030] (v) Open the water valve 14, and adjust the booster pump 11 to the maximum pressure, and observe whether there is water leakage phenomenon, if not, close the water valve 14, otherwise reconnect the booster water supply system until there is no water leakage phenomenon;

[0031] (vii) Open the water valve 14 again, and after the flow rate is stable, adjust the booster pump 11, observe the migration of the loose soil sample, reveal the dynamic evolution process simulation of the loose soil sample piping, and record the water pressure changes of different parts of the loose soil sample during the test process.

[0032] In addition, the test process can also be continuously recorded by camera, which is convenient for observing and determining the water pressure values of different parts of the sample at different time periods during the piping process of the loose soil sample.

[0033] The advantages of the present application are: at the same temperature, the phase change is completed at the smaller diameter first, thereby truly simulating the phenomenon that the upper part is damaged first during the piping process. Based on the progressive phase change of the variable cross-section size ice column, the differential damage process of the loose soil piping can be truly reflected, the pressure measuring hole 8 is buried at different heights in the loose soil sample 9, the water pressure of different parts of the sample during the test process is captured in real time, the flow field change law during the piping process is revealed, thereby simulating the dynamic migration process of the loose soil particles, revealing the piping instability mechanism of the loose soil, and providing technical support for evaluating the dam breach caused by the piping damage of the loose soil.

Claims

1. A method for testing the dynamic migration of loose soil particles based on solid-liquid progressive phase transition, characterized by: The testing equipment used includes a booster water supply system, a test chamber system, and a water pressure monitoring system; The booster water supply system includes a water valve (14) and a booster pump (11) connected to the atmospheric pressure water supply interface (13). The test chamber system includes a visual test chamber (5) enclosed by a side plate (52) and a bottom plate (51). The bottom plate (51) of the test chamber (5) is provided with an inlet (10) with a porous permeable plate (12). A monotonically changing variable cross-sectional size ice column (7) is vertically arranged corresponding to the position of the inlet (10). The large diameter end of the ice column (7) is located on the porous permeable plate (12). Loose soil sample (9) is laid around the ice column (7) on the bottom plate (51) inside the chamber. The loose soil sample (9) is filled in layers according to the set density, and pressure measuring holes (8) are distributed at different layer heights. An overflow port (4) is provided on the side plate (52) above the surface of the loose soil sample (9). The water pressure monitoring system includes a pressure measuring tube (1), a connecting tube (3) and a scale (2). The pressure measuring tube (1) is connected to each pressure measuring hole (8) one by one through the connecting tube (3). The scale (2) is used to measure the liquid level height of each pressure measuring tube (1). The pressurized water supply system supplies water to the test chamber system through the inlet (10), which includes the following steps: (a) Install the test apparatus on a flat experimental site; (b) Fill the test chamber with water through the top opening of the test chamber (5) until the water level reaches the height of the overflow port (4); (c) Adjust the scale (2) and the pressure measuring tube (1) to keep them both vertical; (d) Open the water valve (14), adjust the pressure of the booster pump (11), observe and confirm that there is no water leakage in the test chamber (5), and then close the water valve (14). (e) Open the water valve (14), and after the flow rate stabilizes, adjust the booster pump (11), observe the movement of the loose soil sample (9), simulate the dynamic evolution process of piping in the loose soil sample (9), and record the water pressure changes at different parts of the loose soil sample (9) during the test.

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