Patent Publication Number: US-2022236156-A1

Title: Triaxial test apparatus for measuring eroded soil particle under action of seepage force

Description:
TECHNICAL FIELD 
     The present invention relates to the technical field of geotechnical engineering, in particular to a triaxial test apparatus for measuring eroded soil particles under action of seepage force. 
     BACKGROUND ART 
     The seepage deformation of the soil can be divided into soil flowing, piping (also commonly referred to as internal erosion), contact scouring, and contact run-off. Soil flowing refers to the phenomenon that under action of seepage force, when the effective stress between particles is zero, particle groups suspend and move, which is called as soil flowing or sand flowing, most of the phenomenon occurs in saturated fine sand, silty sand and silt with uniform particle granular composition, it generally occurs suddenly and greatly harms engineering, soil flowing is formed by soil particles with various particle sizes moving, and does not refer to that the fine soil particles pass through the pores of the coarse soil particles to run off; and piping refers to the phenomenon that the fine particles are washed away or brought out of the pores of the coarse particles under the action of seepage. 
     A saturation mode of an existing device for measuring soil sample seepage erosion is that a soil sample is immersed in water for saturation, an erosion water head is provided by a suspension water tank, a seepage erosion path is from top to bottom, and lost particles after soil body erosion and the water are simply collected together. The seepage-erosion test method has the defects: 1, the sample is placed under the water head provided by the hoisted water tank for seepage erosion test, the provided water head range is limited, and the simulation erosion under the condition of coupling water head cyclic change and complex stress cyclic change cannot be achieved; 2, the lost particles after the soil body is eroded are not collected in a graded manner; and 3, the soil sample can only be immersed in water for rough saturation, and the soil body cannot meet the requirement for high saturation of the saturated soil sample in a unit body test, so the influence of saturation on the mechanical property of the sample cannot be avoided. 
     SUMMARY 
     The technical problem to be solved by the present invention is to provide a triaxial test apparatus for measuring eroded soil particles under action of seepage force. The test apparatus may simulate current crustal stress, so as to simulated and dynamically observe erosion phenomenon of a soil sample under the action of specific seepage force. 
     To this end, a triaxial test apparatus for measuring eroded soil particles under action of seepage force provided in the present invention includes a constant-flow seepage system, a soil particle transport grading measurement system, a large-range volume pressure control vacuum system and a data processing and analyzing system, where the constant-flow seepage system is connected to the soil particle transport grading measurement system and the large-range volume pressure control vacuum system by means of pipelines separately, the data processing and analyzing system includes a data acquisition device and a computer, the constant-flow seepage system, the soil particle transport grading measurement system and the large-range volume pressure control vacuum system are connected to the data acquisition device by means of lines separately, and the computer is connected to the data acquisition device by means of a line. 
     Preferably, the constant-flow seepage system includes a triaxial cell, an axial-force applying unit and a confining pressure applying unit, the triaxial cell including a cell outer cover, a base and a top cap, where a soil sample is arranged between the base and the top cap, and the cell outer cover is mounted on the base; the axial applying unit includes a first servo machine box and an upper cover, the base is mounted on the first servo machine box, the first servo machine box is connected to an axial piston rod, an upper portion of the axial piston rod is connected to the base, the upper cover is arranged on the top cap, and the upper cover is provided with an axial displacement sensor and an axial pressure sensor; and the confining pressure applying unit includes a second servo machine box, an oil tank and a confining pressure device, the confining pressure device being connected to the base by means of a pipeline, and the oil tank being mounted on the second servo machine box and connected to the base by means of a fifth pipeline. 
     Preferably, a taper hole is provided in the base, a first open hole and a second open hole are provided in the taper hole, the first open hole is connected to the large-range volume pressure control vacuum system by means of a first pipeline, a first flowmeter is arranged on the pipeline, the second open hole is connected to a confining pressure device by means of a second pipeline, the top cap is provided with an inverted taper hole, a third open hole and a fourth open hole are provided in the inverted taper hole, the third open hole is connected to a pressure sensor by means of a third pipeline, the fourth open hole is connected to the soil particle transport grading measurement system by means of a fourth pipeline, and a sensor and a second flowmeter are arranged on the fourth pipeline. 
     Preferably, the soil particle transport grading measurement system includes a first water storage tank and a multi-stage filter tank, the multi-stage filter tank being arranged in the first water storage tank, a water inlet is provided in the first water storage tank, an end, located in an inner cavity of the first water storage tank, of the water inlet is connected to a bell-mouthed pipeline, the other end of the bell-mouthed pipeline is in butt joint with the multi-stage filter tank, an end, located outside the first water storage tank, of the water inlet is provided with a first volume pressure controller, the first volume pressure controller is connected to the constant-flow seepage system by means of the fourth pipeline, and a water storage device is connected to a bottom of the first water storage tank by means of a sixth pipeline. 
     Preferably, one side of the first water storage tank is connected to a first air pump by means of a seventh pipeline, a two-way valve is arranged at a joint of the first water storage tank and the pipeline, a third flowmeter is arranged on the sixth pipeline, and a turbidimeter is arranged on the water storage device. 
     Preferably, the large-range volume pressure control vacuum system includes a second water storage tank and a second air pump, a blade fan is mounted in the second water storage tank, a two-way valve is arranged at an opening in one side of the second water storage tank, the second air pump is connected to the two-way valve by means of an eighth pipeline, an external second volume pressure controller is connected to a bottom of the second water storage tank by means of a pipeline, and the second volume pressure controller is connected to the constant-flow seepage system by means of the first pipeline. 
     Preferably, the first volume pressure controller, the second volume pressure controller, the first flowmeter, the second flowmeter, the third flowmeter, the confining pressure device, the pressure sensor, the sensor, the axial displacement sensor and the axial pressure sensor are connected to the data acquisition device by means of lines separately. 
     Preferably, an upper end and a lower end of the soil sample are provided with a porous bottom plate and water-permeable paper respectively. 
     Preferably, the multi-stage filter tank consists of at least three steel wire mesh layers, and the steel wire mesh layers have different pore diameters. 
     Preferably, the taper hole and the inverted taper hole are funnel-shaped. 
     The present disclosure has the following beneficial effects: 
     1. By arranging a constant-flow seepage system, a soil particle transport grading measurement system, a large-range volume pressure control vacuum system, and a data processing and analyzing system, an erosion phenomenon of a soil sample under the action of specific seepage force is simulated and dynamically observed, so as to provide an accurate and effective basic test data for research of a geological disaster causing mechanism corresponding to the erosion phenomenon. 
     2. The test apparatus applies seepage force under a back pressure saturation condition based on a triaxial test system and measures a seepage-erosion phenomenon, is suitable for various triaxial instruments, has high compatibility, and may meet different experimental requirements. 
     3. By setting confining pressure and back pressure, the confining pressure and the back pressure are supplied to the soil sample so as to simulate the current crustal stress, by setting the constant-flow seepage system, stable upward seepage is provided for the soil sample, back pressure saturation may be carried out on the soil sample before a test, and the back pressure is maintained in a whole experiment process. 
     4. A porous bottom plate is arranged on a base of a triaxial cell and an upper portion of the soil sample, a soil particle outflow channel is provided in a top cap, and a grading collection device is arranged, such that eroded soil particles may flow into the soil particle transport grading measurement system by means of the soil particle outflow channel of the top cap to be graded and collected, so as to provided basic experimental data for particle component change after the soil sample is corroded. 
     5. A turbidimeter is arranged in a water storage device of the soil particle transport grading measurement system so as to detect whether soil particles flowing out during seepage erosion are completely filtered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural schematic diagram of a triaxial test apparatus for measuring eroded soil particles under action of seepage force provided in the present invention; 
         FIG. 2  is a structural schematic diagram of position A of the triaxial test apparatus for measuring eroded soil particles under action of seepage force in  FIG. 1 ; 
         FIG. 3  is a structural schematic diagram of position B of the triaxial test apparatus for measuring eroded soil particles under action of seepage force in  FIG. 1 ; 
         FIG. 4  is a structural schematic diagram of a large-range volume pressure control vacuum system C of the triaxial test apparatus for measuring eroded soil particles under action of seepage force in  FIGS. 1 ; and 
         FIG. 5  is a structural schematic diagram of a soil particle transport grading measurement system B of the triaxial test apparatus for measuring eroded soil particles under action of seepage force in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be further elaborated hereafter in conjunction with accompanying drawings and the embodiments. The same parts are denoted by the same reference numerals. It should be noted that, as used in the following description, the words “front”, “rear”, “left”, “right”, “upper” and “lower” refer to directions in the accompanying drawings, and the words “bottom” and “top”, “inner” and “outer” refer to directions toward or away from, respectively, a geometric center of a particular component. 
     With reference to  FIG. 1 , the present invention provides a triaxial test apparatus for measuring eroded soil particles under action of seepage force. The triaxial test apparatus includes a constant-flow seepage system A, a soil particle transport grading measurement system B, a large-range volume pressure control vacuum system C and a data processing and analyzing system D. The constant-flow seepage system A is connected to the soil particle transport grading measurement system B and the large-range volume pressure control vacuum system C by means of pipelines separately, the data processing and analyzing system D includes a data acquisition device  41  and a computer  42 , the constant-flow seepage system, the soil particle transport grading measurement system and the large-range volume pressure control vacuum system are connected to the data acquisition device by means of lines separately, and the computer is connected to the data acquisition device by means of a line. 
     The constant-flow seepage system A includes a triaxial cell, an axial-force applying unit and a confining pressure applying unit, the triaxial cell including a cell outer cover  1 , a base  2  and a top cap  3 , where a soil sample  4  is arranged between the base  2  and the top cap  3 , and the cell outer cover  1  is mounted on the base  2 . The axial applying unit includes a first servo machine box  5  and an upper cover  6 , the base  2  is mounted on the first servo machine box  5 , the first servo machine box  5  is connected to an axial piston rod  7 , an upper portion of the axial piston rod  7  is connected to the base  2 . The upper cover  6  is arranged on the top cap  3 , the upper cover  6  is provided with an axial displacement sensor and an axial pressure sensor, and axial pressure is provided for the soil sample by means of the axial piston rod  7 . The confining pressure applying unit includes a second servo machine box  8 , an oil tank  9  and a confining pressure device  10 , the confining pressure device  10  being connected to the base  2  by means of a second pipeline  11 , and the confining pressure device  10  being a confining pressure sensor. The oil tank  9  is mounted on the second servo machine box  8 , the oil tank  9  is connected to the base by means of a fifth pipeline  12 , and the base is in communication with an inner cavity of the cell. Oil is injected into the triaxial cell by means of the oil tank  9 , the second servo machine box  8  and the fifth pipeline  12 , a cavity of the triaxial cell is filled with the oil, the oil is wrapped around a periphery of the soil sample, shaft closing is conducted in an oil filling process, confining pressure is set by means of the confining pressure sensor after oil filling, and the confining pressure is provided for the soil sample  4 . 
     An upper end and a lower end of the soil sample  4  are provided with a porous bottom plate  13  and water-permeable paper  14  respectively, that is, the porous bottom plate  13  and the water-permeable paper  14  are arranged between the soil sample and the base, and the porous bottom plate  13  and the water-permeable paper  14  are also arranged between the soil sample and the top cap. A taper hole  15  is provided in the base, the taper hole  15  is funnel-shaped, a first open hole and a second open hole are provided in the taper hole. The first open hole is connected to the external large-range volume pressure control vacuum system C by means of a first pipeline  16 , a first flowmeter  17  is arranged on the first pipeline  16 , and the constant-flow seepage system A is connected to the large-range volume pressure control vacuum system C by means of the first pipeline  16 . The second open hole is connected to the confining pressure device  10  by means of a second pipeline  11 . During testing, the large-range volume pressure control vacuum system provides inlet water for the constant-flow seepage system A by means of the first pipeline  16 , the water is input into the base  2  by means of the first pipeline and permeates into the soil sample by means of the first open hole and the porous bottom plate  13  and the water-permeable paper  14  at the lower end of the soil sample, and stable upward seepage and erosion are provided for the soil sample. The top cap is provided with an inverted taper hole  20 , the inverted taper hole  20  is funnel-shaped, a third open hole and a fourth open hole are provided in the inverted taper hole, and the inverted taper hole  20  is provided with an outflow channel for the soil particle. The third open hole is connected to a pressure sensor  22  by means of a third pipeline  21 , the fourth open hole is connected to the soil particle transport grading measurement system B by means of a fourth pipeline  23 , and a sensor  24  and a second flowmeter  25  are arranged on the fourth pipeline  23 . One end of the fourth pipeline  23  is connected to the fourth open hole, and the other end of the fourth pipeline  23  penetrates out of the triaxial cell to be connected to the soil particle transport grading measurement system B. The soil sample seeps upwards, and eroded soil particles passes through the porous bottom plate  13  and the water-permeable paper  14  at an upper end of the soil sample, and then are conveyed to a soil particle transport grading measurement system B by means of the inverted taper hole  20  and the fourth pipeline  23 . 
     The soil particle transport grading measurement system B includes a first water storage tank  26  and a multi-stage filter tank  27 , the multi-stage filter tank  27  being arranged in the first water storage tank  26 , and the multi-stage filter tank  27  is hoisted on a cover plate of the first water storage tank  26 . The multi-stage filter tank  27  consists of at least three steel wire mesh layers, the steel wire mesh layers having different pore diameters, and preferably, three steel wire mesh layers are steel wire meshes with three different types of pore diameters. A water inlet is provided in the first water storage tank  26 , an end, located in an inner cavity of the first water storage tank  26 , of the water inlet is connected to a bell-mouthed pipeline  28 , the other end of the bell-mouthed pipeline  28  is in butt joint with the multi-stage filter tank  27 . A water storage device  30  is connected to a bottom of the first water storage tank  26  by means of a sixth pipeline  29 , and a third flowmeter  31  is arranged on the sixth pipeline  29 . The eroded soil particle enters the multi-stage filter tank  27  in the first water storage tank by means of the fourth pipeline  23  and the bell-mouthed pipeline  28 . The eroded soil particle is filtered by the multi-stage filter tank, and the filtered water flows into the water storage device  30  by means of a sixth pipeline  29 . A turbidimeter  19  is arranged on the water storage device  30 , and the turbidimeter  19  is configured to detect whether the soil particles flowing out during seepage erosion are completely filtered. 
     An end, located outside the first water storage tank, of the water inlet of the first water storage tank  26  is provided with a first volume pressure controller  32 , and the other end of the fourth pipeline is connected to the first volume pressure controller  32 . One side of the first water storage tank is connected to a first air pump  34  by means of a seventh pipeline  33 , and a two-way valve  35  is arranged at a joint of the first water storage tank and the seventh pipeline  33 . The first air pump  34  is vacuumized by means of the two-way valve, the water in the first water storage tank  26  is made into air-free water, and back pressure is set for the soil sample by means of the first volume pressure controller  32 . 
     The large-range volume pressure control vacuum system C includes a second water storage tank  36  and a second air pump  37 , a blade fan  38  is mounted in the second water storage tank  36 , a two-way valve  35  is arranged at an opening in one side of the second water storage tank  36 , the second air pump  37  is connected to the two-way valve  35  by means of an eighth pipeline  39 , an external second volume pressure controller  40  is connected to a bottom of the second water storage tank  36  by means of the first pipeline  16 , and the second volume pressure controller  40  is connected to the constant-flow seepage system A by means of the first pipeline  16 . The second air pump  37  is vacuumized by means of the two-way valve  35 , meanwhile, the blade fan  38  works, the water in the second water storage tank  36  is made into air-free water, and back pressure is set for the soil sample by means of the second volume pressure controller  40 . The first volume pressure controller  32  and the second volume pressure controller  40  apply back pressure to the soil sample. 
     The first volume pressure controller  32 , the second volume pressure controller  40 , the first flowmeter  17 , the second flowmeter  25 , the third flowmeter  31 , the confining pressure sensor  10 , the pressure sensor  22 , the sensor  24 , the axial displacement sensor and the axial pressure sensor are connected to the data acquisition device  41  by means of lines separately, and the data acquisition device  41  is connected to the computer  42  by means of a line. The computer sets the back pressure by means of the first volume pressure controller  32  and the second volume pressure controller  40 . Flow of the inlet water is controlled and measured by means of the first flowmeter  17 , flow of the eroded soil particles is controlled and measured by means of the second flowmeter  25 , and flow of outlet water is controlled and measured by means of the third flowmeter  31 . The computer  42  sets confining pressure after oil filling by means of the confining pressure sensor  10 . A constant-flow seepage system, a soil particle transport grading measurement system, a large-range volume pressure control vacuum system, and a data processing and analyzing system are arranged by means of a computer, an erosion phenomenon of a soil sample under the action of specific seepage force is simulated and dynamically observed, so as to provide an accurate and effective basic test data for research of a geological disaster causing mechanism corresponding to the erosion phenomenon. 
     Before the test, the first volume pressure controller  32  and the second volume pressure controller  40  are configured to apply the back pressure to the soil sample  4 , back pressure saturation is carried out on the soil sample  4 , and the back pressure is maintained in the whole experiment process. Oil is injected into the triaxial cell by means of the oil tank  9 , the second servo machine box  8  and the fifth pipeline  12 , the confining pressure is set by means of the confining pressure sensor  10  after oil filling, and the confining pressure is provided for the soil sample. The axial piston rod  7  on the first servo machine box in the constant-flow seepage system A provides axial pressure for the soil sample. By means of the back pressure, the confining pressure and the axial pressure, complex current crustal stress is simulated, and complex stress cyclic change is simulated. During the test, after back pressure saturation is completed, the water in the first water storage tank  26  enters the base of the cell by means of the first pipeline  16 , and permeates and corrodes the soil sample by means of the first open hole, and the porous bottom plate  13  and the water-permeable paper  14  at the lower portion of the soil sample. The soil sample seeps upwards, and the eroded soil particle gushes out by means of the porous bottom plate  13  and the water-permeable paper  14  at the upper end of the soil sample, is conveyed to the bell-mouthed pipeline  28  by means of the fourth pipeline  23  and flows into the multi-stage filter tank  27 . The soil particles in the multi-stage filter tank  27  are subjected to graded filtration and collection, and the filtered water flows into the water storage device  30  by means of the sixth pipeline. The turbidimeter  19  on the water storage device is configured to detect whether the soil particles flowing out during seepage erosion are completely filtered. After the test, the multi-stage filter tank  27  is taken down, iron wire meshes with different pore diameters are separated, corresponding soil particles in the iron wire meshes are poured out, dried and weighed, so as to obtain the weight of the eroded soil particles by grading, and basic data are provided for particle component change after the soil sample is eroded. 
     The test apparatus applies seepage force under a back pressure saturation condition based on a triaxial cell, that is, a triaxial test system and measures a seepage-erosion phenomenon, is suitable for various triaxial instruments, has high compatibility, and may meet different experimental requirements. 
     What is described above is merely a preferred embodiment of the present invention, the scope of protection of the present invention is not limited to the above embodiment, and all the technical schemes belonging to the idea of the present invention belong to the scope of protection of the present invention. Several improvements and modifications are made by those of ordinary skill in the art without departing from the principles of the present disclosure, which should also be considered as the scope of protection of the present disclosure.