CN111579454B

CN111579454B - Test device and test method for simulating horizontal seepage erosion of fine particles in sandy soil

Info

Publication number: CN111579454B
Application number: CN202010408422.8A
Authority: CN
Inventors: 张雪涵; 周明辉; 汪旭玮; 许烨霜
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-05-14
Filing date: 2020-05-14
Publication date: 2021-05-07
Anticipated expiration: 2040-05-14
Also published as: CN111579454A

Abstract

The invention provides a test device and a test method for simulating horizontal seepage erosion of fine particles in sandy soil, which comprises a soil body storage system, a first water tank, a buffer cylinder, a second water tank and a plurality of pressure measuring pipes, wherein the soil body storage system is formed by sequentially assembling a head end test cylinder, a plurality of middle test cylinders and a tail end test cylinder into a whole; the buffer cylinder is used for preventing fine particles of a soil sample in the soil body storage system from reversely permeating into the first water tank and connected to the end part of the head end test cylinder; the second water tank is arranged below the tail end filter screen and used for storing water and collecting fine particles corroded from the soil sample; the pressure measuring pipe is connected with the test cylinder. The invention can simulate the indoor test of the horizontal seepage erosion of fine particles in the sandy soil and research the horizontal seepage erosion process of the fine particles in the sandy soil and the influence rule of the horizontal seepage erosion process on the change of the sandy soil.

Description

Test device and test method for simulating horizontal seepage erosion of fine particles in sandy soil

Technical Field

The invention relates to a seepage erosion test method in the technical field of constructional engineering, in particular to a test device and a test method for simulating horizontal seepage erosion of fine particles in sandy soil.

Background

Seepage erosion refers to the phenomenon that fine particles in soil move and run off in pores among coarse particles under the action of seepage water flow. In recent years, various researches aiming at seepage erosion show that in the field of underground engineering or geological disaster prevention and control, if seepage erosion is given to continue to develop, the porosity ratio of a soil body is increased, the rigidity is reduced, the brittleness is increased, anisotropy is presented, and the engineering safety is endangered. In the field of geological disaster prevention and control, soil around a water collection building can change soil parameters of a retaining dam to finally cause piping after long-term seepage erosion, and geological disasters such as landslide, debris flow and the like can be caused by slope runoff erosion. In the field of underground engineering, particularly in regions with high underground water levels, in the seepage process, pore water erodes and erodes a soil framework to enable fine particles to move in pores to cause fine particle loss, and soil particles are rearranged and deposited to cause the change of mechanical properties such as soil microstructure, permeability, strength and the like, and finally cause the settlement of a building (structure) and the surrounding ground. After the sandy soil seepage erosion, fine particles can be gradually lost, and the change rule of the sandy soil property such as permeability coefficient, particle gradation, dry density and the like caused by the gradual loss of the fine particles is analyzed on a microscopic scale, so that the method has higher requirements on the indoor test precision. Most of the existing experimental researches for seepage erosion adopt a vertical seepage mode, but the experimental researches for seepage in the horizontal direction are less, and even a small amount of horizontal seepage erosion experiments are deficient in the experimental precision.

The prior technical literature is searched to find that: chinese patent with application number CN201820463051.1, disclosing "an experimental apparatus for measuring seepage erosion"; the device can simulate the erosion process of fine particles in the seepage process under different hydraulic gradients, and determine the influence of the seepage erosion on the geometry and hydraulic performance of the soil body, but the simulated seepage direction is only vertical. Chinese patent with application number CN201710807447.3, disclosing a "horizontal seepage experimental device and its experimental method"; the device can effectively simulate the layered accumulation condition of the rock-soil medium body in the nature, can accurately measure the horizontal permeability coefficient of the rock-soil medium body, and is difficult to simulate the soil body seepage erosion process and the change of the soil property after seepage erosion. The Chinese patent with the application number of CN201810056057.1 discloses an indoor test method for simulating seepage erosion of fine particles in deep aquifer sandy soil, which can be used for determining the seepage erosion process of the fine particles in the deep aquifer sandy soil and the influence of the seepage erosion process on the deformation of the aquifer sandy soil and mainly aims to obtain the sandy soil deformation. Although the analysis of the particle change was also conducted, the implementation procedure of this patent was too rough especially in the process of laying the soil sample in the soil reservoir having a relatively large volume, and thus the obtained result of the particle change was likely to be caused by the test error, the test accuracy was low, and the amount of the fine particles lost to the outside of the test tank due to erosion, that is, the amount of the fine particles lost, could not be measured.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a test device and a test method for simulating horizontal seepage erosion of fine particles in sandy soil.

The invention provides a test device for simulating horizontal seepage erosion of fine particles in sandy soil, which comprises:

the soil body storage system comprises a test cylinder for placing a soil sample, wherein the test cylinder comprises a head end test cylinder, a plurality of middle test cylinders and a tail end test cylinder, the head end test cylinder, the plurality of middle test cylinders and the tail end test cylinder are sequentially assembled into a whole head and tail, and the head end test cylinder and the tail end test cylinder are respectively positioned at two ends of the plurality of middle test cylinders; the outer wall of the test cylinder body is provided with a pressure measuring pipe interface for inserting a pressure measuring pipe, and the pressure measuring pipe interface is vertical to the axis direction of the cylinder body; the end face of one side of the tail end test cylinder is provided with a tail end filter screen, the outer side of the tail end filter screen is provided with a base, and the base can seal the end face of the tail end test cylinder;

the first water tank is arranged on one side of the soil body storage system and used for storing water and regulating and controlling the test water level, and a plurality of overflow ports and a plurality of water outlets which are symmetrically distributed are respectively arranged on the two sides of the first water tank along the height direction;

the buffer cylinder is arranged at one end of the head end test cylinder and is used for preventing fine particles of the soil sample in the soil mass storage system from reversely permeating into the first water tank; one end of the buffering cylinder is connected with the end part of the head end test cylinder, and the other end of the buffering cylinder is communicated with the water outlet of the first water tank through a pipeline;

a second water tank having a water outlet disposed below the end screen, the second water tank for storing water and collecting fine particles eroded from the soil sample;

the pressure measuring pipe is arranged above the test cylinder and is perpendicular to the axial direction of the test cylinder, and the lower end of the pressure measuring pipe is inserted into the pressure measuring pipe interface; the pressure measuring pipes obtain pressure measuring water levels of the test cylinders, and the number of the pressure measuring pipes is matched with that of the test cylinders.

Preferably, the head end test cylinder, the middle test cylinder and the tail end test cylinder comprise cylinder bodies and flange plates, and barrier rings perpendicular to the axis direction are respectively arranged on the inner wall of each cylinder body close to openings at two ends of each cylinder body and used for preventing a seepage path along the cylinder wall from being formed; the flange plates are arranged at two end parts of the cylinder body, and the inner diameter of each flange plate is the same as the diameter of the cylinder body; and the flange plate is provided with a bolt port.

Preferably, the buffer cylinder comprises a cylinder body, a partition plate and a cover plate, wherein the partition plate and the cover plate are respectively arranged on two end faces of the cylinder body, and the cylinder body of the buffer cylinder is matched with the test cylinder in shape and size; the outer wall of the cylinder body is provided with an air outlet for discharging air, and the air outlet is vertical to the axial direction of the cylinder body; the baffle plate is provided with a plurality of bolt holes which are uniformly distributed around the circle center and is used for preventing fine particles in the soil sample of the test cylinder from reversely permeating into the buffer cylinder along with water flow; the cover plate is provided with a water inlet used for being connected with the pipeline, so that water flow of the first water tank flows into the barrel body from the water inlet.

Preferably, the partition plate comprises a circular plate area and a porous area, the circular plate area is located at the outer ring of the porous area, the circular plate area is used for connecting the test cylinder, the diameter of the porous area is consistent with the inner diameter of the cylinder body, and the bolt holes are distributed in the circular plate area.

Preferably, the water inlet of the cover plate is provided with a first water stop valve.

Preferably, the pressure measuring tube comprises a span and a threaded segment, wherein: the pipe wall of the measuring range section is marked with scales; the thread section is provided with threads, and the length of the thread section is matched with the pressure measuring pipe interface.

Preferably, the overflow port and the water outlet of the first water tank are provided with second water stop valves; and a third water stop valve is arranged at the water outlet of the second water tank.

Preferably, the type of end screen comprises a mesh screen and an open screen, wherein: the mesh filter screen the opening filter screen is fine steel wire net, and the opening filter screen is equipped with the opening of certain width on fine steel wire net.

Preferably, the test device for simulating horizontal seepage erosion of fine particles in sandy soil comprises a U-shaped bracket for supporting the soil body storage system and the buffer cylinder.

The invention provides a test method for simulating horizontal seepage erosion of fine particles in sandy soil, which comprises the following steps:

s1, preparing a soil sample to be tested, wherein the soil sample is sandy soil containing fine particles, and the initial particle gradation is measured according to geotechnical test specifications;

s2, assembling a soil body storage system and paving a soil sample in the soil body storage system;

s2.1, connecting one end of a tail end test cylinder with a tail end filter screen and a base, vertically placing the tail end test cylinder with the base facing downwards, and closing a pressure measuring pipe interface of the tail end test cylinder to prevent the pressure measuring pipe interface from leaking water;

s2.2, paving the soil sample prepared in the S1 into the tail end test cylinder in an equal thickness mode in a grading mode, adding water to saturate, tamping each paved layer until no air bubbles emerge on the saturated soil sample surface, and completely leveling the soil sample and the opening of the tail end test cylinder after the last paved layer is full;

s2.3, connecting one end of the first middle test cylinder with the upper end of the tail end test cylinder of the paved soil sample, repeating the step S2.2, paving the soil sample in the first middle test cylinder in a graded equal thickness mode, adding water for saturation, closing a pressure measuring pipe interface of the first middle test cylinder, and preventing the pressure measuring pipe interface from leaking water;

s2.4, connecting one end of a second middle test cylinder with the upper end of the first middle test cylinder paved with the soil sample, repeating the step S2.2, paving the soil sample into the second middle test cylinder, adding water for saturation, closing a pressure measuring pipe interface of the second middle test cylinder, and preventing the pressure measuring pipe interface from leaking water;

s2.5, sequentially connecting all the middle test cylinders and the head end test cylinders to complete the assembly of the soil body storage system, laying a soil sample in each test cylinder repeatedly by the step S2.2, adding water for saturation, and closing a pressure measuring pipe interface of each test cylinder;

s3, connecting the buffer cylinder with the soil body storage system, placing one end of a partition plate of the buffer cylinder downwards at the upper end of the head end test cylinder with the spread soil sample, connecting a circular plate area of the partition plate with a flange of the head end test cylinder, and closing an air outlet of the buffer cylinder;

s4, setting an initial water level to enable the soil sample to be detected in the soil mass storage system to be saturated and solidified;

s4.1, horizontally placing the soil body storage system and the buffer cylinders, enabling the pressure measuring pipe interfaces of each test cylinder to face upwards, opening all the pressure measuring pipe interfaces, screwing in the pressure measuring pipes one by one at each pressure measuring pipe interface, and ensuring that each pressure measuring pipe is perpendicular to a horizontal plane;

s4.2, placing a first water tank on a horizontal support table, enabling a water outlet at the lowest part of the first water tank to be higher than the bottom surface of the piezometric tube of the test cylinder by a certain distance, and then communicating the water outlet with a water inlet of the buffer cylinder through a pipeline;

s4.3, continuously injecting water into the first water tank, simultaneously opening an overflow port and a water outlet at the lowest part of the first water tank and a water inlet of the buffer cylinder, and guiding water flow into the buffer cylinder and the soil body storage system until the readings of all the pressure measuring pipes are stabilized at the same horizontal line, and completing the saturated consolidation of the soil sample in the soil body storage system;

s5, dismantling the base of the soil body storage system, setting a normal water level difference, and carrying out a horizontal seepage erosion control test on fine particles in sandy soil; the normal water level difference is set by a control test; the water level difference is the height difference between the water level in the first water tank and the bottom surface of the piezometer tube on the test cylinder;

s5.1, closing the water outlet, the overflow port and the water inlet of the buffering cylinder in the step S4.3, removing the base on the tail end testing cylinder, and placing a second water tank under a tail end filter screen of the tail end testing cylinder;

s5.2, selecting a corresponding water outlet on the first water tank according to the normal water level difference required by the test, connecting the water outlet with the water inlet of the buffering cylinder through a pipeline, opening the water outlet, an overflow port which is positioned on the same horizontal line with the water outlet, the water inlet of the buffering cylinder and the water outlet of the second water tank, and starting a seepage erosion test when water seeps out from a tail end filter screen;

s5.3, in the test process, reading the readings of the pressure measuring pipes of the saturated soil samples in all the test cylinders at intervals in the seepage erosion process to obtain the pressure measuring water level, and drawing a curve relation graph of the pressure measuring water level and the time;

s5.4, when reading the reading of the piezometer tube of the saturated soil sample in the tail end test cylinder in S5.3, placing the measuring cylinder between the tail end filter screen and the second water tank to bear the water yield for a certain time, converting the water yield into flow rate, and drawing a curve relation graph of the flow rate and the time; determining the change rule of the permeability coefficient at each moment along the seepage path according to the flow rate and the pressure measuring water level at each moment by combining the pressure measuring water level and time curve relation diagram of S5.3;

s5.5, after the seepage erosion test is finished, removing the soil body storage system, collecting a plurality of samples in each test cylinder by using a soil sampler according to the principle of in-situ soil sampling, measuring the grain composition and the dry density of the samples after each test according to the geotechnical test specification requirements, and determining the change rule of the grain composition and the dry density after the test along the seepage path;

s6, carrying out horizontal seepage erosion test on fine particles in the sandy soil under the action of different water head;

s6.1, keeping the content of fine particles of the soil sample unchanged, enabling the type of a tail end filter screen to be a mesh filter screen and keeping the aperture of the filter screen unchanged, and controlling the water level difference by adjusting the height of a water outlet of the first water tank to simulate a seepage erosion test under the action of different water level differences; carrying out S1-S5 in the seepage erosion test under the action of each water level difference, and determining the permeability coefficient at different moments under each water level difference, the grain composition after the test and the change rule of the dry density along the seepage path;

s6.2, after all seepage tests with different water head differences are carried out, analyzing the permeability coefficients at different moments determined by the S6.1, and the relationship between the change rule of the grain composition and the dry density along the seepage path after the tests and the water head differences;

s7, carrying out horizontal seepage erosion test on fine particles in the sandy soil under the influence of different fine particle contents;

s7.1, keeping the height of a water outlet of the first water tank constant to ensure that the constant water level difference is constant, selecting a grid filter screen as the type of the tail end filter screen, keeping the aperture of a filter screen of the grid filter screen constant, and carrying out seepage erosion tests under the influence of different fine particle contents by changing the content of fine particles in the soil sample; carrying out S1-S5 on seepage erosion tests under the influence of each fine particle content, and determining the permeability coefficient, the particle gradation after the tests and the change rule of the dry density along the seepage path at different moments under each fine particle content;

s7.2, after all seepage tests with different fine particle contents are carried out, analyzing the seepage coefficients determined at different moments in the S7.1, and the relationship between the change rule of the tested particle gradation and dry density along the seepage path and the fine particle contents;

s8, carrying out horizontal seepage erosion test on fine particles in the sandy soil under the influence of different fine particle loss amounts;

s8.1, keeping the content of fine particles of the soil sample unchanged, keeping the height of a water outlet of the first water tank constant, ensuring that the normal water level difference is unchanged, selecting an open filter screen as a tail end filter screen type, and performing seepage erosion tests under the influence of different fine particle loss amounts by adjusting the opening width of the open filter screen; S1-S5 is firstly carried out in each seepage erosion test under the influence of the fine particle loss, and the permeability coefficient, the particle grading after the test and the change rule of the dry density along the seepage path at different moments under each fine particle loss are determined;

s8.2, after the seepage erosion test under each opening filter screen width condition is finished, collecting all etched fine particles on the filtering device of the second water tank, drying the fine particles, and weighing to obtain the fine particle loss amount;

and S8.3, after the seepage test is completely carried out under the influence of different fine particle seepage quantities, analyzing the seepage coefficients of the S8.1 at different moments, and analyzing the relationship between the change rule of the particle gradation and the dry density along the seepage path after the test and the fine particle seepage quantity.

Compared with the prior art, the invention has at least one of the following beneficial effects:

according to the test device and the test method, the test device is provided with a soil mass storage system for placing a soil sample, a buffer cylinder for preventing fine particles in the soil sample from reversely permeating into a first water tank, the first water tank and a second water tank which are arranged on the upstream and downstream of the soil mass storage system, the first water tank is a water storage device with different water levels, and the second water tank is used for storing water and collecting fine particles corroded from the soil sample in the soil mass storage system; the test method can accurately simulate the horizontal seepage erosion process of fine particles in sandy soil and the influence rule of the horizontal seepage erosion process on the change of the sandy soil property under the conditions of different water level differences, different fine particle contents and different fine particle loss amounts by adopting the test device. Makes up for the deficiency of the horizontal seepage erosion test of fine particles in the sandy soil.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1a is a front view of the overall structure of a test apparatus according to a preferred embodiment of the present invention;

FIG. 1b is a top view of the overall structure of a test apparatus according to a preferred embodiment of the present invention;

FIG. 2a is a front view of a first tank structure in accordance with a preferred embodiment of the present invention;

FIG. 2b is a left side view of the first tank structure in accordance with a preferred embodiment of the present invention;

FIG. 2c is a right side view of the first tank structure in accordance with a preferred embodiment of the present invention;

FIG. 3a is a front view of a second tank structure in accordance with a preferred embodiment of the present invention;

FIG. 3b is a top view of a second tank structure in accordance with a preferred embodiment of the present invention;

figure 4a is a front elevation view of the soil storage system configuration of a preferred embodiment of the present invention;

figure 4b is a left side view of the soil storage system configuration of a preferred embodiment of the present invention;

figure 4c is a right side view of the soil storage system configuration of a preferred embodiment of the present invention;

FIG. 5a is a front view of a trial cylinder configuration according to a preferred embodiment of the invention;

FIG. 5b is a left side view of a trial cylinder configuration of a preferred embodiment of the present invention;

FIG. 5c is a right side view of a trial cylinder configuration of a preferred embodiment of the present invention;

FIG. 6a is a schematic view of a mesh screen of an end screen according to a preferred embodiment of the present invention;

FIG. 6b is an open ended filter of a preferred embodiment of the present invention;

FIG. 7a is a front view of a buffer cylinder structure according to a preferred embodiment of the present invention;

FIG. 7b is a left side view of the buffer cylinder structure in accordance with a preferred embodiment of the present invention;

FIG. 7c is a right side view of a buffer cylinder configuration in accordance with a preferred embodiment of the present invention;

FIG. 8 is a schematic view of a piezometer tube according to a preferred embodiment of the invention;

the scores in the figure are indicated as: 1 is a first water tank, 2 is a second water tank, 3 is a soil mass storage system, 4 is a buffer cylinder, 5 is a pressure measuring pipe, 6 is a rubber water pipe, 11 is a tank body of the first water tank, 12 is an overflow port, 121 is a first overflow port, 122 is a second overflow port, 123 is a third overflow port, 124 is a fourth overflow port, 125 is a fifth overflow port, 126 is a sixth overflow port, 127 is a seventh overflow port, 13 is a water outlet, 131 is a first water outlet, 132 is a second water outlet, 133 is a third water outlet, 134 is a fourth water outlet, 135 is a fifth water outlet, 136 is a sixth water outlet, 137 is a seventh water outlet, 21 is an open-type tank body, 211 is a second water tank water outlet, 22 is a filter device, 221 is an acrylic hollow plate, 222 is a circular steel wire mesh, 31 is a test cylinder, 311 is a cylinder body, 3111 is a pressure measuring pipe joint, 3112 is a barrier ring, 312 is a flange, 32 is a middle test cylinder, 321 is a first middle test cylinder, 322 is a second middle test cylinder, 323 is a third middle test cylinder, 324 is a fourth middle test cylinder, 33 is an end test cylinder, 34 is an end filter screen, 341 is an end filter screen circular plate, 342 is a steel wire filter screen, 3421 is a steel wire filter screen of a grid filter screen, 3422 is a steel wire filter screen of an opening filter screen, 41 is a buffer cylinder body, 411 is a buffer cylinder exhaust port, 42 is a cover plate, 421 is a buffer cylinder water inlet, 43 is a baffle plate, 431 is a circular plate area, 432 is a porous area, 51 is a range section, and 52 is a thread section.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

Referring to fig. 1a and 1b, a front view and a top view of an overall structure of a testing apparatus for simulating horizontal seepage erosion of fine particles in sandy soil according to a preferred embodiment of the present invention are shown, and the testing apparatus includes a soil storage system 3, a first water tank 1, a pipeline 6, a buffer cylinder 4, a second water tank 2, and a plurality of pressure measuring pipes 5. The test device can simulate an indoor test of horizontal seepage erosion of fine particles in sandy soil, so that the horizontal seepage erosion process of the fine particles in the sandy soil and the influence rule of the horizontal seepage erosion process on the change of the sandy soil property are researched.

Referring to figure 1a, the soil storage system 3 comprises a test cylinder for placing a soil sample. Referring to fig. 4a, 4b and 4c, the testing cylinders include a head end testing cylinder 31, a plurality of middle testing cylinders 32 and a tail end testing cylinder 33, the head end testing cylinder 31, the plurality of middle testing cylinders 32 and the tail end testing cylinder 33 are sequentially assembled into a whole, and the head end testing cylinder 31 and the tail end testing cylinder 33 are respectively located at two ends of the plurality of middle testing cylinders 32, so as to form the soil body storage system 3. Referring to fig. 4a, the end face of the end test cylinder 33 is provided with an end screen 34, the outer side of the end screen 34 is provided with a base, the outer side of the end screen 34 is detachably connected with the base, and the base can close the end face of the end test cylinder 33. As a preferable mode, the base can be a circular wood board, the diameter of the circular wood board is 4 times of the diameter of the cylinder body 311 of the end test cylinder 33, a plurality of bolt openings are evenly distributed on the circular wood board around the center of the circle, and the positions, the apertures and the number of the bolt openings are the same as those of the bolt openings on the flange plate 312 of the end test cylinder 33. In one embodiment, a round wood board having a thickness of about 8mm may be used.

As shown in fig. 5a, 5b and 5c, the first test cylinder 31, the plurality of intermediate test cylinders 32 and the last test cylinder 33 are identical in configuration and size. The head end test cylinder 31, the middle test cylinder 32, and the tail end test cylinder 33 are each composed of a cylinder body 311 and a flange 312, and the flange 312 is fixed to both ends of the cylinder body 311 in a direction perpendicular to the cylinder axis. On the inner wall of the cylinder 311 near the openings at both ends, a barrier ring 3112 is disposed perpendicular to the axial direction for preventing the formation of a seepage path along the cylinder wall. Preferably, the inner diameter of the flange 312 is the same as the diameter of the cylinder 311. The outer diameter of the flange 312 is 2.3 times of the inner diameter of the flange, and the positions, the number and the hole diameters of bolt openings on the flange 312 are determined according to the test requirements. The cylinder 311 is a thin-walled acrylic cylinder.

In one embodiment, and as shown in figures 4a, 4b and 4c, the soil storage system 3 is comprised of 1 head test cylinder 31, 4 intermediate test cylinders 32 (first intermediate test cylinder 321, second intermediate test cylinder 322, third intermediate test cylinder 323, fourth intermediate test cylinder 324), 1 end test cylinder 33 and an end screen 34. The head end test cylinder 31, the intermediate test cylinder 32, and the tail end test cylinder 33 are connected to each other, and the head end test cylinder 31 side is connected to the buffer cylinder 4, and the tail end test cylinder 33 side is connected to the tail end screen 34. The cylinder body 311 of the head end test cylinder 31, the middle test cylinder 32 and the tail end test cylinder 33 can be selected from, but not limited to, cylinders having a wall thickness of 12mm, a diameter of 80mm and a length of 125 mm. A barrier ring 3112 with a thickness of 1mm perpendicular to the axial direction is arranged on the inner wall of the cylinder 311 near the opening 10mm at both ends. The two ends of the cylinder body 311 of the test cylinder are opened, vertical axes are fixed with flange plates 312 with the wall thickness of 5mm, the inner diameter of 80mm and the outer diameter of 184mm, and 8 bolt ports with the bore diameter of 6mm are evenly distributed on the flange plates 312 on a circle with the radius of the circle center of 70 mm.

As shown in fig. 5a, 5b, and 5c, a pressure-measuring pipe port 3111 for inserting the pressure-measuring pipe 5 is provided on the outer wall of the cylindrical body 311 of the head end test cylinder 31, the plurality of intermediate test cylinders 32, and the tail end test cylinder 33, the pressure-measuring pipe port 3111 penetrates the inner wall of the cylindrical body 311, and the pressure-measuring pipe port 3111 is perpendicular to the axial direction of the cylindrical body 311 of the test cylinder. As a preferable mode, the pressure measuring pipe connector 3111 is disposed at the midpoint of the outer wall of the barrel 311 of the testing cylinder along the axial direction, and the pressure measuring pipe connector 3111 may be a hollow column with a thread on the inner diameter surface for inserting the pressure measuring pipe 5, and the size of the pressure measuring pipe connector 311is determined according to the experimental requirements. The pressure tube interface 3111 may employ the following dimensional parameters: the opening aperture of the pressure measuring tube connector 3111 is 10mm, the inner diameter of the hollow column is 10mm, the outer diameter is 16mm, and the length is 22 mm.

The end part of the head end test cylinder 31 is provided with a buffer cylinder 4 which can prevent fine particles of a soil sample in the soil body storage system 3 from reversely permeating into the first water tank 1. One end of the buffering cylinder 4 is connected with the end of the head end test cylinder 31, and the water inlet 421 at the other end of the buffering cylinder 4 is communicated with the water outlet 13 of the first water tank 1 through a pipeline.

Referring to fig. 1a, a first water tank 1 is provided at one side of a buffer cylinder 4, upstream of a soil mass storage system 3, and the first water tank 1 is used for storing water and regulating and controlling a test water level. The first water tank 1 is communicated with the buffer cylinder 4 through a pipeline, so that water in the first water tank 1 enters the buffer cylinder 4 through the pipeline and flows into the soil storage system 3. The pipeline can adopt a rubber water pipe 6. Referring to fig. 2a, 2b and 2c, a left side wall of the first tank 11 is provided with a plurality of water outlets 13 uniformly distributed from the bottom to the top along a central line, and a right side wall of the first tank 1 is provided with a plurality of overflow ports 12 uniformly distributed from the bottom to the top along a central line; the first water tank 1 adjusts the water level difference by arranging water outlets 13 with different heights. The water outlets 13 on both sides and the overflow ports 12 are symmetrically arranged one by one, that is, one water outlet 13 at any height corresponds to one overflow port 12 with the same height. The water can be slowly and uninterruptedly filled into the first water tank 1 by being close to the water pipe above the first water tank 1. Preferably, the water outlet 13 of the first water tank 1 is used for connecting the buffer cylinder 4. The aperture, the number and the height of the water outlets 13 of the first water tank 1 are determined according to the test requirements, and all the water outlets 13 are provided with second water stop valves. The overflow ports 12 are used for controlling the water level of the first water tank 1, the aperture, the number and the height of the overflow ports 12 are consistent with those of the water outlet 13 of the first water tank 1, and the second water stop valves are installed on the overflow ports 12 of all the first water tanks 1. The box body 11 of the first water tank is an open organic glass box with a square cross section, and the size of the box body is determined according to the test requirements.

A second water tank 2 is placed just below the end screen 34 downstream of the soil storage system 3, the second water tank 2 being used to store water and collect fine particles eroded from the soil sample. Referring to fig. 3a, the second tank 2 comprises a box 21 open at the top and a filter 22, the filter 22 resting in an open top above the box 21 and being able to collect fine particles eroded from the upper end screen 34. The tank 21 is capable of collecting water flowing from the soil storage system 3. One side of the second water tank 2 is provided with a second water tank water outlet 211, the second water tank water outlet 211 is arranged on the side wall of the tank body 21, and the aperture and the height of the second water tank water outlet 211 are determined according to the test requirements. Preferably, the second water tank 2 is an open plexiglas tank with a square cross-section, and the size of the tank is determined according to the test requirements. And a third water stop valve is arranged at the water outlet 211 of the second water tank.

Referring to fig. 3b, the filter 22 on the second water tank 2 may be an acrylic hollow plate 221 with a square cross section, a circular steel wire mesh 222 is embedded in the hollow portion, the side length of the acrylic hollow plate 221 is slightly larger than that of the cross section of the tank body, the diameter of the circular steel wire mesh 222 is slightly smaller than that of the cross section of the open tank body 21, it is ensured that the circular steel wire mesh 222 is placed in the cross section range of the open tank body 21 of the second water tank 2, and the aperture of the steel wire mesh is determined according to the test requirements.

The testing device comprises a plurality of pressure measuring pipes 5, the pressure measuring pipes 5 are arranged above the testing cylinder and are perpendicular to the axial direction of the testing cylinder, and the lower ends of the pressure measuring pipes 5 are inserted into a pressure measuring pipe interface 3111. And the pressure measuring pipes 5 respectively obtain the pressure measuring water level of each test cylinder. The number of pressure measuring tubes 5 is matched to the number of test cylinders.

In the specific implementation of the above embodiment, the following parameters may be selected and used in the above structure, but are not limited to the following parameters: the first water tank 1 can be an open organic glass tank with the thickness of 570mm multiplied by 1200mm, and the wall thickness of the tank is 10 mm; the central line of the right side wall of the first water tank 1 is provided with 7 overflow ports 12 of the first water tank 1; the central line of the left side wall of the first water tank 1 is provided with 7 water outlets 13 of the first water tank 1; wherein: the overflow ports 12 are provided with a second water stop valve with the aperture of 16mm, are arranged at intervals of 150mm from the bottom of the first water tank 1 upwards, are 7 first overflow ports 121, second overflow ports 122, third overflow ports 123, fourth overflow ports 124, fifth overflow ports 125, sixth overflow ports 126 and seventh overflow ports 127 from bottom to top in sequence, and are respectively 150mm, 300mm, 450mm, 600mm, 750mm, 900mm and 1050mm from the bottom of the first water tank 1. The water outlet 13 is provided with a second water stop valve with the aperture of 16mm, the second water stop valve is arranged at intervals of 150mm upwards from the bottom of the box body 11 of the first water tank, and 7 water stop valves are arranged from bottom to top in sequence from the first water outlet 131, the second water outlet 132, the third water outlet 133, the fourth water outlet 134, the fifth water outlet 135, the sixth water outlet 136 and the seventh water outlet 137 which are respectively at distances of 150mm, 300mm, 450mm, 600mm, 750mm, 900mm and 1050mm from the bottom of the box body 11 of the first water tank. The filtering device 22 is composed of acrylic hollow plates 221 with cross section of 620mm x 620mm and thickness of 10mm and circular steel wire meshes 222. The circular steel wire mesh 222 is a circular filter screen with a diameter of 480mm, has a pore diameter of 0.075mm, and is embedded in the hollow part of the acrylic hollow plate 221.

In other preferred embodiments, referring to fig. 7a, the buffer cylinder 4 includes a buffer cylinder body 41, a partition 43 and a cover plate 42, wherein the partition 43 and the cover plate 42 are respectively disposed on two end surfaces of the buffer cylinder body 41. The cushion cylinder body 41 is matched with the cylinder body 311 of the test cylinder in shape and size. Preferably, a flange gasket is interposed between one end of the cushion cylinder body 41 and the cover plate 42 and fixed by bolts, and a flange gasket is interposed between the other end of the cushion cylinder body 41 and the partition plate 43 and fixed by bolts. In order to discharge the air inside the buffer cylinder 4, an exhaust port perpendicular to the axial direction of the cylinder body is provided in the outer wall of the buffer cylinder body 41, and the exhaust port penetrates the inner wall of the buffer cylinder body 41, so that the air inside the buffer cylinder 4 is discharged to the outside through the exhaust port. As a preferred mode, for more convenient and quick discharge, set up the gas vent at buffering cylinder stack 41 outer wall along axial direction midpoint, and this gas vent can be the hollow column that the internal diameter face has the screw thread, and gas vent structure size is the same with experimental cylinder pressure-measuring pipe interface 3111. The partition plate 43 is a porous plate structure, a plurality of bolt holes are uniformly distributed around the center of the circle on the partition plate 43, the bolt holes penetrate through the thickness of the partition plate 43, and the porous plate structure can prevent the soil sample in the test cylinder from permeating into the buffer cylinder 4 along with the water flow. The cover plate 42 is disposed on an end surface of the buffer cylinder body 41 to seal the end of the buffer cylinder body 41, and the cover plate 42 is provided with a water inlet, which is a buffer cylinder water inlet 421 for connecting with a water outlet of an external pipeline, so that water in the first water tank 1 flows into the buffer cylinder 4 and the soil storage system 3 through the water inlet during a test. Preferably, a first stop valve is provided at the inlet of the cover plate 42 to control the flow rate and the opening/closing of the inlet.

In other preferred embodiments, referring to fig. 7b, the partition 43 comprises a circular plate area 431 and a porous area 432, the circular plate area 431 is located at the outer circle of the porous area 432, wherein the circular plate area 431 is used for connecting the test cylinder, the diameter of the porous area 432 is consistent with the inner diameter of the barrel body 41 of the buffer cylinder, and a plurality of bolt holes are distributed in the circular plate area 431. As a preferable mode, the partition 43 may be an acrylic circular thin plate, and the diameter of the circular thin plate is the same as the outer diameter of the flange of the barrel body 41 of the buffer barrel, so as to prevent the soil sample in the test barrel from permeating into the buffer barrel 4 along with the water flow; uniformly distributing small holes in a circular area with the diameter consistent with the inner diameter of the buffer cylinder body 41, wherein the area is a porous area 432, and the pore diameter of the small holes is determined according to the test requirement; the remaining part is the ring plate region 431, and a plurality of bolt mouths are evenly distributed around the centre of a circle in the ring plate region 431, and the aperture, the number and the position of the bolt mouths are the same as those of the arrangement on the flange plate of the buffering cylinder body 41. In practical application, the partition 43 is a circular thin plate with a wall thickness of 5mm and a diameter of 184mm, the porous area 432 is a circular area with a diameter of 80mm, and small holes with a diameter of 1.0mm are uniformly distributed on the circular area. 8 bolt openings with the aperture of 6mm are uniformly distributed on a circle with the radius of 70mm around the circle center of the partition plate 43 in the circular ring plate area 431.

In other preferred embodiments, as shown in fig. 7a and 7c, the cover plate 42 may be made of acrylic circular thin plate having the same diameter as the outer diameter of the flange of the barrel 41. The water inlet is arranged at the center of the circle of the cover plate 42. In practical implementation, the cover plate 42 can be selected from, but is not limited to, a circular plate with a wall thickness of 5mm and a diameter of 184mm, and the aperture of the water inlet 421 of the buffer cylinder is 16 mm.

In other preferred embodiments, and as shown with reference to fig. 8, the pressure measuring tube 5 includes a range segment 51 and a threaded segment 52, wherein: the pipe wall of the measuring range section 51 is marked with scales, and the maximum scale value and the accuracy of the scales are determined according to the experimental requirements. The threaded section 52 is provided with threads, and the length of the threaded section 52 is matched with the pressure tube interface 3111 on the cylinder wall of the test cylinder. As a preferred way, for ease of reading, the piezometric tube 5 can be an elongated thin-walled glass tube. The number of the pressure measuring tubes 5 is the same as that of the test cylinders, and the tube diameter is determined according to the experiment requirements. In specific implementation, the piezometer tube 5 can be selected, but is not limited to, the following parameters, the length of the measuring range section 51 is 1200mm, a graduated scale is carved upwards from the bottom along the tube wall, the measuring range is 1000mm, and the accuracy is 1 mm. The length of the threaded segment 52 is 22 mm.

In other partially preferred embodiments, end screen 34 comprises a mesh screen and an open screen, wherein: referring to fig. 6a, a mesh filter screen is shown, and the pore size of the mesh filter screen is determined according to the test requirements. Referring to fig. 6b, an open filter screen is shown, the open filter screen is provided with openings with certain width, and the aperture and the opening width of the open filter screen are determined according to the experimental requirements. Preferably, the end screen 34 may be a thin-walled annular plate with a wire screen 342 embedded in the hollow of the thin-walled annular plate. The annular plate is the same shape and size as the flange 312 of the test cylinder. Wire screen 342 may be selected depending on the type of end screen 34. The type of end screen 34 is the mesh screen, open screen, two types, as described above, wherein: the steel wire filter screen 3421 is not provided with openings to form the mesh filter screen, and the aperture of the mesh filter screen is determined according to the test requirement. The open filter screen 3422 is formed by arranging a circle-center-passing elongated slit parallel to the horizontal plane, and the aperture and the opening width of the filter screen are determined according to the experimental requirements. In specific implementation, the end screen 34 may be selected, but not limited to, an end screen circular plate 341 with a wall thickness of 5mm, an inner diameter of 80mm, and an outer diameter of 184mm, and a steel wire screen 342 with an inner diameter of 80 mm. The aperture of the filter screen of the mesh filter screen is 0.075 mm. The sizes of the elongated slits provided in the open mesh 3422 are 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, and 3.0mm, respectively, according to the experimental requirements.

In other preferred embodiments, the test device for simulating horizontal seepage erosion of fine particles in sandy soil comprises a test bed and a U-shaped bracket, wherein the U-shaped bracket is fixed on the test bed. In the test process, the connected soil body storage system 3 and the buffer cylinder 4 need to be horizontally placed, so that the pressure measuring pipe 5 faces upwards and is vertical to the horizontal plane. In order to horizontally fix the soil body storage system 3 and the buffer cylinder 4, a U-shaped support structure is adopted, and the stability of the whole structure in the test process is ensured.

In order to research the horizontal seepage erosion process of fine particles in sandy soil and the influence rule of the horizontal seepage erosion process on the change of the sandy soil, the following test device in the embodiment is combined to provide an embodiment of an indoor test method for simulating the horizontal seepage erosion of the fine particles in the sandy soil, and the method specifically comprises the following steps:

s1, preparing a soil sample.

Preparing a soil sample required by the test, wherein the soil sample is sandy soil containing fine particles, and measuring the initial particle gradation according to the geotechnical test specification.

The sandy soil containing the fine particles is prepared by mixing coarse sand and fine sand with different particle size ranges according to geotechnical test specifications and test requirements. The fine particle content refers to the weight percentage of fine sand in a unit soil sample, and the size of the fine particle content is determined according to the test requirement.

Specifically, firstly, coarse sand with the particle size range of 1.00-3.00 mm and fine sand with the particle size range of 0.075-0.25 mm are taken and prepared into a soil sample with the fine particle content of 20% according to the requirements of geotechnical test specifications, namely the weight ratio of the coarse sand to the fine sand is 8: 2.

and S2, assembling the soil body storage system 3 and paving the soil sample.

S2.1, connecting one end of the tail end test cylinder 33 with the tail end filter screen 34 and the base, vertically placing the tail end test cylinder 33 with the base facing downwards, closing a pressure measuring pipe interface 3111 of the tail end test cylinder 33, and preventing the pressure measuring pipe interface 3111 from leaking water;

s2.2, paving the soil sample prepared in the S1 into the tail end test cylinder 33 with the thickness of 42mm and the like for three times, adding water for saturation, tamping each layer until no air bubbles emerge on the saturated soil sample surface, and completely leveling the opening of the tail end test cylinder 33 after the last layer is paved.

S2.3, connecting one end of the first middle test cylinder 321 with the upper end of the tail end test cylinder 33 of the paved soil sample, specifically, placing a flange gasket with a bolt opening on the flange plate 312 of the cylinder opening of the tail end test cylinder 33 of the paved soil sample and aligning with the bolt opening on the flange plate 312, then covering the first middle test cylinder 321 which is vertically placed, connecting the two test cylinders according to the assembling and fixing requirements, wherein the assembling and fixing requirements refer to that the two adjacent test cylinders are assembled end to end in a flange connection mode, and ensuring that the pressure measuring pipe connectors on the test cylinders are positioned on the same straight line. Specifically, the lower end of the first intermediate testing cylinder 321 is connected to the upper end of the end testing cylinder 33 through a flange, and pressure measuring pipe joints on the first intermediate testing cylinder 321 and the end testing cylinder 33 are ensured to be positioned on the same straight line. S2.2 is repeated to lay the soil sample in equal thickness in portions on the first middle test cylinder 321 and to saturate with water, and the pressure tube interface 3111 is plugged with a piston to prevent water leakage during saturation.

S2.4, connecting one end of a second middle test cylinder 322 with the upper end of a first middle test cylinder 321 paved with the soil sample, specifically, placing a flange gasket with a bolt opening on a flange plate 312 of a cylinder opening of the first middle test cylinder 321 paved with the soil sample and aligning with the bolt opening on the flange plate 312, then covering a vertically placed second middle test cylinder 322, connecting the two test cylinders according to the assembling and fixing requirements, connecting the lower end of the second middle test cylinder 322 with the upper end of the first middle test cylinder 321 through a flange, and ensuring that pressure tube connectors on the second middle test cylinder 322 and the first middle test cylinder 321 are positioned on the same straight line; s2.2 is repeated to lay the soil sample into the second intermediate test cylinder 322 and saturate it with water, and the pressure tube port 3111 is plugged with a piston to prevent water leakage during saturation.

S2.5, sequentially connecting all the middle test cylinders 32 and the head end test cylinders 31 end to end, wherein the connection of the head end test cylinders 31 is specifically that flange gaskets with bolt openings are placed on the flange plate 312 of the cylinder opening of the fourth middle test cylinder 324 paved with the soil sample and are aligned with the bolt openings on the flange plate 312, then the vertically placed head end test cylinders 31 are covered, and the two test cylinders are connected according to the assembly fixing requirement; s2.2 is repeated to lay the soil sample into the head end test cylinder 31 and saturate with water, and the pressure tube interface 3111 is plugged with a piston to prevent water leakage during saturation.

S3, connecting the soil storage system 3 and the buffer cylinder 4.

And (3) placing a flange gasket on the flange plate 312 of the cylindrical opening of the head end test cylinder 31 of the S2.5 paved soil sample, vertically placing one end of the buffer cylinder 4 with the partition plate 43 on the flange gasket downwards, connecting according to the assembling and fixing requirements, and plugging the exhaust opening 411 of the buffer cylinder by a piston.

And S4, setting an initial water level (namely the first water outlet 131 at the lowest part of the first water tank 1) and enabling the soil body to be saturated and solidified.

S4.1, horizontally placing the soil mass storage system 3 and the buffer cylinder 4 connected in the S3 on the U-shaped bracket, and enabling the pressure tube connectors 3111 of the head end test cylinder 31, the 4 middle test cylinders 32 (the first middle test cylinder 321, the second middle test cylinder 322, the third middle test cylinder 323 and the fourth middle test cylinder 324) and the tail end test cylinder 33 to face upwards. All pistons of the head end test cylinder 31, the 4 middle test cylinders 32 and the tail end test cylinder 33 are pulled out, and the 6 pressure measuring pipe thread sections 52 are sequentially screwed into the pressure measuring pipe interfaces 3111 of all the test cylinders, so that the pressure measuring pipes 5 are perpendicular to the horizontal plane.

S4.2, the first water tank 1 is placed on a test bed, the first water outlet 131 of the tank body 11 of the first water tank is 50mm higher than the bottom surface of the piezometer tube 5 on the test cylinder, and the first water outlet 131 of the first water tank 1 and the water inlet 421 of the buffer cylinder are connected through the rubber water pipe 6.

And S4.3, continuously injecting water into the first water tank 1, opening a second water stop valve of the first overflow port 121, opening a second water stop valve of the first water outlet 131 and a first water stop valve of the buffer cylinder water inlet 421 when the water level of the first water tank 1 is kept unchanged, guiding water flow into the buffer cylinder 4 and the soil body storage system 3, and observing the reading of the measuring range 51 of each pressure measuring pipe 5 until the soil sample in the soil body storage system 3 is saturated and solidified when the readings of all the pressure measuring pipes 5 are stabilized at the same horizontal line.

S5, dismantling the base of the soil body storage system, setting a normal water level difference, and carrying out a horizontal seepage erosion control test on fine particles in sandy soil; the normal water head is the water head set by the contrast test; the water level difference is the height difference between the water level in the first water tank and the bottom surface of the piezometer tube on the test cylinder;

s5.1, closing the first water outlet 131, the second water stop valve of the first overflow port 121 and the first water stop valve of the water inlet 421 of the buffering cylinder, and placing the second water tank 2 under the tail end filter screen 34 after the wood board base is removed.

S5.2, setting the normal water level difference to be 0.95m, selecting the corresponding water outlet 13 of the first water tank 1 as a seventh water outlet 137, connecting the rubber water pipe 6 with the seventh water outlet 137 of the first water tank 1, opening the seventh water outlet 137, the corresponding second water stop valve of the seventh overflow port 127, the corresponding first water stop valve of the buffer cylinder water inlet 421 and the corresponding third water stop valve of the water outlet 211 of the second water tank 2, and starting to perform a seepage erosion experiment when the tail end filter screen 34 seeps water.

And S5.3, in the test process, reading the readings of the pressure measuring pipes 5 of the saturated soil samples in the head-end test cylinder 31, all the middle test cylinders 32 and the tail-end test cylinder 33 in the seepage erosion process every 15 minutes to obtain the pressure measuring water level, and drawing a curve relation graph of the pressure measuring water level and the time.

S5.4, in S5.3, when the reading of the piezometer tube 5 of the saturated soil sample in the tail end test cylinder 33 is read each time, placing the measuring cylinder between the tail end filter screen 34 and the second water tank 2 to bear the water yield of one minute, converting the water yield into the flow rate, and drawing a curve relation graph of the flow rate and the time; and (5) determining the change rule of the permeability coefficient at each moment along the seepage path according to the flow rate and the pressure measuring water level at different moments by combining the pressure measuring water level and time curve relation diagram of S5.3.

S5.5, finishing the seepage erosion test for 3 hours, and dismantling the soil body storage system 3. The method comprises the following specific steps: firstly, closing a first water outlet 137 of a corresponding first water tank 1, a second water stop valve of a corresponding first overflow port 127, a first water stop valve of a water inlet 421 of a buffering cylinder and a third water stop valve of a water outlet 211 of a second water tank, and after no water flows out from a tail end filter screen 34, sequentially removing the tail end filter screen 34, a tail end testing cylinder 33, 4 middle testing cylinders 32 and a head end testing cylinder 31; and collecting three samples in each test cylinder according to an in-situ soil sampling principle in the dismantling process, and measuring the grain composition and the dry density of the sample after each test according to the geotechnical test specification so as to determine the change rule of the grain composition and the dry density along the seepage path after the test.

S6, carrying out horizontal seepage erosion test on fine particles in the sandy soil under the action of different water head differences.

S6.1, keeping the content of fine particles of the soil sample unchanged, namely, the weight ratio of coarse sand to fine sand is 8: 2, the type of the tail end filter screen 34 is a grid filter screen, the diameter of a filter screen of a steel wire filter screen 3421 of the grid filter screen is kept to be 0.075mm, the water level difference is controlled to be 0.80m, 0.65m, 0.50m, 0.35m and 0.20m respectively by adjusting a water outlet 13 of the first water tank 1 to be a sixth water outlet 136, a fifth water outlet 135, a fourth water outlet 134, a third water outlet 133 and a second water outlet 132, and seepage erosion tests under the action of different water level differences are simulated; and (3) firstly carrying out S1-S5 steps in each seepage erosion test under the action of different water level differences, and determining the permeability coefficient at different moments under the action of each water level difference, the grain composition after the test and the change rule of the dry density along a seepage path.

S6.2, after all the seepage tests with different water head differences are carried out, analyzing the relation between the seepage coefficients at different moments, the grain composition and the change rule of the dry density along the seepage path after the tests and the water head differences determined by the S6.1.

S7, under the influence of different fine particle contents, carrying out a horizontal seepage erosion test of fine particles in the sandy soil.

S7.1, keeping a seventh water outlet at 137 to ensure that the normal water level difference is 0.95m, keeping the type of the tail end filter screen 34 to be a grid filter screen, keeping the filter screen aperture of a steel wire filter screen 3421 of the grid filter screen to be 0.075mm, changing the content of fine particles in the soil sample, namely, respectively setting the weight ratio of coarse sand to fine sand to be 9: 1. 8.5: 1.5, 8: 2. 7.5: 2.5, 7: 3. 6.5:3.5, carrying out seepage erosion tests under the influence of different fine particle contents; and (3) carrying out S1-S5 steps in each seepage erosion test under the influence of different fine particle contents, and determining the permeability coefficient, the particle gradation after the test and the change rule of the dry density along the seepage path at different moments under the influence of the fine particle contents.

S7.2, after all seepage tests with different fine particle contents are carried out, analyzing the relation between the seepage coefficients of S7.1 at different moments, the particle gradation and the change rule of the dry density along the seepage path after the tests and the fine particle contents.

S8, and carrying out horizontal seepage erosion test on the fine particles in the sandy soil under the influence of different fine particle loss amounts.

S8.1, keeping the seventh water outlet at 137 to ensure that the normal water level difference is 0.95m unchanged; keeping the content of fine particles of the soil sample unchanged, namely, the weight ratio of coarse sand to fine sand is 8: 2; the type of the tail end filter screen 34 is an open filter screen, the width of an opening gap of a steel wire filter screen 3422 of the open filter screen is adjusted to be 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm and 3.0mm respectively, and seepage erosion tests under the influence of different fine particle loss are carried out; S1-S5 are firstly carried out in each seepage erosion test under the influence of the fine particle loss, and the permeability coefficients at different moments, the particle grading after the test and the change rule of the dry density along the seepage path under each fine particle loss are determined.

S8.2, after the seepage erosion test under each opening filter screen width condition is finished, drying etched fine particles on the circular steel wire mesh 222 of the second water tank 2 collected by the brush, and weighing to obtain the fine particle loss amount.

And S8.3, after the seepage test is completely carried out under the influence of different fine particle seepage quantities, analyzing the relation between the seepage coefficient of S8.1 at different moments, the particle grading and the change rule of the dry density along the seepage path after the test and the fine particle seepage quantity.

The test method provided by the invention fills the defects in the horizontal seepage erosion test of fine particles in sandy soil, and simulates the seepage erosion process of the fine particles in the sandy soil under the influence of different water level differences, different fine particle contents and different fine particle loss amounts and the influence rule of the seepage erosion process on the change of the sandy soil property. The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. The utility model provides a test device of fine particle horizontal seepage flow erosion in simulation sand, its characterized in that includes:

the first water tank is arranged on one side of the soil body storage system, is used for storing water and can regulate and control the test water level, and a plurality of overflow ports and a plurality of water outlets which are symmetrically distributed are respectively arranged on two sides of the first water tank along the height direction;

2. The test device for simulating horizontal seepage erosion of fine particles in sandy soil according to claim 1, wherein the head end test cylinder, the middle test cylinder and the tail end test cylinder respectively comprise a cylinder body and a flange plate, and barrier rings perpendicular to the axial direction are respectively arranged on the inner wall of the cylinder body close to openings at two ends of the cylinder body and used for preventing a seepage path along the cylinder wall from being formed; the flange plates are arranged at two end parts of the cylinder body, and the inner diameter of each flange plate is the same as the diameter of the cylinder body; and the flange plate is provided with a bolt port.

3. The test device for simulating horizontal seepage erosion of fine particles in sandy soil according to claim 1, wherein the buffer cylinder comprises a cylinder body, a partition plate and a cover plate, wherein the partition plate and the cover plate are respectively arranged on two end faces of the cylinder body, and the cylinder body of the buffer cylinder is matched with the test cylinder in shape and size; the outer wall of the cylinder body is provided with an air outlet for discharging air, and the air outlet is vertical to the axial direction of the cylinder body; the baffle plate is provided with a plurality of bolt holes which are uniformly distributed around the circle center and is used for preventing fine particles in the soil sample of the test cylinder from reversely permeating into the buffer cylinder along with water flow; the cover plate is provided with a water inlet used for being connected with the pipeline, so that water in the first water tank flows into the barrel body from the water inlet.

4. The device according to claim 3, wherein the partition comprises a circular plate area and a porous area, the circular plate area is located at the outer circle of the porous area, the circular plate area is used for connecting the test cylinder, the diameter of the porous area is consistent with the inner diameter of the cylinder body, and the plurality of bolt holes are distributed in the circular plate area.

5. The test device for simulating horizontal seepage erosion of fine particles in sandy soil according to claim 3, wherein a first water stop valve is arranged at the water inlet of the cover plate.

6. The test device for simulating horizontal seepage erosion of fine particles in sandy soil according to any one of claims 1 to 5, wherein the pressure measuring pipe comprises a measuring range section and a threaded section, wherein: the pipe wall of the measuring range section is marked with scales; the thread section is provided with threads, and the length of the thread section is matched with the pressure measuring pipe interface.

7. The test device for simulating horizontal seepage erosion of fine particles in sandy soil according to any one of claims 1 to 5, wherein the overflow port and the water outlet of the first water tank are provided with second water stop valves; and a third water stop valve is arranged at the water outlet of the second water tank.

8. A test rig for simulating horizontal seepage erosion of fine particles in sandy soil according to any one of claims 1 to 5, wherein the types of end screens include mesh screens and open mesh screens, and wherein: the mesh filter screen the opening filter screen is fine steel wire net, and the opening filter screen is equipped with the opening of certain width on fine steel wire net.

9. A test device for simulating horizontal seepage erosion of fine particles in sandy soil according to any one of claims 1 to 5, further comprising a U-shaped support for supporting the soil mass storage system, the buffer cylinder and the pressure measuring pipe.

10. A test method for simulating horizontal seepage erosion of fine particles in sandy soil by using the test device of any one of claims 1 to 9, which comprises: