A large-scale soil permeability test device and method capable of adjusting water head and seepage direction

Abstract

A large-scale soil permeability performance test device capable of adjusting water head and seepage direction includes a flow meter installed on a water inlet pipe, the end of which is located above a water head control unit and can be used to fill the water head control unit with water; a plurality of overflow pipes are longitudinally arranged on the outer side of the container of the water head control unit, one end of the guide pipe is connected to the overflow pipe, and the other end is connected to a weighing device; a water inlet and a water outlet are arranged at the upper and lower ends of the permeability test unit, and a soil-water separation device is arranged at the water outlet. The water flow in the water inlet pipe is detected by the flow meter to adjust the amount of water discharged from the water inlet pipe; a plurality of overflow pipes are longitudinally arranged on the outer side of the container of the water head control unit, and the water head size can be adjusted according to a variety of different height ranges; a water inlet and a water outlet are arranged at the upper and lower ends of the permeability test unit, and the amount of water seepage and seepage of the soil sample can be detected from both the upper and lower directions.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a large-scale soil permeability performance test device and method capable of adjusting water head and seepage direction. Background Art

[0002] After the construction and operation of large-scale hydropower stations with flood control functions, the water level in the reservoir area fluctuates by tens of meters every year, bringing a corresponding height range of the drawdown zone to the reservoir bank. The fluctuation of the water level provides hydrodynamic effects on the slope of the reservoir bank, which may lead to geological disasters such as landslides on the reservoir bank, seriously threatening the safety of life and property of residents in the reservoir area and the safety of the waterway. Therefore, it is particularly important to conduct permeability tests on the reservoir bank soil to explore the evolution law of soil permeability and the instability mechanism of the reservoir bank slope. When conducting permeability tests on the reservoir bank soil, (1) first, large-size specimens need to be used to reduce test errors. Conventional 55-type and 70-type specimens do not meet the requirements of large specimen sizes; (2) secondly, it is necessary to consider that the actual water level of the reservoir bank soil is changing, and the fluctuation range is large and the frequency is fast. In traditional soil permeability test devices, the characteristic of water level being in a changing state is rarely considered, and the change of water level in the pressure gauge tube is generally achieved by raising or lowering the water supply tank. However, during the test, as the test progresses, the water head is not only difficult to maintain constant, resulting in insufficient accuracy, but also inconvenient to adjust the water head when conducting reservoir bank soil permeability tests under various different seepage water pressures, and the process is cumbersome; (3) At the same time, traditional soil permeability test devices often only target one seepage direction. However, in actual projects, the seepage direction will change with the change of water level. When the water level is low, it will seep from the inside of the bank slope to the outside, and when the water level is high, it will seep from the reservoir to the bank slope. Therefore, the application range of traditional soil permeability test devices is relatively narrow. (4) In addition, during the test simulation, the permeability of the reservoir bank soil is high, and the device is required to ensure long-term water supply. At the same time, the soil sample has a large amount of water seepage during the test, so it is necessary to consider how to effectively monitor the water seepage of the soil sample. (5) Finally, during the infiltration process, fine particles in the soil sample will migrate and change the soil permeability. How to observe the start-up and migration process of fine particles is also worth considering.

[0003] Chinese patent document CN206756653U, published (announced) date: December 15, 2017, discloses a combined device for measuring soil permeability coefficient with constant water head and variable water head. A combined device for measuring soil permeability coefficient with constant water head and variable water head mainly comprises a bracket, the bracket comprises a top plate, a back plate and a base, a Martens flask is placed on the top plate, a fixed water head water supply pipe, a scale, and a variable water head water supply pipe are fixed on the back plate, the upper end of the fixed water head water supply pipe is connected to the Martens flask, and the lower end is connected to the water pipe, the upper end of the variable water head water supply pipe is open, and the lower end is also connected to the water pipe; the lower end of the water pipe is connected to the internal space of the test device. Its characteristics are that it can solve the saturated infiltration coefficient of clay and sandy loam under the same conditions, effectively reduce errors, reduce the complexity of the test process, improve experimental efficiency, and increase the accuracy and reliability of the measurement; its shortcomings are that it cannot simulate the seepage volume of actual reservoir bank soil under different water levels, as well as the experiment of bidirectional infiltration.

[0004] Chinese patent document CN 205670111 U, published (announced) date: November 2, 2016, discloses a simulated constant head infiltration device for measuring the permeability coefficient of a permeable medium, characterized in that it includes a constant head regulating part, a permeation part, and a permeate storage part; the constant head regulating part includes a head water storage unit and a return hose, the permeation part includes a permeation unit and a permeate outlet pipe, water flows from the bottom of the head water storage unit into the permeation unit, and seeps upward through the bottom of the permeation unit to remove the air in the permeable medium to achieve the permeation process; wherein, by raising or lowering the part of the return hose close to the head water storage unit, the water level inside the head water storage unit can be adjusted, thereby achieving the adjustment of the water head. Its characteristics are that it can be operated on an ordinary test platform, and can realize the recycling of excess water to save water resources; it also cannot simulate the seepage of actual reservoir bank soil under different water levels, and the experiment of two-way permeation. Summary of the invention

[0005] The technical problem to be solved by the present invention is to solve the problems existing in the above-mentioned background technology and provide a large-scale soil permeability performance testing device with adjustable water head and seepage direction.

[0006] Another technical problem to be solved by the present invention is to provide an experimental method using a large-scale soil permeability test device with adjustable water head and seepage direction.

[0007] In order to realize the above-mentioned technical features, the purpose of the present invention is achieved as follows: a large-scale soil permeability performance test device with adjustable water head and seepage direction, which includes a flow meter installed on a water inlet pipe, the end of the water inlet pipe is located above the water head control unit, and can fill the water into the water head control unit, one end of the hose is connected to the bottom of the water head control unit, and the other end is connected to the permeability test unit; the water head control unit includes a transparent container with an upper opening, and a plurality of overflow pipes are longitudinally arranged on the outer side of the container, each overflow pipe is provided with an overflow control valve, one end of the guide pipe is connected to the overflow pipe, and the other end is connected to a weighing device; the upper end of the permeability test unit is provided with an upper water inlet and an upper water outlet with a valve, and the lower end is provided with a lower water inlet and a lower water outlet with a valve, and the hose can be selectively connected to the upper water inlet or the lower water inlet; the upper water outlet or the lower water outlet is provided with a soil-water separation device.

[0008] A water inlet control valve is arranged at the front end of the flow meter.

[0009] The water head control unit is arranged on the telescopic bracket.

[0010] The weighing device comprises a receiving container connected to the lower part of the flow guide pipe, and the receiving container is placed on an electronic balance.

[0011] The infiltration experimental unit includes a tank body with an openable upper end for filling experimental soil samples, and permeable layers are arranged at both ends of the tank body. The permeable layers are respectively higher than the upper water inlet and the upper water outlet, as well as the lower water inlet and the lower water outlet and the channel connecting the tank body, and the experimental soil samples are filled between the permeable layers at the upper and lower ends; the tank body is made of transparent material.

[0012] A filter screen is provided on the infiltration surface between the permeable layers at the upper and lower ends and the experimental soil sample, and a steel wire screen is provided on the infiltration surface.

[0013] The outer wall of the tank body is provided with a scale in the longitudinal direction.

[0014] A monitor is also provided, and the monitor performs video monitoring on the tank body.

[0015] The soil-water separation device comprises a funnel arranged at the lower water outlet or the upper water outlet of the infiltration experiment unit tank body and a beaker located below the funnel; a filter screen is arranged inside the funnel.

[0016] An experimental method for a large-scale soil permeability test device capable of adjusting water head and seepage direction, comprising the following steps:

[0017] S1. Connect the hose to the water outlet at the bottom of the water head control unit and the water inlet at the lower end of the permeation test unit, close all overflow pipes and other inlet and outlet valves, open the water inlet control valve, fill the water head control unit and the permeation test unit with water, and conduct a water leakage test to ensure that there is no water leakage during the test. After the test is completed, drain the water in the permeation test unit;

[0018] S2. Fill the tank of the permeability test unit with a permeable layer, and then lay a filter screen with a pore size of 0.03-0.06 mm on the permeable layer;

[0019] S3. Before loading the soil sample, apply vaseline on the inner wall of the transparent tank, load the soil sample that has been compacted by a hammer to reach the set density and thickness into the tank, and then lay a filter screen with a pore size of 0.03-0.06mm on the top of the soil sample, and fill the top of the filter screen with a gravel layer;

[0020] S4. Cover the tank, close the overflow control valve, the lower water outlet valve, and the upper water inlet valve, open the water inlet control valve, slightly open the lower water inlet valve, and keep the water level in the head control unit container level with the top of the soil sample;

[0021] S5. Take out the filter screen and the permeable layer laid on the seepage surface of the upper layer of the soil sample, lay a steel mesh with a pore size of 1-5 mm on the upper part of the soil sample, and fill the permeable layer on the upper part of the steel mesh;

[0022] S6. Place the beaker and the funnel at the lower part of the upper water outlet in sequence, open the upper water outlet valve 16a, and accurately adjust the infiltration head height in the head control unit container to a predetermined value by jointly adjusting the telescopic bracket and the overflow control valve, and then adjust the water inlet control valve according to the flow meter data to keep the water level in the head control unit container unchanged and supply water continuously for a long time;

[0023] S7. Connect an external receiving container and an electronic balance to the flow guide tube, and after a period of seepage, turn on the electronic balance with a storage memory function and turn on the monitor 30;

[0024] S8. Based on the overflow volume Q1 of the diversion pipe read every five minutes by the electronic balance, combined with the cumulative flow Q2 data of the flow meter, the seepage volume Q of the soil sample every five minutes can be indirectly calculated. Combined with the head difference ΔH, soil sample height L, soil sample cross-sectional area A, temperature T and other data, the saturated permeability coefficient of the reservoir bank soil sample under a certain seepage water pressure can be finally calculated. The time variation law, as well as the saturated permeability coefficient K of the reservoir bank soil body at a certain seepage water pressure when the seepage is stable T ; The calculation formula is:

[0025] Q=Q1-Q2

[0026]

[0027] Where: K T is the permeability coefficient of the sample when the water temperature is T℃ cm / s; Q is the water seepage in the time period t after the permeation reaches stability cm 3 ; L is the seepage diameter in cm, i.e. the height of the soil sample in cm; A is the cross-sectional area of ​​the soil sample in cm 2 ; ΔH is the head difference between the upstream and downstream of the sample, cm; t is the penetration time, s;

[0028] S9. Adjust the telescopic bracket and the guide pipe valve to change the infiltration head of the water head control unit to simulate the dynamic water environment of the reservoir bank soil in the actual project, and repeat steps S6-S8 to determine the saturated permeability coefficient K of the reservoir bank soil under different seepage water pressures. T ;

[0029] S10. When the seepage direction needs to be adjusted from top to bottom, close the lower water inlet and upper water outlet valves at the bottom of the permeability test unit tank, connect the hose to the upper water inlet of the permeability test unit tank, and set the soil-water separation device at the lower water outlet to simulate the influence of the dynamic water environment on the seepage direction of the reservoir bank soil in actual engineering. Repeat S6-S9 to determine the saturated permeability coefficient K of the reservoir bank soil under the combined change of seepage direction and seepage water pressure. T .

[0030] The present invention has the following beneficial effects:

[0031] 1. Use a flow meter to detect the water flow in the water inlet pipe. The water inlet pipe is connected to the faucet of the tap water pipe. The amount of water released from the faucet is adjusted according to the reading of the flow meter. The container of the water head control unit is transparent, which is convenient for observing the water level. There are multiple overflow pipes arranged longitudinally on the outer side of the container, which can adjust the water head size according to different height amplitudes. The upper and lower ends of the infiltration test unit are equipped with water inlets and outlets, which can detect the seepage and seepage of the soil sample from both the upper and lower directions.

[0032] 2. The water inlet control valve is connected to the flow meter in turn to supply water to the head control unit container, which can not only ensure long-term automatic water supply, but also monitor the water supply flow through the flow meter and adjust the water supply flow through the faucet.

[0033] 3. The water head control unit is set on the telescopic bracket, which can further adjust the height of the water head control unit to meet the actual water level rise and fall drop test requirements.

[0034] 4. Permeable layers are provided at both ends of the tank body, and the water flow introduced by the hose is buffered. A filter screen is provided on the infiltration surface between the upper and lower permeable layers and the experimental soil sample, and a wire mesh is provided on the infiltration surface. The filter screen is mainly used to control the uniform flow of external water into the soil sample and reduce the impact of the water flow on the soil sample. The wire mesh is mainly used to allow the eroded fine particles to flow out smoothly, avoid gathering at the seepage outlet, block the seepage channel and affect the test effect.

[0035] 5. In view of the large amplitude and fast rate of water level changes in the dynamic water environment where the reservoir bank soil is located in actual projects, the water head size can be quickly and effectively adjusted quantitatively, and even the seepage direction can be changed.

[0036] 6. In view of the strong permeability of the reservoir bank soil in the actual project, it is ensured that the water supply can be continuously and stably for a long time.

[0037] 7. Compared with the traditional permeameter, which requires frequent manual use of measuring cylinders to monitor the water seepage at the same time interval, this system can realize long-term automatic and continuous monitoring of water seepage, which not only saves labor costs, but also reduces the error of manual measurement.

[0038] 8. In actual projects, fine particles will be lost in the reservoir bank soil under the action of high head. The gravel layer and wire mesh can provide a natural loss channel for fine particles. In addition, the start-up and migration change process of fine particles can be observed through video monitoring cameras.

[0039] 9. The soil and water collection and separation system can monitor the particle size range and content of fine particle loss.

[0040] 10. According to the large-size requirements of different soil samples, select the appropriate size of seepage glass cylinder to connect the test device and carry out permeability tests on soil samples of different large sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the main structure of the present invention.

[0042] Figure 2 It is a schematic diagram of the three-dimensional structure of the present invention.

[0043] Figure 3 It is a schematic diagram of the cross-sectional structure of the penetration experiment unit of the present invention.

[0044] In the figure: water inlet pipe 1, water inlet control valve 2, flow meter 3, head control unit 4, overflow pipe 5, overflow control valve 6, guide pipe 7, receiving container 8, electronic balance 9, telescopic bracket 10, hose 11, lower water inlet 12, lower water inlet valve 12a, upper water inlet 13, upper water inlet valve 13a, permeation experiment unit 14, permeable layer 141, filter screen 142, wire mesh 143, scale 15, upper water outlet 16, upper water outlet valve 16a, lower water outlet 17, lower water outlet valve 17a, connecting pipe 18, funnel 19, beaker 20, monitor 30. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are further described below in conjunction with the accompanying drawings.

[0046] Embodiment 1:

[0047] See also Figure 1-3 A large-scale soil permeability performance test device with adjustable water head and seepage direction, comprising a flow meter 3 installed on a water inlet pipe 1, the end of the water inlet pipe 1 is located above a water head control unit 4, and can inject water into the water head control unit 4, one end of a hose 11 is connected to the bottom of the water head control unit 4, and the other end is connected to a permeability test unit 14; the water head control unit 4 comprises a transparent container with an upper end opening, a plurality of overflow pipes 5 are longitudinally arranged on the outer side of the container, each overflow pipe 5 is provided with an overflow control valve 6, one end of a guide pipe 7 is connected to the overflow pipe 5, and the other end is connected to a weighing device; the upper end of the permeability test unit 14 is provided with an upper water inlet 13 and an upper water outlet 16 with a valve, and the lower end is provided with a lower water inlet 12 and a lower water outlet 17 with a valve, and the hose 11 can be selectively connected to the upper water inlet 13 or the lower water inlet 12; the upper water outlet 16 or the lower water outlet 17 is provided with a soil-water separation device. The water flow in the water inlet pipe 1 is detected by the flow meter 3. The water inlet pipe 1 is connected to the faucet of the tap water pipe. The amount of water released from the faucet is adjusted by the reading of the flow meter 3. The container of the water head control unit 4 is transparent, which is convenient for observing the water level. Six overflow pipes 5 are arranged longitudinally on the outer side of the container. The adjacent overflow pipes are 100mm apart. The water head size can be adjusted to a variety of different amplitudes such as 0.1m, 0.2m, and 0.3m. The upper and lower ends of the infiltration test unit 14 are both provided with a water inlet and a water outlet. The hose 11 can be selectively connected to the upper water inlet 13 or the lower water inlet 12, and can detect the seepage and seepage of the soil sample from both the upper and lower directions.

[0048] The faucet is connected to the flow meter 3 in turn to supply water to the container of the water head control unit 4, which can not only ensure long-term automatic water supply, but also monitor the water supply flow through the flow meter 3 and adjust the water supply flow through the faucet. On the one hand, it prevents the water from being unable to be discharged from the overflow pipe 5 in time due to excessive water supply, and thus the water head cannot be adjusted; on the other hand, it prevents excessive overflow and requires manual cleaning and drainage next to the test device. The water head overflow pipe 5 is connected to a weighing device externally, and the overflow water volume is measured by weighing method, which can indirectly calculate the infiltration water volume and the seepage water volume. Compared with the frequent manual measurement of seepage water volume, it can improve data collection efficiency, save labor costs, and reduce test errors.

[0049] In a preferred embodiment, a water inlet control valve 2 is provided on the front water inlet pipe 1 of the flow meter 3. The water inlet control valve 2 can be an ordinary faucet, suitable for situations where there is no faucet in the tap water pipe, or an electric or manual water flow regulating valve.

[0050] In the preferred solution, the water head control unit 4 is arranged on the telescopic bracket 10. The height of the water head control unit 4 can be further adjusted to meet the drop test requirements of the actual water level rise and fall. In this embodiment, the height adjustment range of the telescopic bracket 10 is 400mm to 2400mm, and the combined adjustment of the telescopic bracket 10 and the overflow control valve 6 of the overflow pipe 5 can control the water head at any position of 0.5m to 3m, and the water head size can be adjusted in a variety of different amplitudes such as 0.1m, 0.2m, 0.3m, etc.

[0051] In the preferred embodiment, the weighing device includes a receiving container 8 connected to the bottom of the guide tube 7, and the receiving container 8 is placed on an electronic balance 9. The structure is simple and easy to use. The electronic balance 9 has the function of automatically storing and recording weighing data. By measuring the overflow water volume by weighing, the infiltration water volume and the seepage water volume can be indirectly calculated. Compared with the frequent manual measurement of the seepage water volume, the data collection efficiency can be improved, the labor cost can be saved, and the experimental error can be reduced. In the calculation, within a certain period of time, the cumulative flow displayed by the flow meter 3 is the total water inflow, which is equal to the infiltration water volume and the seepage water volume minus the overflow water volume in the receiving container 8.

[0052] In a preferred solution, the permeability test unit 14 includes a tank body with an openable upper end for filling the experimental soil sample, and a permeable layer 141 is provided at both ends of the tank body, and the permeable layer 141 is respectively higher than the upper water inlet 13 and the upper water outlet 16, and the lower water inlet 12 and the lower water outlet 17 are connected to the tank body through a channel, and the permeable layer 141 at the upper and lower ends is used to fill the experimental soil sample; the tank body is made of transparent material. In this embodiment, the tank body adopts a transparent organic glass cylinder for easy observation, and the cylinder body is 10mm thick, the inner diameter is 200mm, and the height is 440mm. An inlet and an outlet are respectively provided at the upper and lower ends of the tank body to adjust the seepage direction. The lower end outlet 17 and the upper end outlet 16 are 10mm away from the bottom and the top of the tank body, respectively, and the lower end water inlet 12 and the upper end water inlet 13 are located within the height of the permeable layer 141. The permeable layer 141 is gravel or permeable stone.

[0053] When the seepage direction is from bottom to top, close the upper water inlet valve 13a of the upper water inlet 13, connect the lower water inlet 12 to the hose 11, and use the lower water outlet 17 as an exhaust pipe. After the gas in the hose 11 is discharged, close the lower water outlet valve 17a, and open the upper water outlet valve 16a of the upper water outlet 16 to serve as a soil and water overflow pipe to allow the soil and water to overflow into the soil and water separation device.

[0054] When the seepage direction is from top to bottom, close the lower water inlet valve 12a of the lower water inlet 12, connect the upper water inlet 13 to the hose 11, and open the upper water outlet valve 16a of the upper water outlet 16 as an exhaust pipe. After the gas in the hose 11 is discharged, close the upper water outlet valve 16a, and use the lower water outlet 17 as a soil and water overflow pipe to allow the soil and water to overflow into the soil and water separation device.

[0055] When the lower water outlet 17 or the upper water outlet 16 is used as a soil and water overflow pipe, in order to facilitate the introduction into the water separation device, a connecting pipe 18 can be installed at the end of the lower water outlet 17 or the upper water outlet 16 to divert the water.

[0056] Water-permeable layers 141 are provided at both ends of the tank body to buffer the water flow so that the water in the hose 11 can evenly penetrate into the experimental soil sample. Specifically, the upper and lower parts of the experimental soil sample are filled with 20 mm high gravel for water permeability.

[0057] In a preferred embodiment, a filter screen 142 is provided on the infiltration surface between the permeable layer 141 at the upper and lower ends and the experimental soil sample, and a wire mesh 143 is provided on the infiltration surface. The filter screen 142 with a pore size of about 0.03-0.06 mm is laid on the infiltration surface of the soil sample, and the wire mesh 143 with a pore size of about 1-5 mm is laid on the infiltration surface, wherein the filter screen 142 is mainly used to control the external water flow to flow into the soil sample uniformly, and at the same time reduce the impact of the water flow on the soil sample. The wire mesh 143 is mainly used to allow the eroded fine particles to flow out smoothly, avoid gathering at the seepage outlet, block the seepage channel and thus affect the test effect. Among them, the infiltration surface is the interface where water first contacts the soil sample, and the seepage surface is the interface where water exits the soil sample. The filter screen 142 can be made of nylon or metal.

[0058] Furthermore, the outer wall of the tank body is longitudinally provided with a scale 15. The tank body is affixed with a scale with the bottom surface of the soil sample as the starting scale 0, so as to observe and record the position of the upper surface of the soil sample during the test.

[0059] Furthermore, a monitor 30 is provided, and the monitor 30 performs video monitoring on the tank body and the scale 15 to record the starting and migration change process of the fine particles.

[0060] In a preferred solution, the soil-water separation device includes a funnel 19 provided at the lower water outlet 17 or the upper water outlet 16 of the tank body of the infiltration test unit 14 and a beaker 20 located below the funnel 19; a filter is provided inside the funnel 19. When water entrains fine particles from the soil sample and flows into the soil-water separation device, the soil particles will be retained in the filter, and the water will be filtered into the lower beaker 20, thereby separating the soil and water, and the flow rate, the mass of the seeping soil particles, and the content of the soil particles in each particle size range can be measured respectively.

[0061] Embodiment 2:

[0062] An experimental method using a large-scale soil permeability test device with adjustable water head and seepage direction, comprising the following steps:

[0063] S1. Connect the hose 11 to the water outlet at the bottom of the water head control unit 4 and the water inlet 12 at the lower end of the penetration test unit 14, close all overflow pipes 5 and the remaining water inlet and outlet valves, open the water inlet control valve 2, fill the water head control unit 4 and the penetration test unit 14 with water, and conduct a water leakage test to ensure that there is no water leakage during the test. After the test is completed, drain the water in the penetration test unit 14;

[0064] S2. Fill the tank of the infiltration test unit 14 with gravel of 20 mm in height as a buffer permeable layer 141, and then lay a filter with a pore size of about 0.03-0.06 mm on the gravel layer to control the uniform flow of external water into the soil sample and reduce the impact of the water flow on the sample;

[0065] S3. Before loading the soil sample, apply vaseline on the inner wall of the transparent tank to reduce the impact of boundary effect on seepage. Load the soil sample that has been compacted layer by layer by a compacting hammer to reach the set density and thickness into the tank. Then, lay a filter mesh with a pore size of about 0.03-0.06mm on the top of the soil sample, and fill a 20mm high gravel layer on the top of the filter mesh. At this time, the filter mesh laid on the top of the soil sample is mainly to prevent the loss of fine particles during the saturation process of the soil sample.

[0066] S4. Cover the tank, close the overflow control valve 6, the lower water outlet valve 17a, and the upper water inlet valve 13a, open the water inlet control valve 2, slightly open the lower water inlet valve 12a, and keep the water level in the container of the water head control unit 4 level with the top of the soil sample; in order to ensure that the soil sample is fully saturated, maintain a stable water level and let it stand for 24 hours, at which time the volume water content in the sample remains stable;

[0067] S5. Take out the filter screen and gravel laid on the seepage surface of the upper layer of the soil sample, lay a steel mesh with a pore size of about 1-5mm on the upper part of the soil sample, and fill the upper part of the steel mesh with a gravel layer of 20mm in height. The gravel layer at this time can provide a natural loss channel for fine particles of the soil sample and prevent the sample structure from being damaged when filling with water;

[0068] S6. Place the beaker 20 and the funnel 19 at the lower part of the upper water outlet 16 in sequence, open the upper water outlet valve 16a, and adjust the infiltration head height in the water head control unit 4 container to a predetermined value by jointly adjusting the telescopic bracket 10 and the overflow control valve 6, and then adjust the water inlet control valve 2 according to the data displayed by the flow meter 3 to keep the water level in the water head control unit 4 container unchanged and continuously supply water for a long time;

[0069] S7. Connect an external receiving container 8 and an electronic balance 9 to the flow guide tube 7, and after a period of seepage, turn on the electronic balance 9 with a storage memory function, and turn on the monitor 30 to record the start-up and migration changes of fine particles;

[0070] S8. According to the overflow volume Q1 of the diversion pipe 7 read by the electronic balance 9 every five minutes, combined with the cumulative flow Q2 data of the flow meter 3, the seepage volume Q of the soil sample every five minutes can be indirectly calculated. Combined with the head difference ΔH, soil sample height L, soil sample cross-sectional area A, temperature T and other data, the saturated permeability coefficient of the reservoir bank soil sample under a certain seepage water pressure can be finally calculated. The time variation law, as well as the saturated permeability coefficient K of the reservoir bank soil body at a certain seepage water pressure when the seepage is stable T ; Mainly calculated based on the following formula:

[0071] Q=Q1-Q2

[0072]

[0073] Where: K T is the permeability coefficient of the sample when the water temperature is T℃ cm / s; Q is the water seepage in the time period t after the permeation reaches stability cm 3 ; L is the seepage diameter in cm, i.e. the height of the soil sample in cm; A is the cross-sectional area of ​​the soil sample in cm 2 ; ΔH is the head difference between the upstream and downstream of the sample in cm; t is the penetration time in s.

[0074] In order to avoid test errors caused by temperature changes, 20°C is taken as the standard temperature, and the permeability coefficient at the standard temperature is calculated as follows:

[0075]

[0076] Where K 20 is the permeability coefficient of the sample at the standard temperature of 20°C cm / s; η 20 is the dynamic viscosity of water at 20°C kPa·s; η T is the dynamic viscosity of water at T℃, kPa·s. T / η 20 The ratio can be obtained by looking up the table in the "Standard for Geotechnical Test Methods (GB / T 50123-2019)".

[0077] S9. Adjust the telescopic bracket 10 and the valve of the diversion pipe 7 to change the infiltration head of the water head control unit 4 to simulate the dynamic water environment of the reservoir bank soil in the actual project, and repeat steps S6-S8 to determine the saturated permeability coefficient of the reservoir bank soil under different seepage water pressures;

[0078] S10. When it is necessary to adjust the seepage direction from top to bottom, close the valves of the lower water inlet 12 and the upper water outlet 16 at the bottom of the tank of the infiltration test unit 14, connect the hose 11 to the upper water inlet 13 of the tank of the infiltration test unit 14, and set the soil-water separation device at the lower water outlet 17 to simulate the influence of the dynamic water environment on the seepage direction of the reservoir bank soil in actual engineering, and repeat S6-S9 to determine the saturated permeability coefficient of the reservoir bank soil under the combined changes of the seepage direction and the seepage water pressure.

[0079] Working process and principle of the present invention:

[0080] The tank of the infiltration test unit 14 is filled with gravel with a height of 20 mm as a buffer permeable layer 141, and then a filter screen with a pore size of about 0.03-0.06 mm is laid on the gravel layer. Before loading the soil sample, vaseline is applied to the inner wall of the transparent tank, and the soil sample that has been compacted by a hammer to reach the set density and thickness is loaded into the tank, and then a filter screen with a pore size of about 0.03-0.06 mm is laid on the top of the soil sample, and a gravel layer with a height of 20 mm is filled on the top of the filter screen. The tank is covered, the overflow control valve 6, the lower water outlet 17, and the upper water inlet 13 are closed, the water inlet control valve 2 is opened, and the valve of the lower water inlet 12 of the tank is slightly opened, and the water level in the container of the head control unit 4 is kept level with the top of the soil sample, and the water level is kept stable and left to stand for 24 hours to saturate the soil sample. After the soil sample is saturated, take out the filter screen and gravel laid on the seepage surface of the upper layer of the soil sample, lay a wire mesh with an aperture of about 1-5mm on the upper part of the soil sample, and fill the upper part of the wire mesh with a gravel layer of 20mm in height. Place the beaker 20 and the funnel 19 in turn at the lower part of the upper water outlet 16, open the valve of the upper water outlet 16, and adjust the infiltration head height in the container of the head control unit 4 to a predetermined value by jointly adjusting the telescopic bracket 10 and the overflow control valve 6. Then adjust the water inlet control valve 2 according to the data displayed by the flow meter 3 to keep the water level in the container of the head control unit 4 unchanged and supply water continuously for a long time. Connect the receiving container 8 and the electronic balance 9 to the diversion pipe 7, and turn on the electronic balance 9 with storage and memory function after the seepage occurs for a period of time, and turn on the monitor 30 at the same time to record the start-up and migration change process of fine particles. The overflow of the diversion pipe 7 read every five minutes by the electronic balance 9 and combined with the data displayed by the flow meter 3 can indirectly calculate the seepage amount of the soil sample every five minutes. Combined with the head difference, soil sample height, soil sample cross-sectional area, temperature and other data, the variation law of the saturated permeability coefficient of the reservoir bank soil sample with time under a certain seepage water pressure and the saturated permeability coefficient of the reservoir bank soil during stable seepage under a certain seepage water pressure can be finally calculated.

Claims

1. A large-scale soil permeability test method capable of adjusting water head and seepage direction: characterized in that: It includes the following steps: S1. Connect the hose (11) to the water outlet at the bottom of the water head control unit (4) and the water inlet (12) at the lower end of the permeation test unit (14), close all overflow pipes (5) and other inlet and outlet valves, open the water inlet control valve (2), fill the water head control unit (4) and the permeation test unit (14) with water, and conduct a water leakage test to ensure that there is no water leakage during the test. After the test is completed, drain the water in the permeation test unit (14); S2. A water-permeable layer (141) is placed in the tank of the permeation test unit (14), and then a filter screen (142) having a pore size of 0.03-0.06 mm is laid on the water-permeable layer (141); S3. Before loading the soil sample, apply vaseline on the inner wall of the transparent tank, load the soil sample that has been compacted by hammering to reach the set density and thickness into the tank, and then lay a filter screen with a pore size of 0.03-0.06mm on the top of the soil sample, and fill the top of the filter screen with a gravel layer; S4. Cover the tank, close the overflow control valve (6), the lower outlet valve (17a), the upper inlet valve (13a), open the inlet control valve (2), slightly open the lower inlet valve (12a), and keep the water level in the head control unit (4) container level with the top of the soil sample; S5. Remove the filter screen and the permeable layer (141) laid on the seepage surface of the upper layer of the soil sample, lay a steel mesh (143) with a pore size of 1-5 mm on the upper part of the soil sample, and fill the permeable layer (141) on the upper part of the steel mesh (143); S6. placing the beaker (20) and the funnel (19) in sequence at the lower part of the upper water outlet (16), opening the upper water outlet valve 16a, and adjusting the infiltration head height in the container of the water head control unit (4) to a predetermined value by jointly adjusting the telescopic bracket (10) and the overflow control valve (6), and then adjusting the water inlet control valve (2) according to the data displayed by the flow meter (3) to keep the water level in the container of the water head control unit (4) unchanged and to continuously supply water for a long time; S7. Connect an external receiving container (8) and an electronic balance (9) to the flow guide tube (7), and after the seepage occurs for a period of time, turn on the electronic balance with a storage memory function (9), and turn on the monitor (30); S8. Read the overflow volume of the flow guide tube (7) every five minutes using the electronic balance (9). , combined with flow meter (3) to accumulate flow The data shows that the water seepage of the soil sample every five minutes can be indirectly calculated. , combined with the head difference ∆H, soil sample height L, soil sample cross-sectional area A and temperature T data, we can finally calculate the time variation law of the saturated permeability coefficient of the reservoir bank soil sample under a certain seepage water pressure, and the saturated permeability coefficient of the reservoir bank soil under a certain seepage water pressure when the seepage is stable ; The calculation formula is: ； （2）； Where: is the permeability coefficient of the sample when the water temperature is T℃, cm / s; is the water seepage in the time period t after the infiltration reaches stability, cm 3 ; L is the seepage diameter in cm, i.e. the height of the soil sample in cm; A is the cross-sectional area of ​​the soil sample in cm 2 ; ΔH is the head difference between the upstream and downstream of the sample, cm; t is the penetration time, s; S9. Adjust the valves of the telescopic support (10) and the diversion pipe (7) to change the infiltration head of the water head control unit (4) to simulate the dynamic water environment of the reservoir bank soil in the actual project, and repeat steps S6-S8 to determine the saturated permeability coefficient of the reservoir bank soil under different seepage water pressures. ; S10. When the seepage direction needs to be adjusted from top to bottom, close the valves of the lower water inlet (12) and the upper water outlet (16) at the bottom of the infiltration test unit (14) tank, connect the hose (11) to the upper water inlet (13) of the infiltration test unit (14) tank, and set the soil-water separation device at the lower water outlet (17) to simulate the influence of the dynamic water environment on the seepage direction of the reservoir bank soil in actual engineering. Repeat S6-S9 to determine the saturated permeability coefficient of the reservoir bank soil under the combined change of the seepage direction and the seepage water pressure. .

2. A large-scale soil permeability test device with adjustable water head and seepage direction, used to implement the large-scale soil permeability test method with adjustable water head and seepage direction as described in claim 1, characterized in that: The large-scale soil permeability test device capable of adjusting water head and seepage direction comprises a flow meter (3) installed on a water inlet pipe (1), the end of the water inlet pipe (1) being located above a water head control unit (4) and capable of injecting water into the water head control unit (4), one end of a hose (11) being connected to the bottom of the water head control unit (4) and the other end being connected to a permeability test unit (14); the water head control unit (4) comprising a transparent container with an upper end opening, a plurality of overflow pipes (5) being longitudinally arranged on the outer side surface of the container, each overflow pipe (11) 5) are provided with an overflow control valve (6); one end of the guide pipe (7) is connected to the overflow pipe (5), and the other end is connected to a weighing device; the upper end of the infiltration test unit (14) is provided with an upper water inlet (13) and an upper water outlet (16) with a valve, and the lower end is provided with a lower water inlet (12) and a lower water outlet (17) with a valve, and the hose (11) can be selectively connected to the upper water inlet (13) or the lower water inlet (12); the upper water outlet (16) or the lower water outlet (17) is provided with a soil-water separation device.

3. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 2, characterized in that: A water inlet control valve (2) is provided at the front end of the flow meter (3).

4. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 2, characterized in that: The water head control unit (4) is arranged on the telescopic bracket (10).

5. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 2, characterized in that: The weighing device comprises a receiving container (8) connected to the bottom of the flow guide tube (7), and the receiving container (8) is placed on an electronic balance (9).

6. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 2, characterized in that: The infiltration experimental unit (14) comprises a tank body with an openable upper end for filling an experimental soil sample, and water-permeable layers (141) are provided at both ends of the tank body. The water-permeable layers (141) are respectively higher than the upper water inlet (13) and the upper water outlet (16), and the lower water inlet (12) and the lower water outlet (17) are connected to the tank body through a channel, and the experimental soil sample is filled between the water-permeable layers (141) at the upper and lower ends. The tank body is made of a transparent material.

7. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 6, characterized in that: A filter screen (142) is provided on the infiltration surface between the water-permeable layer (141) at the upper and lower ends and the experimental soil sample, and a steel wire screen (143) is provided on the infiltration surface.

8. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 6, characterized in that: A scale (15) is longitudinally arranged on the outer wall of the tank.

9. A large-scale soil permeability test device capable of adjusting water head and seepage direction according to claim 2, characterized in that: A monitor (30) is also provided, and the monitor (30) performs video monitoring of the tank body.

10. The large-scale soil permeability testing device capable of adjusting water head and seepage direction according to claim 2, characterized in that: The soil-water separation device comprises a funnel (19) arranged at a water outlet (17) at the lower end or a water outlet (16) at the upper end of a tank body of a permeability test unit (14) and a beaker (20) located below the funnel (19); a filter screen is provided inside the funnel (19).

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