CN115112531A - Multifunctional osmotic piping test device and method - Google Patents
Multifunctional osmotic piping test device and method Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 113
- 238000000034 method Methods 0.000 title claims abstract description 73
- 230000003204 osmotic effect Effects 0.000 title claims abstract description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 261
- 239000002689 soil Substances 0.000 claims abstract description 200
- 230000008569 process Effects 0.000 claims abstract description 56
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- 239000011148 porous material Substances 0.000 claims abstract description 40
- 230000001105 regulatory effect Effects 0.000 claims abstract description 37
- 239000007788 liquid Substances 0.000 claims abstract description 35
- 238000000926 separation method Methods 0.000 claims abstract description 33
- 238000006073 displacement reaction Methods 0.000 claims abstract description 26
- 230000035699 permeability Effects 0.000 claims abstract description 17
- 230000006378 damage Effects 0.000 claims abstract description 16
- 239000002245 particle Substances 0.000 claims description 29
- 230000008595 infiltration Effects 0.000 claims description 20
- 238000001764 infiltration Methods 0.000 claims description 20
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- 239000004575 stone Substances 0.000 claims description 4
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- 239000004927 clay Substances 0.000 claims description 3
- 239000003822 epoxy resin Substances 0.000 claims description 3
- 230000005251 gamma ray Effects 0.000 claims description 3
- 229920000647 polyepoxide Polymers 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims description 3
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/04—Investigating osmotic effects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D21/00—Measuring or testing not otherwise provided for
- G01D21/02—Measuring two or more variables by means not covered by a single other subclass
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/06—Investigating concentration of particle suspensions
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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Abstract
The invention discloses a multifunctional osmotic piping test device and a method, wherein the test device comprises a test box system, a water supply regulating system, a loading system, a measuring system and a water outlet system, the test box system comprises a sample cylinder, a top cover, a permeable plate and a lower moving plate, a soil sample to be tested is placed between the permeable plate and the lower moving plate, and the loading system is connected with the lower moving plate to pressurize the soil sample in the sample cylinder; the water outlet system comprises a flow guide pipe, a solid-liquid separation box, a downstream water tank and a measuring cup, and the observation chamber is sequentially communicated with the solid-liquid separation box, the downstream water tank and the measuring cup which are sequentially connected in series through the flow guide pipe; the measuring system comprises a flowmeter, a pore pressure sensor, a displacement sensor, a weight sensor, a turbidity sensor and a data collector. The method can acquire the permeability coefficient of the soil body, the critical hydraulic gradient of the phase change of the soil body and various parameter indexes in the piping generation process in a time-saving and labor-saving manner when the soil body is close to the actual engineering state, and is favorable for the research of the piping damage mechanism of the soil body.
Description
Technical Field
The invention relates to the technical field of geotechnical parameter indoor testing equipment, in particular to a multifunctional permeation piping testing device and method applied to hydraulic engineering and geotechnical engineering.
Background
Seepage refers to the phenomenon that liquid moves in a porous medium, and the flow of water in soil pores inevitably causes the change of the stress state in the soil body, so that the deformation strength of the soil is changed. The seepage can directly influence the stability and safety of various geotechnical buildings, and according to statistics, over 30% of dam break accidents in the world are caused by seepage and piping, and in addition, the instability damage in landslide, tunnel excavation processes and the like is mostly related to the seepage, so that the research on the permeability of soil, the mastering of the permeation rule of water in the soil and the permeation damage mechanism of soil have important theoretical value and practical significance.
An important quantitative index for characterization of soil permeability is permeability coefficient, the existing geotechnical test regulations recommend constant head and variable head tests to be used for measuring the permeability coefficient aiming at sandy soil and cohesive soil respectively, and the conventional permeability tests have 3 defects: 1) the permeameter is small in size and cannot avoid size effect; 2) the actual stress state of the soil body cannot be considered; 3) the water supply wastes resource space, the constant head test needs to continuously inject water into the test barrel to keep stable water level, so that water resource waste is caused, the variable head test needs large head difference, the requirements on the test space and equipment are high, the test time is long, the efficiency is low, the operation is inconvenient, and time and labor are wasted.
The phenomenon that fine particles in the soil body are brought out of a boundary surface along pores formed by soil framework particles under the action of a certain hydraulic gradient is called piping, and the phenomenon that the soil body near the boundary surface is wholly suspended and moved is called flowing soil. Piping mainly occurs in sandy soil, is a gradual destruction process, often accompanies fine particles to continuously run off, the soil body is continuously eroded, the porosity is continuously changed, the soil body structure is continuously weakened, and the permeability is continuously increased. For the research on the damage of the piping of the soil body, some exploratory work has been carried out at home and abroad, but the method still has the defects in several aspects: 1) the research is generally directed at sandy soil, and compared with the sandy soil, the critical hydraulic gradient of the cohesive soil is greatly dependent on mineral characteristics, physicochemical characteristics, structural characteristics and the like of the cohesive soil, but not particle grading, the conventional determination device and determination method for the critical hydraulic gradient of the cohesive soil have no uniform specification, and the conventional determination device and determination method for the critical hydraulic gradient of the cohesive soil are difficult to perform tests in actual engineering and often depend on experience to determine and have large errors; 2) the conventional test device is limited by size and observation, the research on the piping is usually only limited to obtain the critical condition of the phase change of the piping, namely obtaining the critical hydraulic gradient of the piping, and due to the heterogeneity and anisotropy of the upper body and the complexity of the external stress condition and the hydraulic condition, the related parameters representing the actual piping generation process cannot be obtained through the critical hydraulic gradient, and the mesoscopic mechanism of the piping formation process cannot be represented.
In conclusion, the conventional infiltration piping test device and method still have some defects, the characterization of soil permeability and the research on infiltration piping damage are often split, and reasonable quantitative research is still lacked in the piping development process, so that people lack a complete, comprehensive and systematic understanding on the soil permeability rule and the infiltration piping damage development process and mechanism.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a multifunctional seepage piping test device and a method for testing the seepage piping by adopting the test device, and the device and the method can completely, comprehensively and systematically represent the soil body seepage rule and the seepage damage phenomenon, namely realize the following functions: 1) the real and credible permeability coefficient of the soil body can be obtained in a time-saving and labor-saving manner; 2) obtaining a critical hydraulic gradient of the phase change of the soil body; 3) the method has the advantages that various parameter indexes in the piping generation process, such as the particle loss and the change process of porosity, are obtained, favorable theoretical support is provided for the research of the soil body piping damage mechanism, and reasonable and effective parameters are provided for the anti-seepage design of various large projects.
The invention is realized by the following technical scheme:
a multifunctional osmotic piping test device comprises a test box system, a water supply adjusting system, a loading system, a measuring system and a water outlet system.
The test box system comprises a sample cylinder, a top cover, a water permeable plate and a lower moving plate, wherein the sample cylinder is used for loading a test soil sample, the top cover is fixed at the top of the sample cylinder, and the top cover is provided with exhaust holes for exhausting residual gas in a previous pipeline and the sample; the water permeable plate is arranged in the sample cylinder and positioned below the top cover, a plurality of water permeable holes are uniformly distributed in the water permeable plate, an observation chamber is formed in the space between the top cover and the water permeable plate in the sample cylinder and used for observing the water sand gushing condition in the piping process, and an overflow port is arranged on the side wall of the observation chamber; the lower moving plate is arranged at the bottom of the sample cylinder and can move up and down along the sample cylinder, a soil sample to be tested is placed between the porous disk and the lower moving plate, the upper surface of the soil sample is in contact with the porous disk, the lower surface of the soil sample is in contact with the lower moving plate, and the lower moving plate is tightly attached to the inner wall of the sample cylinder. The sample cylinder, the top cover and the lower moving plate can be made of transparent materials, such as acrylic materials, so that the change condition of a soil sample in the test process can be observed conveniently, and the soil sample bin can be directly used for CT (computed tomography), nuclear magnetic resonance tests and the like after the test is finished.
The water supply adjusting system is communicated with the water inlet on the lower moving plate through a pipeline so as to supply test water with set pressure into the sample cylinder. The loading system is connected with the lower moving plate and used for pushing the lower moving plate to move upwards along the sample cylinder so as to pressurize the soil sample in the sample cylinder.
The water outlet system comprises a flow guide pipe, a solid-liquid separation box, a downstream water tank and a measuring cup, wherein one end of the flow guide pipe is communicated with an overflow port of the observation chamber, the other end of the flow guide pipe is communicated with a plurality of solid-liquid separation boxes which are sequentially connected in series, a water inlet of each solid-liquid separation box is arranged at the upper part, a water outlet of each solid-liquid separation box is arranged at the lower part, a filter screen is arranged in each solid-liquid separation box, and the pore diameters of the filter screens in the solid-liquid separation boxes which are connected in series are sequentially reduced; the water outlet of the last solid-liquid separation tank is connected with the downstream water tank, the upper part of the downstream water tank is provided with an overflow port, and the overflow port is communicated with the measuring cup through a pipeline; the soil water flowing out of the overflow port of the observation chamber is filtered by a plurality of solid-liquid separation tanks connected in series, then enters the downstream water tank and then enters the measuring cup through the downstream water tank.
The measuring system comprises a flowmeter, a pore pressure sensor, a camera and a data collector, wherein the flowmeter is arranged on a pipeline between the downstream water tank and the measuring cup and is used for measuring the water volume gushed in a certain time period in the test process; the pore pressure sensors are arranged at intervals along the height direction of the sample cylinder and are used for measuring the pore water pressure at different heights in the sample cylinder; the cameras are arranged at the test box system and the water outlet system and used for monitoring the change conditions of the test box system and the water outlet system in the test process; the data acquisition unit is respectively connected with the flowmeter, the pore pressure sensor and the camera through data lines so as to acquire data information of each sensor.
Furthermore, the measuring system also comprises a displacement sensor, a weight sensor and a turbidity sensor, wherein the displacement sensor is arranged at the position of the lower moving plate and is used for measuring the moving distance of the lower moving plate; the weight sensors are arranged at the bottoms of the solid-liquid separation boxes and the downstream water tank and are used for measuring the loss conditions of particles with different particle sizes gushed in the piping process in real time; the turbidity sensor enters the observation chamber through the exhaust hole and is used for measuring the turbidity change of the gushed water in the test process so as to judge the occurrence of soil body phase change; and the displacement sensor, the weight sensor and the turbidity sensor are respectively connected with the data acquisition unit through data lines.
Furthermore, four solid-liquid separation boxes are connected in series, and the aperture is 0.5mm, 0.25mm, 0.075mm and 0.005mm in sequence; the inner diameter of the sample cylinder is more than or equal to 10 times of the maximum grain size of the soil body to be detected, and the height of the sample cylinder is more than or equal to two times of the inner diameter of the sample cylinder; the aperture of the water permeable hole is 8 mm.
Further, the loading system comprises an air cylinder, a first air compressor and a loading pressure regulating valve, wherein a telescopic rod of the air cylinder is connected with the downward moving plate, the first air compressor is connected with an air inlet of the air cylinder through the loading pressure regulating valve, and the air cylinder pushes the downward moving plate to move upwards along the sample cylinder so as to apply target axial pressure to the soil sample in the sample cylinder.
The air cylinder is arranged on the lower bottom plate, and is characterized by further comprising a fixing support, wherein the fixing support comprises an upper top plate, a lower bottom plate, stand columns, a support frame and fixing bolts; the top cover is provided with a positioning column, the upper top plate is provided with a positioning hole matched with the positioning column, and the test box system is positioned by matching the positioning column on the top cover with the positioning hole on the upper top plate (the positioning column penetrates into the positioning hole); the sample cylinder is fixed on the support frame, and the support frame is fixed on the two upright posts through fixing bolts.
Further, the water supply regulating system comprises a water supply tank, a second air compressor and a pressure tank, wherein the pressure tank is used for supplying test water with set pressure into the sample cylinder, a water outlet of the water supply tank is communicated with a water inlet of the pressure tank through a pipeline, a water outlet of the pressure tank is communicated with a water inlet of the lower moving plate through a pipeline, and the second air compressor is communicated with an air inlet of the pressure tank through an air supply pressure regulating valve; the pipeline between the water supply tank and the pressure tank and the pipeline between the pressure tank and the lower moving plate are provided with water inlet and outlet control valves for controlling the opening and closing and the flow rate of inlet and outlet water; the pipeline between the pressure tank and the lower moving plate is also provided with a pressure gauge, a pressure reducing valve and a water supply pressure regulating valve, the pressure gauge is used for detecting the water pressure output by the pressure tank, the pressure reducing valve is used for reducing the water pressure output by the pressure tank so as to maintain stable pressure supply, and the water supply pressure regulating valve is used for regulating the water pressure to accurate target water pressure.
Furthermore, the top cover is in a cylinder shape with a closed upper part and an open lower part, an annular sinking step is arranged at the opening end of the cylinder close to the inner side of the hollow cavity, a flange is arranged at the outer side of the opening end of the cylinder, a flange is also arranged at the position of the sample cylinder connected with the top cover, the top cover is connected with the sample cylinder in a sealing way through the flange, the edge of the water permeable plate is embedded in the sinking step, and the lower surface of the water permeable plate is contacted with the upper surface of a soil sample to be tested in the sample cylinder; the observation chamber is a space enclosed by the water permeable plate and the top cover, and the overflow gap is arranged on the wall of the top cover barrel.
Furthermore, the lower moving plate is of a cylinder structure with an opening at the upper end, gravels are filled in the cylinder for buffering a pressurized water body, the opening end of the cylinder is closed by a water-permeable sand-isolating net, and the water-permeable sand-isolating net can penetrate through the pressurized water body and is in direct contact with the bottom of the test soil sample but cannot penetrate through the test soil sample; the water inlet of the lower moving plate is arranged on the closed lower end of the lower moving plate, and the loading system is connected with the closed lower end of the lower moving plate; the outer side wall of the lower moving plate cylinder body is provided with a sealing ring or a sealing air bag, so that the lower moving plate is tightly attached to the sample cylinder.
A multifunctional seepage piping test method is applied to the multifunctional seepage piping test device and comprises the following steps:
s1, preparation of a sample: filling undisturbed or remolded clay into a sample cylinder, respectively attaching filter paper and permeable stones to two ends of the sample cylinder, fixing, and placing the sample cylinder in a vacuum cylinder for vacuumizing saturation to obtain a saturated soil sample; calculating the initial porosity n of the soil sample according to the following formula 0 In%:
where ρ is w The density of the test water is given in g/cm 3 ；w sat The saturated water content of the soil sample is shown in unit; rho d Is the dry density of the soil sample and has the unit of g/cm 3 (ii) a Gs is the specific gravity of the soil sample and is dimensionless;
s2, mounting a soil sample and a device: connecting a sample cylinder filled with a saturated soil sample to a lower moving plate, fixing a porous plate and a top cover on the upper part of the sample cylinder, enabling the upper surface of the saturated soil sample to be in contact with the porous plate and the lower surface of the saturated soil sample to be in contact with the lower moving plate, and connecting a water supply adjusting system, a loading system, a measuring system and a water outlet system; measuring the initial height of the soil sample to be L, the bottom area to be A and the vertical distance from the top of the soil sample to the overflow port to be h;
s3, emptying pipelines of the system and residual gas in the soil sample: opening an exhaust hole on the top cover, starting a water supply regulating system to enable water with certain pressure to slowly flow through the soil sample until the water overflows from the exhaust hole, and continuing for a period of time to empty residual gas in the pipeline and the soil sample; then, sleeving a waterproof joint on the exhaust hole and inserting a turbidity sensor into the observation window;
s4, applying axial pressure: pushing the lower moving plate to move upwards through a loading system so as to apply constant axial pressure to the soil sample;
s5, applying a pressure head: applying stable water inlet with a set water head height to the soil sample through a water supply adjusting system to form a seepage path from bottom to top;
s6, permeability coefficient measurement: after the reading of the flowmeter is stable, the pore water pressures of pore pressure sensors at the bottom and the top of the soil sample are respectively read to be P 1 And P 2 Reading the flow rate Q flowing through the flowmeter within a certain time t, and calculating the permeability coefficient k of the soil sample according to the following formula:
wherein Q is the displacement in m within a certain time t 3 (ii) a L is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample and the unit is m 2 ；γ w Is the water gravity with the unit of kN/m 3 ；(P 1 -P 2 ) The pressure difference between the upper surface and the lower surface of the soil sample is expressed in kPa; and h is the vertical height from the upper surface of the soil sample to the overflow port, and the unit is m.
Further, the method also comprises the following steps:
s7, critical hydraulic gradient measurement: adjusting a water supply adjusting system, increasing hydraulic gradient step by step at certain water head height intervals, keeping large hydraulic gradient of each stage for a certain time, applying next large hydraulic gradient after the reading of the flowmeter is stable, and monitoring data changes of a flow sensor, a turbidity sensor and a pore pressure sensor; when the data of the pore pressure sensor, the flow meter and the turbidity sensor are changed temporarily and the water in the observation chamber is turbid temporarily and obviously under a certain level of hydraulic gradient, the hydraulic gradient can be judged as a critical hydraulic gradient, and a critical hydraulic gradient i is calculated according to the following formula cr ：
Wherein L is the initial height of the soil sample and the unit is m; gamma ray w Is the water gravity with the unit of kN/m 3 ；(P 1 -P 2 ) cr Under the critical hydraulic gradient, the upper surface and the lower surface of a soil samplePressure differential in kPa; h is the vertical height from the upper surface of the soil sample to the overflow port, and the unit is m;
s8, measuring the piping development process: when critical hydraulic gradient i occurs cr During the process, the hydraulic gradient action and the axial pressure are kept unchanged, the piping generation process is recorded by a camera, the data change conditions of the pore pressure sensor, the weight sensor, the flowmeter and the displacement sensor in the piping generation process are recorded by a data collector, the pore pressure change, the vertical displacement change, the water inflow change and the mass change of different gushed particle sizes of the soil body in any time period in the piping generation process are obtained, and the t in the piping generation process is calculated according to the following formula 1 Soil porosity n at the moment 1 In%:
wherein n is 0 Is the initial porosity of the soil sample in%; l is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample and the unit is m 2 (ii) a S is t 1 The unit of the vertical displacement of the soil sample at the moment is m; m is t1 Is t 1 The loss mass of the particles at that time; gs is the specific gravity of the soil sample and is dimensionless;
s9, after the infiltration is finished, injecting the epoxy resin with high fluidity into the soil sample, finishing consolidation at normal temperature, and after the consolidation is finished, carrying out microscopic scanning to observe the microstructure change rule of the sample;
s10, changing the test hydraulic gradient to be larger than the critical hydraulic gradient, repeating the steps S8 and S9, and comparing and analyzing differences of the soil body piping damage process under the action of different hydraulic gradients, wherein the differences comprise particle loss, water inflow and soil body porosity change;
s11, changing the initial conditions of the soil body, such as particle grading, porosity ratio and the like, repeating the steps from S1 to S10, and comparing and analyzing the damage rule of the infiltration piping under different initial conditions of the soil sample.
Compared with the prior art, the invention has the following advantages:
(1) the method can simulate the processes of soil body infiltration and piping in real time by functional design and mutual cooperation of units such as a test box system, a water supply adjusting system, a loading system, a measuring system and a water outlet system, can monitor a plurality of index data such as flow, water turbidity, different particle size particle contents in outlet water and water pressure in the test process in real time by arranging monitoring devices such as a flowmeter, a pore pressure sensor, a camera, a displacement sensor, a weight sensor and a turbidity sensor, can comprehensively acquire the permeability coefficient of the soil body, the critical hydraulic gradient of the phase change of the soil body and various parameter indexes such as particle loss and porosity in the piping generation process, and can carry out complete and comprehensive treatment on the soil body infiltration rule and the piping development process by adjusting the parameters such as water head pressure, loading pressure and initial conditions of a soil sample, Researching a system;
(2) the whole test method has novel thought, simple structure, simple and convenient operation process and low input cost;
(3) the test box has reasonable size, can effectively avoid size effect, can consider the action of axial pressure and can be more close to the stress state of the actual engineering of the soil body;
(4) the water supply regulating system can provide a higher stable pressure water head, avoids the limitation of the test caused by the need of installing the water supply tank at a higher position due to higher water pressure, saves the test space, can change the water pressure setting as required and saves water resources;
(5) the loss conditions of particles with different particle sizes in the piping process can be obtained in real time by utilizing the solid-liquid separation boxes connected in series;
(6) the data change of each sensor can be intelligently collected in real time by using a measuring system; the accuracy of the test data is ensured by comparing the test data with the data recorded by the camera, the automation degree is higher, and the labor and the time are saved;
(7) by adopting a relatively perfect sample solidification means, the sample micro-section analysis after the permeation is finished is facilitated, the change rule of the sample microstructure is easy to observe, and a favorable theoretical support is provided for the research of the soil body piping damage mechanism.
Drawings
FIG. 1 is a schematic structural diagram of a testing apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic structural diagram of a test box system in the testing apparatus according to the embodiment of the present invention.
FIG. 3 is a schematic structural diagram of a top cover of a test box system in the testing apparatus according to the embodiment of the present invention.
FIG. 4 is a schematic structural view of a permeable plate on a test box system in the testing apparatus according to the embodiment of the present invention.
FIG. 5 is a schematic structural diagram of a lower moving plate in a test box system of the testing apparatus according to the embodiment of the present invention.
FIG. 6 is a block diagram of a measurement system in a test apparatus according to an embodiment of the present invention.
Reference numerals: 1-fixing a bracket; 2-test chamber system; 3-a water supply regulating system; 4-loading the system; 5-a water outlet system; 6-a measurement system; 7-soil sample; 11-upright post; 12-upper top plate; 13-lower base plate; 14-a fixing bolt; 15-positioning holes; 16-a support frame; 21-a top cover; 22-permeable plate; 23-a sample cartridge; 24-a lower moving plate; 25-an observation room; 211-a positioning post; 212-overflow; 213-vent hole; 214-sink step; 215-flange plate; 221-water permeable holes; 241-cylinder body; 242-water permeable sand-separating net; 243-gravel; 244-lower moving plate water inlet; 245-a sealed bladder; 31-a water supply tank; 32-a second air compressor; 33-pressure tank; 34-air supply pressure regulating valve; 35-water inlet and outlet control valves; 36-pressure gauge; 37-a pressure reducing valve; 38-water supply pressure regulating valve; 331-inlet holes; 332-pressure tank vent hole; 333-pressure tank water inlet; 334-pressure tank water outlet; 41-a first air compressor; 42-loading a pressure regulating valve; 43-cylinder; 431-a telescopic rod; 51-a draft tube; 52-a solid-liquid separation tank; 53-downstream water tank; 54-measuring cup; 521-a filter screen; 61-pore pressure sensor; 62-a turbidity sensor; 63-a camera; 64-a weight sensor; 65-a displacement sensor; 66-a flow meter.
Detailed Description
A multifunctional infiltration piping test device is shown in figure 1 and comprises a fixed support 1, a test box system 2, a water supply adjusting system 3, a loading system 4, a measuring system 6 and a water outlet system 5. The test chamber system 2 is fixed on the fixed support 1.
As shown in fig. 1 and 2, the test chamber system 2 includes a sample cylinder 23, a top cover 21, a water permeable plate 22 and a downward moving plate 24, the sample cylinder 23 is used for loading a test soil sample, the top cover 21 is fixed on the top of the sample cylinder 23, and the top cover 21 is provided with an exhaust hole 213 for exhausting residual gas in a front-stage pipeline and the sample; the permeable plate 22 is arranged in the sample cylinder 23 and located below the top cover 21, as shown in fig. 4, a plurality of permeable holes 221 are uniformly distributed on the permeable plate 22, the aperture of each permeable hole 221 can be set to be 8mm, an observation chamber 25 is formed in the sample cylinder 23 in the space between the top cover 21 and the permeable plate 22 and used for observing the water and sand gushing condition in the piping process, and an overflow port 212 is arranged on the side wall of the observation chamber 25 and used for discharging the water and sand gushed in the piping process out of the test box; the lower moving plate 24 is arranged at the bottom of the sample cylinder 23 and can move up and down along the sample cylinder 23, the soil sample 7 to be tested is placed between the porous plate 22 and the lower moving plate 24, the upper surface of the soil sample 7 is in contact with the porous plate 22, the lower surface of the soil sample 7 is in contact with the lower moving plate 24, and the lower moving plate 24 is tightly attached to the inner wall of the sample cylinder 23. The sample cylinder 23, the top cover 21 and the lower moving plate 24 can be made of transparent materials, such as acrylic materials, so that the change condition of the soil sample in the test process can be observed conveniently, and the soil sample bin can be directly used for CT, nuclear magnetic resonance test and the like after the test is finished.
The top cover 21 is closed on the top of the sample tube 23, the top cover 21 and the permeable plate 22 can be fixed on the sample tube 23 in various forms such as a snap fit, as shown in fig. 3, in this embodiment, the top cover 21 is in a cylinder shape with a closed upper part and an open lower part, a ring-shaped sunken step 214 capable of accommodating the permeable plate 22 is arranged near the open end of the cylinder near the hollow inner side, a flange 215 is arranged on the outer side of the open end of the cylinder, a flange 215 is also arranged on the sample tube 23 at the position connected with the top cover 21, the top cover 21 and the sample tube 23 are connected through the flange 215 and bolts in a sealing manner, and the top cover 21 and the sample tube 23 are connected into a sealed whole.
The edge of the permeable plate 22 is embedded in the sunken step 214, the upper edge of the permeable plate 22 abuts against the sunken step 214, and the lower surface of the permeable plate 22 is in contact with the upper surface of the test soil sample in the sample cylinder 23; the observation chamber 25 is a space enclosed by the permeable plate 22 and the top cover 21, and the overflow port 212 is arranged on the cylindrical wall of the top cover 21.
The function of the lower moving plate 24 is to support the soil sample in the sample cylinder 23, and to move along the interior of the sample cylinder 23 to apply vertical pressure to the soil sample, and the water for sample is also introduced from the lower moving plate 24. In this embodiment, as shown in fig. 1 and 5, the lower moving plate 24 is a cylindrical structure with an open upper end, the cylindrical body 241 is filled with gravel 243 for buffering pressurized water, the open end of the cylindrical body 241 is sealed by a water-permeable sand-separating net 242, the water-permeable sand-separating net 242 can penetrate the pressurized water but cannot penetrate the soil sample, and the water-permeable sand-separating net 242 directly contacts the bottom of the test soil sample; a water inlet (a lower moving plate water inlet 244 in the figure) of the lower moving plate 24 is arranged at the bottom of the lower moving plate 24, and the loading system 4 is connected with the closed lower end of the lower moving plate 24; the outer side wall of the cylinder 241 of the lower moving plate 24 is provided with a sealing ring or a sealing air bag 245, so that the lower moving plate 24 is tightly attached to the sample cylinder 23.
The loading system 4 is connected with the lower moving plate 24 and used for pushing the lower moving plate 24 to move upwards along the sample cylinder 23 so as to pressurize the soil sample in the sample cylinder 23.
The loading system 4 functions to apply an axial force to the test soil sample through the lower shift plate 24. In this embodiment, the loading system 4 includes an air cylinder 43, a first air compressor 41 and a loading pressure regulating valve 42, wherein the telescopic rod 431 of the air cylinder 43 is connected to the lower moving plate 24, the first air compressor 41 is connected to the air inlet 331 of the air cylinder 43 through the loading pressure regulating valve 42, the loading pressure regulating valve 42 is used for controlling an input pressure value, the air cylinder 43 is controlled according to an air pressure value input by the first air compressor 41, and the air cylinder 43 pushes the lower moving plate 24 to move upwards along the sample cylinder 23 so as to apply a target axial pressure to the soil sample in the sample cylinder 23.
As one embodiment, the fixing bracket 1 includes an upper top plate 12, a lower bottom plate 13, upright posts 11, a supporting frame 16 and fixing bolts 14, the upper top plate 12 and the lower bottom plate 13 are respectively connected with two upright posts 11 vertically arranged through the fixing bolts 14, and the air cylinder 43 is arranged on the lower bottom plate 13; the top cover 21 is provided with a positioning column 211, the upper top plate 12 is provided with a positioning hole 15 matched with the positioning column 211, and the test box system 2 is fixed and positioned by matching the positioning column 211 on the top cover 21 with the positioning hole 15 on the upper top plate 12 (the positioning column 211 penetrates into the positioning hole 15); the sample tube 23 is fixed on the support frame 16, and the support frame 16 is fixed on the two columns 11 through fixing bolts 14. The fixed support 1 is used for stabilizing the test box system 2 and providing a loading space for the air cylinder 43, and the camera 63 can be arranged on the upright post 11 and used for monitoring the change conditions of the test box system 2 and the water outlet system in the test process.
The water supply adjusting system 3 is connected to the upper water inlet 244 of the lower moving plate 24 through a pipe to supply test water of a set pressure to the sample cartridge 23.
The water supply adjusting system 3 is used for supplying test water with a set head height, and may be of a conventional structure or form capable of achieving the function, and in this embodiment, the water supply adjusting system 3 includes a water supply tank 31, a second air compressor 32, and a pressure tank 33, the pressure tank is used for supplying test water with a set pressure into the sample cylinder, and may be a common pressure tank of a conventional constant pressure water supply system, and water with a certain water pressure is obtained. The pressure tank 33 is provided with an air inlet 331 and an air outlet (pressure tank air outlet 332 in the figure) at the top, and a water inlet (pressure tank water inlet 333 in the figure) and a water outlet (pressure tank water outlet 334 in the figure) at the bottom. The water outlet of the water supply tank 31 is communicated with the water inlet of the pressure tank 33 through a pipeline, and the water outlet of the pressure tank 33 is communicated with the lower moving plate 24 through a pipeline. The second air compressor 32 is connected to an air inlet 331 of the pressure tank 33 through an air supply pressure regulating valve 34, and the air supply pressure regulating valve 34 is used for controlling the pressure of the air supplied to the pressure tank 33 by the second air compressor 32.
The pressure tank 33 supplies test water of a set pressure to the sample tube 23 by air-water equilibrium. The pipeline between the water supply tank 31 and the pressure tank 33 and the pipeline between the pressure tank 33 and the lower moving plate 24 are provided with water inlet and outlet control valves 35 for controlling the opening and closing and the flow rate of inlet and outlet water; a pressure gauge 36, a pressure reducing valve 37 and a water supply pressure regulating valve 38 are further arranged on a pipeline between the pressure tank 33 and the lower moving plate 24, the pressure gauge 36 is used for detecting the water pressure output by the pressure tank 33, the pressure reducing valve 37 is used for reducing the water pressure output by the pressure tank to maintain stable pressure supply, and the water supply pressure regulating valve 38 is used for regulating the water pressure to an accurate target water pressure.
In one embodiment, the second air compressor 32 can provide a maximum pressure of 1.2Mpa, the pressure tank 33 can bear a maximum pressure of 1.6Mpa, the second air compressor 32 can blow a gas of 1.2Mpa into the pressure tank 33, and when the pressure value of the pressure tank 33 is less than 1.0Mpa, the second air compressor 32 can automatically supplement the pressure, so that the pressure of the pressure tank 33 is maintained at 1.0Mpa or more, and the pressure tank 33 can provide a water pressure of about 1.0 Mpa.
The water outlet system 5 comprises a guide pipe 51, a solid-liquid separation box 52, a downstream water tank 53 and a measuring cup 54, wherein one end of the guide pipe 51 is communicated with an overflow port 212 of the observation chamber 25, the other end of the guide pipe is communicated with a plurality of solid-liquid separation boxes 52 which are sequentially connected in series, a water inlet of each solid-liquid separation box 52 is arranged at the upper part, a water outlet of each solid-liquid separation box 52 is arranged at the lower part, a filter screen 521 is arranged in each solid-liquid separation box 52, and the aperture of each filter screen 521 in the plurality of solid-liquid separation boxes 52 which are connected in series is sequentially reduced, so that the water outlet system can be used for observing the loss condition of each particle size in the piping process in real time. The water outlet of the last solid-liquid separation tank 52 is connected with the downstream water tank 53, the upper part of the downstream water tank 53 is provided with an overflow port, the overflow port is communicated with the measuring cup 54 through a pipeline, the downstream water tank 53 can keep a stable liquid level, and the soil water flowing out from the overflow port 212 of the observation chamber 25 sequentially passes through the plurality of solid-liquid separation tanks 52 connected in series, then enters the downstream water tank 53, and then enters the measuring cup 54 through the downstream water tank 53.
In one embodiment, the solid-liquid separation boxes 52 are four in series, and the pore diameters are 0.5mm, 0.25mm, 0.075mm and 0.005mm in sequence; the inner diameter of the sample cylinder 23 is larger than or equal to 10 times of the maximum grain diameter of the soil body to be tested, and the height of the sample cylinder 23 is larger than or equal to twice of the inner diameter of the sample cylinder, so that the size effect caused by oversize grains existing in the soil body can be effectively avoided.
As shown in fig. 1 and 6, the measuring system 6 comprises a flow meter 66, an orifice pressure sensor 61, a displacement sensor 65, a weight sensor 64, a turbidity sensor 62, a camera 63 and a data collector, wherein the flow meter 66 is arranged on a pipeline between the downstream water tank 53 and the measuring cup 54 and is used for measuring the water amount gushing out in a certain period of time during the test; the pore pressure sensors 61 are arranged at intervals along the height direction of the sample cylinder 23 and are used for measuring the pore water pressure at different heights in the sample cylinder 23, in the embodiment, the number of the pore pressure sensors 61 is 3 along the height direction at equal intervals, and the pore water pressure of the upper surface, the lower surface and the middle part of the soil sample are respectively measured. The cameras 63 are arranged at the test box system 2 and the water outlet system 5 and used for monitoring the change conditions of the test box system 2 and the water outlet system in the test process; the displacement sensor 65 is arranged at the lower moving plate 24 and used for measuring the moving distance of the lower moving plate 24 so as to measure the axial displacement change of soil; the weight sensors 64 are arranged at the bottoms of the solid-liquid separation tanks 52 and the downstream water tank 53, and in the embodiment, five weight sensors are correspondingly arranged and used for measuring the loss conditions of particles with different particle sizes flowing out in the piping process in real time; the turbidity sensor 62 enters the observation chamber through the exhaust hole 213 and is used for measuring the change of turbidity of the gushed water in the test process so as to judge the occurrence of soil body phase change. The data acquisition unit is respectively connected with the flow meter 66, the pore pressure sensor 61, the displacement sensor 65, the weight sensor 64, the turbidity sensor 62 and the camera 63 through data lines so as to acquire data information of each sensor.
A multifunctional seepage piping test method is applied to the multifunctional seepage piping test device and comprises the following steps:
s1, preparation of a sample: the undisturbed or remolded cohesive soil is filled into the sample cylinder 23, the two ends of the sample cylinder 23 are respectively stuck with filter paper and permeable stone, and the sample cylinder is placed in a vacuum cylinder for vacuumizing saturation after being fixed, and the specific method can refer to a method for vacuumizing saturation in a geotechnical test: attaching filter paper and permeable stones to two ends of a sample cylinder, fixing, placing the sample cylinder into a vacuum cylinder, exhausting air, enabling the pressure in the vacuum cylinder to reach-100 kPa, generally exhausting air for 1h by using clay soil, and then injecting water and soaking for more than 10h to fully saturate the sample to obtain a saturated soil sample; calculating the initial porosity n of the soil sample according to the following formula 0 In%:
where ρ is w The density of the test water is given in g/cm 3 ；w sat The saturated water content of the soil sample is shown in unit; rho d Is the dry density of the soil sample and has the unit of g/cm 3 (ii) a Gs is the specific gravity of the soil sample and is dimensionless;
s2, mounting a soil sample and a device: connecting a sample cylinder 23 filled with a saturated soil sample to a lower moving plate 24, fixing a top cover 21 on the upper part of the sample cylinder 23 through a flange plate 215 and a bolt, tightly pressing a water permeable plate 22 between the top cover 21 and the sample cylinder 23, enabling the upper surface of the saturated soil sample to be in contact with the water permeable plate 22 and the lower surface to be in contact with the lower moving plate 24, and connecting a water supply adjusting system 3, a loading system 4, a measuring system 6 and a water outlet system 5; measuring that the initial height of the soil sample is L, the bottom area is A, and the vertical distance from the top of the soil sample to the overflow port 212 is h;
s3, emptying pipelines of the system and residual gas in the soil sample: opening the vent hole 213 on the top cover 21, starting the water supply regulating system 3 to make water with a certain pressure (such as 10kPa) slowly flow through the soil sample until the water overflows from the vent hole 213, and continuing for a period of time (such as 10min) to exhaust residual gas in the pipeline and the soil sample; then, a waterproof joint is sleeved on the exhaust hole 213 and the turbidity sensor 62 is inserted into the observation window;
s4, applying axial pressure: the air cylinder 43, the first air compressor 41 and the loading pressure regulating valve 42 push the lower moving plate 24 to move upwards, so that constant axial pressure is applied to the soil sample;
s5, applying a pressure head: applying stable water inlet with a set water head height to the soil sample through the water supply regulating system 3, and regulating the air supply pressure regulating valve 34 and the water supply pressure regulating valve 38 to obtain stable water inlet pressure to form a seepage path from bottom to top;
s6, permeability coefficient measurement: after the reading of the flowmeter 66 is stable, the pore water pressures of the pore pressure sensors 61 at the bottom and the top of the soil sample are respectively read as P 1 And P 2 Reading the flow rate of water through flow meter 66 over a certain time t as Q, based on, for exampleCalculating the permeability coefficient k of the soil sample by the following formula:
wherein Q is the displacement in m within a certain time t 3 (ii) a L is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample and the unit is m 2 ；γ w Is the water gravity in kN/m 3 ；(P 1 -P 2 ) The pressure difference between the upper surface and the lower surface of the soil sample is expressed in kPa; h is the vertical height from the upper surface of the soil sample to the overflow 212, and is m.
In order to further study the occurrence process and mechanism of the infiltration piping, the method can further comprise the following steps:
s7, critical hydraulic gradient measurement: adjusting the water supply adjusting system 3, gradually increasing the hydraulic gradient at certain water head height intervals (such as pressure intervals of 2 kPa) by adjusting the pressure adjusting valve, keeping the large hydraulic gradient of each stage for a certain time (such as 10min), applying the next large hydraulic gradient after the reading of the flowmeter 66 is stable, and simultaneously monitoring the data changes of the flow sensor, the turbidity sensor 62 and the pore pressure sensor 61; when the data of the pore pressure sensor 61, the flow meter 66 and the turbidity sensor 62 are changed transiently and the water body in the observation chamber 25 is turbid transiently and obviously under a certain level of hydraulic gradient, the hydraulic gradient can be judged to be a critical hydraulic gradient, and a critical hydraulic gradient i is calculated according to the following formula cr ：
Wherein L is the initial height of the soil sample and the unit is m; gamma ray w Is the water gravity with the unit of kN/m 3 ；(P 1 -P 2 ) cr The pressure difference of the upper surface and the lower surface of the soil sample under the critical hydraulic gradient is expressed in kPa; h is the vertical height from the upper surface of the soil sample to the overflow port 212, and the unit is m;
s8, measuring the piping development process: when critical hydraulic gradient i occurs cr During the process, the hydraulic gradient action and the axial pressure are kept unchanged, the piping occurrence process is recorded by a camera 63, the data change conditions of a pore pressure sensor 61, a weight sensor 64, a flowmeter 66 and a displacement sensor 65 in the piping occurrence process are recorded by a data acquisition unit, the pore pressure change, the vertical displacement change, the water inflow change and the mass change of different gushed particle sizes of soil in any time period in the piping occurrence process are obtained, and the t in the piping occurrence process is calculated according to the following formula 1 Soil porosity n at a time 1 In%:
wherein n is 0 Is the initial porosity of the soil sample in%; l is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample and the unit is m 2 (ii) a S is t 1 The unit of the vertical displacement of the soil sample at the moment is m; m is t1 Is t 1 The loss mass of the particles at that time; gs is the specific gravity of the soil sample and is dimensionless;
s9, after the infiltration is finished, injecting the epoxy resin with high fluidity into the soil sample, finishing consolidation at normal temperature, and after the consolidation is finished, carrying out microscopic scanning to observe the microstructure change rule of the sample;
s10, changing the test hydraulic gradient to be larger than the critical hydraulic gradient, repeating the steps S8 and S9, and comparing and analyzing differences of the soil body piping damage process under the action of different hydraulic gradients, wherein the differences include particle loss, water inflow and soil body porosity change;
s11, changing the initial conditions of the soil body, such as particle grading, porosity ratio and the like, repeating the steps from S1 to S10, and comparing and analyzing the damage rule of the infiltration piping under different initial conditions of the soil sample.
The above detailed description is specific to possible embodiments of the present invention, and the embodiments are not intended to limit the scope of the present invention, and all equivalent implementations or modifications that do not depart from the scope of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A multifunctional infiltration piping test device is characterized by comprising a test box system, a water supply adjusting system, a loading system, a measuring system and a water outlet system;
the test box system comprises a sample cylinder, a top cover, a water permeable plate and a lower moving plate, wherein the sample cylinder is used for loading a test soil sample, the top cover is fixed at the top of the sample cylinder, and the top cover is provided with an exhaust hole for exhausting residual gas in an early-stage pipeline and the sample; the water permeable plate is arranged in the sample cylinder and positioned below the top cover, a plurality of water permeable holes are uniformly distributed in the water permeable plate, an observation chamber is formed in the space between the top cover and the water permeable plate in the sample cylinder and used for observing the water sand gushing condition in the piping process, and an overflow port is arranged on the side wall of the observation chamber; the lower moving plate is arranged at the bottom of the sample cylinder and can move up and down along the sample cylinder, a soil sample to be detected is placed between the water permeable plate and the lower moving plate, the upper surface of the soil sample is contacted with the water permeable plate, the lower surface of the soil sample is contacted with the lower moving plate, and the lower moving plate is tightly attached to the inner wall of the sample cylinder;
the water supply regulating system is communicated with a water inlet on the lower moving plate through a pipeline so as to supply test water with set pressure into the sample cylinder; the loading system is connected with the downward moving plate and used for pushing the downward moving plate to move upwards along the sample cylinder so as to apply axial pressure to the soil sample in the sample cylinder;
the water outlet system comprises a flow guide pipe, a solid-liquid separation box, a downstream water tank and a measuring cup, wherein one end of the flow guide pipe is communicated with an overflow port of the observation chamber, the other end of the flow guide pipe is communicated with a plurality of solid-liquid separation boxes which are sequentially connected in series, a water inlet of each solid-liquid separation box is arranged at the upper part, a water outlet of each solid-liquid separation box is arranged at the lower part, a filter screen is arranged in each solid-liquid separation box, and the pore diameters of the filter screens in the plurality of solid-liquid separation boxes which are connected in series are sequentially reduced; the water outlet of the last solid-liquid separation tank is connected with the downstream water tank, the upper part of the downstream water tank is provided with an overflow port, and the overflow port is communicated with the measuring cup through a pipeline;
the measuring system comprises a flowmeter, a pore pressure sensor, a camera and a data collector, wherein the flowmeter is arranged on a pipeline between the downstream water tank and the measuring cup and is used for measuring the water volume gushed in a certain time period in the test process; the pore pressure sensors are arranged at intervals along the height direction of the sample cylinder and are used for measuring the pore water pressure at different heights in the sample cylinder; the cameras are arranged at the test box system and the water outlet system and used for monitoring the change conditions of the test box system and the water outlet system in the test process; the data acquisition unit is respectively connected with the pore pressure sensor, the flowmeter and the camera through data lines so as to acquire data information.
2. The multifunctional infiltration piping test device of claim 1, wherein the measuring system further comprises a displacement sensor, a weight sensor and a turbidity sensor, the displacement sensor is arranged at the lower moving plate and is used for measuring the moving distance of the lower moving plate; the weight sensors are arranged at the bottoms of the solid-liquid separation boxes and the downstream water tank and are used for measuring the loss condition of particles with different particle sizes gushed in the piping process in real time; the turbidity sensor enters the observation chamber through the exhaust hole and is used for measuring the turbidity change of the gushed water in the test process so as to judge the occurrence of soil body phase change; and the displacement sensor, the weight sensor and the turbidity sensor are respectively connected with the data acquisition unit through data lines.
3. The multifunctional infiltration piping test device of claim 1, wherein the solid-liquid separation tank has four in series, and the aperture is 0.5mm, 0.25mm, 0.075mm and 0.005mm in sequence; the inner diameter of the sample cylinder is more than or equal to 10 times of the maximum grain size of the soil body to be detected, and the height of the sample cylinder is more than or equal to two times of the inner diameter of the sample cylinder; the aperture of the water permeable hole is 8 mm.
4. The multifunctional infiltration piping test device of claim 1, wherein the loading system comprises an air cylinder, a first air compressor and a loading pressure regulating valve, the telescopic rod of the air cylinder is connected with the downward moving plate, the first air compressor is connected with the air inlet hole of the air cylinder through the loading pressure regulating valve, and the air cylinder pushes the downward moving plate to move upward along the sample cylinder so as to apply a target axial pressure to the soil sample in the sample cylinder.
5. The multifunctional infiltration piping test device according to claim 4, further comprising a fixing bracket, wherein the fixing bracket comprises an upper top plate, a lower bottom plate, columns, a support frame and fixing bolts, the upper top plate and the lower bottom plate are respectively connected with the two vertically arranged columns through the fixing bolts, and the air cylinder is arranged on the lower bottom plate; the top cover is provided with a positioning column, the upper top plate is provided with a positioning hole matched with the positioning column, and the test box system is positioned by matching the positioning column on the top cover with the positioning hole on the upper top plate; the sample cylinder is fixed on the support frame, and the support frame is fixed on the two upright posts through fixing bolts.
6. The multifunctional infiltration piping test device of claim 1, wherein the water supply regulating system comprises a water supply tank, a second air compressor and a pressure tank, the pressure tank is used for supplying test water with set pressure into the sample cylinder, the water outlet of the water supply tank is communicated with the water inlet of the pressure tank through a pipeline, the water outlet of the pressure tank is communicated with the water inlet of the lower moving plate through a pipeline, and the second air compressor is communicated with the air inlet of the pressure tank through an air supply pressure regulating valve; the pipeline between the water supply tank and the pressure tank and the pipeline between the pressure tank and the lower moving plate are provided with water inlet and outlet control valves for controlling the opening and closing and the flow rate of inlet and outlet water; the pipeline between the pressure tank and the lower moving plate is also provided with a pressure gauge, a pressure reducing valve and a water supply pressure regulating valve, the pressure gauge is used for detecting the water pressure output by the pressure tank, the pressure reducing valve is used for reducing the water pressure output by the pressure tank so as to maintain stable pressure supply, and the water supply pressure regulating valve is used for regulating the water pressure to accurate target water pressure.
7. The multifunctional infiltration piping test device of claim 1, wherein the top cover is a cylinder with a closed upper part and an open lower part, an annular sunken step is arranged at the open end of the cylinder near the hollow inner side, a flange is arranged at the outer side of the open end of the cylinder, a flange is also arranged at the position on the sample cylinder connected with the top cover, the top cover is connected with the sample cylinder in a sealing way through the flange, the edge of the water permeable plate is embedded in the sunken step, and the lower surface of the water permeable plate is in contact with the upper surface of a test soil sample in the sample cylinder; the observation chamber is a space enclosed by the water permeable plate and the top cover, and the overflow gap is arranged on the wall of the top cover barrel.
8. The multifunctional seepage piping test device of claim 1, wherein the lower moving plate is in a cylinder shape with an open upper end, gravels are filled in the cylinder for buffering a pressurized water body, the open end of the cylinder of the lower moving plate is sealed by a water-permeable sand-isolation net, and the water-permeable sand-isolation net can penetrate through the pressurized water body and is in direct contact with the bottom of a test soil sample; the water inlet of the lower moving plate is arranged on the closed lower end of the lower moving plate, and the loading system is connected with the closed lower end of the lower moving plate; the outer side wall of the lower moving plate cylinder body is provided with a sealing ring or a sealing air bag, so that the lower moving plate is tightly attached to the sample cylinder.
9. A multifunctional osmotic piping test method using the multifunctional osmotic piping test device according to any one of claims 1 to 8, comprising the steps of:
s1, preparation of a sample: filling undisturbed or remolded clay into a sample cylinder, respectively attaching filter paper and permeable stones to two ends of the sample cylinder, fixing, and placing the sample cylinder in a vacuum cylinder for vacuumizing saturation to obtain a saturated soil sample; calculating the initial porosity n of the soil sample according to the following formula 0 In%:
where ρ is w The density of the test water is given in g/cm 3 ；w sat The saturated water content of the soil sample is shown in unit; rho d Is the dry density of the soil sample and has the unit of g/cm 3 (ii) a Gs is the specific gravity of the soil sample and is dimensionless;
s2, mounting a soil sample and a device: connecting a sample cylinder filled with a saturated soil sample to a lower moving plate, fixing a porous plate and a top cover on the upper part of the sample cylinder, enabling the upper surface of the saturated soil sample to be in contact with the porous plate and the lower surface of the saturated soil sample to be in contact with the lower moving plate, and connecting a water supply adjusting system, a loading system, a measuring system and a water outlet system; measuring the initial height of the soil sample to be L, the bottom area to be A and the vertical distance from the top of the soil sample to the overflow port to be h;
s3, emptying pipelines of the system and residual gas in the soil sample: opening an exhaust hole on the top cover, starting a water supply regulating system to enable water with certain pressure to slowly flow through the soil sample until the water overflows from the exhaust hole, and continuing for a period of time to empty residual gas in the pipeline and the soil sample; then, sleeving a waterproof joint on the exhaust hole and inserting a turbidity sensor into the observation window;
s4, applying axial pressure: pushing the lower moving plate to move upwards through a loading system so as to apply constant axial pressure to the soil sample;
s5, applying a pressure head: applying stable water inlet with a set water head height to the soil sample through a water supply adjusting system to form a seepage path from bottom to top;
s6, permeability coefficient measurement: after the reading of the flowmeter is stable, the pore water pressures of pore pressure sensors at the bottom and the top of the soil sample are respectively read to be P 1 And P 2 Reading the flow rate Q of the water flowing through the flowmeter within a certain time t, and calculating the permeability coefficient k of the soil sample according to the following formula, wherein the unit is m/s:
wherein Q is the displacement in m within a certain time t 3 (ii) a L is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample, and the unit is m 2 ；γ w Is the water gravity with the unit of kN/m 3 ；(P 1 -P 2 ) Is the upper and lower parts of a soil sampleSurface pressure differential in kPa; h is the vertical height from the upper surface of the soil sample to the overflow port, and the unit is m.
10. The multifunctional osmotic piping test method according to claim 9, further comprising the steps of:
s7, critical hydraulic gradient measurement: adjusting a water supply adjusting system, increasing hydraulic gradient step by step at certain water head height intervals, keeping large hydraulic gradient of each stage for a certain time, applying next large hydraulic gradient after the reading of the flowmeter is stable, and monitoring data changes of a flow sensor, a turbidity sensor and a pore pressure sensor; when the data of the pore pressure sensor, the flow meter and the turbidity sensor are changed temporarily and the water in the observation chamber is turbid temporarily and obviously under a certain level of hydraulic gradient, the hydraulic gradient can be judged as a critical hydraulic gradient, and a critical hydraulic gradient i is calculated according to the following formula cr ：
Wherein L is the initial height of the soil sample and the unit is m; gamma ray w Is the water gravity with the unit of kN/m 3 ；(P 1 -P 2 ) cr The pressure difference of the upper surface and the lower surface of the soil sample under the critical hydraulic gradient is expressed in kPa; h is the vertical height from the upper surface of the soil sample to the overflow port, and the unit is m;
s8, measuring the piping development process: when critical hydraulic gradient i occurs cr During the process, the hydraulic gradient action and the axial pressure are kept unchanged, the piping occurrence process is recorded by a camera, the data change conditions of a pore pressure sensor, a weight sensor, a flowmeter and a displacement sensor in the piping occurrence process are recorded by a data collector, the pore pressure change, the vertical displacement change, the water inflow change and the mass change of different gushed particle sizes of the soil body in any time period in the piping occurrence process are obtained, and the t-shaped pore pressure change, the vertical displacement change, the water inflow change and the mass change of gushed particles with different particle sizes in the piping occurrence process are calculated according to the following formula 1 Soil porosity n at the moment 1 In%:
wherein n is 0 Is the initial porosity of the soil sample in%; l is the initial height of the soil sample, and the unit is m; a is the bottom area of the soil sample and the unit is m 2 (ii) a S is t 1 The unit of the vertical displacement of the soil sample at the moment is m; m is t1 Is t 1 The loss mass of the particles at that time; gs is the specific gravity of the soil sample and is dimensionless;
s9, after the infiltration is finished, injecting the epoxy resin with high fluidity into the soil sample, finishing consolidation at normal temperature, and after the consolidation is finished, carrying out microscopic scanning to observe the microstructure change rule of the sample;
s10, changing the test hydraulic gradient to be larger than the critical hydraulic gradient, repeating the steps S8 and S9, and comparing and analyzing differences of the soil body piping damage process under the action of different hydraulic gradients, wherein the differences comprise particle loss, water inflow and soil body porosity change;
s11, changing the initial conditions of the soil body, including particle grading and porosity ratio, repeating the steps from S1 to S10, and comparing and analyzing the damage rule of the infiltration piping under different initial conditions of the soil sample.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202210794960.4A CN115112531A (en) | 2022-07-07 | 2022-07-07 | Multifunctional osmotic piping test device and method |
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| CN202210794960.4A CN115112531A (en) | 2022-07-07 | 2022-07-07 | Multifunctional osmotic piping test device and method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116559047A (en) * | 2023-05-06 | 2023-08-08 | 中国地质大学（武汉） | Permeation experiment device and method for evaluating permeation coefficient and flow state |
| CN116773780A (en) * | 2023-08-16 | 2023-09-19 | 中国科学院、水利部成都山地灾害与环境研究所 | Vegetation slope soil seepage erosion experiment measurement system and measurement method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116559047A (en) * | 2023-05-06 | 2023-08-08 | 中国地质大学（武汉） | Permeation experiment device and method for evaluating permeation coefficient and flow state |
| CN116773780A (en) * | 2023-08-16 | 2023-09-19 | 中国科学院、水利部成都山地灾害与环境研究所 | Vegetation slope soil seepage erosion experiment measurement system and measurement method |
| CN116773780B (en) * | 2023-08-16 | 2023-12-08 | 中国科学院、水利部成都山地灾害与环境研究所 | Vegetation slope soil seepage erosion experiment measurement system and measurement method |
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