Pressing fault fracture zone seepage deformation test device and method under reciprocating seepage action

Abstract

The invention discloses a device and a method for testing seepage deformation of a compressive fault fracture zone under the action of reciprocating seepage. Comprising a water supply system, an upstream seepage pressure control system, a downstream seepage pressure control system, a water return system, a seepage pressure chamber, a soil-water separation system, a particle collection system, a confining pressure loading system, a flow monitoring system and a computer servo system, the method comprises the following steps: analyzing the loss particle size distribution and loss amount of fine particles collected by a particle collection system to obtain the relationship among parameters such as permeability coefficient, porosity, particle loss condition, effective stress, time and the like in a fault fracture zone sample seepage deformation process under the conditions of reciprocating seepage and different effective stress; the seepage deformation evolution process of the fault fracture zone sample under the action of reciprocating seepage-different effective stress is explored, and a theoretical basis and technical support are provided for guaranteeing long-term seepage stability of water conservancy and hydropower engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy and hydropower, and specifically relates to a device and method for testing the seepage deformation of a compressive fault fracture zone under the action of reciprocating seepage; in particular, it relates to a device and method for testing the influence of the gradient loading rate and effective stress change on the seepage characteristics of the fault fracture zone during the reciprocating seepage process. Background Art

[0002] Fault zones are the product of long-term geological tectonic movements. They are generally composed of fault-fragmented zones dominated by compaction and shearing, and fault-affected zones dominated by induced zones and fissure zones. They can be divided into five types based on the mechanical properties of the fractured structural surface: compressional faults, compression-torsion faults, torsional faults, tension-torsion faults, and tensional faults. Northwest China is located at the junction of plates, with strong tectonic movements, crisscrossing faults, and large-scale, mainly compressional faults. These fault-fragmented zones have dense structures, weak cementation, low permeability, and complex material compositions. Some of them are mixed with fault mud, and their mineral components are easily disintegrated and muddied when exposed to water. After the completion of large-scale water conservancy and hydropower hub projects, underground caverns such as hydraulic tunnels and traffic tunnels have to pass through fault zones and other unfavorable geology, changing the original seepage path. After the completion of water storage, the water pressure in the reservoir area will increase or decrease rapidly due to the influence of high water head and large-scale reservoir water level regulation. The fault fracture zone has low permeability, which makes it difficult for the internal pore water pressure to dissipate in a short period of time, resulting in reciprocating changes in the seepage direction of the local fault fracture zone and an increase or decrease in the effective stress in the zone, which can easily lead to changes in the seepage characteristics of the fault zone, causing the seepage stability of the fault fracture zone to deteriorate, which is not conducive to the long-term seepage safety of underground projects.

[0003] Traditional permeability tests mostly adopt the loading method of "unidirectional step-by-step pressurization and free outflow of water", that is, the hydraulic gradient increases monotonically in steps until the rock and soil sample is destroyed. This method cannot take into account the change in effective stress caused by the change in pore water pressure in the fault fracture zone and its influence on the seepage characteristics of the fault zone. The permeability coefficient, critical slope drop, and failure slope drop obtained in the test have certain deviations from the actual engineering situation. Therefore, most scholars began to use improved permeameters to carry out permeability tests to study the internal stability of the fault fracture zone. In order to study the variable mass permeability test of the filling medium in the fault zone, Yao Banghua, Ma Dan and others improved the permeameter by adding a piston to the outlet of the permeameter to reflect the loss of fine particles in real time. Since the influence of the normal stress of the fault zone on the permeability deformation was ignored, the influence of the deformation and destruction process under the coupling of the permeability coefficient and effective stress of the fault zone could not be truly reflected. Although the multi-field coupled permeability test system developed by Sheng Jinchang and others can carry out permeability deformation tests under in-situ stress state, because the sample is in a completely sealed state, it cannot reflect the particle loss and migration behavior under the coupling of permeability coefficient and effective stress. The currently improved permeability instruments can only control the permeability pressure in one direction, that is, the one-way circulation effect in the seepage path direction, and cannot change the seepage direction and realize the influence of the reciprocating circulating water pressure gradient in the seepage path direction on the long-term seepage characteristics of the fault fracture zone.

[0004] During the operation of the reservoir, the water level of the reservoir fluctuates greatly due to rainfall, reservoir water level regulation and other reasons. In addition, the fault fracture zone in the reservoir area obliquely crosses the hydraulic tunnel, shortening the seepage path and placing it under complex hydraulic conditions for a long time, such as water pressure loading path, loading rate, seepage direction, etc. At present, there are many cases of seepage damage of hydraulic tunnels passing through the fault fracture zone caused by water level fluctuation. However, there is insufficient experimental research on the seepage characteristics of the fault fracture zone under the coupling effect of reciprocating seepage direction-large change of hydraulic gradient-effective stress change caused by fluctuating reservoir water level, and little is known about the mechanism of fine particle loss after seepage damage of the fault fracture zone under this complex coupling effect. Therefore, it is urgent to develop a seepage deformation test device for compressive fault fracture zone under reciprocating seepage, which can control the upstream and downstream seepage pressures at any time, carry out research on the coupling mechanism of permeability coefficient-effective stress of the fault fracture zone under different confining pressure conditions, and consider the weakening effect of the anti-seepage strength of the fault fracture zone during the reciprocating seepage direction-effective stress change. At the same time, it can also obtain the particle quality and migration behavior during the seepage deformation damage process. It is of great significance for evaluating the influence of reciprocating seepage direction-effective stress change on the long-term seepage characteristics of the fault fracture zone and ensuring the safe operation of engineering facilities, especially the impact of large-scale rise and fall of reservoir water level in a short period of time. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a seepage deformation test device and method for a compressive fault fracture zone under the action of reciprocating seepage, so as to solve the problem of weakened conductivity, ion dissolution, fine particle loss, etc. caused by the seepage-stress-chemical coupling effect in a dense fault fracture zone under the influence of reciprocating cyclic fluctuating water level in the prior art, thereby inducing seepage deformation damage.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present invention discloses a seepage deformation test device for compressive fault fracture zone under the action of reciprocating seepage, comprising: a water supply system, an upstream seepage pressure control system, a downstream seepage pressure control system, a backwater system, a seepage pressure chamber, a soil-water separation system, a particle collection system, a confining pressure loading system, a flow monitoring system and a computer servo system;

[0008] The water supply system is respectively connected to the upstream seepage pressure control system and the soil-water separation system; the return water system is respectively connected to the downstream seepage pressure control system, the soil-water separation system, and the flow monitoring system; the seepage pressure chamber is respectively connected to the confining pressure loading system and the soil-water separation system; the soil-water separation system is respectively connected to the water supply system, the seepage pressure chamber, the return water system, and the particle collection system; the computer servo system is respectively connected to the confining pressure loading system and the flow monitoring system;

[0009] The water supply system comprises: a first gas-water exchange tank, a first pressure valve, a first support rod, a first support plate and a plurality of pipelines, wherein the first gas-water exchange tank is supported by the first support rod and the first support plate, and the three are connected in sequence, the first gas-water exchange tank is externally connected to the first pressure valve, and the pipelines are respectively connected to the first gas-water exchange tank and the first pressure valve;

[0010] The water return system comprises: a second gas-water exchange tank, a second pressure valve, a second support rod, a second support plate and a plurality of pipelines, wherein the second gas-water exchange tank is supported by the second support rod and the second support plate, and the three are connected in sequence, the second gas-water exchange tank is externally connected to the second pressure valve, and the pipelines are respectively connected to the second gas-water exchange tank and the second pressure valve;

[0011] The upstream permeation pressure control system comprises: a nitrogen tank, a pressure regulating valve, a pressure stabilizing system and an air pressure buffer tank, and the pressure stabilizing system consists of three pressure control systems with different ranges: a low pressure control system, comprising a first air inlet, a 0-0.25MPa air pressure regulating valve, a 0.25MPa pressure sensor and a first low-pressure gas filling port, which are connected in sequence through pipelines; a medium pressure control system, comprising a second air inlet, a 0-1.0MPa air pressure regulating valve, a 1.0MPa pressure sensor and a second low-pressure gas filling port, which are connected in sequence through pipelines; a high pressure control system, comprising a third air inlet, a 0-3.0MPa air pressure regulating valve, a 3.0MPa pressure sensor and a third low-pressure gas filling port, which are connected in sequence through pipelines; the downstream permeation pressure control system has the same structure as the upstream permeation pressure control system, comprising: a nitrogen tank, a pressure regulating valve, a pressure stabilizing system and an air pressure buffer tank;

[0012] The seepage pressure chamber comprises: a sample cap, a pressure chamber top cover, a pressure chamber pull rod, a pressure chamber cavity, a pressure chamber base, a pressure chamber sealing cover, a porous water-permeable plate, a pressure chamber inlet / drainage joint, a sample positioning strip, a latex film, a sample exhaust hole, a pressure chamber water inlet hole, a pressure chamber exhaust hole and a sample; the pressure chamber pull rod is respectively connected to the pressure chamber top cover and the pressure chamber base; the porous water-permeable plate is respectively connected to the sample cap and the sample, and the outer sleeve of the porous water-permeable plate is provided with a latex film; the sample positioning strip is respectively connected to the sample cap and the pressure chamber base to fix the two ends of the sample; the pressure chamber top cover and the pressure chamber base are both connected to the pressure chamber cavity, the pressure chamber sealing cover and the pressure chamber inlet / drainage joint; the pressure chamber water inlet hole is arranged in the pressure chamber base; the pressure chamber drainage hole is arranged in the pressure chamber top cover; the sample exhaust hole is arranged in the pressure chamber sealing cover;

[0013] The soil-water separation system comprises: a permeation joint, a permeation sealing cover, a forward inner and outer ball valve, a filter screen, a reverse inner and outer ball valve, and a four-way permeation joint; wherein the water inlet / outlet at both ends of the soil-water separation system are composed of a permeation joint, a forward inner and outer ball valve / reverse inner and outer ball valve, a filter screen, and a permeation sealing cover, and are connected in sequence; the permeation joint is respectively connected to the permeation pressure chamber, the water supply system, the return water system, and the particle collection system; the permeation sealing cover is respectively connected to the permeation joint and the four-way permeation joint;

[0014] The particle collection system comprises: an external thread short pipe, an internal thread ball valve, a particle collection tank and a collection tank drainage joint, which are connected in sequence; the particle collection tank is composed of a collection tank upper cover, a collection tank exhaust hole, a collection tank pull rod, a collection tank bottom plate and a collection tank body; the collection tank upper cover is respectively connected to the external thread short pipe and the collection tank body; the collection tank pull rod is respectively connected to the collection tank upper cover and the collection tank bottom plate; the collection tank exhaust hole is arranged in the collection tank upper cover;

[0015] The confining pressure loading system loads pressure in real time and reads and measures the volume change of the sample;

[0016] The flow monitoring system monitors the quality of the return water system tank in real time and sends the monitoring data to the computer servo system;

[0017] The computer servo system is connected to the confining pressure loading system and the flow monitoring system respectively, and is used to read and record the changes of the confining pressure value, the sample volume, and the water output in real time.

[0018] The sample is sealed by a latex membrane and a porous water-permeable plate and fixed by a sample positioning strip to ensure that the sample will not produce axial shear deformation due to its own weight when placed horizontally. At the same time, the sample cap pull rod ensures the sample height and ensures that the sample only produces circumferential deformation but not axial deformation.

[0019] Furthermore, the confining pressure loading system adopts a YC70-6 pressure volume controller with a capacity of 1000ml, a pressure range of 0-6.0MPa, and a data accuracy of 1kPa / 1mm. 3 , load pressure in real time and read and measure the volume change of the sample.

[0020] Furthermore, the air pressure buffer tank can not only keep the air pressure in the pressure stabilization system stable, but also effectively prevent water in the water supply device from flowing back through the pipeline into the pressure sensor and affecting the sensitivity of the sensor.

[0021] Furthermore, there are two first gas-water exchange tanks with a volume capacity of 6L, and the two first gas-water exchange tanks are independent of each other and are used alternately to meet the continuous water supply status upstream.

[0022] Furthermore, the number of the second gas-water exchange tank is one, and the volume capacity is 20L.

[0023] Furthermore, the first gas-water exchange tank comprises: a water inlet, a pressure port, an upper cover, a water level pipe interface, a pull rod, a cylinder, a bottom plate and a water outlet; the cylinder is respectively fixed to the upper cover and the bottom plate through a slot and is connected by a pull rod, and a water level measuring tube is provided on one side of the pull rod; the upper cover is respectively connected to the water inlet and the pressure port; the bottom plate is respectively connected to the water level pipe interface and the water outlet; the water level pipe interface is connected to the water level measuring tube.

[0024] Furthermore, a circular filter screen is provided at the end of the infiltration joint to intercept fine particles and prevent them from entering the tank in the water supply or return system, while ensuring that the particles in the seepage pressure chamber automatically enter the particle collection system by using the particle sedimentation method by their own weight.

[0025] A method for testing the seepage deformation of a compressive fault fracture zone under reciprocating seepage flow according to the present invention is based on the above device and comprises the following steps:

[0026] Step 1): Cover the prepared fault fracture zone sample with a latex film, place a porous water-permeable plate at the bottom of the sample, and put it into a vacuum saturation barrel for saturation, and take it out after 12 hours of saturation;

[0027] Step 2): The seepage pressure chamber is placed vertically, the saturated sample is placed at the bottom of the seepage pressure chamber, and the latex membrane is placed on the surface of the sample cap at the bottom of the seepage pressure chamber, and a layer of 704 silicone rubber is applied between the latex membrane and the sample cap;

[0028] Step 3): Place a porous permeable plate and a sample cap on the upper end of the sample in sequence, and fix the sample cap on the upper end of the sample using a sample positioning strip to ensure that no axial displacement occurs at both ends of the sample. At the same time, apply a layer of 704 silicone rubber between the latex film on the upper end of the sample and the sample cap;

[0029] Step 4): After the 704 silicone rubber solidifies, the pressure chamber cavity is clamped on the pressure chamber top cover at the bottom, and the pressure chamber sealing cover is covered. After the infiltration pressure chamber is completely sealed, the infiltration pressure chamber is placed horizontally, and then the pressure chamber water inlet joint and the pressure chamber water outlet joint are connected to form a closed space;

[0030] Step 5): Open the nitrogen tank, adjust the pressure regulating valve to 0.3MPa, then open the sample exhaust hole, adjust the low and medium pressure control systems of the upstream / downstream permeation pressure control system respectively, and exhaust the air in the sample cap through the sample exhaust hole to ensure that both ends of the sample are completely filled with water;

[0031] Step 6): Open the water inlet and exhaust holes of the pressure chamber in the osmotic pressure chamber, and load the confining pressure to the preset value σ step by step through the computer servo system. When the confining pressure reaches the preset value σ and the injection volume changes little, check whether the inlet / outlet pipes, the osmotic pressure chamber, the confining pressure loading system, and the osmotic pressure loading system are normal. If they are normal, proceed to step 7);

[0032] Step 7): Open the forward flow inner and outer thread valves, adjust the upstream / downstream permeation pressure control system to a small pressure difference ΔP, observe the water output in the flow monitoring system after a period of time, and calculate the permeability coefficient k under the pressure difference ΔP after the water output and confining pressure volume changes are stable;

[0033] Step 8): According to the cross-sectional area A of the fault fracture zone sample, the seepage path length L, the water density ρ, the gravity acceleration g and the water flow rate Q, the average seepage gradient i of the sample when the seepage is stable under the pressure difference ΔP, i=ΔP / ρLg, the average flow velocity v, v=Q / A, and the permeability coefficient k under the pore water pressure P is obtained using the formula lgv=lgk+lgi;

[0034] Step 9): Use the method in step 7) to load the upstream / downstream osmotic pressure step by step, ensure that the upstream and downstream pressure difference is always stable at a small pressure difference value ΔP, and load the pore water pressure inside the sample from the initial value P to the maximum value P step by step. max , use the method of step 8) to obtain the permeability coefficient under different pore water pressures. At the same time, after the water output and injection volume readings are stable each time, close the ball valve at the upper end of the particle collection system, open the drainage joint of the collection tank, use a beaker to collect the solution and observe whether the fine particles migrate, so as to determine the change of the permeability characteristic parameters caused by the change of effective stress in the overall deformation and destruction process of the sample. If there is no fine particle migration in the solution or the ion concentration of the solution does not change significantly, proceed to step 10); if there is a large change in the ion concentration and fine particle migration in the solution, it is considered that the sample has entered the permeability deformation and destruction stage;

[0035] Step 10): Calculate the effective stress σ′ corresponding to the pore water pressure P, σ′=σ-P, draw a scatter plot of k~σ′, and select k=k0·exp(-α·σ′) exponential empirical formula for fitting to obtain the permeability coefficient k0 and stress sensitivity coefficient α under the condition of no seepage;

[0036] Step 11): Reduce the upstream and downstream osmotic pressures step by step according to the method of step 9) to reduce the internal pore water pressure of the sample from the maximum value P max Reduce to the initial value P, and then use the method in step 8) to obtain the permeability coefficient under different pore water pressures;

[0037] Step 12): Process the measured data using the method of step 10) and draw the lgv-lgi curve, and compare it with the pore water pressure in step 10) to observe the permeability evolution law of the fault fracture zone sample during the seepage-stress coupling process;

[0038] Step 13): After step 9), the seepage direction is changed, and the loading method of steps 7) to 12) is used to compare with the forward flow process to observe the changes in the seepage characteristics of the fault fracture zone sample under the action of reciprocating seepage.

[0039] Furthermore, in step 6), when the confining pressure value and the injected water volume change slightly, the confining pressure value is always stable at a certain value, and the range in which the injected water volume changes slightly is such that the value change value shall not exceed 0.1% of the original volume.

[0040] Furthermore, in step 7), the specific method of adjusting the upstream / downstream osmotic pressure control system to a small pressure difference ΔP is as follows: the initial pressure difference in the upstream / downstream osmotic pressure control system is adjusted to 0.005 MPa. If it is a low permeability sample, the pressure gradient is loaded step by step with an increase of 0.005 MPa each time to ensure a stable water outlet flow rate within a certain period of time, and the range is about 0.005 to 0.04 MPa.

[0041] Furthermore, the specific method for loading or reducing the upstream / downstream osmotic pressure step by step in step 9) and step 11) is: simultaneously adjust the upstream / downstream osmotic pressure control system to increase the osmotic pressure in the same direction and with the same pressure difference, and increase or decrease step by step by 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.6MPa, 0.8MPa, and 1.0MPa.

[0042] Furthermore, the specific method for changing the seepage direction in step 13) is: closing the inner and outer thread valves of the forward flow, opening the inner and outer thread valves of the reverse flow, adjusting the upstream / downstream seepage pressure control system to a small pressure difference ΔP, and then loading or reducing the upstream / downstream seepage pressure step by step to realize the dynamic evolution process of the coupling effect of water pressure gradient-permeability coefficient-effective stress of the fault fracture zone sample under reciprocating seepage conditions, and the loading process is carried out according to the loading method of steps 9) to 12).

[0043] Beneficial effects of the present invention:

[0044] (1) The device of the present invention is provided with an upstream and downstream osmotic pressure control system, which can arbitrarily adjust the upstream and downstream osmotic pressure values, and effectively control the changes in the pore pressure value inside the sample and the upper and lower osmotic pressure difference during the reciprocating seepage process; it is simple to operate, highly sensitive, and highly practical.

[0045] (2) The present invention cleverly designs a four-way permeable component in the soil-water separation system and sets a filter screen at the end to separate fine particles from the permeate solution in real time, providing a new method for exploring the mechanism of fine particle loss after permeation damage in the fault fracture zone under the coupling effect of reciprocating seepage direction-permeability coefficient-effective stress.

[0046] (3) The particle collection system of the present invention uses an inner thread ball valve switch to control the fine particle collection process. First, open the inner thread ball valve switch, and the fine particles flow into the particle collection tank by their own weight. After the current level of osmotic loading is completed, close the inner thread ball valve switch, open the exhaust hole and the drainage joint, and let the solution containing fine particles flow out from the lower end and fall into the preset beaker. The loss of fine particles in the sample (particle size distribution and loss amount) can be measured in real time.

[0047] (4) The present invention measures the permeability coefficient of the fault fracture zone sample under different effective stress conditions by gradually increasing or decreasing the internal pore pressure of the sample in one direction while keeping the upstream and downstream permeability pressure difference unchanged, and obtains the coupled constitutive relationship between the permeability coefficient and effective stress of the fault fracture zone sample.

[0048] (5) The present invention can also realize a reciprocating step-by-step loading method in the seepage direction, and test in real time the evolution process of the seepage characteristics of the fault fracture zone sample under the coupling of reciprocating seepage direction, large changes in hydraulic gradient, and effective stress, so as to obtain the change in the anti-seepage strength of the fault fracture zone sample during the dynamic development process.

[0049] (6) The present invention analyzes the particle size distribution and loss of fine particles collected by the particle collection system to obtain the relationship between the permeability coefficient, porosity and particle loss, effective stress, time and other parameters during the seepage deformation of the fault fracture zone sample under the conditions of reciprocating seepage and different effective stresses, explore the seepage deformation evolution process of the fault fracture zone sample under the action of reciprocating seepage and different effective stresses, and provide a theoretical basis and technical support for ensuring the long-term seepage stability of water conservancy and hydropower projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the principle of the test device of the present invention.

[0051] Figure 2 It is a schematic diagram of the structure of the test device of the present invention.

[0052] Figure 3 Schematic diagram of a water supply system in an embodiment of the present invention.

[0053] Figure 4 Schematic diagram of an upstream / downstream seepage pressure regulating system according to an embodiment of the present invention.

[0054] Figure 5 Schematic diagram of a seepage pressure chamber according to an embodiment of the present invention.

[0055] Figure 6 Schematic diagram of a soil-water separation system and a particle collection system according to an embodiment of the present invention.

[0056] Figure 7 Schematic diagram of the pressure loading path process according to an embodiment of the present invention.

[0057] Figure 8 Schematic diagram of the seepage-stress coupling process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0059] Reference Figure 1-Figure 6As shown, a seepage deformation test device for compressive fault fracture zone under reciprocating seepage action of the present invention comprises: a water supply system 1, an upstream seepage pressure control system 2, a downstream seepage pressure control system 3, a backwater system 4, a seepage pressure chamber 5, a soil-water separation system 6, a particle collection system 7, a confining pressure loading system 8, a flow monitoring system 9 and a computer servo system 10;

[0060] The water supply system 1 is respectively connected to the upstream seepage pressure control system 2 and the soil-water separation system 6; the return water system 4 is respectively connected to the downstream seepage pressure control system 3, the soil-water separation system 6, and the flow monitoring system 9; the seepage pressure chamber 5 is respectively connected to the confining pressure loading system 8 and the soil-water separation system 6; the soil-water separation system 6 is respectively connected to the water supply system 1, the seepage pressure chamber 5, the return water system 4, and the particle collection system 7; the computer servo system 10 is respectively connected to the confining pressure loading system 8 and the flow monitoring system 9;

[0061] The water supply system 1 comprises: a first gas-water exchange tank, a first pressure valve, a first support rod 1-9, a first support plate 1-10 and a plurality of pipelines, wherein the first gas-water exchange tank is supported by the first support rod 1-9 and the first support plate 1-10, and the three are connected in sequence, the first gas-water exchange tank is externally connected to the first pressure valve, and the pipelines are respectively connected to the first gas-water exchange tank and the first pressure valve;

[0062] The water return system 4 comprises: a second gas-water exchange tank, a second pressure valve, a second support rod, a second support plate and a plurality of pipelines, wherein the second gas-water exchange tank is supported by the second support rod and the second support plate, and the three are connected in sequence, the second gas-water exchange tank is externally connected to the second pressure valve, and the pipelines are respectively connected to the second gas-water exchange tank and the second pressure valve;

[0063] The upstream permeation pressure control system comprises: a nitrogen tank 2-1, a pressure regulating valve 2-2, a pressure stabilizing system 2-3 and an air pressure buffer tank 2-4. The pressure stabilizing system is composed of three pressure control systems with different ranges: a low pressure control system, comprising a first air inlet 2-5, a 0-0.25 MPa air pressure regulating valve 2-8, a 0.25 MPa pressure sensor 2-11 and a first low pressure gas filling port 2-14, which are connected in sequence through pipelines; a medium pressure control system, comprising a second air inlet 2-6, a 0-1.0 MPa air pressure regulating valve 2-8, a 0.25 MPa pressure sensor 2-11 and a first low pressure gas filling port 2-14, which are connected in sequence through pipelines; The air pressure regulating valve 2-9, the 1.0MPa pressure sensor 2-12 and the second low-pressure gas filling port 2-15 are connected in sequence through pipelines; the high pressure control system includes the third air inlet 2-7, the 0-3.0MPa air pressure regulating valve 2-10, the 3.0MPa pressure sensor 2-13 and the third low-pressure gas filling port 2-16, and are connected in sequence through pipelines; the downstream permeation pressure control system has the same structure as the upstream permeation pressure control system, including: a nitrogen tank, a pressure regulating valve, a pressure stabilizing system and an air pressure buffer tank;

[0064] The seepage pressure chamber 5 comprises: a sample cap 5-1, a pressure chamber top cover 5-2, a pressure chamber pull rod 5-3, a pressure chamber cavity 5-4, a pressure chamber base 5-5, a pressure chamber sealing cover 5-6, a porous water-permeable plate 5-7, a pressure chamber inlet / outlet joint 5-8, a sample positioning strip 5-9, a latex film 5-10, a sample exhaust hole 5-11, a pressure chamber water inlet hole 5-12, a pressure chamber exhaust hole 5-13 and a sample 5-14; the pressure chamber pull rod 5-3 is respectively connected to the pressure chamber top cover 5-2 and the pressure chamber base 5-5; the porous water-permeable plate 5-7 is respectively connected to the sample cap 5-1, the sample 5 -14 is connected, and the outer sleeve of the porous water-permeable plate 5-7 is provided with a latex film 5-10 (to prevent the chamber from penetrating with the inside of the sample); the sample positioning strip 5-9 is respectively connected with the sample cap 5-1 and the pressure chamber base 5-5 to fix the two ends of the sample; the pressure chamber top cover 5-2 and the pressure chamber base 5-5 are connected with the pressure chamber cavity 5-4, the pressure chamber sealing cover 5-6, and the pressure chamber inlet / drainage joint 5-8; the pressure chamber water inlet hole 5-12 is provided in the pressure chamber base 5-5; the pressure chamber drainage hole 5-13 is provided in the pressure chamber top cover 5-2; the sample exhaust hole 5-11 is provided in the pressure chamber sealing cover 5-6;

[0065] The soil-water separation system comprises: a permeation joint 6-1, a permeation sealing cover 6-2, a forward inner and outer ball valve 6-3, a filter screen 6-4, a reverse inner and outer ball valve 6-5, and a four-way permeation joint 6-6; wherein the water inlet / outlet at both ends of the soil-water separation system are composed of a permeation joint 6-1, a forward inner and outer ball valve 6-3 / reverse inner and outer ball valve 6-5, a filter screen 6-4, and a permeation sealing cover 6-2, and are connected in sequence; the permeation joint 6-1 is respectively connected to the permeation pressure chamber 5, the water supply system 1, the return water system 4, and the particle collection system 7; the permeation sealing cover 6-2 is respectively connected to the permeation joint 6-1 and the four-way permeation joint 6-6;

[0066] The particle collection system 7 comprises: an external thread short pipe 7-1, an internal thread ball valve 7-2, a particle collection tank 7-3 and a collection tank drainage joint 7-7, which are connected in sequence; the particle collection tank 7-3 is composed of a collection tank upper cover 7-4, a collection tank exhaust hole 7-8, a collection tank pull rod 7-5, a collection tank bottom plate 7-6 and a collection tank body 7-9; the collection tank upper cover 7-4 is respectively connected to the external thread short pipe 7-1 and the collection tank body 7-9; the collection tank pull rod 7-5 is respectively connected to the collection tank upper cover 7-4 and the collection tank bottom plate 7-6; the collection tank exhaust hole 7-8 is provided in the collection tank upper cover 7-4;

[0067] The confining pressure loading system 8 loads pressure in real time and reads and measures the volume change of the sample; in the example, the confining pressure loading system 8 uses a YC70-6 pressure volume controller with a capacity of 1000ml, a pressure range of 0 to 6.0MPa, and a data accuracy of 1kPa / 1mm 3, load pressure in real time and read and measure the volume change of the sample.

[0068] The flow monitoring system 9 monitors the quality of the return water system tank in real time and sends the monitoring data to the computer servo system;

[0069] The computer servo system 10 is connected to the confining pressure loading system 8 and the flow monitoring system 9 respectively, and is used to read and record the confining pressure value, sample volume, and changes in water output in real time (in the example, the time interval is 1 s).

[0070] The sample is sealed by a latex membrane and a porous water-permeable plate and fixed by a sample positioning strip to ensure that the sample will not produce axial shear deformation due to its own weight when placed horizontally. At the same time, the sample cap pull rod ensures the sample height and ensures that the sample only produces circumferential deformation but not axial deformation.

[0071] Specifically, the air pressure buffer tank 2-14 can not only keep the air pressure in the pressure stabilization system stable, but also effectively prevent water in the water supply device from flowing back through the pipeline into the pressure sensor and affecting the sensitivity of the sensor.

[0072] Specifically, the number of the first gas-water exchange tanks is two, and the volume capacity is 6L, and the two first gas-water exchange tanks are independent of each other and are used alternately to meet the continuous water supply status upstream.

[0073] Specifically, the number of the second gas-water exchange tank is one, and the volume capacity is 20L.

[0074] Specifically, the first gas-water exchange tank includes: a water inlet 1-1, a pressurizing port 1-2, an upper cover 1-3, a water level pipe interface 1-4, a pull rod 1-5, a cylinder 1-6, a bottom plate 1-7 and a water outlet 1-8; the cylinder 1-6 is respectively fixed to the upper cover 1-3 and the bottom plate 1-7 through a slot, and is connected by the pull rod 1-5, and a water level measuring tube 1-10 is provided on one side of the pull rod 1-5; the upper cover 1-3 is respectively connected to the water inlet 1-1 and the pressurizing port 1-2; the bottom plate 1-7 is respectively connected to the water level pipe interface 1-4 and the water outlet 1-8; the water level pipe interface 1-4 is connected to the water level measuring tube.

[0075] Specifically, a circular filter screen is provided at the end of the infiltration joint, which can intercept fine particles and prevent them from entering the tank in the water supply or return system. At the same time, the particles are precipitated by their own weight to ensure that the particles in the seepage pressure chamber automatically enter the particle collection system.

[0076] A method for testing the seepage deformation of a compressive fault fracture zone under reciprocating seepage flow according to the present invention is based on the above device and comprises the following steps:

[0077] Step 1): Cover the prepared fault fracture zone sample with a latex film, place a porous water-permeable plate at the bottom of the sample, and put it into a vacuum saturation barrel for saturation, and take it out after 12 hours of saturation;

[0078] Step 2): The seepage pressure chamber is placed vertically, the saturated sample is placed at the bottom of the seepage pressure chamber, and the latex membrane is placed on the surface of the sample cap at the bottom of the seepage pressure chamber, and a layer of 704 silicone rubber is applied between the latex membrane and the sample cap;

[0079] Step 3): Place a porous permeable plate and a sample cap on the upper end of the sample in sequence, and fix the sample cap on the upper end of the sample using a sample positioning strip to ensure that no axial displacement occurs at both ends of the sample. At the same time, apply a layer of 704 silicone rubber between the latex film on the upper end of the sample and the sample cap;

[0080] Step 4): After the 704 silicone rubber solidifies, the pressure chamber cavity is clamped on the pressure chamber top cover at the bottom, and the pressure chamber sealing cover is covered. After the infiltration pressure chamber is completely sealed, the infiltration pressure chamber is placed horizontally, and then the pressure chamber water inlet joint and the pressure chamber water outlet joint are connected to form a closed space;

[0081] Step 5): Open the nitrogen tank, adjust the pressure regulating valve to 0.3 MPa, then open the sample exhaust hole, adjust the low and medium pressure control systems of the upstream / downstream permeation pressure control system respectively, and exhaust the air in the sample cap through the sample exhaust holes 5-11 to ensure that both ends of the sample are completely filled with water;

[0082] Step 6): Open the water inlet and exhaust holes of the pressure chamber in the osmotic pressure chamber, and load the confining pressure to the preset value σ step by step through the computer servo system. When the confining pressure reaches the preset value σ and the injection volume changes little, check whether the inlet / outlet pipes, the osmotic pressure chamber, the confining pressure loading system, and the osmotic pressure loading system are normal. If they are normal, proceed to step 7);

[0083] Step 7): Open the forward flow inner and outer thread valves, adjust the upstream / downstream permeation pressure control system to a small pressure difference ΔP, observe the water output in the flow monitoring system after a period of time, and calculate the permeability coefficient k under the pressure difference ΔP after the water output and confining pressure volume changes are stable;

[0084] Step 8): According to the cross-sectional area A of the fault fracture zone sample, the seepage path length L, the water density ρ, the gravity acceleration g and the water flow rate Q, the average seepage gradient i of the sample when the seepage is stable under the pressure difference ΔP, i=ΔP / ρLg, the average flow velocity v, v=Q / A, and the permeability coefficient k under the pore water pressure P is obtained using the formula lgv=lgk+lgi;

[0085] Step 9): Use the method in step 7) to load the upstream / downstream osmotic pressure step by step, ensure that the upstream and downstream pressure difference is always stable at a small pressure difference value ΔP, and load the pore water pressure inside the sample from the initial value P to the maximum value P step by step. max , use the method of step 8) to obtain the permeability coefficient under different pore water pressures. At the same time, after the water output and injection volume readings are stable each time, close the ball valve at the upper end of the particle collection system, open the drainage joint of the collection tank, use a beaker to collect the solution and observe whether the fine particles migrate, to determine the change of the permeability characteristic parameters caused by the change of effective stress during the overall deformation and destruction of the sample. If there is no fine particle migration in the solution or the solution ion concentration does not change significantly, proceed to step 10); if there is a large change in the ion concentration and fine particle migration in the solution, it is considered that the sample has entered the permeability deformation and destruction stage, such as Figure 7 As shown;

[0086] Step 10): Calculate the effective stress σ′ corresponding to the pore water pressure P, σ′=σ-P, draw a scatter plot of k~σ′, and select k=k0·exp(-α·σ′) exponential empirical formula for fitting to obtain the permeability coefficient k0 and stress sensitivity coefficient α under no confining pressure conditions, such as Figure 8 As shown;

[0087] Step 11): Reduce the upstream and downstream osmotic pressures step by step according to the method of step 9) to reduce the internal pore water pressure of the sample from the maximum value P max Reduce to the initial value P, and then use the method in step 8) to obtain the permeability coefficient under different pore water pressures;

[0088] Step 12): Process the measured data using the method of step 10) and draw the lgv-lgi curve, and compare it with the pore water pressure in step 10) to observe the permeability evolution law of the fault fracture zone sample during the seepage-stress coupling process; such as whether the permeability changes, whether fine particles are lost, etc.;

[0089] Step 13): After step 9) is completed, the seepage direction can also be changed, and the loading method of steps 7) to 12) can be used to compare with the forward flow process to observe the changes in the seepage characteristics of the fault fracture zone sample under the action of reciprocating seepage, such as changes in permeability coefficient, impermeability strength, and fine particle loss.

[0090] Among them, in the step 6), when the confining pressure value and the water injection volume change slightly, the confining pressure value remains stable at a certain value, such as when the loading confining pressure is 0.5MPa, the computer servo data reads 0.5MPa; the range of small water injection volume change is that its numerical change value shall not exceed 0.1% of the original volume.

[0091] Among them, the specific method of adjusting the upstream / downstream osmotic pressure control system to a small pressure difference ΔP in step 7) is: adjusting the initial pressure difference in the upstream / downstream osmotic pressure control system to 0.005MPa, if it is a low permeability sample, then loading step by step according to the pressure gradient of increasing 0.005MPa each time to ensure a stable water outlet flow within a certain period of time, and the range is about 0.005~0.04MPa.

[0092] Among them, the specific method of loading or reducing the upstream / downstream osmotic pressure step by step in steps 9) and 11) is: simultaneously adjust the upstream / downstream osmotic pressure control system, increase the osmotic pressure in the same direction and with the same pressure difference, and increase or decrease step by step by 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, 0.6MPa, 0.8MPa, and 1.0MPa.

[0093] Among them, the specific method for changing the seepage direction in step 13) is: closing the inner and outer thread valves of the forward flow, opening the inner and outer thread valves of the reverse flow, adjusting the upstream / downstream seepage pressure control system to a small pressure difference ΔP, and then loading or reducing the upstream / downstream seepage pressure step by step to realize the dynamic evolution process of the coupling effect of water pressure gradient-permeability coefficient-effective stress of the fault fracture zone sample under reciprocating seepage conditions, and the loading process is carried out according to the loading method of steps 9) to 12).

[0094] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A device for testing the seepage deformation of a compressive fault fracture zone under reciprocating seepage, characterized in that: include: Water supply system, upstream seepage pressure control system, downstream seepage pressure control system, return water system, seepage pressure chamber, soil-water separation system, particle collection system, confining pressure loading system, flow monitoring system and computer servo system; The water supply system is respectively connected to the upstream seepage pressure control system and the soil-water separation system; the return water system is respectively connected to the downstream seepage pressure control system, the soil-water separation system, and the flow monitoring system; the seepage pressure chamber is respectively connected to the confining pressure loading system and the soil-water separation system; the soil-water separation system is respectively connected to the water supply system, the seepage pressure chamber, the return water system, and the particle collection system; the computer servo system is respectively connected to the confining pressure loading system and the flow monitoring system; The water supply system comprises: a first gas-water exchange tank, a first pressure valve, a first support rod, a first support plate and a plurality of pipelines, wherein the first gas-water exchange tank is supported by the first support rod and the first support plate, and the three are connected in sequence, the first gas-water exchange tank is externally connected to the first pressure valve, and the pipelines are respectively connected to the first gas-water exchange tank and the first pressure valve; The water return system comprises: a second gas-water exchange tank, a second pressure valve, a second support rod, a second support plate and a plurality of pipelines, wherein the second gas-water exchange tank is supported by the second support rod and the second support plate, and the three are connected in sequence, the second gas-water exchange tank is externally connected to the second pressure valve, and the pipelines are respectively connected to the second gas-water exchange tank and the second pressure valve; The upstream permeation pressure control system comprises: a nitrogen tank, a pressure regulating valve, a pressure stabilizing system and an air pressure buffer tank, and the pressure stabilizing system consists of three pressure control systems with different ranges: a low pressure control system, comprising a first air inlet, a 0-0.25MPa air pressure regulating valve, a 0.25MPa pressure sensor and a first low-pressure gas filling port, which are connected in sequence through pipelines; a medium pressure control system, comprising a second air inlet, a 0-1.0MPa air pressure regulating valve, a 1.0MPa pressure sensor and a second low-pressure gas filling port, which are connected in sequence through pipelines; a high pressure control system, comprising a third air inlet, a 0-3.0MPa air pressure regulating valve, a 3.0MPa pressure sensor and a third low-pressure gas filling port, which are connected in sequence through pipelines; the downstream permeation pressure control system has the same structure as the upstream permeation pressure control system; The seepage pressure chamber comprises: a sample cap, a pressure chamber top cover, a pressure chamber pull rod, a pressure chamber cavity, a pressure chamber base, a pressure chamber sealing cover, a porous water-permeable plate, a pressure chamber inlet / drainage joint, a sample positioning strip, a latex film, a sample exhaust hole, a pressure chamber water inlet hole, a pressure chamber exhaust hole and a sample; the pressure chamber pull rod is respectively connected to the pressure chamber top cover and the pressure chamber base; the porous water-permeable plate is respectively connected to the sample cap and the sample, and the outer sleeve of the porous water-permeable plate is provided with a latex film; the sample positioning strip is respectively connected to the sample cap and the pressure chamber base to fix the two ends of the sample; the pressure chamber top cover and the pressure chamber base are both connected to the pressure chamber cavity, the pressure chamber sealing cover and the pressure chamber inlet / drainage joint; the pressure chamber water inlet hole is arranged in the pressure chamber base; the pressure chamber drainage hole is arranged in the pressure chamber top cover; the sample exhaust hole is arranged in the pressure chamber sealing cover; The soil-water separation system comprises: a permeation joint, a permeation sealing cover, a forward inner and outer ball valve, a filter screen, a reverse inner and outer ball valve, and a four-way permeation joint; wherein the water inlet / outlet at both ends of the soil-water separation system are composed of a permeation joint, a forward inner and outer ball valve / reverse inner and outer ball valve, a filter screen, and a permeation sealing cover, and are connected in sequence; the permeation joint is respectively connected to the permeation pressure chamber, the water supply system, the return water system, and the particle collection system; the permeation sealing cover is respectively connected to the permeation joint and the four-way permeation joint; The particle collection system comprises: an external thread short pipe, an internal thread ball valve, a particle collection tank and a collection tank drainage joint, which are connected in sequence; the particle collection tank is composed of a collection tank upper cover, a collection tank exhaust hole, a collection tank pull rod, a collection tank bottom plate and a collection tank body; the collection tank upper cover is respectively connected to the external thread short pipe and the collection tank body; the collection tank pull rod is respectively connected to the collection tank upper cover and the collection tank bottom plate; the collection tank exhaust hole is arranged in the collection tank upper cover; The confining pressure loading system loads pressure in real time and reads and measures the volume change of the sample; The flow monitoring system monitors the quality of the return water system tank in real time and sends the monitoring data to the computer servo system; The computer servo system is connected to the confining pressure loading system and the flow monitoring system respectively, and is used to read and record the changes of the confining pressure value, the sample volume, and the water output in real time.

2. The seepage deformation test device for compressive fault fracture zone under reciprocating seepage according to claim 1 is characterized in that: The confining pressure loading system adopts the YC70-6 pressure volume controller with a capacity of 1000ml, a pressure range of 0-6.0MPa, and a data accuracy of 1kPa / 1mm. 3 , load pressure in real time and read and measure the volume change of the sample.

3. The seepage deformation test device for compressive fault fracture zone under reciprocating seepage according to claim 1, characterized in that: There are two first gas-water exchange tanks with a volume capacity of 6L, and the two first gas-water exchange tanks are independent of each other and are used alternately to meet the continuous water supply status upstream.

4. The seepage deformation test device for compressive fault fracture zone under reciprocating seepage according to claim 1, characterized in that: The number of the second gas-water exchange tank is one, and the volume capacity is 20L.

5. The seepage deformation test device for compressive fault fracture zone under reciprocating seepage according to claim 1, characterized in that: The first gas-water exchange tank comprises: a water inlet, a pressure port, an upper cover, a water level pipe interface, a pull rod, a cylinder, a bottom plate and a water outlet; the cylinder is fixed to the upper cover and the bottom plate through slots respectively, and is connected by a pull rod, and a water level measuring tube is provided on one side of the pull rod; the upper cover is connected to the water inlet and the pressure port respectively; the bottom plate is connected to the water level pipe interface and the water outlet respectively; the water level pipe interface is connected to the water level measuring tube.

6. The seepage deformation test device for compressive fault fracture zone under reciprocating seepage according to claim 1, characterized in that: A circular filter screen is provided at the end of the penetration joint to intercept fine particles and prevent them from entering the tank in the water supply or return system. At the same time, the particles are precipitated by their own weight to ensure that the particles in the seepage pressure chamber automatically enter the particle collection system.

7. A method for testing the seepage deformation of a compressive fault fracture zone under reciprocating seepage, based on the device described in any one of claims 1 to 6, characterized in that: Here are the steps: Step 1): Cover the prepared fault fracture zone sample with a latex film, place a porous water-permeable plate at the bottom of the sample, and put it into a vacuum saturation barrel for saturation, and take it out after 12 hours of saturation; Step 2): The seepage pressure chamber is placed vertically, the saturated sample is placed at the bottom of the seepage pressure chamber, and the latex membrane is placed on the surface of the sample cap at the bottom of the seepage pressure chamber, and a layer of 704 silicone rubber is applied between the latex membrane and the sample cap; Step 3): Place a porous permeable plate and a sample cap on the upper end of the sample in sequence, and fix the sample cap on the upper end of the sample using a sample positioning strip to ensure that no axial displacement occurs at both ends of the sample. At the same time, apply a layer of 704 silicone rubber between the latex film on the upper end of the sample and the sample cap; Step 4): After the 704 silicone rubber solidifies, the pressure chamber cavity is clamped on the pressure chamber top cover at the bottom, and the pressure chamber sealing cover is covered. After the infiltration pressure chamber is completely sealed, the infiltration pressure chamber is placed horizontally, and then the pressure chamber water inlet joint and the pressure chamber water outlet joint are connected to form a closed space; Step 5): Open the nitrogen tank, adjust the pressure regulating valve to 0.3MPa, then open the sample exhaust hole, adjust the low and medium pressure control systems of the upstream / downstream permeation pressure control system respectively, and exhaust the air in the sample cap through the sample exhaust hole to ensure that both ends of the sample are completely filled with water; Step 6): Open the water inlet and exhaust holes of the pressure chamber in the osmotic pressure chamber, and load the confining pressure to the preset value σ step by step through the computer servo system. When the confining pressure reaches the preset value σ and the injection volume changes little, check whether the inlet / outlet pipes, the osmotic pressure chamber, the confining pressure loading system, and the osmotic pressure loading system are normal. If they are normal, proceed to step 7); Step 7): Open the forward flow inner and outer thread valves, adjust the upstream / downstream permeation pressure control system to a small pressure difference ΔP, observe the water output in the flow monitoring system after a period of time, and calculate the permeability coefficient k under the pressure difference ΔP after the water output and confining pressure volume changes are stable; Step 8): According to the cross-sectional area A of the fault fracture zone sample, the seepage path length L, the water density ρ, the gravity acceleration g and the water flow rate Q, the average seepage gradient i of the sample when the seepage is stable under the pressure difference ΔP, i=ΔP / ρLg, the average flow velocity v, v=Q / A, and the permeability coefficient k under the pore water pressure P is obtained using the formula lgv=lgk+lgi; Step 9): Use the method in step 7) to load the upstream / downstream osmotic pressure step by step, ensure that the upstream and downstream pressure difference is always stable at a small pressure difference value ΔP, and load the pore water pressure inside the sample from the initial value P to the maximum value P step by step. max , use the method of step 8) to obtain the permeability coefficient under different pore water pressures. At the same time, after the water output and injection volume readings are stable each time, close the ball valve at the upper end of the particle collection system, open the drainage joint of the collection tank, use a beaker to collect the solution and observe whether the fine particles migrate, so as to determine the change of the permeability characteristic parameters caused by the change of effective stress in the overall deformation and destruction process of the sample. If there is no fine particle migration in the solution or the ion concentration of the solution does not change significantly, proceed to step 10); if there is a large change in the ion concentration and fine particle migration in the solution, it is considered that the sample has entered the permeability deformation and destruction stage; Step 10): Calculate the effective stress σ′ corresponding to the pore water pressure P, σ′=σ-P, draw a scatter plot of k~σ′, and select k=k0·exp(-α·σ′) exponential empirical formula for fitting to obtain the permeability coefficient k0 and stress sensitivity coefficient α under the condition of no seepage; Step 11): Reduce the upstream and downstream osmotic pressures step by step according to the method of step 9) to reduce the internal pore water pressure of the sample from the maximum value P max Reduce to the initial value P, and then use the method in step 8) to obtain the permeability coefficient under different pore water pressures; Step 12): Process the measured data using the method of step 10) and draw the lgv-lgi curve, and compare it with the pore water pressure in step 10) to observe the permeability evolution law of the fault fracture zone sample during the seepage-stress coupling process; Step 13): After step 9), the seepage direction is changed, and the loading method of steps 7) to 12) is used to compare with the forward flow process to observe the changes in the seepage characteristics of the fault fracture zone sample under the action of reciprocating seepage.

8. The test method for seepage deformation of compressive fault fracture zone under reciprocating seepage according to claim 7, characterized in that: In step 6), when the confining pressure value and the injected water volume change slightly, the confining pressure value is always stable at a certain value, and the range in which the injected water volume changes slightly is such that the value change value shall not exceed 0.1% of the original volume.

9. The test method for seepage deformation of compressive fault fracture zone under reciprocating seepage according to claim 7, characterized in that: The specific method of adjusting the upstream / downstream osmotic pressure control system to a small pressure difference ΔP in step 7) is as follows: the initial pressure difference in the upstream / downstream osmotic pressure control system is adjusted to 0.005MPa. If it is a low permeability sample, the pressure gradient is loaded step by step with an increase of 0.005MPa each time to ensure a stable water outlet flow rate within a certain period of time, and the range is about 0.005-0.04MPa.

10. The test method for seepage deformation of compressive fault fracture zone under reciprocating seepage according to claim 7, characterized in that: The specific method for changing the seepage direction in step 13) is: closing the inner and outer thread valves of the forward flow, opening the inner and outer thread valves of the reverse flow, adjusting the upstream / downstream seepage pressure control system to a small pressure difference ΔP, and then loading or reducing the upstream / downstream seepage pressure step by step to realize the dynamic evolution process of the coupling effect of water pressure gradient-permeability coefficient-effective stress of the fault fracture zone sample under reciprocating seepage conditions, and the loading process is carried out according to the loading method of steps 9) to 12).

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