Permeability coefficient testing device suitable for unloading seepage condition

Abstract

The invention provides a permeability coefficient testing device suitable for an unloading seepage condition, which comprises a rubber sleeve for sleeving a sample, a confining pressure chamber, a water replenishing tank, an upper pore pressure volume controller, a confining pressure volume controller and a lower pore pressure volume controller, the confining pressure chamber base is provided with a water replenishing port connected with the water replenishing tank, an upper hole connected with the upper pore pressure volume controller, a lower hole connected with the lower pore pressure volume controller and a confining pressure hole connected with the confining pressure volume controller, and a sample supporting seat and a sample sealing cover are arranged in the confining pressure chamber; the confining pressure chamber cover is provided with a pressing block for pressing the sample sealing cover, a pressing block driving structure for driving the pressing block to lift and a pressing force detector for detecting the pressure intensity generated by the pressing block on the sample sealing cover. The device has the advantage of accurate confining pressure data, and solves the problem of poor test accuracy caused by confining pressure of the same size in existing constant pressure measurement.

Description

Technical Field

[0001] The present application relates to the technical field of indoor geotechnical testing, and in particular to a permeability coefficient testing device suitable for use under unloading seepage conditions. Background Art

[0002] As the development of shallow underground space in cities tends to be saturated, underground projects are developing towards deep underground space, and a number of deep foundation pit projects with excavation depths exceeding 30m have emerged. In water-rich soft soil areas represented by Shanghai, clay and sand layers are alternately distributed to form a multi-aquifer system, and the average pressure water level is 7~9m underground. During the excavation of deep foundation pits, the stress level of the soil in the pit decreases under the action of unloading, which is much lower than the initial stress state. The change in stress state causes the soil to expand and rebound, the porosity increases, and the bottom of the pit rises. At the same time, during the excavation process, the pressure water level in the pressure layer is still relatively high, and the water gradient from the pressure layer to the excavation surface increases, causing upward seepage from the pressure layer to the overlying weak permeable layer. When the excavation surface continues to approach the interface between the weak permeable layer and the pressure aquifer, the effective stress of the soil is further reduced, the porosity increases, resulting in an increase in the soil permeability coefficient, and the upward seepage effect is obvious, which may cause risks such as sudden surges in the foundation pit. On the other hand, geological surveys show that there are extensive silt layers in coastal soft soil areas. The permeability of silt layers is between clay and sand, and the permeability development under unloading is more complicated. Therefore, accurately measuring the permeability coefficient of soil during unloading is of great significance to the risk assessment of foundation pit inrush.

[0003] At present, the study of the permeability characteristics of soil under different stress states mainly considers the change of permeability coefficient during loading. The compression modulus and rebound modulus of soil during loading and unloading are very different, and the soil shows different nonlinear deformation characteristics. In addition, the pressure on the side and top of the soil is different and known in practice. The existing permeability test is to conduct confining pressure through water, and the pressure on the side and top is the same, resulting in poor accuracy of the sample; when conducting unloading permeability test, the amount of air in the confining pressure chamber has a great influence on the accuracy of the sample structure; when a sample is tested for a long time, the water in the volume controller will be used up, and the test needs to be stopped, and the water in the upper hole volume controller (for receiving water) will be converged to the lower hole volume controller (for delivering water) through the confining pressure chamber. This method not only leads to low test efficiency but also reverse osmosis of water, resulting in poor accuracy of the sample. Summary of the invention

[0004] The first purpose of the present invention is to provide a permeability coefficient testing device suitable for unloading seepage conditions in which pressure measurement and top pressure are applied independently, thereby solving the problem of poor test accuracy caused by the same confining pressure as the existing constant pressure measurement.

[0005] The second purpose of the present invention is to further provide a permeability coefficient testing device suitable for unloading seepage conditions with low air content in confined pressure water, thereby solving the problem of poor test accuracy caused by high air content in confined pressure water.

[0006] The third object of the present invention is to provide a permeability coefficient testing device suitable for unloading seepage conditions that can perform uninterrupted tests, thereby solving the problem of poor test accuracy caused by stopping reverse osmosis water replenishment of the sample when the existing test water volume is insufficient.

[0007] In order to achieve the above-mentioned invention objectives, the present invention adopts the following technology: a permeability coefficient testing device suitable for unloading seepage conditions, comprising a rubber sleeve for covering a sample, a confining pressure chamber, a water replenishment tank, an upper pore pressure volume controller, a confining pressure volume controller and a lower pore pressure volume controller, the confining pressure chamber comprising a confining pressure chamber base and a confining pressure chamber cover which is detachably and sealedly connected to the chamber base and is provided with an exhaust valve, the confining pressure chamber base and the confining pressure chamber cover enclose a sealed confining pressure chamber, the confining pressure chamber base is provided with a water replenishment port connected to the water replenishment tank, an upper hole connected to the upper pore pressure volume controller, a lower hole connected to the lower pore pressure volume controller and a confining pressure hole connected to the confining pressure volume controller, a sample support seat and a sample cover are provided in the confining pressure chamber, characterized in that a pressing block for pressing the sample cover, a pressing block driving structure for driving the pressing block to rise and fall and a pressing force detector for detecting the pressure generated by the pressing block on the sample cover. When in use, the rubber sleeve is sleeved on the sample, the sample is placed on the sample support seat and covered with the sample cover, the upper end of the rubber sleeve is sleeved on the sample cover, and the lower end is sleeved on the sample support seat, the water in the water supply tank is input into the confining pressure chamber through the water supply port to fill the confining pressure chamber, and then the exhaust valve is closed, the confining pressure volume controller pressurizes the confining pressure chamber to the set first side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the first top surface confining pressure value through the pressing block to apply pressure to the top surface of the test, and water with a set first water inlet pressure is input into the sample through the lower hole through the lower hole through the lower hole pressure volume controller, and the water penetrates through the sample and is output from the upper hole to the upper hole pressure volume controller, and the upper hole pressure volume controller is maintained at the set first water outlet Pressure, calculate the first permeability coefficient according to the existing permeability calculation formula; the confining pressure volume controller pressurizes the confining pressure chamber to the set second side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the second top confining pressure value through the pressing block to apply pressure to the top surface of the test, and inputs water of the set second water inlet pressure to the sample through the lower hole through the lower hole through the lower hole pressure volume controller. After the water penetrates through the sample, it is output from the upper hole to the upper hole pressure volume controller and the upper hole pressure volume controller is maintained at the second water outlet pressure received. According to the existing permeability calculation formula, the second permeability coefficient is calculated, and the confining pressure value, input pressure and output pressure are reduced in turn by the same method, so as to obtain the permeability coefficient under various pressures when the sample is depressurized. The top surface of the sample is independently pressurized by water instead of being controlled by the confining pressure volume controller at the same value on the same circumference, so that the pressure on the side and top surfaces of the sample is close to the actual pressure, so that the measured depressurization confining pressure data is more accurate.

[0008] Preferably, the water replenishment tank is provided with a water pump for outputting the water in the water replenishment tank, a vacuum pump for evacuating the water replenishment tank and a vibrator for causing the water in the water replenishment tank to shake, and the outlet end of the water pump is connected to the water replenishment port.

[0009] Preferably, the lower pore pressure volume controller comprises a three-way valve of the lower pore pressure volume controller, a threaded rod of the lower pore pressure volume controller, a guide rod of the lower pore pressure volume controller, a motor of the lower pore pressure volume controller for driving the threaded rod of the lower pore pressure volume controller to rotate, a driving block of the lower pore pressure volume controller threadedly connected to the threaded rod of the lower pore pressure volume controller, a locking switching structure of the lower pore pressure volume controller, a first cylinder of the lower pore pressure volume controller, a first piston of the lower pore pressure volume controller connected in a sliding seal in the first cylinder of the lower pore pressure volume controller, and one end of the lower pore pressure volume controller connected to the lower pore pressure volume controller. The first piston is connected together and the other end is passed through the first piston rod of the lower pore pressure volume controller in the lower pore pressure volume controller driving block, the first pressure sensor of the lower pore pressure volume controller, the second cylinder of the lower pore pressure volume controller, the second piston of the lower pore pressure volume controller connected in the second cylinder of the lower pore pressure volume controller with a sliding seal, the second piston of the lower pore pressure volume controller connected together with the second piston of the lower pore pressure volume controller at one end and the other end is passed through the lower pore pressure volume controller driving block, and the second piston rod of the lower pore pressure volume controller and the second pressure sensor of the lower pore pressure volume controller, the lower pore pressure volume controller The first piston isolates the first liquid storage chamber of the lower pore pressure volume controller in the first cylinder of the lower pore pressure volume controller, the first pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the first liquid storage chamber of the lower pore pressure volume controller, the first liquid storage chamber of the lower pore pressure volume controller is connected to a branch hole of the three-way valve of the lower pore pressure volume controller, the second piston of the lower pore pressure volume controller isolates the second liquid storage chamber of the lower pore pressure volume controller in the second cylinder of the lower pore pressure volume controller, and the second pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the second liquid storage chamber of the lower pore pressure volume controller The second liquid storage chamber of the lower pore pressure volume controller is connected with another branch hole of the three-way valve of the lower pore pressure volume controller, and the main port of the three-way valve of the lower pore pressure volume controller is connected with the lower hole. The locking switching structure of the lower pore pressure volume controller is used to make the driving block of the lower pore pressure volume controller only be fixed with one of the first piston rod of the lower pore pressure volume controller and the second piston rod of the lower pore pressure volume controller at the same time. The guide rod of the lower pore pressure volume controller is penetrated in the driving block of the lower pore pressure volume controller to prevent the driving block of the lower pore pressure volume controller from rotating;The upper pore pressure volume controller comprises an upper pore pressure volume controller three-way valve, an upper pore pressure volume controller threaded rod, an upper pore pressure volume controller guide rod, an upper pore pressure volume controller motor for driving the upper pore pressure volume controller threaded rod to rotate, an upper pore pressure volume controller drive block threadedly connected to the upper pore pressure volume controller threaded rod, an upper pore pressure volume controller first cylinder, an upper pore pressure volume controller first piston slidingly sealed and connected to the upper pore pressure volume controller first cylinder, an upper pore pressure volume controller first piston rod connected to the upper pore pressure volume controller first piston at one end and fixed to the upper pore pressure volume controller drive block at the other end, and an upper pore pressure volume controller The first pressure sensor of the device part, the second cylinder of the upper pore pressure volume controller part, the second piston of the upper pore pressure volume controller part which is connected in a sliding seal in the second cylinder of the upper pore pressure volume controller part, the second piston rod of the upper pore pressure volume controller part which is connected to the second piston of the upper pore pressure volume controller part at one end and fixed to the driving block of the upper pore pressure volume controller part at the other end, and the second pressure sensor of the upper pore pressure volume controller part, the first piston of the upper pore pressure volume controller part isolates the first liquid storage chamber of the upper pore pressure volume controller part in the first cylinder of the upper pore pressure volume controller part, the first pressure sensor of the upper pore pressure volume controller part is used to detect the pressure in the first liquid storage chamber of the upper pore pressure volume controller part, and the upper pore pressure volume controller part The first liquid storage chamber of the upper pore pressure volume controller is connected with a branch hole of the three-way valve of the upper pore pressure volume controller, the second piston of the upper pore pressure volume controller isolates the second liquid storage chamber of the upper pore pressure volume controller in the second cylinder of the upper pore pressure volume controller, the second pressure sensor of the upper pore pressure volume controller is used to detect the pressure in the second liquid storage chamber of the upper pore pressure volume controller, the second liquid storage chamber of the upper pore pressure volume controller is connected with another branch hole of the three-way valve of the upper pore pressure volume controller, the main port of the three-way valve of the upper pore pressure volume controller is connected with the upper hole, and the guide rod of the upper pore pressure volume controller is penetrated in the driving block of the upper pore pressure volume controller to prevent the driving block of the upper pore pressure volume controller from rotating ; The first liquid storage chamber of the lower pore pressure volume controller part is connected with the first liquid storage chamber of the upper pore pressure volume controller part through the first valve, and the second liquid storage chamber of the lower pore pressure volume controller part is connected with the second liquid storage chamber of the upper pore pressure volume controller part through the first valve; when in use, water is delivered through the first liquid storage chamber of the lower pore pressure volume controller part and water is received through the first liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment. After the water in the first liquid storage chamber of the lower pore pressure volume controller part is delivered or the first liquid storage chamber of the upper pore pressure volume controller part is filled, the first valve is opened and water is delivered through the second liquid storage chamber of the lower pore pressure volume controller part and water is received through the second liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment;The process of resetting the driving block of the lower pore pressure volume controller to drive the second piston rod of the lower pore pressure volume controller resets the first liquid storage chamber of the lower pore pressure volume controller, and the process of resetting the driving block of the upper pore pressure volume controller resets the first liquid storage chamber of the upper pore pressure volume controller and the second liquid storage chamber of the upper pore pressure volume controller, so that the water in the first liquid storage chamber of the lower pore pressure volume controller flows back to the first liquid storage chamber of the upper pore pressure volume controller, and the first valve is closed; after the water in the second liquid storage chamber of the lower pore pressure volume controller is transported or the second liquid storage chamber of the upper pore pressure volume controller is filled, the second valve is opened and the lower pore pressure volume controller is connected. The first liquid storage chamber of the part delivers water and the first liquid storage chamber of the upper pore pressure volume controller part receives water to perform a permeability coefficient test experiment; the process of resetting the driving block of the lower pore pressure volume controller part to drive the first piston rod of the lower pore pressure volume controller part resets the second liquid storage chamber of the lower pore pressure volume controller part, and the process of resetting the driving block of the upper pore pressure volume controller part resets the second liquid storage chamber of the upper pore pressure volume controller part and the first liquid storage chamber of the upper pore pressure volume controller part, so that the water in the second liquid storage chamber of the lower pore pressure volume controller part flows back to the second liquid storage chamber of the upper pore pressure volume controller part, and the second valve is closed; repeat the above process to test the sample uninterruptedly through the permeability system. It can avoid the problem of insufficient water and interruption of the test. The water in the first liquid storage chamber of the upper pore pressure volume controller is returned to the lower pore pressure volume controller through the confining pressure chamber. This is equivalent to reverse osmosis of the sample, which will affect the accuracy of the test data and the test efficiency. ;

[0010] Preferably, the first piston of the upper pore pressure volume controller is located at the upper end of the first cylinder of the upper pore pressure volume controller, the second piston of the upper pore pressure volume controller is located at the upper end of the second cylinder of the upper pore pressure volume controller, the first piston of the lower pore pressure volume controller is located at the upper end of the first cylinder of the lower pore pressure volume controller, and the second piston of the lower pore pressure volume controller is located at the upper end of the second cylinder of the lower pore pressure volume controller. The cylinder is arranged vertically, so that the volume of the liquid storage chamber can be maintained at the current state when the part is in use.

[0011] Preferably, the first cylinder of the upper pore pressure volume controller part and the second cylinder of the upper pore pressure volume controller part are connected side by side, and the first cylinder of the lower pore pressure volume controller part and the second cylinder of the lower pore pressure volume controller part are connected side by side. It is convenient to drive and has a compact structure.

[0012] Preferably, when the volume of the first liquid storage chamber of the upper pore pressure volume controller is at its maximum state, the height of the first liquid storage chamber of the upper pore pressure volume controller is less than 5 cm, when the volume of the second liquid storage chamber of the upper pore pressure volume controller is at its maximum state, the height of the first liquid storage chamber of the lower pore pressure volume controller is less than 5 cm, when the volume of the first liquid storage chamber of the lower pore pressure volume controller is at its maximum state, the height of the first liquid storage chamber of the lower pore pressure volume controller is less than 5 cm, and when the volume of the second liquid storage chamber of the lower pore pressure volume controller is at its maximum state, the length of the second liquid storage chamber of the lower volume controller is less than 5 cm. This can shorten the time it takes for the liquid storage chamber to reset.

[0013] Preferably, the locking and switching structure of the lower pore pressure volume controller part includes a first fixed lock of the lower pore pressure volume controller part and a second fixed lock of the lower pore pressure volume controller part, the first fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block with the first piston rod of the lower pore pressure volume controller part, the second fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block with the second piston rod of the lower pore pressure volume controller part, and only one of the first fixed lock of the lower pore pressure volume controller part and the second fixed lock of the lower pore pressure volume controller part is kept in a locked state at the same time. A specific technical solution of the locking and switching structure of the lower pore pressure volume controller part is provided.

[0014] Preferably, the first fixed lock of the lower pore pressure volume controller part includes a first locking pin of the lower pore pressure volume controller part hinged on the upper end of the first piston rod of the lower pore pressure volume controller part, a first locking hole of the lower pore pressure volume controller part arranged on the side of the driving block of the lower pore pressure volume controller part, and a first driving cylinder of the lower pore pressure volume controller part for driving the first locking pin of the lower pore pressure volume controller part to insert and pull out the locking hole of the lower pore pressure volume controller part. When the first locking pin of the lower pore pressure volume controller part is inserted into the first locking hole of the lower pore pressure volume controller part, the piston rod of the lower pore pressure volume controller part is fixed together with the driving block of the lower pore pressure volume controller part. The second fixed lock of the lower pore pressure volume controller comprises a second locking pin of the lower pore pressure volume controller hinged on the upper end of the second piston rod of the lower pore pressure volume controller, a second locking hole of the lower pore pressure volume controller arranged on the side of the driving block of the lower pore pressure volume controller, and a second driving cylinder of the lower pore pressure volume controller for driving the second locking pin of the lower pore pressure volume controller to insert and pull out of the locking hole of the lower pore pressure volume controller. When the second locking pin of the lower pore pressure volume controller is inserted into the second locking hole of the lower pore pressure volume controller, the piston rod of the lower pore pressure volume controller is fixed together with the driving block of the lower pore pressure volume controller. A specific technical solution of the locking structure is provided.

[0015] As a preference, it also includes a pressure sensor in the confining pressure chamber that is input to the bottom of the sample to check the water inlet pressure, so that the water inlet pressure can be retested to improve the accuracy of the test.

[0016] Preferably, the upper opening or the lower hole uses a flow meter to accurately measure the amount of permeated water during the test.

[0017] The present invention has the following beneficial effects: constant pressure and pressure measurement can simulate actual sample testing; the amount of air contained in the confining pressure water is small; when the amount of water is insufficient, the test can be carried out without stopping and the water can be recycled; and the accuracy during the test is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the present invention; Figure 2 is a schematic diagram of an upper pore pressure volume controller and a lower pore pressure volume controller; Figure 3 yes Figure 2 A local enlarged schematic diagram of point A; Figure 4 yes Figure 2 A local enlarged schematic diagram of point B; Figure 5 It is a cross-sectional schematic diagram of the confining pressure chamber.

[0019] In the figure: sample 1, rubber sleeve 2, confining pressure chamber 3, water supply tank 4, upper pore pressure volume controller 5, confining pressure volume controller 6, lower pore pressure volume controller 7, confining pressure chamber pressure sensor 8, confining pressure chamber base 9, exhaust valve 10, confining pressure chamber cover 11, water supply port 12, upper hole 13, lower hole 14, confining pressure hole 15, sample support seat 16, sample cover 17, pressing block 18, water pump 19, vacuum pump 20, vibrator 21, three-way valve of lower pore pressure volume controller 22, threaded rod of lower pore pressure volume controller 24, motor of lower pore pressure volume controller 25, lower pore pressure volume controller The device driving block 26, the first cylinder body 27 of the lower pore pressure volume controller part, the first piston 28 of the lower pore pressure volume controller part, the first piston rod 29 of the lower pore pressure volume controller part, the first pressure sensor 30 of the lower pore pressure volume controller part, the second cylinder body 31 of the lower pore pressure volume controller part, the second piston 32 of the lower pore pressure volume controller part, the second piston rod 33 of the lower pore pressure volume controller part, the second pressure sensor 34 of the lower pore pressure volume controller part, the first liquid storage chamber 35 of the lower pore pressure volume controller part, the frame 36 of the lower pore pressure volume controller part, the second liquid storage chamber 37 of the lower pore pressure volume controller part, the upper The three-way valve 38 of the pore pressure volume controller part, the threaded rod 39 of the upper pore pressure volume controller part, the motor 40 of the upper pore pressure volume controller part, the driving block 41 of the upper pore pressure volume controller part, the first cylinder 42 of the upper pore pressure volume controller part, the first piston 43 of the upper pore pressure volume controller part, the first piston rod 44 of the upper pore pressure volume controller part, the first pressure sensor 45 of the upper pore pressure volume controller part, the second cylinder 46 of the upper pore pressure volume controller part, the second piston 47 of the upper pore pressure volume controller part, the second piston rod 48 of the upper pore pressure volume controller part, and the second pressure sensor 49 of the upper pore pressure volume controller part , the first liquid storage chamber 50 of the upper pore pressure volume controller part, the second liquid storage chamber 51 of the upper pore pressure volume controller part, the frame 52 of the upper pore pressure volume controller part, the first valve 53, the second valve 54, the first fixed lock 55 of the lower pore pressure volume controller part, the second fixed lock 56 of the lower pore pressure volume controller part, the first locking pin 57 of the lower pore pressure volume controller part, the first locking hole 58 of the lower pore pressure volume controller part, the first driving cylinder 59 of the lower pore pressure volume controller part, the second locking pin 60 of the lower pore pressure volume controller part, the second locking hole 61 of the lower pore pressure volume controller part, and the second driving cylinder 62 of the lower pore pressure volume controller part. DETAILED DESCRIPTION

[0020] The present invention is described below in conjunction with the accompanying drawings and specific embodiments. The anchor rod is tilted in a state where one end connected to the inner retaining wall is high and the other end is low, and the lower end of the anchor rod is lower than the bottom of the inner pit.

[0021] See also Figures 1 to 5A permeability coefficient testing device suitable for unloading seepage conditions includes a rubber sleeve 2 for covering a sample 1, a confining pressure chamber 3, a water replenishment tank 4, an upper pore pressure volume controller 5, a confining pressure volume controller 6, a lower pore pressure volume controller 7 and a confining pressure chamber pressure sensor 8 input to the bottom of the sample to check the water inlet pressure.

[0022] The confining pressure chamber includes a confining pressure chamber base 9 and a confining pressure chamber cover 11 which is detachably and hermetically connected to the chamber base and is provided with an exhaust valve 10. The confining pressure chamber base and the confining pressure chamber cover enclose a sealed confining pressure chamber. The confining pressure chamber base is provided with a water replenishment port 12 connected to a water replenishment tank, an upper hole 13 connected to an upper pore pressure volume controller, a lower hole 14 connected to a lower pore pressure volume controller, and a confining pressure hole 15 connected to a confining pressure volume controller. A sample support seat 16 and a sample cover 17 are provided in the confining pressure chamber. The confining pressure chamber cover is provided with a pressing block 18 for pressing the sample cover, a pressing block driving structure for driving the pressing block to rise and fall, and a pressing force detector for detecting the pressure exerted by the pressing block on the sample cover.

[0023] The water supply tank is provided with a water pump 19 for outputting the water in the water supply tank, a vacuum pump 20 for evacuating the water supply tank, and a vibrator 21 for shaking the water in the water supply tank. The outlet end of the water pump is connected to the water supply port. When in use, the vacuum pump and the vibrator are first used to remove air from the water in the water supply tank, and then the water is input into the confining pressure chamber.

[0024] When in use, the rubber sleeve is sleeved on the sample, the sample is placed on the sample support seat and covered with the sample cover, the upper end of the rubber sleeve is sleeved on the sample cover, and the lower end is sleeved on the sample support seat, the water in the water supply tank is input into the confining pressure chamber through the water supply port to fill the confining pressure chamber, and then the exhaust valve is closed, the confining pressure volume controller pressurizes the confining pressure chamber to the set first side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the first top surface confining pressure value through the pressing block to apply pressure to the top surface of the test, and water with a set first water inlet pressure is input into the sample through the lower hole through the lower hole through the lower hole pressure volume controller, and the water penetrates through the sample and is output from the upper hole to the upper hole pressure volume controller, and the upper hole pressure volume controller is maintained at the set first water outlet Pressure, calculate the first permeability coefficient according to the existing permeability calculation formula; the confining pressure volume controller pressurizes the confining pressure chamber to the set second side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the second top confining pressure value through the pressing block to apply pressure to the top surface of the test, and inputs water of the set second water inlet pressure to the sample through the lower hole through the lower hole through the lower hole pressure volume controller. After the water penetrates through the sample, it is output from the upper hole to the upper hole pressure volume controller and the upper hole pressure volume controller is maintained at the second water outlet pressure received. According to the existing permeability calculation formula, the second permeability coefficient is calculated, and the confining pressure value, input pressure and output pressure are reduced in turn by the same method, so as to obtain the permeability coefficient under various pressures when the sample is depressurized. The top surface of the sample is independently pressurized by water instead of being controlled by the confining pressure volume controller at the same value on the same circumference, so that the pressure on the side and top surfaces of the sample is close to the actual pressure, so that the measured depressurization confining pressure data is more accurate.

[0025] The confining pressure volume controller is an existing structure.

[0026] The lower pore pressure volume controller comprises a three-way valve 22 of the lower pore pressure volume controller, a vertically arranged threaded rod 24 of the lower pore pressure volume controller, a guide rod of the lower pore pressure volume controller, a motor 25 of the lower pore pressure volume controller for driving the threaded rod of the lower pore pressure volume controller to rotate, a driving block 26 of the lower pore pressure volume controller threadedly connected to the threaded rod of the lower pore pressure volume controller, a locking switching structure of the lower pore pressure volume controller, a first cylinder 27 of the lower pore pressure volume controller, a first piston 28 of the lower pore pressure volume controller connected in a sliding seal in the first cylinder of the lower pore pressure volume controller, one end of which is connected to the first piston of the lower pore pressure volume controller and the other end of which is penetrated in the lower pore pressure volume controller. The first piston rod 29 of the lower pore pressure volume controller in the volume controller driving block, the first pressure sensor 30 of the lower pore pressure volume controller, the second cylinder 31 of the lower pore pressure volume controller, the second piston 32 of the lower pore pressure volume controller connected in the second cylinder of the lower pore pressure volume controller in a sliding seal, the second piston rod 33 of the lower pore pressure volume controller connected to the second piston of the lower pore pressure volume controller at one end and the second pressure sensor 34 of the lower pore pressure volume controller at the other end, and the first piston of the lower pore pressure volume controller isolates the first liquid storage chamber 35 of the lower pore pressure volume controller in the first cylinder of the lower pore pressure volume controller. The motor of the lower pore pressure volume controller and the first cylinder of the lower pore pressure volume controller are connected together with the frame 36 of the lower pore pressure volume controller. The guide rod of the lower pore pressure volume controller is parallel to the threaded rod of the lower pore pressure volume controller. The guide rod of the lower pore pressure volume controller is fixed together with the frame of the lower pore pressure volume controller. The first pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the first liquid storage chamber of the lower pore pressure volume controller. The first liquid storage chamber of the lower pore pressure volume controller is connected to a branch hole of the three-way valve of the lower pore pressure volume controller. The second piston of the lower pore pressure volume controller isolates the second liquid storage chamber 37 of the lower pore pressure volume controller in the second cylinder of the lower pore pressure volume controller. The second pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the second liquid storage chamber of the lower pore pressure volume controller. The second liquid storage chamber of the lower pore pressure volume controller is connected to another branch hole of the three-way valve of the lower pore pressure volume controller. The total port of the three-way valve of the lower pore pressure volume controller is connected to the lower hole. The locking switching structure of the lower pore pressure volume controller is used to enable the driving block of the lower pore pressure volume controller to be fixed to only one of the first piston rod of the lower pore pressure volume controller and the second piston rod of the lower pore pressure volume controller at the same time.The guide rod of the lower pore pressure volume controller is inserted into the driving block of the lower pore pressure volume controller to prevent the driving block of the lower pore pressure volume controller from rotating; the upper pore pressure volume controller includes an upper pore pressure volume controller three-way valve 38, an upper pore pressure volume controller threaded rod 39, an upper pore pressure volume controller guide rod, an upper pore pressure volume controller motor 40 for driving the upper pore pressure volume controller threaded rod to rotate, an upper pore pressure volume controller driving block 41 threadedly connected to the upper pore pressure volume controller threaded rod, an upper pore pressure volume controller first cylinder 42, an upper pore pressure volume controller first piston 43 connected in a sliding seal in the first cylinder of the upper pore pressure volume controller, and one end of the upper pore pressure volume controller first piston connected to the upper pore pressure volume controller The first piston rod 44 of the upper pore pressure volume controller, which is fixed to the upper pore pressure volume controller driving block at the other end, the first pressure sensor 45 of the upper pore pressure volume controller, the second cylinder 46 of the upper pore pressure volume controller, the second piston 47 of the upper pore pressure volume controller connected in the second cylinder of the upper pore pressure volume controller with a sliding seal, the second piston rod 48 of the upper pore pressure volume controller, which is connected to the second piston of the upper pore pressure volume controller at one end and fixed to the driving block of the upper pore pressure volume controller at the other end, and the second pressure sensor 49 of the upper pore pressure volume controller, the first piston of the upper pore pressure volume controller isolates the first liquid storage chamber 50 of the upper pore pressure volume controller in the first cylinder of the upper pore pressure volume controller. The first pressure sensor of the upper pore pressure volume controller is used to detect the pressure in the first liquid storage chamber of the upper pore pressure volume controller, the first liquid storage chamber of the upper pore pressure volume controller is connected to a branch hole of the three-way valve of the upper pore pressure volume controller, and the second piston of the upper pore pressure volume controller isolates the second liquid storage chamber 51 of the upper pore pressure volume controller in the second cylinder of the upper pore pressure volume controller. The upper pore pressure volume controller motor and the first cylinder of the upper pore pressure volume controller are connected together with the upper pore pressure volume controller frame 52. The upper pore pressure volume controller guide rod is parallel to the upper pore pressure volume controller threaded rod. The upper pore pressure volume controller guide rod is fixed together with the upper pore pressure volume controller frame.The second pressure sensor of the upper pore pressure volume controller part is used to detect the pressure in the second liquid storage chamber of the upper pore pressure volume controller part. The second liquid storage chamber of the upper pore pressure volume controller part is connected to another branch hole of the three-way valve of the upper pore pressure volume controller part. The total port of the three-way valve of the upper pore pressure volume controller part is connected to the upper hole. The guide rod of the upper pore pressure volume controller part is penetrated in the driving block of the upper pore pressure volume controller part to prevent the driving block of the upper pore pressure volume controller part from rotating; the first liquid storage chamber of the lower pore pressure volume controller part is connected to the first liquid storage chamber of the upper pore pressure volume controller part through the first valve 53, and the first liquid storage chamber of the lower pore pressure volume controller part is connected to the second liquid storage chamber of the upper pore pressure volume controller part through the first valve 53. The second liquid storage chamber is connected with the second liquid storage chamber of the upper pore pressure volume controller part through the second valve 54; when in use, water is delivered through the first liquid storage chamber of the lower pore pressure volume controller part and water is received through the first liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment. After the water in the first liquid storage chamber of the lower pore pressure volume controller part is delivered or the first liquid storage chamber of the upper pore pressure volume controller part is filled, the first valve is opened and water is delivered through the second liquid storage chamber of the lower pore pressure volume controller part and water is received through the second liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment; the lower pore pressure volume controller part drive block is reset to drive the lower The process of the second piston rod of the pore pressure volume controller part resets the first liquid storage chamber of the lower pore pressure volume controller part, and the process of resetting the driving block of the upper pore pressure volume controller part resets the first liquid storage chamber of the upper pore pressure volume controller part and the second liquid storage chamber of the upper pore pressure volume controller part, so that the water in the first liquid storage chamber of the lower pore pressure volume controller part flows back to the first liquid storage chamber of the upper pore pressure volume controller part, and the first valve is closed; after the water in the second liquid storage chamber of the lower pore pressure volume controller part is delivered or the second liquid storage chamber of the upper pore pressure volume controller part is filled, the second valve is opened and water is delivered through the first liquid storage chamber of the lower pore pressure volume controller part and The permeability coefficient test experiment is conducted by receiving water through the first liquid storage chamber of the upper pore pressure volume controller; the process of resetting the driving block of the lower pore pressure volume controller to drive the first piston rod of the lower pore pressure volume controller resets the second liquid storage chamber of the lower pore pressure volume controller, and the process of resetting the driving block of the upper pore pressure volume controller resets the second liquid storage chamber of the upper pore pressure volume controller and the first liquid storage chamber of the upper pore pressure volume controller, so that the water in the second liquid storage chamber of the lower pore pressure volume controller flows back to the second liquid storage chamber of the upper pore pressure volume controller, and the second valve is closed; the above process is repeated to test the sample of the uninterrupted permeability system. It can avoid the water shortage and interrupt the test to make the water in the first liquid storage chamber of the water part in the upper pore pressure volume controller return to the lower pore pressure volume controller through the confining pressure chamber, which is equivalent to reverse osmosis of the sample, which will affect the accuracy of the test data and the test efficiency.

[0027] The first piston of the upper pore pressure volume controller is located at the upper end of the first cylinder of the upper pore pressure volume controller, the second piston of the upper pore pressure volume controller is located at the upper end of the second cylinder of the upper pore pressure volume controller, the first piston of the lower pore pressure volume controller is located at the upper end of the first cylinder of the lower pore pressure volume controller, and the second piston of the lower pore pressure volume controller is located at the upper end of the second cylinder of the lower pore pressure volume controller. The first cylinder of the upper pore pressure volume controller and the second cylinder of the upper pore pressure volume controller are connected side by side, and the first cylinder of the lower pore pressure volume controller and the second cylinder of the lower pore pressure volume controller are connected side by side. When the volume of the first liquid storage chamber of the upper pore pressure volume controller part is at its maximum state, the height of the first liquid storage chamber of the upper pore pressure volume controller part is less than 5 cm; when the volume of the second liquid storage chamber of the upper pore pressure volume controller part is at its maximum state, the height of the liquid storage chamber of the upper pore pressure volume controller part is less than 5 cm; when the volume of the first liquid storage chamber of the lower pore pressure volume controller part is at its maximum state, the height of the first liquid storage chamber of the lower pore pressure volume controller part is less than 5 cm; when the volume of the second liquid storage chamber of the lower pore pressure volume controller part is at its maximum state, the length of the second liquid storage chamber of the lower pore pressure volume controller part is less than 5 cm.

[0028] The locking switching structure of the lower pore pressure volume controller part includes a first fixed lock 55 of the lower pore pressure volume controller part and a second fixed lock 56 of the lower pore pressure volume controller part. The first fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block together with the first piston rod of the lower pore pressure volume controller part, and the second fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block together with the second piston rod of the lower pore pressure volume controller part. Only one of the first fixed lock of the lower pore pressure volume controller part and the second fixed lock of the lower pore pressure volume controller part remains in a locked state at the same time. The first fixed lock of the lower pore pressure volume controller part includes a first locking pin 57 of the lower pore pressure volume controller part hinged on the upper end of the first piston rod of the lower pore pressure volume controller part, a first locking hole 58 of the lower pore pressure volume controller part arranged on the side of the driving block of the lower pore pressure volume controller part, and a first driving cylinder 59 of the lower pore pressure volume controller part for driving the first locking pin of the lower pore pressure volume controller part to insert and pull out of the locking hole of the lower pore pressure volume controller part. When the first locking pin of the lower pore pressure volume controller part is inserted into the first locking hole of the lower pore pressure volume controller part, the piston rod of the lower pore pressure volume controller part is fixed together with the driving block of the lower pore pressure volume controller part; The second fixed lock of the lower pore pressure volume controller includes a second locking pin 60 of the lower pore pressure volume controller hinged on the upper end of the second piston rod of the lower pore pressure volume controller, a second locking hole 61 of the lower pore pressure volume controller arranged on the side of the driving block of the lower pore pressure volume controller, and a second driving cylinder 62 of the lower pore pressure volume controller for driving the second locking pin of the lower pore pressure volume controller to insert and pull out of the locking hole of the lower pore pressure volume controller. When the second locking pin of the lower pore pressure volume controller is inserted into the second locking hole of the lower pore pressure volume controller, the piston rod of the lower pore pressure volume controller is fixed together with the driving block of the lower pore pressure volume controller. A flow meter is used for the upper or lower hole.

Claims

1. A permeability coefficient testing device suitable for unloading seepage conditions, comprising a rubber sleeve for covering a sample, a confining pressure chamber, a water replenishment tank, an upper pore pressure volume controller, a confining pressure volume controller and a lower pore pressure volume controller, the confining pressure chamber comprising a confining pressure chamber base and a confining pressure chamber cover provided with an exhaust valve which is detachably and hermetically connected to the chamber base, the confining pressure chamber base and the confining pressure chamber cover enclose a sealed confining pressure chamber, the confining pressure chamber base is provided with a water replenishment port connected to the water replenishment tank, an upper hole connected to the upper pore pressure volume controller, a lower hole connected to the lower pore pressure volume controller and a confining pressure hole connected to the confining pressure volume controller, a sample support seat and a sample cover are provided in the confining pressure chamber, characterized in that, The confining pressure chamber cover is provided with a pressing block for pressing the sample cover, a pressing block driving structure for driving the pressing block to rise and fall, and a pressing force detector for detecting the pressure exerted by the pressing block on the sample cover. When in use, the rubber sleeve is sleeved on the sample, the sample is placed on the sample support seat and covered with the sample cover, the upper end of the rubber sleeve is sleeved on the sample cover, and the lower end is sleeved on the sample support seat, the water in the water replenishment tank is input into the confining pressure chamber through the water replenishment port to fill the confining pressure chamber, and then the exhaust valve is closed, the confining pressure volume controller pressurizes the confining pressure chamber to the set first side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the first top surface confining pressure value through the pressing block to apply pressure to the top surface of the test, and the water of the set first water inlet pressure is input into the sample through the lower hole through the lower hole through the lower hole pressure volume controller, and the water is output from the upper hole to the upper hole pressure volume controller after penetrating through the sample, and the upper hole pressure volume controller is maintained at the set first water outlet Pressure, calculate the first permeability coefficient according to the existing permeability calculation formula; the confining pressure volume controller pressurizes the confining pressure chamber to the set second side confining pressure value to apply pressure to the surrounding surface of the sample and presses the sample cover to the second top confining pressure value through the pressing block to apply pressure to the top surface of the test, and inputs water of the set second water inlet pressure to the sample through the lower hole through the lower hole through the lower hole pressure volume controller. After the water penetrates through the sample, it is output from the upper hole to the upper hole pressure volume controller and the upper hole pressure volume controller is maintained at the second water outlet pressure received. According to the existing permeability calculation formula, the second permeability coefficient is calculated, and the confining pressure value, input pressure and output pressure are reduced in turn by the same method, so as to obtain the permeability coefficient under various pressures when the sample is depressurized. The top surface of the sample is independently pressurized by water instead of being controlled by the confining pressure volume controller at the same value on the same circumference, so that the pressure on the side and top surfaces of the sample is close to the actual pressure, so that the measured depressurization confining pressure data is more accurate.

2. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 1, characterized in that: The water replenishment tank is provided with a water pump for outputting the water in the water replenishment tank, a vacuum pump for evacuating the water replenishment tank, and a vibrator for causing the water in the water replenishment tank to shake, and the outlet end of the water pump is connected to the water replenishment port.

3. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 1, characterized in that: The lower pore pressure volume controller comprises a three-way valve of the lower pore pressure volume controller, a threaded rod of the lower pore pressure volume controller, a guide rod of the lower pore pressure volume controller, a motor of the lower pore pressure volume controller for driving the threaded rod of the lower pore pressure volume controller to rotate, a driving block of the lower pore pressure volume controller threadedly connected to the threaded rod of the lower pore pressure volume controller, a locking switching structure of the lower pore pressure volume controller, a first cylinder of the lower pore pressure volume controller, a first piston of the lower pore pressure volume controller connected in a sliding seal in the first cylinder of the lower pore pressure volume controller, and one end of the first piston of the lower pore pressure volume controller The first piston rod of the lower pore pressure volume controller part connected together and the other end of which is passed through the lower pore pressure volume controller part driving block, the first pressure sensor of the lower pore pressure volume controller part, the second cylinder of the lower pore pressure volume controller part, the second piston of the lower pore pressure volume controller part which is slidingly sealed and connected in the second cylinder of the lower pore pressure volume controller part, the second piston rod of the lower pore pressure volume controller part which is connected together with the second piston of the lower pore pressure volume controller part and the other end of which is passed through the lower pore pressure volume controller part driving block, and the second pressure sensor of the lower pore pressure volume controller part, the first active part of the lower pore pressure volume controller part The plug is inserted into the first cylinder of the lower pore pressure volume controller to isolate the first liquid storage chamber of the lower pore pressure volume controller. The first pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the first liquid storage chamber of the lower pore pressure volume controller. The first liquid storage chamber of the lower pore pressure volume controller is connected to a branch hole of the three-way valve of the lower pore pressure volume controller. The second piston of the lower pore pressure volume controller is inserted into the second cylinder of the lower pore pressure volume controller to isolate the second liquid storage chamber of the lower pore pressure volume controller. The second pressure sensor of the lower pore pressure volume controller is used to detect the pressure in the second liquid storage chamber of the lower pore pressure volume controller. force, the second liquid storage chamber of the lower pore pressure volume controller is connected with another branch hole of the three-way valve of the lower pore pressure volume controller, the total port of the three-way valve of the lower pore pressure volume controller is connected with the lower hole, the locking switching structure of the lower pore pressure volume controller is used to make the lower pore pressure volume controller drive block only be fixed with one of the first piston rod of the lower pore pressure volume controller and the second piston rod of the lower pore pressure volume controller at the same time, and the guide rod of the lower pore pressure volume controller is penetrated in the drive block of the lower pore pressure volume controller to prevent the drive block of the lower pore pressure volume controller from rotating;The upper pore pressure volume controller comprises an upper pore pressure volume controller three-way valve, an upper pore pressure volume controller threaded rod, an upper pore pressure volume controller guide rod, an upper pore pressure volume controller motor for driving the upper pore pressure volume controller threaded rod to rotate, an upper pore pressure volume controller drive block threadedly connected to the upper pore pressure volume controller threaded rod, an upper pore pressure volume controller first cylinder, an upper pore pressure volume controller first piston slidingly sealed and connected to the upper pore pressure volume controller first cylinder, an upper pore pressure volume controller first piston rod connected to the upper pore pressure volume controller first piston at one end and fixed to the upper pore pressure volume controller drive block at the other end, and an upper pore pressure volume controller The first pressure sensor of the device part, the second cylinder of the upper pore pressure volume controller part, the second piston of the upper pore pressure volume controller part which is connected in a sliding seal in the second cylinder of the upper pore pressure volume controller part, the second piston rod of the upper pore pressure volume controller part which is connected to the second piston of the upper pore pressure volume controller part at one end and fixed to the driving block of the upper pore pressure volume controller part at the other end, and the second pressure sensor of the upper pore pressure volume controller part, the first piston of the upper pore pressure volume controller part isolates the first liquid storage chamber of the upper pore pressure volume controller part in the first cylinder of the upper pore pressure volume controller part, the first pressure sensor of the upper pore pressure volume controller part is used to detect the pressure in the first liquid storage chamber of the upper pore pressure volume controller part, and the upper pore pressure volume controller part The first liquid storage chamber of the upper pore pressure volume controller is connected with a branch hole of the three-way valve of the upper pore pressure volume controller, the second piston of the upper pore pressure volume controller isolates the second liquid storage chamber of the upper pore pressure volume controller in the second cylinder of the upper pore pressure volume controller, the second pressure sensor of the upper pore pressure volume controller is used to detect the pressure in the second liquid storage chamber of the upper pore pressure volume controller, the second liquid storage chamber of the upper pore pressure volume controller is connected with another branch hole of the three-way valve of the upper pore pressure volume controller, the main port of the three-way valve of the upper pore pressure volume controller is connected with the upper hole, and the guide rod of the upper pore pressure volume controller is penetrated in the driving block of the upper pore pressure volume controller to prevent the driving block of the upper pore pressure volume controller from rotating ; The first liquid storage chamber of the lower pore pressure volume controller part is connected with the first liquid storage chamber of the upper pore pressure volume controller part through the first valve, and the second liquid storage chamber of the lower pore pressure volume controller part is connected with the second liquid storage chamber of the upper pore pressure volume controller part through the second valve; when in use, water is delivered through the first liquid storage chamber of the lower pore pressure volume controller part and water is received through the first liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment. After the water in the first liquid storage chamber of the lower pore pressure volume controller part is delivered or the first liquid storage chamber of the upper pore pressure volume controller part is filled, the first valve is opened and water is delivered through the second liquid storage chamber of the lower pore pressure volume controller part and water is received through the second liquid storage chamber of the upper pore pressure volume controller part to perform a permeability coefficient test experiment;The process of resetting the driving block of the lower pore pressure volume controller to drive the second piston rod of the lower pore pressure volume controller resets the first liquid storage chamber of the lower pore pressure volume controller, and the process of resetting the driving block of the upper pore pressure volume controller resets the first liquid storage chamber of the upper pore pressure volume controller and the second liquid storage chamber of the upper pore pressure volume controller, so that the water in the first liquid storage chamber of the lower pore pressure volume controller flows back to the first liquid storage chamber of the upper pore pressure volume controller, and the first valve is closed; after the water in the second liquid storage chamber of the lower pore pressure volume controller is transported or the second liquid storage chamber of the upper pore pressure volume controller is filled, the second valve is opened and the lower pore pressure volume controller is connected. The first liquid storage chamber of the upper pore pressure volume controller is used to send water and the first liquid storage chamber of the upper pore pressure volume controller is used to receive water for the permeability coefficient test experiment; the process of resetting the lower pore pressure volume controller driving block to drive the first piston rod of the lower pore pressure volume controller resets the second liquid storage chamber of the lower pore pressure volume controller, and the process of resetting the upper pore pressure volume controller driving block resets the second liquid storage chamber of the upper pore pressure volume controller and the first liquid storage chamber of the upper pore pressure volume controller, so that the water in the second liquid storage chamber of the lower pore pressure volume controller flows back to the second liquid storage chamber of the upper pore pressure volume controller, and the second valve is closed; repeat the above process to test the sample of the uninterrupted permeability system. ; 4. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 3, characterized in that: The first piston of the upper pore pressure volume controller part is located at the upper end of the first cylinder of the upper pore pressure volume controller part, the second piston of the upper pore pressure volume controller part is located at the upper end of the second cylinder of the upper pore pressure volume controller part, the first piston of the lower pore pressure volume controller part is located at the upper end of the first cylinder of the lower pore pressure volume controller part, and the second piston of the lower pore pressure volume controller part is located at the upper end of the second cylinder of the lower pore pressure volume controller part.

5. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 3 or 4, characterized in that: The first cylinder of the upper pore pressure volume controller part and the second cylinder of the upper pore pressure volume controller part are connected side by side, and the first cylinder of the lower pore pressure volume controller part and the second cylinder of the lower pore pressure volume controller part are connected side by side.

6. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 2 or 3, characterized in that: When the volume of the first liquid storage chamber of the upper pore pressure volume controller part is at its maximum state, the height of the first liquid storage chamber of the upper pore pressure volume controller part is less than 5 cm; when the volume of the second liquid storage chamber of the upper pore pressure volume controller part is at its maximum state, the height of the liquid storage chamber of the upper pore pressure volume controller part is less than 5 cm; when the volume of the first liquid storage chamber of the lower pore pressure volume controller part is at its maximum state, the height of the first liquid storage chamber of the lower pore pressure volume controller part is less than 5 cm; when the volume of the second liquid storage chamber of the lower pore pressure volume controller part is at its maximum state, the length of the second liquid storage chamber of the lower pore pressure volume controller part is less than 5 cm.

7. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 2 or 3, characterized in that: The locking switching structure of the lower pore pressure volume controller part includes a first fixed lock of the lower pore pressure volume controller part and a second fixed lock of the lower pore pressure volume controller part. The first fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block together with the first piston rod of the lower pore pressure volume controller part, and the second fixed lock of the lower pore pressure volume controller part is used to fix the lower pore pressure volume controller part drive block together with the second piston rod of the lower pore pressure volume controller part. Only one of the first fixed lock of the lower pore pressure volume controller part and the second fixed lock of the lower pore pressure volume controller part remains in a locked state at the same time.

8. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 7, characterized in that: The first fixed lock of the lower pore pressure volume controller part comprises a first locking pin of the lower pore pressure volume controller part hinged on the upper end of the first piston rod of the lower pore pressure volume controller part, a first locking hole of the lower pore pressure volume controller part arranged on the side of the driving block of the lower pore pressure volume controller part, and a first driving cylinder of the lower pore pressure volume controller part for driving the first locking pin of the lower pore pressure volume controller part to insert and pull out of the locking hole of the lower pore pressure volume controller part. When the first locking pin of the lower pore pressure volume controller part is inserted into the first locking hole of the lower pore pressure volume controller part, the piston rod of the lower pore pressure volume controller part is fixed together with the driving block of the lower pore pressure volume controller part; The second fixed lock of the lower pore pressure volume controller part includes a second locking pin of the lower pore pressure volume controller part hinged on the upper end of the second piston rod of the lower pore pressure volume controller part, a second locking hole of the lower pore pressure volume controller part arranged on the side of the driving block of the lower pore pressure volume controller part, and a second driving cylinder of the lower pore pressure volume controller part driving the second locking pin of the lower pore pressure volume controller part to insert and pull out the locking hole of the lower pore pressure volume controller part. When the second locking pin of the lower pore pressure volume controller part is inserted into the second locking hole of the lower pore pressure volume controller part, the piston rod of the lower pore pressure volume controller part is fixed together with the driving block of the lower pore pressure volume controller part.

9. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 1, 2 or 3, characterized in that: It also includes a confining pressure chamber pressure sensor that inputs into the bottom of the specimen to check the water inlet pressure.

10. A permeability coefficient testing device suitable for unloading seepage conditions according to claim 1, 2 or 3, characterized in that: The upper port or the lower hole uses a flow meter.

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