Seepage experimental device of layered low-permeability system and in-situ permeability coefficient measuring method

Abstract

This invention provides a seepage experimental apparatus for a layered low-permeability system and a method for in-situ determination of permeability coefficient, relating to the field of layered media seepage technology. The seepage experimental apparatus for a layered low-permeability system includes: a fixing unit, a pressure stabilizing unit, an overflow unit, a monitoring unit, and a data acquisition unit. The fixing unit includes a side-confining column and several independent sub-settling devices. Each independent sub-settling device includes a settling plate, a rotating shaft, and a settling rod. The settling plate includes several settling plate blades, which are stacked and engaged on the rotating shaft and can rotate independently around the shaft. One end of the settling rod is connected to the rotating shaft, and the settling plate, along with one end of the settling rod, is inserted into the interior of the side-confining column. The other end of the settling rod extends beyond the top of the side-confining column. The seepage experimental apparatus for a layered low-permeability system provided by this invention can easily achieve in-situ acquisition of the permeability coefficient of each layer of a layered low-permeability medium and long-term, continuous, and high-precision monitoring of seepage flow.

Description

Technical Field

[0001] This invention relates to the field of layered media seepage technology, specifically to a seepage experimental apparatus for a layered low-permeability system and a method for in-situ determination of the permeability coefficient. Background Technology

[0002] Saturated soil and rock masses will experience seepage deformation under conditions of hydraulic head difference or pore water extraction. Groundwater is a recyclable resource; if the amount of groundwater extracted is less than its recharge, the extracted groundwater can be replenished and regenerated. However, if the amount of groundwater extracted exceeds the recharge under the extraction conditions, it will cause a drop in the groundwater level. For saturated soil and rock masses, when a hydraulic head difference exists, pore water is gradually discharged. According to the effective stress principle, the stress in a material consists of two parts: pore water pressure and effective stress. As pore water decreases, the pore water pressure is gradually borne by the effective stress of the soil skeleton, ultimately causing deformation of the strata. Traditional and currently available consolidated seepage devices can only conduct tests on homogeneous media. Although some devices can monitor continuous deformation, they are not suitable for layered media or geological bodies with irregular interlayered structures. Furthermore, they cannot obtain accurate seepage flow rates and in-situ permeability coefficients for low-permeability media.

[0003] In current seepage deformation calculations, a series of parameters of the soil and rock mass are typically determined through laboratory tests, and then solved using differential equations based on seepage consolidation theory. However, traditional consolidation instruments and calculation models employ approximations, neglecting the distribution characteristics of soil and rock strata parameters. Furthermore, traditional and current consolidation instruments are inadequate for testing complex layered media, and for low-permeability media, accurate seepage flow rates are difficult to obtain. In-situ methods for obtaining permeability coefficients for each layer are also unresolved. These factors contribute to significant discrepancies between calculated and experimental data. Therefore, developing a testing method under different hydraulic head conditions to study the trends in permeability coefficients, permeability, and deformation of complex layered geological bodies in the vertical direction, and investigating their regularities, would be of significant guiding importance for engineering project construction, underground fluid resource extraction, and monitoring of heterogeneous ground settlement. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a seepage test apparatus for a layered low-permeability system and an in-situ method for measuring the permeability coefficient, in order to solve at least one of the following problems: performing deformation tests on layered low-permeability media, obtaining accurate seepage flow for layered low-permeability media, and obtaining the permeability coefficient in situ.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a seepage experimental apparatus for a layered low-permeability system, comprising: a fixed unit, a pressure stabilizing unit, an overflow unit, a monitoring unit, and a data acquisition unit; the pressure stabilizing unit is used to supply water to the fixed unit, the overflow unit is used to overflow water from the fixed unit for conducting an overflow mode experiment, the monitoring unit is used to monitor the pore water pressure and deformation data of the layered low-permeability system, as well as the drainage volume of the overflow unit and the fixed unit, and the data acquisition unit is communicatively connected to the monitoring unit; wherein...

[0007] The fixed unit includes a side-confining column and several independent sub-settling devices for testing each layer of the low-permeability system. Each independent sub-settling device includes a settling plate, a rotating shaft, and a settling rod. The settling plate includes several settling plate blades, which are stacked and locked onto the rotating shaft and can rotate independently around the rotating shaft. One end of the settling rod is connected to the rotating shaft. The settling plate and one end of the settling rod are inserted into the interior of the side-confining column, and the other end of the settling rod extends out of the top of the side-confining column. A top overflow port is provided on the upper side wall of the side-confining column.

[0008] Preferably, the rotating shaft is hinged to one end of the settling rod.

[0009] Preferably, in the same independent sub-settling device, the number of settling plate blades is 2 to 8.

[0010] Preferably, in the same independent sub-settling device, the shape of the settling plate blades is the same.

[0011] Preferably, in the same independent sub-settling device, the radius r of the settling plate fan blades is the same or different, and each is independently 3-5cm.

[0012] Preferably, the settling plate fan blades are provided with several through holes.

[0013] Preferably, in the same independent sub-settling device, when the settling plate blades overlap, the through holes on adjacent settling plate blades are arranged in an alternating pattern.

[0014] Preferably, the overflow unit includes an overflow trough that can move up and down, a bottom drain outlet is provided at the bottom of the side limiting column, the overflow trough is connected to the bottom drain outlet, and an overflow outlet is provided at the upper part of the overflow trough.

[0015] Preferably, the side wall of the side limiting column is provided with a plurality of drainage outlets arranged longitudinally from bottom to top, and the drainage outlets are arranged at equal intervals.

[0016] Preferably, the monitoring unit includes a water pressure sensor for monitoring the pore water pressure of the layered low-permeability system. The water pressure sensor is disposed on the side wall of the side confinement column and is symmetrical to the drain outlet.

[0017] Preferably, the monitoring unit includes a micro-flow continuous monitoring device, which is used to monitor the drainage volume of the overflow unit and / or the drainage volume of the fixed unit; the micro-flow continuous monitoring device is located below the overflow outlet of the overflow trough and / or below the drain outlet.

[0018] Preferably, the micro-flow continuous monitoring device includes a funnel, a support frame, a weighing wheel, a drainage trough, a weighing device, and a weighing shaft. The funnel is disposed on top of the support frame to receive fluid. The weighing wheel is vertically disposed below the funnel. One end of the weighing shaft is rotatably hinged to the weighing wheel, and the other end of the weighing shaft is supported on the weighing device. Several weighing grooves are provided on the outer circumferential surface of the weighing wheel, and the drainage trough is disposed below the weighing wheel.

[0019] Preferably, the monitoring unit further includes a displacement sensor for monitoring deformation data of the layered low-permeability system, the displacement sensor being connected to one end of the settlement rod extending from the top of the lateral confinement column.

[0020] Secondly, the present invention provides a seepage deformation testing method, which is performed in a seepage test apparatus for the layered low-permeability system, the method comprising the following steps:

[0021] Step 1: Fill the lateral confinement column with water and a layered low-permeability system, and place an independent sub-sedimentation device on the upper surface of each layer of low-permeability system;

[0022] Step 2: Apply negative pressure inside the side confinement column;

[0023] Step 3: Only when the top overflow outlet can drain water, the pressure stabilizing unit supplies water to the side confinement column. Excess water flows out from the top overflow outlet of the side confinement column. The monitoring unit records the pore water pressure data and the deformation data of the layered low-permeability system until the pore water pressure at each position in the side confinement column is the same as the hydrostatic pressure at that position and the deformation does not change at different burial depths.

[0024] Step 4: Activate the overflow unit to enter overflow mode, adjust the overflow height of the overflow unit, and during the overflow mode, the monitoring unit records the changes in pore water pressure at different locations of the layered low-permeability system and the deformation data of each layer of medium in real time until the excess pore water pressure is completely dissipated and the deformation of the target soil layer remains unchanged.

[0025] Preferably, the method further includes step 5: obtaining the permeability coefficient, stopping the overflow height change of the overflow unit, opening the drain outlets corresponding to the locations of the layered low-permeability system to be tested, measuring the seepage flow of each layer of medium through a micro-flow continuous monitoring device located below the opened drain outlet, and finally calculating the in-situ permeability coefficient based on Darcy's law. The calculation formula for constant head is shown in Formula 1, and the calculation formula for variable head is shown in Formula 2.

[0026]

[0027]

[0028] In Formula 1 and Formula 2: K v ′ represents the effective permeability coefficient (LT) -1 ); K v For the uncorrected permeability coefficient (LT) -1 Q is the seepage flow rate per unit time (L). 3 T -1 ); l is the total thickness of the medium (L); Δh is the head difference between the upper and lower boundaries (L); A is the cross-sectional area of ​​the layered medium (L). 2 );k n is the calibration coefficient for the permeability coefficient, which is related to the medium characteristics; for this example, the empirical value is taken as 7.5; 'a' is the cross-sectional area (L) of the variable head pipe. 2 ); t1 and t2 are the start and end times (T); H1 and H2 are the start and end heads (L);

[0029] Preferably, in step 2, the negative pressure is -0.02 to -0.1 MPa.

[0030] Beneficial effects:

[0031] The seepage experimental device for layered low-permeability systems provided by this invention can easily achieve in-situ acquisition of the permeability coefficient of each layer of the layered low-permeability medium and long-term, continuous, and high-precision monitoring of the seepage flow. It can obtain the variation law of parameters such as the regional deformation, seepage flow, and permeability coefficient of the saturated layered medium in the vertical direction under various head difference conditions, providing effective data and experimental support for the one-dimensional seepage deformation problem of saturated layered low-permeability media. Attached Figure Description

[0032] Figure 1 A schematic diagram of the seepage test apparatus for the layered low-permeability system provided by the present invention;

[0033] Figure 2The diagram shows the structure of the independent sub-settlement device provided by the present invention; wherein, (a) is a side view, (b) is a schematic diagram of the settlement plate without rotation and folding, (c) is a schematic diagram of the settlement plate partially rotated and folded, and (d) is a schematic diagram of the settlement plate fully rotated and folded.

[0034] Figure 3 A schematic diagram of the layered low-permeability system provided by the present invention; wherein, (a) is an irregular lens body, and (b) is a complex angled interlayer;

[0035] Figure 4 The following is a schematic diagram of simulated boundary conditions provided for this invention: (a) a V-shaped water level change that continuously increases or decreases with constant acceleration; (b) a U-shaped water level change in which the load increases or decreases instantaneously at maximum acceleration; and (c) a sinusoidal wave water level change under the influence of tides.

[0036] Figure 5 This is a schematic diagram of the micro-flow continuous monitoring device provided by the present invention;

[0037] Among them, 1-constant pressure and constant flow pump; 2-water tank; 3-top support beam; 4-displacement sensor; 5-top vent; 6-independent sub-sedimentation device; 7-water pressure sensor; 8-side limiting column; 9-connecting wire; 10-filter layer; 11-bottom sealing plate; 12-top inlet; 13-top sealing plate; 14-drainage outlet; 15-drainage valve; 16-layered low-permeability system; 17-bottom drainage outlet; 18-support column; 19-hub; 20-data acquisition end; 21-base; 22-computer; 23-... - Overflow trough; 24- Micro-flow continuous monitoring device; 25- Controllable motor; 26- Threaded column; 27- Top overflow port; 28- Moving platform; 61- Settling plate; 62- Rotating shaft; 63- Limiting device; 64- Settling rod; 611- Settling plate blade; 612- Through hole; 241- Funnel; 242- Support frame; 243- Weighing wheel; 244- Drainage trough; 245- Weighing device; 246- Foot; 247- Flow meter; 248- Data acquisition end; 249- Weighing shaft; 2431- Weighing trough. Detailed Implementation

[0038] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0039] This invention aims to disclose a seepage device for complex layered low-permeability systems and an experimental method for determining the in-situ permeability coefficient. It can be used to study complex layered rock and soil masses. Firstly, it can simulate various hydraulic head conditions and obtain high-precision data on the permeability coefficient, permeability, and deformation of each stratum in the vertical direction in real time. Studying its regularity has important guiding significance for engineering project construction, underground fluid resource extraction, and monitoring of heterogeneous ground settlement.

[0040] Firstly, referring to Figure 1 This invention provides a seepage experimental device for a layered low-permeability system, comprising: a fixing unit, a pressure stabilizing unit, an overflow unit, a monitoring unit, and a data acquisition unit, wherein...

[0041] The fixing unit serves as the main structure of the experimental device, supporting the layered hypopermeable system 16 and also providing support and fixation for the overall structure of the experimental device.

[0042] The pressure stabilizing unit is used to supply water to the stationary unit and plays a role in stabilizing the pressure during the experiment.

[0043] The overflow unit is connected to the fixed unit and is used to overflow and drain water from the fixed unit to realize the overflow mode experiment;

[0044] The monitoring unit is used to monitor various tests of the experimental setup. Specifically, it can monitor the pore water pressure and deformation data of the layered low-permeability system, the water flow rate of the overflow unit, and the drainage volume of the stationary unit during the acquisition of the permeability coefficient.

[0045] The data acquisition unit communicates with the monitoring unit. The monitoring unit can be connected to the data acquisition unit via a connection line to collect and record data.

[0046] In some specific embodiments of the present invention, the fixing unit includes a side-limiting column 8 and more than one independent sub-settling device 6. The side-limiting column 8 is made of transparent acrylic material, is hollow, open at the top and bottom and can be sealed. The height of the side-limiting column 8 is 50-70cm, preferably 60cm, and the diameter is 15-25cm, preferably 20cm. The upper side wall of the side-limiting column 8 is provided with a top overflow port 27. The independent sub-settling device 6 is vertically inserted into the interior of the side-limiting column 8 and can move up and down. Each independent sub-settling device 6 is set separately from each other and does not interfere with each other. Specifically, it can be set at the corresponding position of each layer of medium in different layered low-permeability systems.

[0047] In some specific embodiments of the present invention, the structure of the independent sub-sedimentation device 6 is as follows: Figure 2 As shown, refer to Figure 2The independent sub-settling device 6 includes a settling plate 61, a rotating shaft 62, and a settling rod 64. The settling plate 61 includes more than one settling plate blade 611, which are stacked and respectively engaged with the rotating shaft 62. The settling plate blade 611 can rotate 360° around the center of the rotating shaft 62. One end of the settling rod 64 is connected to the rotating shaft 62. The settling plate 61 together with one end of the settling rod 64 is inserted into the interior of the side limiting post 8, and the other end of the settling rod 64 extends out of the top of the side limiting post 8.

[0048] In this invention, the settling plate fan blade 611 and the rotating shaft 62 can be connected by a snap-fit ​​connection, in which the settling plate fan blade 611 and the rotating shaft 62 are tightly fitted together and installed, and the rotation and fixation of the settling plate fan blade 611 are achieved by friction.

[0049] In some specific embodiments of the present invention, the number of settling plate blades 611 in the same independent sub-settling device 6 can be 2-8, for example 3, 4, 5, 6, 7, etc.

[0050] In some specific embodiments of the present invention, the rotating shaft 62 and the settling rod 64 are hinged in such a way that the rotating shaft 62 can tilt and rotate up and down, thereby realizing the tilting and rotation of the settling plate 61 up and down.

[0051] In some specific embodiments of the present invention, the settling plate blades 611 in the same independent settling device 6 have the same shape, for example, they can be semicircles, quarter circles, etc.

[0052] In some specific embodiments of the present invention, in the same independent sub-settling device 6, the radius r of the settling plate fan blades 611 is the same or different, and each is 3-5cm independently; preferably, the radius r of the uppermost settling plate fan blade 611 near the settling rod 64 is 3-5cm, and the radius r of the stacked settling plate fan blades (611) decreases sequentially according to the folding path, and the difference in radius r of the successively decreasing settling plate fan blades 611 is 1-3mm.

[0053] In some specific embodiments of the present invention, the thickness of the settling plate fan blade 611 is 1-3 cm.

[0054] In some specific embodiments of the present invention, a plurality of through holes 612 are provided on the settling plate fan blade 611, the diameter of which can be 1-3mm, for example 1, 2, 3mm, etc. In the same independent sub-settling device 6, after the settling plate fan blade 611 is rotated and folded, the through holes 612 of the overlapping settling plate fan blade 611 are arranged in an alternating manner, and the adaptable round holes can be arranged in various layers according to requirements.

[0055] In some specific embodiments of the present invention, the independent sub-settling device 6 may further include a position limiting device 63, which may be disposed at the top end of the settlement rod 64 extending out of the side limiting post 8, and restricts the position movement of the independent sub-settling device 6 when necessary.

[0056] In this invention, to address complex layered media, the experimental setup includes multiple independent sub-settlement devices 6. The lateral confinement columns 8 are filled from top to bottom with soils of varying structures and properties. The independent sub-settlement devices 6 can be embedded at any location within each soil layer (interfaces between different strata, specific locations within a single soil layer, boundaries of irregular lenses, etc.), enabling real-time monitoring of deformation and settlement in different soil layers. To meet the requirements for precise measurement of complex layered media, this invention provides independent sub-settlement devices, different from traditional settlement plates. These devices can accurately locate complex media interfaces, and their large number can meet the monitoring needs of different layered media. In this invention, the independent sub-settlement devices 6 can:

[0057] (1) Allows for rotation at any angle: Based on the rotation axis 62, specifically, the setting of the rotation axis 62 allows the settling plate 61 to tilt and rotate up and down, or rotate 360°.

[0058] (2) Arbitrary depth positioning: Based on the position limiting device 63, specifically, during the filling of the layered low-permeability system, independent sub-settling devices 6 can be set on the top of different layered media, and the setting of the position limiting device 63 makes it possible to set the independent sub-settling devices 6 at any position.

[0059] (3) Positioning complex-shaped media: Based on the adjustable area, specifically, when different numbers of settling plate fan blades 611 are folded, the area of ​​the settling plate 6 is different, which can position media of various complex shapes.

[0060] (4) Adaptive permeability: The settling plate 61 has evenly spaced regular circular holes. When different numbers of settling plate blades 611 are folded, the permeability decreases accordingly. For example, refer to... Figure 2 The settling plate 6 is equipped with four settling plate blades 611, each of which can be folded. Furthermore, the positions of the through holes 612 in each settling plate blade 611 overlap. Therefore, when folded, the permeability of the settling plate decreases, resulting in three permeability gradients: ① without folding, corresponding to... Figure 2 (b) in the middle; ② semicircle, corresponding to Figure 2 (c) in the middle; ③ 1 / 4 circle, corresponding to Figure 2 In (d), the permeability decreases accordingly.

[0061] This invention can be considered for complex layered systems composed of different rocks, soils, filling media, etc., such as Figure 3As shown. To accurately determine the interfaces between different layered media, such as in sand-mud interlayer structures with mixed gradient zones and small-area irregular interlayers or non-horizontal soil layers, this invention utilizes acrylic transparent side-confining columns 8 to precisely determine the location of complex interfaces. Simultaneously, the independent sub-settlement device 6 enables segmented and independent measurements. The design of the independent sub-settlement device 6 facilitates material filling. A positioning device 63 is provided on the settlement rod. During installation, the positioning device 63 fixes the settlement plate 61 to the surface of the pre-buried first type of medium. Then, the second type of medium is filled, and after reaching a certain thickness, the positioning device 63 of the settlement rod 6 confines it to the surface of the second type of medium, and so on. Meanwhile, for complex interfaces (such as small-area interlayers and non-horizontal soil layers), the independent sub-settlement device 6 can be precisely set on the required irregular interface. The independent sub-settlement device 6 of the present invention has a large coverage area, which can flexibly and accurately limit and lock the interface between small-area interlayers and non-horizontal soil layers. Therefore, such a design satisfies the complex layered media envisioned in the present invention and satisfies other situations not limited to those envisioned in this application.

[0062] In some specific embodiments of the present invention, the bottom of the side limiting column 8 is provided with a bottom drain outlet 17, the overflow unit includes an overflow trough 23, the overflow trough 23 is movable up and down and communicates with the bottom drain outlet 17, and the upper part of the overflow trough 23 is also provided with an overflow outlet.

[0063] In some specific embodiments of the present invention, the monitoring unit includes a micro-flow continuous monitoring device 24, which can be installed below the overflow outlet of the overflow tank 23 to monitor the drainage volume of the overflow tank 23.

[0064] In some specific embodiments of the present invention, such as Figure 5 As shown, the micro-flow continuous monitoring device 24 provided by the present invention includes a funnel 241, a support frame 242, a weighing wheel 243, a drainage trough 244, a weighing device 245, and a weighing shaft 249.

[0065] In some specific embodiments of the present invention, a funnel 241 is disposed on top of a support frame 242 for receiving water flow from the overflow outlet of an overflow trough 23, a rotating wheel 243 is vertically disposed below the funnel 241 for weighing the water flow received by the funnel 241, and a plurality of weighing grooves 2431 are provided on the outer circumferential surface of the rotating wheel 243; a drainage trough 244 is disposed below the rotating wheel 243, and the drainage trough 244 can be a sloping design to allow water to be discharged more smoothly.

[0066] In some specific embodiments of the present invention, the weighing shaft 249 is hinged to the rotating wheel 243 and supported on the weighing device 245.

[0067] In some specific embodiments of the present invention, a foot 246 may also be provided at the bottom of the support frame 242 to support and adjust the balance of the support frame 242.

[0068] In some specific embodiments of the present invention, a flow meter 247 may also be installed at the outlet of the drainage trough 244, which can acquire the micro-flow medium a second time while the weighing device 245 is measuring, thereby further ensuring the accuracy of the device monitoring.

[0069] In some specific embodiments of the present invention, the weighing device 245 or the flow meter 247 may be connected to the acquisition terminal 248 or to the data acquisition unit.

[0070] In some specific embodiments of the present invention, the side wall of the side limiting column 8 is provided with more than one drain outlet 14 from bottom to top. The drain outlets 14 are arranged at equal intervals. The number of drain outlets 14 can be 8-11, such as 8, 9, 10, 11, etc. The distance between two adjacent drain outlets 14 is 2-4cm, such as 2, 3, 4cm, etc. In the present invention, when filling the layered system, the drain outlets 14 should be kept to correspond to different layered media as much as possible. For example, 1-2 drain outlets are in the same layer of media.

[0071] In some specific embodiments of the present invention, the micro-flow continuous monitoring device 24 can be installed below the drain outlet 14 to monitor the drainage volume of the drain outlet 14. That is, in the present invention, multiple micro-flow continuous monitoring devices 24 can be installed and placed below the drain outlet where the drainage volume needs to be measured, or only one device can be installed and its position can be moved to monitor the water volume when needed.

[0072] In some specific embodiments of the present invention, the pressure stabilizing unit includes a constant pressure and constant flow pump 1 and a water tank 2 connected to each other, and the water tank 2 is connected to the side limiting column 8.

[0073] In some specific embodiments of the present invention, the monitoring unit further includes a water pressure sensor 7 and a displacement sensor 4. The water pressure sensor 7 is disposed on the side wall of the side limiting column 8 and is symmetrical to the drain outlet 14. The displacement sensor 4 is connected to one end of the settling rod 64 of the independent sub-settling device 6 that extends out of the side limiting column 8.

[0074] This invention introduces a micro-flow continuous monitoring device 6. Since the seepage flow of a low-permeability system is extremely small, traditional and existing metering devices are insufficient for continuous and accurate measurement of micro-flow. Therefore, the micro-flow continuous monitoring device 6 is provided. It collects the micro-flow liquid through a funnel 241 and weighs it with high precision via a weighing wheel 243 connected to the weighing shaft 249 in the weighing device 245, ensuring structural stability and long-term monitoring capability. When the weighing trough 2431 in the weighing wheel 243 reaches 1 / 3 of the weighing range of the weighing device 245, the weighing wheel 243 rotates 45° for alternating cumulative weighing. Simultaneously, a drainage trough 244 at the bottom collects the trace fluid flowing out of the weighing wheel 243 due to rotation. Because the drainage trough 244 is designed with a sloping bottom, the flow meter 247 performs a secondary acquisition of the micro-flow medium while the weighing device 245 is measuring, further ensuring the accuracy of the device's monitoring.

[0075] In this invention, in order to target low-permeability or ultra-low-permeability (whose permeability coefficient ranges from 10) -4 cm / s-10 -7 The present invention designs a monitoring unit including several pore water pressure sensors 7. The pore water pressure sensors 7 are arranged longitudinally from top to bottom along the side wall of the side confinement column 8. On the other side wall, several drainage holes 14 are also symmetrically arranged from top to bottom. This allows for independent and targeted measurement of the permeability coefficient of each stratum without changing the in-situ state of the soil, based on the characteristics of soil with different particle sizes, by selecting an appropriate seepage mode (i.e., free selection and alternating measurement of constant head seepage test and variable head seepage test).

[0076] In some specific embodiments of the present invention, the fixing unit may further include a support column 18, a top support beam 3, and a base 21. The side limiting column 8 is vertically arranged on the base 21, and the support column 18 is arranged on both sides of the side limiting column 8 and is vertically connected to the top support beam 3.

[0077] In some specific embodiments of the present invention, a top sealing plate 13 may be provided at the upper end of the side limiting post 8 and a bottom sealing plate 11 may be provided at the lower end, so that the side limiting post 8 can be sealed from top to bottom, and the simulated layered medium can be better buried.

[0078] In some specific embodiments of the present invention, the independent sub-settling device 6 can be inserted into the interior of the side limiting column 8 through the top sealing plate 11 and can move up and down.

[0079] In some specific embodiments of the present invention, the bottom sealing plate 11 may have a bottom drain outlet 17 that communicates with the interior of the side limiting post 8.

[0080] In some specific embodiments of the present invention, the top sealing plate 13 is provided with a top vent 5 and a top water inlet 12, both of which are in communication with the interior of the side limiting post 8.

[0081] In some specific embodiments of the present invention, the constant pressure and constant flow pump 1 and the water tank 2 are installed above the load-bearing beam 3, and the water tank 2 is connected to the top water inlet 12 of the top sealing plate 11. The constant pressure and constant flow pump 1 is connected to the water tank 2.

[0082] In some specific embodiments of the present invention, the base 21 is provided with four adjustable feet, and the height of each foot can be adjusted by a level to ensure that the device is placed horizontally.

[0083] In some specific embodiments of the present invention, a movable platform 28 may be provided on the support column 18, which can move up and down along the support column 18. Specifically, the movable platform 28 may be connected to a controllable motor 25, and move up and down under the control of the controllable motor 25. More specifically, a threaded column 26 is vertically provided on the upper surface of the movable platform 28, and the threaded column 26 is connected to the controllable motor 25, thereby realizing the up and down movement of the movable platform 28.

[0084] In some specific embodiments of the present invention, the overflow trough 23 is connected to the bottom drain outlet 17 of the bottom sealing plate 11, and the overflow trough 23 and the micro-flow continuous monitoring device 24 are installed on the mobile platform 28.

[0085] In some specific embodiments of the present invention, the data acquisition system includes a connecting cable 9, a hub 19, a data acquisition terminal 20 and a computer 22 connected in sequence. The connecting cable 9 can be connected to a water pressure sensor 7, a displacement sensor 4 and a micro-flow continuous monitoring device 24.

[0086] In some embodiments of the present invention, a filter layer 10 may be provided at the bottom of the interior of the side limiting column 8 to prevent the filling medium from clogging the bottom drain outlet 17.

[0087] The device provided by this invention can be used to study complex layered low-permeability rock and soil masses. Firstly, it can simulate various hydraulic head environmental conditions, and by controlling the water supply and overflow units, different hydraulic head changes and fluctuation patterns can be obtained, such as... Figure 4 As shown in the figure. Simultaneously, high-precision data on the permeability coefficient, permeability, and deformation of various strata in the vertical direction can be obtained in real time. Studying their regularity has important guiding significance for engineering project construction, underground fluid resource extraction, and heterogeneous ground settlement monitoring.

[0088] In summary, the device provided by this invention can continuously and accurately monitor micro-flow systems or media, and can obtain in-situ seepage flow rates of different layered low-permeability media based on vertically distributed drainage outlets within the error range, providing data support for obtaining in-situ permeability coefficients.

[0089] Secondly, this invention provides a method for testing seepage deformation in complex layered media and a method for in-situ determination of permeability coefficient, comprising the following steps:

[0090] Step 1: Fill the lateral confinement column 8 with water and a layered low-permeability system, and place an independent sub-sedimentation device 6 on the upper surface of each layer of low-permeability system;

[0091] Step 2: Apply negative pressure inside the side limiting column 8;

[0092] Step 3: Only when the top overflow port 27 can drain water, the pressure stabilizing unit supplies water to the side confinement column 8. Excess water flows freely out from the top overflow port 27 of the side confinement column. Record the data of the water pressure sensor 7 and the displacement sensor 4 until the pore water pressure at each position in the side confinement column 8 is the same as the hydrostatic pressure at that position and the deformation at different burial depths does not change significantly. Then, the preparation stage of the test is considered to be completed and the system has reached the stable state before the load stage (step 4).

[0093] Step 4: Activate the overflow drainage of the overflow unit to enter the overflow mode (open the bottom drain 17), adjust the overflow height of the overflow unit, for example, by moving the overflow trough 23 up and down to achieve the overflow mode. During the overflow mode, record the data of water pressure sensor 7 and displacement sensor 4 at different positions in real time until the excess pore water pressure is basically completely dissipated and the deformation of the target soil layer remains basically unchanged (the total deformation per hour is less than 0.05 mm). Then the system is considered to have reached the stable state of the water level environment at the upper and lower boundaries.

[0094] Step 5: Obtain the permeability coefficient. After reaching the stable state described in Step 4, stop the overflow height change of the overflow unit. Open the valves of the single drain outlet 14 corresponding to the side confinement column 8 and the layered low-permeability system under test, respectively. Measure the seepage flow of each layer of medium multiple times using the micro-flow continuous monitoring device 24 below the drain outlet 14. Finally, calculate the in-situ permeability coefficient based on Darcy's law. The calculation formula for constant head is shown in Formula 1, and the calculation formula for variable head is shown in Formula 2.

[0095]

[0096] In Formula 1 and Formula 2: K v ′ represents the effective permeability coefficient (LT) -1 ); K v For the uncorrected permeability coefficient (LT) -1 Q is the seepage flow rate per unit time (L). 3 T -1 ); l is the total thickness of the medium (L); Δh is the head difference between the upper and lower boundaries (L); A is the cross-sectional area of ​​the layered medium (L). 2 );k nis the calibration coefficient for the permeability coefficient, which is related to the medium characteristics; for this example, the empirical value is taken as 7.5; 'a' is the cross-sectional area (L) of the variable head pipe. 2 ); t1 and t2 are the start and end times (T); H1 and H2 are the start and end heads (L).

[0097] In this invention, the in-situ permeability coefficient measurement method includes constant head and constant head, which can be alternately selected based on the permeability of different layered media, so as to obtain accurate permeability coefficient without damaging the in-situ environment of the layered media.

[0098] In some specific embodiments of the present invention, in step 2, the negative pressure is -0.02 to -0.1 MPa.

[0099] In some specific embodiments of the present invention, in step 4, whether the overflow port 27 is opened depends on the setting of the upper boundary water level. If a fixed water level is set, the overflow port is opened; otherwise, it is closed.

[0100] In this invention, the height of the overflow trough 23 in step 5 is not limited, as long as it is not lower than the height of the reverse filter layer 10.

[0101] In some specific embodiments of the present invention, the specific steps of the in-situ permeability coefficient determination method provided by the present invention are as follows:

[0102] (1) Check the test platform: First, we should ensure that all valves, pipelines and sensor ports are sealed and unobstructed; all types of sensors can collect and transmit data normally; and the computer interface of the measurement and control system can control the start, pause and end of the test platform normally.

[0103] (2) Filling the Layered Low-Permeability System: Clean the soil column system, especially the inner wall of the acrylic side-confining column 8, ensuring it is smooth and dry. Then, evenly apply a layer of petroleum jelly to the inner wall. The purpose is to ensure that the filled layered system completely adheres to the inner wall of the side-confining column, eliminating preferential flow channels and reducing frictional resistance between the inner wall and the soil layer. Then, slowly inject boiled pure water into the side-confining column through the valve of the bottom drain outlet 17, raising the water level to slightly above the designed filling medium thickness. Remove the medium, which consists of gravel, sand, clay, etc., that has been pre-immersed in pure water to form a complex layered system. Then, according to the experimental design, fill in different media sequentially, with each medium slowly filled underwater into the designed area of ​​the side-confining column 8. During the water injection and filling process, we should pay attention to the air bubble retention in the layered system while filling each layer of medium and try to avoid this situation as much as possible, especially in strata with larger particle sizes. After the bottom gravel layer is filled, it is pre-compacted and allowed to stand for 12 hours. Filter screens are installed between adjacent soil layers to ensure normal flow of pore water while reducing the loss of fine particles. During the backfilling of low-permeability media, a lateral confinement column is required for 12 hours after every 5cm of filling. Due to variations in the thickness of each media layer in different experimental designs, and the presence of complex and irregular lenticular bodies... Figure 3 [a] and low-permeability interlayers exhibiting different dip angles [ Figure 3 [b] requires the use of multiple independent sub-settling devices 6 developed in this invention. In order to ensure the accuracy of deformation measurement of each layer of medium, if the test medium is irregular or has an arbitrary tilt angle during the entire test process, the fan blades of the settling plate can be adjusted to ensure the contact area between the settling plate and the complex medium. The settling rod 64 should always be kept perpendicular to the test platform.

[0104] (3) Saturation of the side confinement column: The top and bottom flanges of the side confinement column 8 are fixed to the top sealing plate 13 and the bottom sealing plate 11 by bolts. Sealing rings are installed in the top sealing plate 13 and the bottom sealing plate 11 to ensure the sealing performance of the side confinement column 8. Except for the top exhaust port 5, close all other valves of the side confinement column 8, and use a vacuum pump connected to the air extraction valve to extract the air from the side confinement column. The negative pressure in the side confinement column 8 should be increased step by step, from -0.02, -0.04, -0.06, -0.08 to -0.1MPa. The side confinement column 8 is kept at each level of negative pressure for 6 hours until the negative pressure increases to -0.1MPa and is kept constant for 12 hours.

[0105] (4) Steady State of the Layered System: Maintain a constant test environment of 25±1℃. After filling the layered low-permeability system designed for the experiment, connect the water supply system to the valve of the top inlet 12, and control an appropriate and constant flow rate to supply water to the side confinement column 8, providing a constant upper boundary water level. When the free water level gradually increases to the valve of the overflow port 27 of the side confinement column, open the valve of the overflow port 27 and the measurement and control system, allowing excess water to flow out freely through the valve of the overflow port 27. Connect all pore water pressure sensors 7 and displacement sensors 4, and record the pore water pressure data and deformation data of the multilayer media at multiple locations in the layered system through the computer terminal of the measurement and control system. When the pore water pressure at each location in the side confinement column is the same as the hydrostatic pressure at that location and the deformation at different burial depths is basically unchanged, the preparation stage of the experiment is considered to be completed and the system has reached the steady state before the loading stage.

[0106] (5) Start the test: There are several overflow modes, see details. Figure 4 The system uses a computer-based control interface to precisely control the up-and-down movement of the overflow trough by manipulating the motor. Multiple water level stages can be set and maintained at a constant level through the interface. The monitoring unit records real-time and accurate changes in pore water pressure and deformation data of each soil layer in real time. The system is considered to have reached a stable state under this load stage when the excess pore water pressure has essentially dissipated and the deformation of the target soil layer remains essentially constant (total deformation per hour is less than 0.05 mm).

[0107] (6) Obtaining the permeability coefficient: After each head difference stabilizes, stop moving the overflow trough 23 up and down, open the valves of the drain outlets 14 at different positions of the side limit column 8, and measure the seepage flow of each layer of medium multiple times through the micro-flow continuous monitoring device 24. Finally, the in-situ permeability coefficient is calculated based on Darcy's law.

[0108] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0109] Example 1

[0110] The specific steps of the in-situ permeability measurement method are as follows:

[0111] (1) Check the test platform: First, we should ensure that all valves, pipes and sensor ports are sealed and unobstructed; all types of sensors can collect and transmit data normally; the computer interface of the measurement and control system can control the opening, pausing and ending of the test platform normally. The side limit column 8 is 60cm high and 20cm in diameter. There are 10 drainage outlets 14. The distance between adjacent drainage outlets 14 is 3cm. In each independent sub-settling device 6, the radius of the topmost stacked settlement plate fan blade 611 is 4cm. The radius decreases sequentially according to the folding path. The radius difference between adjacent settlement plate fan blades 611 is 2mm. The diameter of the through hole 612 on the settlement plate fan blade 611 is 2mm.

[0112] (2) Filling the Layered Low-Permeability System: Clean the soil column system, especially the inner wall of the acrylic side-confining column 8, ensuring it is smooth and dry. Then, apply a layer of petroleum jelly evenly to the inner wall. This is to ensure that the filled layered system completely adheres to the inner wall of the side-confining column, eliminating preferential flow channels and reducing frictional resistance between the inner wall and the soil layer. Then, slowly inject boiled pure water into the side-confining column 8 through the valve of the bottom drain outlet 17, raising the water level to slightly above the designed filling medium thickness. Remove the medium from the complex layered system that has been pre-immersed in pure water, and then fill different media sequentially according to the experimental design. All media are slowly filled into the designed area of ​​the side-confining column 8 underwater. During the water injection and filling process, we should pay attention to the air bubble retention in the layered system while filling each layer of medium and try to avoid this situation as much as possible, especially in strata with larger particle sizes. In this embodiment, the filling media are horizontally layered, with two media of equal thickness in alternating layers. From bottom to top, the media are ① medium sand (5cm) and medium ② clay (5cm), alternating for a total thickness of 30cm. The settlement plate 61 is fully expanded for medium sand (high permeability) and layered in a 1 / 4 circle for clay (low permeability).

[0113] (3) Saturation of the side confinement column: The top and bottom flanges of the side confinement column 8 are fixed to the top sealing plate 13 and the bottom sealing plate 11 by bolts. Sealing rings are installed in the top sealing plate 13 and the bottom sealing plate 11 to ensure the sealing performance of the side confinement column 8. Except for the top exhaust port 5, close all other valves of the side confinement column and use a vacuum pump connected to the extraction valve to extract the air from the side confinement column. The negative pressure in the side confinement column 8 should be increased step by step, from -0.02, -0.04, -0.06, -0.08 to -0.1MPa. The side confinement column 8 is kept at each level of negative pressure for 6 hours until the negative pressure increases to -0.1MPa and is kept constant for 12 hours.

[0114] (4) Steady State of the Layered System: Maintain a constant test environment of 25±1℃. After filling the layered low-permeability system designed for the experiment, connect the water supply system to the valve of the top inlet 12, control an appropriate and constant flow rate to supply water to the side confinement column 8, and provide a constant upper boundary water level. When the free water level gradually increases to the valve of the overflow port 27 of the side confinement column, open the valve of the overflow port 27 and the measurement and control system, allowing excess water to flow out freely through the valve of the overflow port 27. Connect all pore water pressure sensors 7 and displacement sensors 4, and record the pore water pressure data and deformation data of the multilayer media at multiple locations in the layered system through the computer terminal of the measurement and control system. When the pore water pressure at each location in the side confinement column 8 is the same as the hydrostatic pressure at that location and the deformation at different burial depths is basically unchanged, the preparation stage of the experiment is considered to be completed and the system has reached the steady state before the loading stage.

[0115] (5) Start the test: There are several overflow modes, see details. Figure 4 The motor 25 is controlled via a computer interface to precisely control the up-and-down movement of the overflow tank 23. Multiple water level stages can be set and maintained constant through the interface. The monitoring unit records the changes in pore water pressure and the deformation data of each layer of medium in real time and accurately. When the excess pore water pressure is basically completely dissipated and the deformation of the target soil layer remains basically constant (total deformation per hour is less than 0.05 mm), the system is considered to have reached a stable state under this load stage.

[0116] (6) Obtaining the permeability coefficient: After each head difference stabilizes, the drain outlets 14 at different positions of the side confinement column 8 are opened, and the seepage flow of each layer of medium is measured multiple times using the micro-flow continuous monitoring device 24. Finally, the in-situ permeability coefficient is calculated based on Darcy's law. The calculation formulas for constant head and variable head are as follows:

[0117]

[0118] In Equation 1-2: K v ′ represents the effective permeability coefficient (LT) -1 ); K v For the uncorrected permeability coefficient (LT) -1 Q is the seepage flow rate per unit time (L). 3 T -1 ); l is the total thickness of the medium (L); Δh is the head difference between the upper and lower boundaries (L); A is the cross-sectional area of ​​the layered medium (L). 2 );k n is the calibration coefficient for the permeability coefficient, which is related to the medium characteristics; for this example, the empirical value is taken as 7.5; 'a' is the cross-sectional area (L) of the variable head pipe. 2 ); t1 and t2 are the start and end times (T); H1 and H2 are the start and end heads (L).

[0119] Example 2

[0120] This embodiment is basically the same as Embodiment 1, except that the layered medium filled inside the side confinement column 8 is horizontally layered, with multiple media stacked in random thicknesses: medium ① fine sand (5cm), medium ② medium sand (10cm), medium ③ silty clay (10cm), and medium ④ sandy clay (5cm), totaling 30cm. The settlement plate is fully expanded for medium sand (high permeability), the layers for silty clay and sandy clay are 1 / 4 circle (low permeability), and the layer for fine sand is semi-circular.

[0121] Example 3

[0122] This embodiment is basically the same as Embodiment 1, except that the layered medium filling the side confinement column 8 is an inclined sandwich system, and the 10cm and 20cm positions in the uniform fine sand medium (30cm) are filled with 30° inclined sandwich systems (similar). Figure 3 b) The interlayer is silty clay with a thickness of 5cm. Settlement plate 6 is semi-circular for fine sand and 1 / 4 circle for clay layer (low permeability).

[0123] Example 4

[0124] This embodiment is basically the same as Embodiment 1, except that the layered medium filling the side confinement column 8 contains a lens system. The two layers of medium, from bottom to top, are fine sand and sandy clay, each with a thickness of 15cm. Irregular lenses exist at the interface between the clay and fine sand. Pure kaolin is used for filling (similar). Figure 3 a) The settlement plate is semi-circular for fine sand and 1 / 4 circle for clay and pure kaolin (for low permeability, the lens area is small and requires a 1 / 4 circle).

[0125] Example 5

[0126] This embodiment is basically the same as Embodiment 1, except that the layered medium filling the lateral confinement column 8 is a complex and irregular layered system. This system of layered medium is not horizontal or at any arbitrary dip angle, exhibiting obvious interfaces, which is closer to the complex sedimentary strata of nature. The designed medium includes layers of coarse sand, medium sand, fine sand, silty clay, and sandy clay, which are filled into the lateral confinement column from bottom to top. During the filling process, no clear interfaces between layers are retained, and the layer thickness is approximately controlled at about 6 cm. Settlement plates are set in the interlayer transition zone (a full circle for coarse and medium sand, a semi-circle for fine sand, and a quarter circle for clay).

[0127] In this invention, the permeability coefficient ranges obtained from tests in Examples 1 to 5 are shown in Table 1.

[0128] Table 1. Results of in-situ permeability coefficients in the embodiments.

[0129] Media type Permeability coefficient range (cm / s) coarse sand <![CDATA[(5.2~6.2)×10 -2 ]]> medium sand <![CDATA[(2.8~3.2)×10 -3 ]]> fine sand <![CDATA[(4.6~5.1)×10 -4 ]]> sandy clay <![CDATA[(2.8~4.4)×10 -5 ]]> Silty clay <![CDATA[(6.8~9.7)×10 -6 ]]> Pure kaolin <![CDATA[(6.2~7.5)×10 -9 ]]>

[0130] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A seepage experimental apparatus for a layered low-permeability system, characterized in that, include: The system comprises a fixed unit, a pressure stabilizing unit, an overflow unit, a monitoring unit, and a data acquisition unit. The pressure stabilizing unit supplies water to the fixed unit; the overflow unit overflows water from the fixed unit for overflow mode experiments; the monitoring unit monitors the pore water pressure and deformation data of the layered low-permeability system, as well as the drainage volume of the overflow unit and the fixed unit; and the data acquisition unit is communicatively connected to the monitoring unit. The fixed unit includes a side-limiting column (8) and several independent sub-settling devices (6) for testing each layer of the low-permeability system. Each independent sub-settling device (6) includes a settling plate (61), a rotating shaft (62), and a settling rod (64). The settling plate (61) includes several settling plate blades (611). The settling plate blades (611) are stacked and fitted onto the rotating shaft (62) and can rotate independently around the rotating shaft (62). One end of the settling rod (64) is connected to the rotating shaft (62). The settling plate (61) together with one end of the settling rod (64) is inserted into the interior of the side-limiting column (8). The other end of the settling rod (64) extends out of the top of the side-limiting column (8). The upper side wall of the side-limiting column (8) is provided with a top overflow port (27).

2. The apparatus according to claim 1, characterized in that, The rotating shaft (62) is hinged to one end of the settling rod (64); And / or, in the same independent sub-settling device (6), the number of settling plate blades (611) is 2 to 8; And / or, in the same independent sub-settling device (6), the settling plate blades (611) have the same shape; And / or, in the same independent sub-settling device (6), the radius r of the settling plate blades (611) is the same or different, and each is 3-5 cm independently.

3. The apparatus according to claim 1, characterized in that, The settling plate fan blade (611) is provided with several through holes (612). Preferably, in the same independent sub-settling device (6), when the settling plate blades (611) overlap, the through holes (612) on adjacent settling plate blades (611) are arranged in an alternating manner.

4. The apparatus according to claim 1, characterized in that, The overflow unit includes an overflow trough (23) that can move up and down. The bottom of the side limiting column (8) is provided with a bottom drain outlet (17). The overflow trough (23) is connected to the bottom drain outlet (17), and the upper part of the overflow trough (23) is also provided with an overflow outlet.

5. The apparatus according to claim 1, characterized in that, The side wall of the side limiting column (8) is provided with a plurality of drainage outlets (14) arranged longitudinally from bottom to top, and the drainage outlets (14) are arranged at equal intervals; And / or, the monitoring unit includes a water pressure sensor (7) for monitoring the pore water pressure of the layered low-permeability system, the water pressure sensor (7) being disposed on the side wall of the side confinement column (8) and symmetrically positioned with respect to the drain outlet (14).

6. The apparatus according to any one of claims 1-5, characterized in that, The monitoring unit includes a micro-flow continuous monitoring device (24), which is used to monitor the drainage volume of the overflow unit and / or the drainage volume of the fixed unit; the micro-flow continuous monitoring device (24) is located below the overflow outlet of the overflow trough (23) and / or below the drain outlet (14); Preferably, The micro-flow continuous monitoring device (24) includes a funnel (241), a support frame (242), a weighing wheel (243), a drainage trough (244), a weighing device (245), and a weighing shaft (249), wherein, The funnel (241) is located on top of the support frame (242) to receive fluid. The weighing wheel (243) is vertically located below the funnel (241). One end of the weighing shaft (249) is rotatably hinged to the weighing wheel (243), and the other end of the weighing shaft (249) is supported on the weighing device (245). Several weighing grooves (2431) are provided on the outer circumferential surface of the weighing wheel (3), and the drainage groove (244) is located below the weighing wheel (243).

7. The apparatus according to any one of claims 1-4, characterized in that, The monitoring unit also includes a displacement sensor (4) for monitoring deformation data of the layered low-permeability system, the displacement sensor (4) being connected to one end of the settlement rod (64) extending out of the top of the side limiting column (8).

8. A method for testing seepage deformation, characterized in that, The method, performed in the apparatus of any one of claims 1-7, comprises the following steps: Step 1: Fill the lateral confinement column (8) with water and fill it with a layered low-permeability system, and place an independent sub-sedimentation device (6) on the upper surface of each layer of low-permeability system; Step 2: Apply negative pressure inside the side confinement column (8); Step 3: Only when the top overflow port (27) can drain water, the pressure stabilizing unit supplies water to the side confinement column (8). Excess water flows out from the top overflow port (27) of the side confinement column (8). The monitoring unit records the pore water pressure data and the deformation data of the layered low-permeability system until the pore water pressure at each position in the side confinement column (8) is the same as the hydrostatic pressure at that position and the deformation does not change at different burial depths. Step 4: Activate the overflow unit to enter overflow mode, adjust the overflow height of the overflow unit, and during the overflow mode, the monitoring unit records the changes in pore water pressure at different locations of the layered low-permeability system and the deformation data of each layer of medium in real time until the excess pore water pressure is completely dissipated and the deformation of the target soil layer remains unchanged.

9. The method according to claim 8, characterized in that, The process also includes step 5: obtaining the permeability coefficient, stopping the overflow height change of the overflow unit, opening the drain outlets (14) corresponding to the locations of the layered low-permeability system to be tested, measuring the seepage flow of each layer of medium through the micro-flow continuous monitoring device (24) located below the opened drain outlets (14), and finally calculating the in-situ permeability coefficient based on Darcy's law. The calculation formula for constant head is shown in Formula 1, and the calculation formula for variable head is shown in Formula 2. In Formula 1 and Formula 2: K v ′ represents the effective permeability coefficient (LT) -1 ); K v For the uncorrected permeability coefficient (LT) -1 Q is the seepage flow rate per unit time (L). 3 T -1 ); l is the total thickness of the medium (L); Δh is the head difference between the upper and lower boundaries (L); A is the cross-sectional area of ​​the layered medium (L). 2 );k n is the calibration coefficient for the permeability coefficient, which is related to the medium characteristics; for this example, the empirical value is taken as 7.5; 'a' is the cross-sectional area (L) of the variable head pipe. 2 ); t1 and t2 are the start and end times (T); H1 and H2 are the start and end heads (L).

10. The method according to claim 9, characterized in that, In step 2, the negative pressure is -0.02 to -0.1 MPa.

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