Hydraulic zonal isolation testing device and method for complex formations

Abstract

This invention relates to the field of hydraulic engineering, providing a stratified testing device and method for hydraulic connections in complex strata. The testing device includes a model box, a pressurization unit, a drainage simulation unit, and a data acquisition unit. The model box has multiple filling layers arranged vertically, with anti-connection baffles between adjacent filling layers. The pressurization unit includes a circulating water tank and an overflow water tank. The overflow water tank has an inlet chamber, an outlet chamber, and an overflow chamber. Both the inlet and overflow chambers are connected to the circulating water tank, and the outlet chamber is connected to the model box. The drainage simulation unit includes an inner and outer nested cylinder, each with multiple seepage holes. The annular area between the outer and inner cylinders is connected to the circulating water tank via a second valve, and the inner cylinder is connected to the circulating water tank via a first valve. The data acquisition unit is also included. This invention overcomes the shortcomings of existing models, completely reproducing the real hydraulic response of the entire tunnel construction process in complex strata within the device.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering technology, and in particular to a stratification test device and method for hydraulic connections in complex strata. Background Technology

[0002] As water conservancy, hydropower, and transportation tunnel projects extend deeper into the earth, deeply buried tunnels increasingly traverse complex strata composed of rock layers with varying permeability and water-conducting fractures. The groundwater seepage patterns directly impact the structural safety of the tunnels and the surrounding groundwater ecosystem. Indoor physical model testing is a crucial method for studying the evolution of groundwater seepage during tunnel construction. Existing model testing devices typically use an open-top box as the model chamber, with layers of similar materials of different permeability coefficients filled inside to simulate multi-layered surrounding rock strata. Lateral water head boundaries are applied to the strata through a pressurization unit, the tunnel drainage process is simulated through a drainage structure, and data such as pore water pressure and groundwater level within the strata are collected through a monitoring unit.

[0003] The existing test setups described above have the following shortcomings when used for layered hydraulic connection testing in complex strata: Lateral seepage channels easily form between the model box sidewall and the similar filling materials, leading to hydraulic cross-layering of strata with different permeability coefficients along the box wall. This results in the test results failing to reflect the true hydraulic connection between strata. The pressurization unit often uses direct pumping to supply water to the model box, resulting in fluctuating water head and insufficient uniformity at the lateral boundaries, affecting the consistency and reproducibility of the test data. The drainage structure is usually a single pipe or a single opening, only simulating one of the following states: excavation drainage or single lining. It cannot continuously present the entire construction process of the tunnel from excavation through lining closure to the opening of the lining drainage hole within the same device. During the sensor installation process of the monitoring unit, the wiring harness exiting the model box easily forms new seepage paths, interfering with the original seepage field distribution of the strata. Furthermore, the layered monitoring coverage is limited, making it difficult to simultaneously acquire hydraulic response data of each stratum throughout the entire construction process. Summary of the Invention

[0004] This invention provides a stratified testing device and method for hydraulic connections in complex formations, addressing the shortcomings of existing technologies and achieving the following effects: Firstly, the anti-connection baffle eliminates the interference of boundary effects on stratified hydraulic connection testing at the source; secondly, the overflow tank provides stable and reliable head boundary conditions for the entire system; thirdly, the double-cylinder, double-valve structure enables continuous hydraulic response simulation throughout the entire construction process; and simultaneously, the stratified data acquisition unit fully captures the multi-parameter spatiotemporal evolution data of the above process.

[0005] In a first aspect, the present invention provides a stratification test device for hydraulic connections in complex formations, comprising a model box, a pressurization unit, a drainage simulation unit, and a data acquisition unit; The top of the model box is open, and the interior of the model box is provided with multiple filling layers along the vertical direction. The multiple filling layers are used to fill similar materials with different permeability coefficients in layers. Each filling layer has an internal water tank connected to its opposite inner walls on both sides. A water-proof baffle is provided between each two adjacent filling layers. The pressurization unit includes a circulating water tank and an overflow water tank. The overflow water tank is provided with an inlet chamber, an outlet chamber, and an overflow chamber. The inlet chamber and the overflow chamber are both connected to the circulating water tank, and the outlet chamber is connected to the interior of the model box. The drainage simulation unit is located inside the model box and includes an outer cylinder and an inner cylinder nested inside each other. Both the outer cylinder and the inner cylinder are provided with multiple seepage holes. The annular area between the outer cylinder and the inner cylinder is connected to the circulating water tank through a second valve. The interior of the inner cylinder is connected to the circulating water tank through a first valve. The data acquisition unit includes multiple pore water pressure sensors and groundwater level sensors installed in different filling layers within the model box, as well as a flow sensor for measuring the outflow of water from the drainage simulation unit.

[0006] According to some embodiments of the present invention, the anti-connection water-proof plate is a plate that is continuously closed along the circumference of the inner wall of the model box, extends horizontally into the box and is embedded in the filling layer, and the boundary position between the anti-connection water-proof plate and the adjacent filling layer is correspondingly set.

[0007] According to some embodiments of the present invention, the first valve and the second valve have three combined states, wherein both valves are open corresponding to the tunnel excavation and drainage state, both valves are closed corresponding to the impermeable lining state, and the first valve is open and the second valve is closed corresponding to the lining drainage hole conduction state.

[0008] According to some embodiments of the present invention, the overflow tank is internally divided into an inlet chamber and an outlet chamber by a porous partition and into an overflow chamber by an impermeable partition. The heights of the porous partition and the impermeable partition are both lower than the total wall height of the overflow tank. An overflow weir is formed at the top of the impermeable partition. The liquid level in the outlet chamber overflows into the overflow chamber after exceeding the top elevation of the overflow weir. The water head applied from the outlet chamber to the inside of the model tank is determined by the top elevation of the overflow weir.

[0009] According to some embodiments of the present invention, the model box is welded from multiple stainless steel plates, the front panel is provided with a transparent observation window, and a clamping crossbeam is provided on the outside of the transparent observation window; the rear panel is provided with a tunnel installation port, multiple pressure measuring pipe installation holes and sensor wiring holes; the left and right panels are provided with internal water tank installation ports.

[0010] Secondly, this invention also provides a method for testing the hydraulic connection of complex formations, comprising: The pore water pressure sensor was calibrated, and the pressure measuring pipe joint, inner cylinder, outer cylinder and internal water tank were treated to prevent leakage and reverse filter. The layered filling boundary and monitoring point were marked on the surface of the transparent observation window. Prepare similar materials with different permeability coefficients according to the formula, fill and compact them in layers from bottom to top, install anti-connection waterproofing plates at the boundary between adjacent filling layers, and simultaneously bury pore water pressure sensors and groundwater level sensors, and roughen the layers. Connect the pipelines of the pressurization unit, drainage simulation unit and data acquisition unit, debug the acquisition equipment, adjust the overflow tank to the set elevation, start the submersible pump to supply water to the overflow tank, apply a constant lateral water head to each filling layer in the model box, and let it stand until the pore water pressure stabilizes. The opening and closing combinations of the first and second valves were switched in sequence to simulate three working conditions: tunnel excavation, impermeable lining construction, and lining construction with drainage holes. Data on pore water pressure, groundwater level, and water inflow of each filling layer were collected under each working condition. Based on the collected data, seepage field cloud maps were drawn, and the interlayer hydraulic conductivity, hydraulic connectivity and hydraulic lag time between different filling layers were calculated to evaluate the hydraulic connection strength between each filling layer.

[0011] According to some embodiments of the present invention, the steps of calibrating the pore water pressure sensor, performing leak-proof and reverse filtration treatment on the pressure measuring pipe joint, inner cylinder, outer cylinder and internal water tank, and marking the layered filling boundary and monitoring points on the surface of the transparent observation window include: After soaking the pore water pressure sensor to remove air bubbles, it is placed in the calibration tube. The water head is changed by injecting and pumping water. The standard water head is compared with the sensor reading to determine the correction coefficient. The geotextile is cut and wrapped around the inside of the pressure measuring tube joint and the outer cylinder surface of the drainage simulation unit. The steps of preparing similar materials with different permeability coefficients according to the specified ratio, filling and compacting them in layers from bottom to top, installing anti-connection water-proof plates at the boundaries of adjacent filling layers, simultaneously burying pore water pressure sensors and groundwater level sensors, and roughening the interlayer surface include: According to the target permeability coefficient of each filling layer, weigh sand, gypsum and water according to the ratio, mix them evenly and fill them into the model box in layers. After each layer is filled, compact it to the height marked on the transparent observation window. Use a steel brush to roughen the surface between layers before filling the next layer. During the filling process, pore water pressure sensors are buried at predetermined coordinate positions and the wire harness is passed out of the model box through a sealing device.

[0012] According to some embodiments of the present invention, the steps of connecting the pressurization unit, the drainage simulation unit, and the data acquisition unit, debugging the acquisition equipment, adjusting the overflow tank to a set elevation, starting the submersible pump to supply water to the overflow tank, applying a constant lateral water head to each filling layer in the model box, and allowing it to stand until the pore water pressure stabilizes include: Place the submersible pump into the circulating water tank, and connect the overflow water tank outlet to the internal water tanks on both sides of the model box with a hose. After turning on the submersible pump, the water flows through the porous baffle of the overflow water tank into the outlet chamber. After the water level in the outlet chamber reaches the top elevation of the impermeable baffle, the excess water overflows into the overflow chamber and flows back to the circulating water tank. The outlet chamber supplies water to the internal water tank with a constant water head.

[0013] According to some embodiments of the present invention, the step of sequentially switching the opening and closing combinations of the first valve and the second valve to simulate three working conditions—tunnel excavation, impermeable lining construction, and lining construction with drainage holes—and collecting pore water pressure, groundwater level, and inflow data for each filling layer under each working condition includes: First, open the first valve and the second valve simultaneously and continue to collect data until the data stabilizes. Then, close the first valve and the second valve simultaneously and monitor the recovery process of pore water pressure in each filling layer. After the recovery stabilizes, open the first valve and keep the second valve closed, and monitor the water pressure distribution and inflow of each filling layer.

[0014] According to some embodiments of the present invention, the steps of drawing seepage field cloud maps based on collected data, calculating the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time between different filling layers, and evaluating the hydraulic connection strength between each filling layer include: The pore water pressure data of each monitoring point under each working condition are interpolated according to spatial coordinates to generate a seepage field distribution map; the groundwater level drawdown data of each filling layer under different inflow conditions are statistically analyzed, the correspondence between inflow and drawdown is compared, and the drawdown data of hydraulic lag time and seepage control timing are combined to determine the timing of lining construction under this stratum condition. The calculation formulas for the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time are as follows: Interlayer hydraulic conductivity: In the formula, Let be the hydraulic conductivity coefficient between the i-th and j-th filling layers. Let L be the steady-state seepage flow rate between the two filling layers, L be the direct seepage path length between the two filling layers, and A be the cross-sectional area of ​​the interlayer water passage. The steady-state head difference between formations i and j; Dimensionless hydraulic connectivity: In the formula, The hydraulic connectivity of filling layers i and j, with a value range of 0 < ≤1, This represents the maximum interlayer hydraulic conductivity coefficient of the entire strata. Hydraulic response lag time: In the formula, Let be the lag time for the change in water head at layer i to be transmitted to layer j. This represents the maximum head drop in the upper layer. This represents the interlayer seepage conduction velocity.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) In view of the technical defects of existing physical models, such as lateral seepage through the box wall and distortion of the test results of the hydraulic connection between layers, the present invention sets up a circumferentially continuous closed anti-connection water-proof plate at the interface of each stratum. The water-proof plate is embedded in the stratum and can completely block the seepage path between similar materials and the side wall of the box, thereby eliminating the interference of boundary effect on the layer test from the root. In conjunction with the layered filling of complex strata, it can truly restore the spatial distribution characteristics of the hydraulic connection between strata in actual engineering, and solve the problem that the existing device can only simulate homogeneous strata and cannot reflect the hydraulic differences between layers. (2) The tunnel drainage structure with internal and external cavities is adopted. By combining the opening and closing of two valves, the complete construction process of tunnel excavation, impermeable lining construction and lining construction with drainage holes can be continuously simulated. It can test the dynamic changes of the hydraulic connection between different layers under different construction stages, which makes up for the shortcomings of the existing device that can only test a single working condition and cannot reflect the hydraulic response of the entire construction process. (3) The present invention adopts an overflow water tank pressure-stabilizing pressurization system, which provides a uniform and stable lateral constant head boundary by forming a constant liquid surface through overflow, completely avoiding the water pressure pulsation and head fluctuation caused by direct pumping, providing stable and reliable basic parameters for quantitative calculation of layered hydraulic connection, and ensuring that the test data can be repeated; (4) This test method proposes three sets of quantitative calculation formulas for inter-layer hydraulic conductivity coefficient, hydraulic connectivity and hydraulic lag time, which can transform experimental monitoring data into standardized hydraulic connection quantitative parameters, solving the technical problem that existing technologies can only make qualitative judgments and cannot evaluate quantitatively; combined with the layered monitoring system, it can finely characterize the strength of hydraulic connection between different strata. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the overall structure of the complex formation hydraulic connection stratification test device provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the pressurization unit provided in an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the internal three-dimensional structure and pressure measuring tube installation provided for an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the internal structure of the overflow tank provided in an embodiment of the present invention.

[0020] Figure 5 This is a three-dimensional schematic diagram of a tunnel lining structure provided in an embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram of a tunnel valve control structure provided in an embodiment of the present invention.

[0022] Figure 7 This is a schematic diagram of the drainage simulation unit provided in an embodiment of the present invention.

[0023] Figure 8 This is a schematic diagram of the sensor harness sealing device provided in an embodiment of the present invention.

[0024] Figure 9 This is a schematic diagram of the arrangement of the pressure measuring tube and pore water pressure gauge provided in an embodiment of the present invention.

[0025] Figure 10 This is a schematic diagram of the groundwater level logging well layout provided in an embodiment of the present invention.

[0026] Figure 11 A schematic diagram illustrating the steps of a stratified testing method for hydraulic connections in complex formations provided in an embodiment of the present invention.

[0027] Figure label: 1. Model box; 11. Front panel; 11-1. Transparent observation window; 12. Rear panel; 12-1. Pressure measuring tube mounting hole; 12-2. Sensor wiring hole; 12-3. Pressure measuring tube connector; 12-31. Inner side of pressure measuring tube connector; 12-32. Outer side of pressure measuring tube connector; 13. Left panel; 14. Right panel; 15. Base plate; 16. Waterproof barrier plate; 17. Compression beam; 21. Circulating water tank; 22. Overflow water tank; 22A. First overflow water tank; 22B. Second overflow water tank; 22C. Third overflow water tank; 22-1. Impermeable baffle; 22-2. Perforated baffle; 22-3. Overflow outlet; 22-4. Inlet; 22-5. Outlet; 23. Internal water tank; 24. Submersible pump; 25. Connecting pipes; 31. Lining; 31-1. Outer cylinder; 31-2. Inner cylinder; 31-3. Drainage hole; 31-4. Flange; 31-5. Flange connection hole A; 31-6. Flange connection hole B; 31-7. Flange bolt hole; 31-8. First valve; 31-9. Second valve; 41. Sensor wiring harness; 42. Sealing device; 43. Hollow bolt; 44. Rubber gasket; 45. Wire hole; 5. Filler layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] The following description, in conjunction with the accompanying drawings, describes the complex formation hydraulic connection stratification test apparatus and its test method of the present invention.

[0030] like Figure 1 and Figure 2 As shown, the complex formation hydraulic connection stratification test device according to the first aspect of the present invention includes a model box 1, a pressurization unit, a drainage simulation unit and a data acquisition unit.

[0031] Model box 1 is used to contain and layer similar materials with different permeability coefficients to construct a physical model of multi-layered surrounding rock strata. Model box 1 is a hollow rectangular box with an open top, made of rigid plates, and its internal cavity is divided into multiple filling layers 5 along the vertical direction. Each filling layer 5 can be filled with a mixture of raw materials such as sand, gypsum, and water with a specific permeability coefficient according to the test requirements. The difference in permeability coefficient between the filling layers 5 is used to reproduce the complex geological conditions of adjacent rock strata with different permeability in actual engineering.

[0032] Internal water tanks 23 are fixed to the left and right sides of the model box 1. Each internal water tank 23 is a flat box extending along its height, with a permeable structure on its side facing the filling layer 5, allowing water to evenly infiltrate into adjacent filling layers 5, providing lateral water head boundaries for each stratum. Each filling layer 5 has an internal water tank 23 corresponding to and connected to it on both its left and right sides. In some embodiments, the wall of the internal water tank 23 facing the filling layer 5 has multiple rows of small holes or a perforated plate structure, allowing water to evenly infiltrate adjacent filling layers 5 in a small-flow, multi-point dispersed manner, avoiding concentrated jets that could erode the filling material.

[0033] A water-blocking baffle 16 is installed between each pair of adjacent filling layers 5 on the box wall. The water-blocking baffle 16 is a thin plate of impermeable material, arranged circumferentially along the inner wall of the model box 1, extending from the box wall inward and embedded inside the filling layer 5. The function of the aforementioned water-blocking baffle 16 is to cut off the potential seepage channels between the filling material and the box wall at the boundary, so that the groundwater of adjacent filling layers 5 can only undergo hydraulic exchange through the interlayer contact surface, avoiding uncontrolled lateral flow along the box wall and ensuring the authenticity of the layered hydraulic connection test results.

[0034] The pressurization unit is used to apply a constant lateral water head to each filling layer 5 within the model tank 1. The pressurization unit includes a circulating water tank 21, an overflow water tank 22, a submersible pump 24, and piping and valves connecting the various components. The circulating water tank 21 stores the test water and continuously supplies water to the overflow water tank 22. The submersible pump 24, located within the circulating water tank 21, lifts and delivers water to the overflow water tank 22.

[0035] The overflow tank 22 is a separate tank from the model tank 1, and its interior is divided into three compartments by two partitions. A porous partition 22-2 separates the overflow tank 22 into an inlet compartment and an outlet compartment. Multiple through holes are formed on the surface of the porous partition 22-2, allowing water to flow from the inlet compartment through these holes into the outlet compartment. The damping effect of the through holes dissipates energy and slows the water flow during its passage. An impermeable partition 22-1 separates the overflow tank 22 into an inlet compartment and an overflow compartment. This impermeable partition 22-1 is a solid plate, preventing water from passing directly through it. The inlet compartment is connected to the outlet 22-5 of the submersible pump 24 via a pipe, receiving continuous water supply from the circulating water tank 21. The overflow compartment returns to the circulating water tank 21 via a pipe, recycling excess water. The water outlet 22-5 of the water outlet chamber is connected to the internal water tanks 23 on both sides of the model box 1 through pipelines, and the pressure-stabilized water is transported to the lateral boundary of the filling layer 5.

[0036] The drainage simulation unit is used to simulate the drainage status of the tunnel at different construction stages. The drainage simulation unit is set in the internal space of the model box 1, including an outer cylinder 31-1 and an inner cylinder 31-2 nested inside each other.

[0037] Both the outer cylinder 31-1 and the inner cylinder 31-2 are cylindrical structures, horizontally arranged inside the model box 1, with their axes extending along the front-to-back direction of the model box 1. The outer cylinder 31-1 is fitted over the inner cylinder 31-2, forming an annular gap between them. Multiple seepage holes 31-3 are provided on the walls of both the outer cylinder 31-1 and the inner cylinder 31-2, allowing groundwater in the filling layer 5 to enter the cylinder body through the seepage holes 31-3, thus simulating the process of groundwater seeping into the tunnel from the surrounding rock.

[0038] The annular area between the outer cylinder 31-1 and the inner cylinder 31-2 is connected to a second valve 31-9 via a pipeline, and the other end of the second valve 31-9 is connected to the circulating water tank 21. The internal space of the inner cylinder 31-2 is connected to a first valve 31-8 via a pipeline, and the other end of the first valve 31-8 is also connected to the circulating water tank 21. By controlling the opening or closing of the first valve 31-8 and the second valve 31-9, the drainage path connection status of the inner and outer cylinders 31-1 can be changed, realizing the simulation of different construction conditions.

[0039] The data acquisition unit is used to synchronously acquire hydraulic response data of each stratum during the experiment. The data acquisition unit includes multiple pore water pressure sensors, multiple groundwater level sensors, and flow sensors. The pore water pressure sensors are layered and deployed at different depths and horizontal positions within each filling layer 5 of the model box 1, measuring the pore water pressure values ​​at each monitoring point in the filling layer 5. The groundwater level sensors are layered within different filling layers 5 to monitor the changes in groundwater level over time in each stratum. The flow sensors are located on the outlet path of the drainage simulation unit to measure the inflow of water discharged through the inner and outer cylinders 31-1. These three types of sensors operate synchronously, achieving real-time synchronous acquisition of multiple parameters, including pore water pressure, groundwater level, and tunnel inflow, in each stratum.

[0040] In related technologies, traditional indoor model tests of tunnel seepage often lack effective isolation measures between the sidewall of model box 1 and the filling material. This leads to lateral crossflow of groundwater along the box wall in strata with different permeability coefficients, causing the stratified test data to fail to reflect the true hydraulic relationship of the strata themselves. The pressurization system typically uses a pump to directly pump water into model box 1, resulting in significant head fluctuations due to variations in pump flow rate, and poor uniformity and stability of the lateral head boundary. Drainage structures are often single-pipe or single-aperture designs, only capable of corresponding to one drainage state and unable to continuously represent the hydraulic response changes throughout the entire construction process within the same device. Furthermore, insufficient sealing measures at the sensor wiring points allow gaps between the wiring harness and the box wall to easily create additional seepage paths, interfering with the original seepage field.

[0041] Therefore, to address the technical deficiencies in the aforementioned related technologies, this invention provides a layered testing device for hydraulic connections in complex strata. This device solves the above problems through the following four improvements: First, a water-blocking baffle 16 is installed on the tank wall between every two adjacent filling layers 5 to cut off the lateral seepage channels in the tank wall at the boundary. Second, an overflow tank 22 is used to achieve constant head water supply through a combination of energy dissipation by a porous baffle 22-2 and an overflow weir by an impermeable baffle 22-1, so that the head is determined only by the top elevation of the overflow weir, decoupling it from the fluctuation of the water pump flow. Third, a nested double-cylinder structure is used with two independent valves, and different combinations of valve opening and closing are used to achieve continuous switching between three working conditions within the same device: excavation drainage, impermeable lining 31 closure, and drainage hole conduction of lining 31. Fourth, pore water pressure sensors and groundwater level sensors are arranged in layers within the model box 1, and in conjunction with flow sensors, synchronous layered acquisition of hydraulic response data for each stratum is achieved.

[0042] It is understandable that the four improvements mentioned above work synergistically. On the one hand, the anti-connection baffle 16 eliminates the interference of boundary effects on the stratified hydraulic connection test at its source; secondly, the overflow tank 22 provides stable and reliable head boundary conditions for the entire system; on the other hand, the double-cylinder, double-valve structure enables continuous hydraulic response simulation throughout the entire construction process; simultaneously, the stratified data acquisition unit fully captures the multi-parameter spatiotemporal evolution data of the above process. These four improvements complement each other and together constitute a complete testing system from formation construction, boundary control, working condition simulation to data acquisition.

[0043] According to some embodiments of the present invention, the anti-connection water-blocking plate 16 is a plate that is continuously closed along the circumference of the inner wall of the model box 1. The anti-connection water-blocking plate 16 extends end to end along the inner wall surfaces of the front panel 11, rear panel 12, left panel 13 and right panel 14 of the model box 1, forming an uninterrupted closed loop on the same horizontal plane of the box wall, completely enclosing the seepage path on one side of the inner wall surface, leaving no gaps for water to bypass the plate along the wall surface.

[0044] Furthermore, the anti-connection water-blocking plate 16 extends horizontally into the tank, with the plate extending from the tank wall into the filling layer 5 and embedding itself into the completed similar material, so that the filling layers 5 on both sides of the plate are physically separated by the plate in the area near the tank wall. The anti-connection water-blocking plate 16 is set at the boundary position of the adjacent filling layer 5, that is, each anti-connection water-blocking plate 16 is installed at the joint height between two adjacent filling layers 5.

[0045] It is understandable that after the anti-connection water-blocking plate 16 is installed, during the filling and testing of the filling layer 5, although there are still tiny contact gaps between the similar materials on both sides of the plate and the tank wall due to material shrinkage and the wall surface smoothing effect, these gaps are cut off into two discontinuous segments at the plate location, located in the tank wall areas corresponding to the two adjacent filling layers 5, and are not connected to each other. When there is a water head difference between the two filling layers 5, water cannot flow continuously from the upper layer to the lower layer along the tank wall, and the lateral seepage path of the tank wall no longer exists. The hydraulic exchange between adjacent filling layers 5 can only occur through the interlayer contact surface of the filling material itself. The measured pore water pressure change truly reflects the permeability characteristics of the interlayer contact surface, and the concept of stratification is physically guaranteed.

[0046] like Figure 1 and Figure 2 As shown, according to some embodiments of the present invention, the first valve 31-8 and the second valve 31-9 have three combined states, wherein both valves are open corresponding to the tunnel excavation and drainage state, both valves are closed corresponding to the impermeable lining 31 state, and the first valve 31-8 is open and the second valve 31-9 is closed corresponding to the drainage hole conduction state of the lining 31.

[0047] In this embodiment, both the first valve 31-8 and the second valve 31-9 are independently controllable fluid valves, connected in series in the drainage pipe inside the inner cylinder 31-2 and the drainage pipe in the annular area between the outer cylinder 31-1 and the inner cylinder 31-2, respectively. The inlet end of the first valve 31-8 is connected to the internal space of the inner cylinder 31-2 via a pipe, and the outlet end of the first valve 31-8 is connected to the circulating water tank 21. The inlet end of the second valve 31-9 is connected to the annular area between the outer cylinder 31-1 and the inner cylinder 31-2 via a pipe, and the outlet end of the second valve 31-9 is connected to the circulating water tank 21.

[0048] The three possible combinations are as follows.

[0049] The first combined state is with both valves open. At this time, the interior of the inner cylinder 31-2 and the annular area are connected to the circulating water tank 21 through their respective pipelines. Groundwater in the filling layer 5 can enter the annular area through the seepage hole 31-3 of the outer cylinder 31-1 and then be discharged directly to the circulating water tank 21 through the pipeline containing the second valve 31-9. Alternatively, it can continue to enter the interior of the inner cylinder 31-2 through the seepage hole 31-3 at the arch of the inner cylinder 31-2 and then be discharged to the circulating water tank 21 through the pipeline containing the first valve 31-8. With both drainage paths open simultaneously, drainage resistance is minimized, corresponding to the state of free discharge of groundwater from the surrounding rock into the tunnel interior after excavation.

[0050] The second combined state is that both valves are closed. At this time, the drainage pipes inside the inner cylinder 31-2 and the annular area are cut off, and the space between the inner and outer cylinders 31-1 forms a closed cavity. Although the groundwater in the filling layer 5 can enter the annular area and the interior of the inner cylinder 31-2 through the seepage holes 31-3, it cannot continue to drain. The water accumulates in the space between the inner and outer cylinders 31-1, causing the pore water pressure in this area to gradually rise. This corresponds to the state after the tunnel construction is completed and the impermeable lining 31 is installed, where the groundwater is blocked by the lining 31 and the surrounding water pressure gradually recovers.

[0051] The third combined state is that the first valve 31-8 is open and the second valve 31-9 is closed. At this time, the drainage pipe inside the inner cylinder 31-2 is open, while the drainage pipe in the annular area is cut off. The groundwater in the filling layer 5 must first pass through the seepage hole 31-3 of the outer cylinder 31-1 into the annular area, then through the seepage hole 31-3 at the top of the inner cylinder 31-2 into the interior of the inner cylinder 31-2, and finally be discharged through the pipe where the first valve 31-8 is located. Although the drainage path is not completely blocked, the seepage holes 31-3 of the outer cylinder 31-1 and the seepage holes 31-3 of the inner cylinder 31-2 constitute a series of two-stage water resistance, which limits the drainage volume. This corresponds to a controllable drainage state in which groundwater can be discharged through the drainage holes of the lining 31 after the drainage holes are set on the tunnel lining 31.

[0052] As described above, the three combined states can be switched by simply opening and closing two valves, without requiring any disassembly or replacement of the drainage simulation unit. During the test, following the construction sequence of excavation, lining 31 sealing, and lining 31 drilling, the valves were sequentially switched from the first combined state to the second combined state and then to the third combined state. This allowed for the continuous acquisition of formation hydraulic response data throughout the entire tunnel construction process within the same device, fully presenting the spatiotemporal evolution of pore water pressure in each formation as the construction progressed.

[0053] like Figure 1 and Figure 2 As shown, according to some embodiments of the present invention, the overflow tank 22 is a rectangular box with an open top, having a bottom plate 15 and four walls. The overflow tank 22 is internally provided with a perforated partition 22-2 and a waterproof partition 22-1. The heights of both the perforated partition 22-2 and the waterproof partition 22-1 are lower than the total wall height of the overflow tank 22, that is, the top elevation of both partitions is lower than the upper edge elevation of the overflow tank 22 wall, allowing water to overflow from the top of the partitions without spilling from the overflow tank 22 wall.

[0054] A porous baffle 22-2 is disposed between the inlet and outlet chambers. Multiple through holes are formed on the surface of the porous baffle 22-2. The total area of ​​the through holes relative to the surface is equal to the sum of the areas of the smaller holes, creating a damping effect on the flowing water. After the submersible pump 24 pumps water from the circulating water tank 21 into the inlet chamber via pipeline, the water flows into the inlet chamber and towards the porous baffle 22-2. The water is slowed down by the porous baffle 22-2 and then flows uniformly into the outlet chamber at a lower velocity through the through holes. The porous baffle 22-2 also acts as a flow straightener, making the uneven flow on one side of the inlet chamber more uniform after passing through the through holes.

[0055] An impermeable baffle 22-1 is located between the inlet chamber and the overflow chamber. The impermeable baffle 22-1 is a solid plate; water cannot pass directly through it, but can only overflow from the top. The top of the impermeable baffle 22-1 forms an overflow weir, the elevation of which is the control liquid level elevation within the overflow tank 22. The outlet 22-5 of the outlet chamber is located at the bottom of the outlet chamber and is connected to the internal water tanks 23 on both sides of the model box 1 via pipes. The bottom of the overflow chamber has an overflow port 22-3, which returns to the circulating water tank 21 via pipes.

[0056] During operation, the inlet chamber receives a continuous water supply from the submersible pump 24. The water flows through the porous baffle 22-2 to dissipate energy before entering the outlet chamber. The liquid level in the outlet chamber rises continuously. When the liquid level reaches the top elevation of the impermeable baffle 22-1, excess water overflows from the inlet chamber, passing over the top of the impermeable baffle 22-1 and entering the overflow chamber. From the overflow port 22-3 at the bottom of the overflow chamber, the water flows back to the circulating water tank 21 through a pipeline. During this process, as long as the water supply from the submersible pump 24 is greater than the water flow from the outlet port 22-5 of the outlet chamber to the model tank 1, the liquid level in the outlet chamber remains constant at the top elevation of the impermeable baffle 22-1. The outlet port 22-5 supplies water to the internal water tank 23 of the model tank 1 at a constant head. This head is equal to the elevation difference between the top elevation of the impermeable baffle 22-1 and the outlet port 22-5, and is independent of the flow rate and fluctuations of the submersible pump 24.

[0057] The overflow tank 22 can change the elevation of the top of the overflow weir by adjusting the installation height of the impermeable baffle 22-1, thereby changing the lateral head applied to the model tank 1. In the experiment, multiple overflow tanks 22 can be set up and their impermeable baffles 22-1 heights can be adjusted to apply different lateral heads to different filling layers 5, simulating the differences in natural water heads in complex strata.

[0058] It needs to be explained that in the traditional direct pumping method, the impeller rotation of the pump causes periodic pulsations in the outlet flow rate. These pulsations are directly transmitted to the lateral boundary of model box 1, causing the water head boundary conditions of each stratum to fluctuate over time. Different batches of experiments are difficult to reproduce due to differences in the fluctuation patterns.

[0059] The overflow tank 22 of this invention decouples the dynamic fluctuations of the water supply system from the head boundary of the model tank 1 through two structural measures: energy dissipation by the porous baffle 22-2 and liquid level locking by the overflow weir. The porous baffle 22-2 eliminates the pulsating kinetic energy of the incoming flow, and the liquid level in the outlet tank achieves self-stabilization at the overflow weir elevation. Excess water automatically overflows and flows back, forming a self-balancing pressure-stabilized water supply system. The head control accuracy depends only on the machining and installation accuracy of the overflow weir top elevation, and the value can be precisely set and remains stable over a long period.

[0060] In some specific embodiments, the overflow tank 22 achieves constant head control through continuous overflow, which must meet the following requirements: In the formula, H is the constant water head applied laterally to the model formation. The elevation of the top of the overflow weir of the impermeable baffle plate in the overflow tank 22 is given. The submersible pump 24 continuously supplies water to the inlet chamber. After the water flow passes through the porous baffle plate 22-2 to dissipate energy, it enters the outlet chamber. When the liquid level exceeds the top of the overflow weir, excess water overflows into the overflow chamber and flows back, ensuring that the liquid level in the outlet chamber is always flush with the weir top. The water supply head is uniquely determined solely by the weir installation height and is independent of pump flow fluctuations. The relative error of the head control satisfies: In the formula, This is the relative error of the water head. To measure the stable liquid level height.

[0061] like Figure 1 and Figure 2 As shown, according to some embodiments of the present invention, the model box 1 is welded from five stainless steel plates: a front panel 11, a rear panel 12, a left panel 13, a right panel 14, and a bottom plate 15, with an open top. The five panels are fully welded at the joints, forming a rectangular box with sufficient rigidity and sealing, capable of withstanding the lateral pressure generated by the weight of the filling material and water, and without leakage at the welded joints.

[0062] The front panel 11 is fitted with a transparent observation window 11-1. The transparent observation window 11-1 is an embedded transparent material plate installed in the middle of the front panel 11, with its inner surface in direct contact with the interior space of the model box 1, and its outer surface facing the operator. Through the transparent observation window 11-1, the filling situation inside the model box 1, the change in liquid level in the pressure measuring tube, and the advancement of the water infiltration line during the formation saturation process can be directly observed from the outside. A clamping beam 17 is provided on the outer side of the transparent observation window 11-1, spanning the transparent observation window 11-1 and fixed at both ends to the front panel 11. The lateral pressure provided during the filling process is distributed to the box frame through the beam, protecting the transparent observation window 11-1 from deformation or displacement due to lateral compression during the compaction of the filling material.

[0063] The rear panel 12 has a tunnel mounting opening, multiple pressure measuring tube mounting holes 12-1, and sensor wiring holes 4512-2. The tunnel mounting opening is a circular opening penetrating the rear panel 12, with a diameter matching the outer diameter of the outer cylinder 31-1. It is used to install the outer cylinder 31-1 and inner cylinder 31-2 of the drainage simulation unit. The outer cylinder 31-1 is fixed to the tunnel mounting opening by a flange 31-4. The pressure measuring tube mounting holes 12-1 are multiple small circular holes penetrating the rear panel 12, arranged in a matrix. Each pressure measuring tube mounting hole 12-1 corresponds to a monitoring point. The pressure measuring tube connector 12-3 passes through the mounting holes and then seals the gap around the holes with a sealant. The sensor wiring holes 4512-2 are used to lead the wiring harness of the pore water pressure sensor pre-embedded in the filling layer 5 from inside the model box 1 to the external data acquisition equipment.

[0064] The left and right panels 14 are respectively provided with installation ports for internal water tanks 23. The internal water tanks 23 are fixed to the inner wall of the model box 1 through the installation ports. The inlet and outlet water interfaces of the internal water tanks 23 are connected to the outlet chamber of the overflow water tank 22 through pipes after passing through the installation ports.

[0065] The overall rigidity of the stainless steel welded enclosure ensures that model box 1 does not deform during filling and testing, and the box walls remain flat. The transparent observation window 11-1 on the front panel 11, in conjunction with the clamping beam 17, provides visual observation conditions while ensuring the structural safety of the observation window. The rear panel 12 centrally arranges the tunnel installation port, the pressure measuring pipe installation hole 12-1, and the sensor wiring hole 4512-2, unifying the installation interfaces of the drainage simulation unit and the monitoring unit onto a single panel, reducing the weakening of the box's strength and the potential risk of leakage caused by multiple panel openings. The internal water tank 23 installation ports on the left and right panels 14 allow the water supply structure to be built into the side of the box, resulting in a short water supply path and uniform water flow distribution.

[0066] like Figure 5 As shown, according to some embodiments of the present invention, the outer surface of the outer cylinder 31-1 is wrapped with geotextile. The geotextile is a permeable fabric that completely covers the outer cylinder 31-1. Groundwater in the filling layer 5 must be filtered by the geotextile before entering the seepage holes 31-3 of the outer cylinder 31-1. While allowing water to pass through, the geotextile prevents fine particles or similar materials in the filling layer 5 from entering the cylinder and blocking the seepage holes 31-3, thus forming a reverse filtration structure. The seepage holes 31-3 in the arch area of ​​the inner cylinder 31-2 are arranged in a staggered pattern along the arch surface of the inner cylinder 31-2, that is, adjacent rows of seepage holes 31-3 are staggered in the circumferential position to avoid the holes being concentrated on the same generatrix and causing local weakening. The seepage holes 31-3 are hollow rivet nuts that penetrate the walls of the inner and outer cylinders 31-1. The hollow rivet nuts are fixed to the inner cylinder 31-2 wall by a riveting process, and their inner holes connect the space of the inner and outer cylinders 31-1. The installation method of hollow rivet nuts does not damage the overall structural integrity of the cylinder wall, and the nut body is made of metal, with stable hole size that does not deform due to long-term immersion in water.

[0067] Furthermore, the outer cylinder 31-1 is provided with a flange 31-4 at its end, and the outer cylinder 31-1 is bolted to the tunnel mounting port of the rear panel 12 of the model box 1 via the flange 31-4. The flange 31-4 has two connection holes corresponding to the annular area of ​​the outer cylinder 31-1 and the interior of the inner cylinder 31-2, respectively. These two connection holes are connected to the second valve 31-9 and the first valve 31-8 via pipelines, respectively. The axial length of the outer cylinder 31-1 and the inner cylinder 31-2 matches the thickness of the model box 1 in the front-rear direction. After installation, the rear ends of the outer cylinder 31-1 and the inner cylinder 31-2 pass through the rear panel 12, while the front ends are closed or extend into the interior of the model box 1.

[0068] like Figure 1 and Figure 2 As shown, according to some embodiments of the present invention, a pore water pressure sensor is installed in the pressure measuring pipe mounting hole 12-1 of the rear panel 12 of the model box 1 via a pressure measuring pipe connector 12-3. The pressure measuring pipe connector 12-3 is a hollow screw, the main body of which is a metal screw penetrating the rear panel 12, with a through hole in the center along the axial direction to connect the inside of the filling layer 5 with the external hose. The inner end of the pressure measuring pipe connector 12-3 extends into the filling layer 5, and the end is wrapped with geotextile to prevent fine particles in similar materials from entering the through hole and clogging the pipe. The outer end of the pressure measuring pipe connector 12-3 protrudes outside the model box 1 and is connected to an external data reading device via a hose. A color developing solution is added to the hose, which produces a color change upon contact with water. The test personnel can directly read the liquid level in the tube through the transparent hose, forming a data redundancy verification with the electronic sensor.

[0069] The wiring harness of the pore water pressure sensor passes through the sensor wiring hole 4512-2 on the rear panel 12 of the model box 1 via a sealing device 42. The sealing device 42 includes a hollow bolt 43 and a rubber washer 44 fitted onto the wiring harness. The hollow bolt 43 is a hollow tubular screw, and the wiring harness passes through the central hole of the hollow bolt 43. The rubber washer 44 is located in the annular gap between the hollow bolt 43 and the sensor wiring hole 4512-2. After tightening the hollow bolt 43, the rubber washer 44 expands radially under the action of axial clamping force, tightly fitting the inner wall of the wiring hole 45 and the outer surface of the wiring harness, sealing the gap between the wiring harness and the wiring hole 45, and preventing water in the filling layer 5 from seeping out along the gap.

[0070] The groundwater level sensor is installed inside the logging well. The logging well is a hollow tube with multiple small holes drilled in it, and the outer wall of the tube is wrapped with geotextile. The logging well is inserted vertically into the filling layer 5. Groundwater in the filling layer 5 is filtered through the small holes in the tube and the geotextile before entering the tube. The liquid level inside the tube rises and falls synchronously with the groundwater level in the filling layer 5. A pore water pressure gauge is placed inside the logging well. By measuring the water pressure at the bottom of the tube, the water depth inside the tube is calculated to obtain the groundwater level value at the location of the logging well. Multiple logging wells are arranged at equal intervals along the depth direction of the filling layer 5, corresponding to different filling layers 5. Each logging well independently monitors the groundwater level changes at its corresponding elevation.

[0071] The flow sensor is an automatic data acquisition electronic scale. A water container is placed on the weighing tray of the electronic scale, and the outlet pipes of the first valve 31-8 and the second valve 31-9 of the drainage simulation unit extend above the water container. During the drainage process, the electronic scale automatically records the weight of the water in the water container at set time intervals and transmits the weight data to the computing device in real time via a serial port. The computing device calculates the average inflow rate for that period based on the difference between two consecutive weighing values ​​and the time interval.

[0072] like Figure 11 As shown, the method for testing the hydraulic connection of complex formations according to a second aspect of the present invention includes: Step S1: Calibrate the pore water pressure sensor, perform leak-proof and reverse filtration treatment on the pressure measuring pipe joint 12-3, inner cylinder 31-2, outer cylinder 31-1 and internal water tank 23, and mark the layered filling boundary and monitoring point on the surface of the transparent observation window 11-1. Step S2: Prepare similar materials with different permeability coefficients according to the ratio, fill and compact them in layers from bottom to top, install anti-connection waterproofing plates 16 at the boundary of adjacent filling layers 5, and simultaneously bury pore water pressure sensors and groundwater level sensors, and roughen the layers. Step S3: Connect the pipelines of the pressurization unit, drainage simulation unit and data acquisition unit, debug the acquisition equipment, adjust the overflow tank 22 to the set elevation, start the submersible pump 24 to supply water to the overflow tank 22, apply a constant lateral water head to each filling layer 5 in the model box 1, and let it stand until the pore water pressure is stable. Step S4: Sequentially switch the opening and closing combination of the first valve 31-8 and the second valve 31-9 to simulate three working conditions: tunnel excavation, impermeable lining 31 construction, and lining 31 construction with drainage holes. Under each working condition, collect data on pore water pressure, groundwater level, and water inflow of each filling layer 5. Step S5: Draw a seepage field cloud map based on the collected data, calculate the interlayer hydraulic conductivity, hydraulic connectivity and hydraulic lag time between different filling layers 5, and evaluate the hydraulic connection strength between each filling layer 5.

[0073] According to some embodiments of the present invention, the steps of calibrating the pore water pressure sensor, performing leak-proof and reverse filtration treatment on the pressure measuring pipe joint 12-3, the inner cylinder 31-2, the outer cylinder 31-1 and the internal water tank 23, and marking the layered filling boundaries and monitoring points on the surface of the transparent observation window 11-1 include: After soaking the pore water pressure sensor to remove air bubbles, it is placed in the calibration tube. The water head is changed by injecting and pumping water. The standard water head is compared with the sensor reading to determine the correction coefficient. The geotextile is cut and wrapped around the inside of the pressure measuring pipe joint 12-3 and the surface of the outer cylinder 31-1 of the drainage simulation unit.

[0074] According to some embodiments of the present invention, similar materials with different permeability coefficients are prepared according to a certain ratio, and then filled and compacted in layers from bottom to top. A water-tight barrier 16 is installed at the boundary between adjacent filling layers 5. A pore water pressure sensor and a groundwater level sensor are simultaneously buried. The interlayer roughening process includes: According to the target permeability coefficient of each filling layer 5, sand, gypsum and water are weighed according to the ratio, mixed evenly and then filled into the model box 1 in layers. After each layer is filled, it is compacted to the marked height on the transparent observation window 11-1. The surface between layers is roughened with a steel brush before the next layer is filled. During the filling process, pore water pressure sensors are buried at the predetermined coordinate positions and the wire harness is passed out of the model box 1 through the sealing device 42.

[0075] According to some embodiments of the present invention, the steps of connecting the pipelines of the pressurization unit, the drainage simulation unit, and the data acquisition unit, debugging the acquisition equipment, adjusting the overflow tank 22 to a set elevation, starting the submersible pump 24 to supply water to the overflow tank 22, applying a constant lateral water head to each filling layer 5 in the model box 1, and allowing it to stand until the pore water pressure stabilizes include: Submersible pump 24 is placed in circulating water tank 21. The outlet 22-5 of overflow water tank 22 is connected to the internal water tanks 23 on both sides of model box 1 with a hose. After the submersible pump 24 is turned on, the water flows through the porous baffle 22-2 of overflow water tank 22 and enters the outlet chamber. After the liquid level in the outlet chamber reaches the top elevation of the impermeable baffle 22-1, the excess water overflows into the overflow chamber and flows back to circulating water tank 21. The outlet chamber supplies water to the internal water tank 23 with a constant water head.

[0076] According to some embodiments of the present invention, the steps of sequentially switching the opening and closing combinations of the first valve 31-8 and the second valve 31-9 to simulate three working conditions—tunnel excavation, impermeable lining 31 construction, and lining 31 construction with drainage holes—and collecting pore water pressure, groundwater level, and inflow data for each filling layer 5 under each working condition include: First, open the first valve 31-8 and the second valve 31-9 simultaneously and continue to collect data until the data is stable. Then, close the first valve 31-8 and the second valve 31-9 simultaneously and monitor the recovery process of the pore water pressure in each filling layer 5. After the recovery is stable, open the first valve 31-8 and keep the second valve 31-9 closed, and monitor the water pressure distribution and water inflow in each filling layer 5.

[0077] According to some embodiments of the present invention, the steps of plotting a seepage field cloud map based on collected data, calculating the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time between different filling layers 5, and evaluating the hydraulic connection strength between each filling layer 5 include: The pore water pressure data of each monitoring point under each working condition were interpolated according to spatial coordinates to generate a seepage field distribution map; the groundwater level drawdown data of each filling layer 5 under different water inflow conditions were statistically analyzed, the correspondence between water inflow and water level drawdown was compared, and the water level drawdown data of hydraulic lag time and seepage control timing were combined to determine the timing of lining 31 construction under this stratum condition.

[0078] The formulas for calculating the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time are as follows: Interlayer hydraulic conductivity: In the formula, Let be the hydraulic conductivity coefficient between the i-th layer and the j-th layer of the filling layer 5. Let L be the steady-state seepage flow rate between the two filling layers, L be the direct seepage path length between the two filling layers, and A be the cross-sectional area of ​​the water passage between the layers. The steady-state head difference between formations i and j; Dimensionless hydraulic connectivity: In the formula, The hydraulic connectivity of filling layers i and j, with a value range of 0 < ≤1, This represents the maximum interlayer hydraulic conductivity coefficient of the entire strata. Hydraulic response lag time: In the formula, Let be the lag time for the change in water head at layer i to be transmitted to layer j. This represents the maximum head drop in the upper layer. This represents the interlayer seepage conduction velocity.

[0079] The following is a specific embodiment of the complex formation hydraulic connection stratification test device and test method of the present invention with reference to the accompanying drawings.

[0080] The model box 1 consists of a front panel 11, a rear panel 12, a left panel 13, a right panel 14, and a base plate 15, all welded from 304 stainless steel plates. Its overall dimensions are 3.2m × 0.7m × 2.4m (length × width × height). The front panel 11 has a transparent observation window 11-1. The rear panel 12 has pre-drilled tunnel mounting openings, 244 pressure testing pipe mounting holes 12-1, and sensor wiring holes 4512-2. The left panel 13 and right panel 14 have mounting openings for the internal water tank 23.

[0081] A water-blocking baffle 16, 3mm thick, is installed on the inner wall of the tank at the boundary positions of each filling layer 5, extending 60mm into the filling layer 5. The water-blocking baffle 16 is arranged continuously and closedly along the circumference of the inner wall of the model tank 1, corresponding to the boundary positions of each filling layer 5. This blocks the seepage path between the similar materials and the side wall of the tank, preventing hydraulic crossflow between different filling layers 5 along the tank wall and ensuring the accuracy of the stratified hydraulic connection test. Internal water tanks 23 are symmetrically fixed on the left and right sides inside the model tank 1. The internal space of the tank is used for stratified filling of similar materials with different permeability coefficients, forming multiple filling layers 5. A clamping beam 17 is provided on the outside of the transparent observation window 11-1.

[0082] like Figure 2 , Figure 4 As shown, the pressurization unit consists of a circulating water tank 21, an overflow water tank 22, an internal water tank 23, a submersible pump 24, connecting pipes 25, a first valve 31-8, and a second valve 31-9. The submersible pump 24 is placed at the bottom of the circulating water tank 21, and the outlet 22-5 is connected to the inlet chambers of multiple overflow water tanks 22 via a DN25 hose. The inlet 22-4 is located at the bottom of the inlet chamber. The overflow water tank 22 includes three overflow water tanks 22 corresponding to three filling layers 5, namely the first overflow water tank 22A, the second overflow water tank 22B, and the third overflow water tank 22C.

[0083] like Figure 4 As shown, the overflow tank 22 is internally divided into an inlet chamber and an outlet chamber by a porous baffle 22-2. Water flows evenly into the outlet chamber after energy dissipation through the porous baffle 22-2. Simultaneously, it is divided into an inlet chamber and an overflow chamber by an impermeable baffle 22-1. Excess water overflows the top of the impermeable baffle 22-1 and enters the overflow chamber, then flows back to the circulating water tank 21 through the overflow port 22-3 and pipelines. The heights of both the porous baffle 22-2 and the impermeable baffle 22-1 are lower than the total wall height of the overflow tank 22. Through continuous overflow, a stable liquid surface can be formed at the top of the impermeable baffle 22-1, and the constant head applied laterally to the model is equal to the elevation of the overflow weir top. The test head can be controlled by adjusting the overall installation height of the overflow tank 22. The outlet 22-5 of the outlet chamber is connected to the internal water tanks 23 on both sides of the model tank 1 via a DN50 hose, providing a uniform and stable lateral head boundary for the filling layer 5.

[0084] like Figures 5 to 7 As shown, the drainage simulation unit adopts a nested double-cylinder structure with a geometric similarity ratio of 1:50, corresponding to a circular tunnel with a prototype diameter of 8m. Both the outer cylinder 31-1 and the inner cylinder 31-2 are made of stainless steel. The outer cylinder 31-1 is fixedly installed on the rear panel 12 of the model box 1 via a flange 31-4, with the tunnel axis 50cm above the bottom plate 15 of the model box 1. The flange 31-4 has connection holes A and B. Connection hole A connects to the interior of the inner cylinder 31-2 via a pipe and is connected to the first valve 31-8. Connection hole B connects to the annular area between the outer cylinder 31-1 and the inner cylinder 31-2 via a pipe and is connected to the second valve 31-9. Bolt holes are also evenly distributed around the circumference of the flange 31-4, which is then fixed to the tunnel installation opening on the rear panel 12 using bolts.

[0085] The outer cylinder 31-1 is wrapped with geotextile to form a filter layer structure. Drip holes 31-3 are densely arranged in the cylinder body, allowing groundwater from the filling layer 5 to freely enter the outer cylinder 31-1 while simultaneously blocking similar material particles. Drip holes 31-3 are arranged in a staggered pattern within a 120° radius of the arch, with adjacent holes 31-3 in the same row forming a 60° angle, and the row spacing is half the diameter of the inner cylinder 31-2. The drip holes 31-3 utilize hollow rivet nuts and penetrate the walls of both the inner and outer cylinders 31-1. The annular area between the outer cylinder 31-1 and the inner cylinder 31-2 is connected to a second valve 31-9 via a pipeline, and the interior of the inner cylinder 31-2 is connected to a first valve 31-8 via a pipeline.

[0086] By combining the opening and closing of the first valve 31-8 and the second valve 31-9, three typical construction conditions can be simulated: both valves are open, corresponding to the tunnel excavation and drainage state; both valves are closed, corresponding to the impermeable lining 31 state; and the first valve 31-8 is open and the second valve 31-9 is closed, corresponding to the drainage hole conduction state of the lining 31, thus realizing continuous simulation of the entire construction process.

[0087] The data acquisition unit includes a stratified pore water pressure monitoring unit, a flow monitoring unit, and a stratified groundwater level monitoring unit. The pore water pressure monitoring section consists of 244 piezometers and multiple sets of BWMK-type pore water pressure gauges. The piezometer connector 12-3 is a hollow screw rod, installed with a nut into the pre-drilled piezometer mounting hole 12-1 on the rear panel 12 of the model box 1. The inner side is wrapped with geotextile for anti-clogging, and the outer side connects to a flexible hose. The piezometers are arranged in layers, with denser spacing within the designated area of ​​the tunnel filling layer 5, and conventional spacing in other areas, allowing for precise capture of the seepage field distribution in each filling layer 5. The piezometer connector 12-3 is a hollow screw rod with an inner diameter of 4mm, installed with a nut into the pre-drilled piezometer mounting hole 12-1 on the rear panel 12. The inner side of the piezometer connector 12-3 extends into the filling layer 5 and is wrapped with geotextile for anti-clogging; the outer side of the piezometer connector 12-3 protrudes outside the model box 1 and connects to a PVC flexible hose.

[0088] like Figure 8 As shown, the wiring harness of the pore water pressure sensor exits the model box 1 through a sealing device 42. The sealing device 42 consists of a hollow bolt 43 and a rubber washer 44. After tightening, it can effectively seal the wire hole 45, preventing water leakage and seepage along the wiring harness. The BWMK type pore water pressure sensor has a measurement range of 50 kPa, a resolution of 0.01 kPa, an accuracy error of ≤0.3% F·S, and a dynamic refresh rate of 1000 Hz.

[0089] The flow sensor uses an automatic data acquisition electronic scale with a range of 100kg, a measurement accuracy of 1.0g, and a minimum sampling interval of 50ms. It is connected to a computing device via a serial port to automatically calculate the tunnel water inflow. The groundwater level sensor is installed in the logging wells. In this embodiment, four logging wells are arranged at equal intervals. The logging wells are 40cm long and 2.5cm in diameter. The pipes are drilled and wrapped with geotextile, and buried at the top of the model at positions corresponding to different filling layers 5. A pore water pressure gauge is placed in the logging well to monitor the dynamic changes of the groundwater level in real time.

[0090] Based on the above apparatus, the specific implementation steps of the stratified testing method for hydraulic connectivity in complex formations in this embodiment are as follows: S1. Number all pore water pressure gauges horizontally as RT2-1RT2-5, vertically as RT3-1RT3-5, and around the tunnel as W1W8. After soaking all pore water pressure gauges to remove air bubbles, place them in a 3m long PVC calibration tube. Control the water head within a 0.3m range by injecting and pumping water, comparing the standard water head with the sensor readings, and calibrating using correction coefficients to ensure that the measurement error of all sensors is ≤±5%. Cut geotextile into 0.5cm×0.5cm pieces, wrap the inside of the pressure measuring tube connector 12-3, and tighten with a rigid tube to prevent similar materials from leaking in and clogging the pressure measuring tube. Cut geotextile to wrap the outer cylinder 31-1 and the surface of the inner water tank 23, and attach and fix it to serve as a filter and prevent clogging. Mark the layered filling boundary and monitoring point coordinates on the surface of the transparent observation window 11-1 as a benchmark for filling construction.

[0091] S2. Based on the target permeability coefficient of each filling layer 5, weigh the raw materials such as sand, gypsum, and water according to the proportion, pour them into the mixer and mix thoroughly, then weigh them separately for later use. Fill the first layer in order from bottom to top, and compact the entire layer to the marked height.

[0092] Install a water-proof barrier 16 at the corresponding boundary of the filling layer 5 to ensure that the embedding depth meets the design requirements. Bury a pore water pressure gauge at the predetermined position, wrap the sensor end with gauze for protection, and wrap the wire harness with waterproof tape every 20cm to extend the seepage path; the wire harness passes through the sealing device 42 of the rear panel 12 of the model box 1, and tighten the hollow bolt 43 to compact the rubber gasket 44 to achieve a seal.

[0093] After each layer of filling is completed, the surface between layers is roughened with a steel brush to enhance the integrity of the upper and lower layers. The same method is used until all filling layers 5 are completed; at the same time, logging wells are installed at the corresponding positions on the top of the model, with pre-drilled holes in the logging pipes and wrapped with geotextile; where the logging wells pass through filling layers 5, overlap treatment is performed to ensure hydraulic communication between the logging wells and the surrounding filling layers 5. After filling is completed, pore water pressure gauges are placed in the logging wells and fixed.

[0094] S3. Connect the overflow water tank 22 outlet 22-5 to the internal water tanks 23 on both sides of the model box 1 using a DN50 hose, and tighten the joint with clamps; place the submersible pump 24 into the circulating water tank 21, and connect the outlet 22-5 to the water inlet of the overflow water tank 22; connect the drain pipes of the first valve 31-8 and the second valve 31-9, and connect the outlet to the water receiving container of the automatic data acquisition scale. Connect the pressure measuring tubes sequentially to the joints on the rear panel 12 of the model box 1, and fix them to the background plate according to the numbers; install the camera and aim it at the pressure measuring tube area, and adjust the focus to ensure that the liquid surface is clear; connect the pore water pressure gauge and the scale to the data acquisition instrument and computing equipment, and debug all acquisition channels to ensure that the data transmission is normal.

[0095] Adjust the installation height of the overflow tank 22 so that the stable liquid level is 1.58m above the ground, reaching the initial design head; turn on the submersible pump 24 to supply water, let it stand for more than 24 hours, observe that the liquid level and pore water pressure readings of all pressure measuring tubes are stable and reach the design head, and determine that the filling layer 5 is saturated and each filling layer 5 forms a stable seepage field.

[0096] S4. After the filling layer 5 is saturated and stabilized, record the initial values ​​of pore water pressure and groundwater level in each filling layer 5, and record the reference flow rate in the valve closed state as the initial reference for the test.

[0097] Simultaneously open the first valve 31-8 and the second valve 31-9 to simulate the tunnel excavation and drainage state; start the data acquisition system to continuously record the pore water pressure, groundwater level and inflow of each filling layer 5 at different times; continue the test until all monitoring data are stable and the seepage field reaches a steady state.

[0098] After the excavation reaches a steady state, the first valve 31-8 and the second valve 31-9 are closed simultaneously to simulate the state of the impermeable lining 31. The water pressure recovery process of each filling layer 5 is continuously monitored, and the water pressure changes over time are recorded until the pressure recovers to near the initial head.

[0099] After the pressure in lining 31 stabilizes, open the first valve 31-8 while keeping the second valve 31-9 closed to simulate the open state of the drainage holes in lining 31. Monitor the stratified water pressure distribution and inflow rate under steady-state conditions to analyze the effectiveness of seepage control measures. Depending on the research needs, adjust the valve opening to set different inflow rates, or apply lining 31 at different time points after excavation, repeating the above experimental procedure to obtain stratified hydraulic response data under different conditions.

[0100] S5. Organize the layered monitoring data under various working conditions, and generate a seepage field distribution cloud map by interpolating the pore water pressure data of each monitoring point according to the spatial coordinates, so as to intuitively show the spatiotemporal evolution law of groundwater pressure.

[0101] Calculate the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time between different filling layers 5. The formulas for calculating the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time are as follows: Interlayer hydraulic conductivity: In the formula, Let be the hydraulic conductivity coefficient between the i-th layer and the j-th layer of the filling layer 5. Let L be the stable seepage flow rate between the two filling layers 5, L be the direct seepage path length between the two filling layers 5, and A be the cross-sectional area of ​​the water passage between the layers. The steady-state head difference between formations i and j; Dimensionless hydraulic connectivity: In the formula, The hydraulic connectivity of filling layers 5i and j, with a value range of 0 < ≤1, This represents the maximum interlayer hydraulic conductivity coefficient of the entire strata. Hydraulic response lag time: In the formula, Let be the lag time for the change in water head at layer i to be transmitted to layer j. This represents the maximum head drop in the upper layer. This represents the interlayer seepage conduction velocity.

[0102] The strength of hydraulic connection between each filling layer was quantitatively evaluated, and the groundwater level drawdown data corresponding to different inflow volumes were statistically analyzed. The correspondence between inflow volume and drawdown was compared. Combined with the hydraulic lag time and drawdown data at different seepage control times, and compared with the groundwater ecological red line, the timing of lining construction under this stratum condition was determined.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stratification testing device for hydraulic connections in complex formations, characterized in that, It includes a model box, a pressurization unit, a drainage simulation unit, and a data acquisition unit; The top of the model box is open, and the interior of the model box is provided with multiple filling layers along the vertical direction. The multiple filling layers are used to fill similar materials with different permeability coefficients in layers. Each filling layer has an internal water tank connected to its opposite inner walls on both sides. A water-proof baffle is provided between each two adjacent filling layers. The pressurization unit includes a circulating water tank and an overflow water tank. The overflow water tank is provided with an inlet chamber, an outlet chamber, and an overflow chamber. The inlet chamber and the overflow chamber are both connected to the circulating water tank, and the outlet chamber is connected to the interior of the model box. The drainage simulation unit is located inside the model box and includes an outer cylinder and an inner cylinder nested inside each other. Both the outer cylinder and the inner cylinder are provided with multiple seepage holes. The annular area between the outer cylinder and the inner cylinder is connected to the circulating water tank through a second valve. The interior of the inner cylinder is connected to the circulating water tank through a first valve. The data acquisition unit includes multiple pore water pressure sensors and groundwater level sensors installed in different filling layers within the model box, as well as a flow sensor for measuring the outflow of water from the drainage simulation unit.

2. The stratification testing device for hydraulic connections in complex formations according to claim 1, characterized in that, The anti-connection water-proof plate is a continuously closed plate along the circumference of the inner wall of the model box, extending horizontally into the filling layer, and the boundary position between the anti-connection water-proof plate and the adjacent filling layer is set accordingly.

3. The stratification testing device for hydraulic connections in complex formations according to claim 1, characterized in that, The first valve and the second valve have three combined states: both valves are open, corresponding to the tunnel excavation and drainage state; both valves are closed, corresponding to the impermeable lining state; and the first valve is open and the second valve is closed, corresponding to the lining drainage hole being open.

4. The stratification testing device for hydraulic connections in complex formations according to claim 1, characterized in that, The overflow tank is divided into an inlet chamber and an outlet chamber by a porous partition and into an overflow chamber by an impermeable partition. The height of both the porous partition and the impermeable partition is lower than the total wall height of the overflow tank. An overflow weir is formed at the top of the impermeable partition. The liquid level in the outlet chamber overflows into the overflow chamber after exceeding the top elevation of the overflow weir. The water head applied from the outlet chamber to the inside of the model box is determined by the top elevation of the overflow weir.

5. The stratification testing apparatus for hydraulic connections in complex formations according to any one of claims 1 to 4, characterized in that, The model box is welded from multiple stainless steel plates. The front panel is fitted with a transparent observation window, and a clamping crossbeam is provided on the outside of the transparent observation window. The rear panel has a tunnel installation port, multiple pressure measuring pipe installation holes and sensor wiring holes. The left and right panels have internal water tank installation ports.

6. A method for stratifying hydraulic connections in complex formations, based on the stratifying apparatus for stratifying hydraulic connections in complex formations as described in any one of claims 1 to 5, characterized in that, include: The pore water pressure sensor was calibrated, and the pressure measuring pipe joint, inner cylinder, outer cylinder and internal water tank were treated to prevent leakage and reverse filter. The layered filling boundary and monitoring point were marked on the surface of the transparent observation window. Prepare similar materials with different permeability coefficients according to the formula, fill and compact them in layers from bottom to top, install anti-connection waterproofing plates at the boundary between adjacent filling layers, and simultaneously bury pore water pressure sensors and groundwater level sensors, and roughen the layers. Connect the pipelines of the pressurization unit, drainage simulation unit and data acquisition unit, debug the acquisition equipment, adjust the overflow tank to the set elevation, start the submersible pump to supply water to the overflow tank, apply a constant lateral water head to each filling layer in the model box, and let it stand until the pore water pressure stabilizes. The opening and closing combinations of the first and second valves were switched in sequence to simulate three working conditions: tunnel excavation, impermeable lining construction, and lining construction with drainage holes. Data on pore water pressure, groundwater level, and water inflow of each filling layer were collected under each working condition. Based on the collected data, seepage field cloud maps were drawn, and the interlayer hydraulic conductivity, hydraulic connectivity and hydraulic lag time between different filling layers were calculated to evaluate the hydraulic connection strength between each filling layer.

7. The method for layered testing of hydraulic connections in complex formations according to claim 6, characterized in that, The steps of calibrating the pore water pressure sensor, performing leak-proof and reverse filtration treatment on the pressure measuring pipe joint, inner cylinder, outer cylinder, and internal water tank, and marking the layered filling boundaries and monitoring points on the surface of the transparent observation window include: After soaking the pore water pressure sensor to remove air bubbles, it is placed in the calibration tube. The water head is changed by injecting and pumping water. The standard water head is compared with the sensor reading to determine the correction coefficient. The geotextile is cut and wrapped around the inside of the pressure measuring tube joint and the outer cylinder surface of the drainage simulation unit. The steps of preparing similar materials with different permeability coefficients according to the specified ratio, filling and compacting them in layers from bottom to top, installing anti-connection water-proof plates at the boundaries of adjacent filling layers, simultaneously burying pore water pressure sensors and groundwater level sensors, and roughening the interlayer surface include: According to the target permeability coefficient of each filling layer, weigh sand, gypsum and water according to the ratio, mix them evenly and fill them into the model box in layers. After each layer is filled, compact it to the height marked on the transparent observation window. Use a steel brush to roughen the surface between layers before filling the next layer. During the filling process, pore water pressure sensors are buried at predetermined coordinate positions and the wire harness is passed out of the model box through a sealing device.

8. The method for layered testing of hydraulic connections in complex formations according to claim 6, characterized in that, The steps of connecting the pressurization unit, drainage simulation unit, and data acquisition unit, debugging the acquisition equipment, adjusting the overflow tank to the set elevation, starting the submersible pump to supply water to the overflow tank, applying a constant lateral water head to each filling layer in the model box, and allowing it to stand until the pore water pressure stabilizes include: Place the submersible pump into the circulating water tank, and connect the overflow water tank outlet to the internal water tanks on both sides of the model box with a hose. After turning on the submersible pump, the water flows through the porous baffle of the overflow water tank into the outlet chamber. After the water level in the outlet chamber reaches the top elevation of the impermeable baffle, the excess water overflows into the overflow chamber and flows back to the circulating water tank. The outlet chamber supplies water to the internal water tank with a constant water head.

9. The method for layered testing of hydraulic connections in complex formations according to claim 6, characterized in that, The step of sequentially switching the opening and closing combinations of the first and second valves to simulate three working conditions—tunnel excavation, impermeable lining construction, and lining construction with drainage holes—and collecting pore water pressure, groundwater level, and inflow data for each filling layer under each working condition includes: First, open the first valve and the second valve simultaneously and continue to collect data until the data stabilizes. Then, close the first valve and the second valve simultaneously and monitor the recovery process of pore water pressure in each filling layer. After the recovery stabilizes, open the first valve and keep the second valve closed, and monitor the water pressure distribution and inflow of each filling layer.

10. The method for stratified testing of hydraulic connections in complex formations according to any one of claims 6 to 9, characterized in that, The steps of drawing seepage field cloud maps based on collected data, calculating the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time between different filling layers, and evaluating the hydraulic connection strength between each filling layer include: The pore water pressure data of each monitoring point under each working condition are interpolated according to spatial coordinates to generate a seepage field distribution map; the groundwater level drawdown data of each filling layer under different inflow conditions are statistically analyzed, the correspondence between inflow and drawdown is compared, and the drawdown data of hydraulic lag time and seepage control timing are combined to determine the timing of lining construction under this stratum condition. The calculation formulas for the interlayer hydraulic conductivity, hydraulic connectivity, and hydraulic lag time are as follows: Interlayer hydraulic conductivity: In the formula, Let be the hydraulic conductivity coefficient between the i-th and j-th filling layers. Let L be the steady-state seepage flow rate between the two filling layers, L be the direct seepage path length between the two filling layers, and A be the cross-sectional area of ​​the interlayer water passage. The steady-state head difference between formations i and j; Dimensionless hydraulic connectivity: In the formula, The hydraulic connectivity of filling layers i and j, with a value range of 0 < ≤1, This represents the maximum interlayer hydraulic conductivity coefficient of the entire strata. Hydraulic response lag time: In the formula, Let be the lag time for the change in water head at layer i to be transmitted to layer j. This represents the maximum head drop in the upper layer. This represents the interlayer seepage conduction velocity.

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