Test device and method for determining hydraulic gradient of seepage failure in dislocation zone by one-way flow in-situ test

Abstract

The present invention discloses a test device and method for determining the hydraulic gradient of seepage failure of a dislocation zone by a one-way flow in-situ test, aiming to overcome the shortcomings of the existing technical solutions for determining the hydraulic gradient of seepage failure of a dislocation zone, and provides a method for determining the hydraulic gradient of seepage failure of a dislocation zone based on the one-way flow in-situ test device and the analytical solution of the non-steady flow formula in the dislocation zone under the condition of step boundary head. The device includes a water inlet tank, a water outlet tank, a pressure measuring tube, a pressure gauge and a water injection pressurizing device. The method steps include selecting a suitable test point in an on-site flat tunnel to form an in-situ sample; conducting an on-site test to record flow data and damage sign time; obtaining the permeability parameters of the dislocation zone based on the test data; and calculating the hydraulic gradient of seepage failure of the dislocation zone.

Description

Technical Field

[0001] The present invention relates to a test device and method for determining the seepage failure hydraulic gradient of a dislocation zone by a unidirectional flow in-situ test, in particular to a test device and method for determining the critical hydraulic gradient and the failure hydraulic gradient of a dislocation zone under an unstable flow state on site. Background Art

[0002] Dislocation zones mainly refer to weak structural surfaces with slow dip angles formed in hard rock layers due to tectonic movements during geological history. Dislocation zones can be divided into interlayer dislocation zones and intralayer dislocation zones according to their development location. They are ubiquitous in nature and are much larger in scale than rock mass engineering structures, causing seepage control, rock mass stability problems and geological disasters in many projects. Interlayer dislocation zones and intralayer dislocation zones with slow dip angles are widely developed in the basalts in the dam sites of the Xiluodu Hydropower Station that has been built in the lower reaches of the Jinsha River and the Baihetan Hydropower Station that is under construction. These dislocation zone materials are generally a mixture of mud, debris, and gravel, and their permeability is much greater than that of the original rock. Xiluodu Hydropower Station and Baihetan Hydropower Station are both high dams and large reservoirs with a dam height of more than 280m. After the reservoir is filled with water, the head difference between upstream and downstream is more than 200m. The underground hydraulic structures in the dam site area are subject to huge problems of seepage force of the slip zone, seepage damage and drainage. Therefore, the permeability of the slip zone and the hydraulic gradient value of seepage damage directly affect the design of the underground powerhouse, tunnel and dam foundation drainage plan in the dam site area.

[0003] In the past, the permeability of the dislocation zone can generally be determined through indoor or on-site permeability deformation tests based on the steady flow Darcy formula to determine the critical hydraulic gradient and the failure hydraulic gradient. However, in the test, the permeability failure of the sample may occur before the water flow reaches a stable state. If the steady flow Darcy formula is used to calculate at this time, there will be a certain error in the result. It is a very valuable method to accurately obtain the hydraulic gradient when the dislocation zone undergoes permeability failure through a simple, feasible, and time-saving in-situ test. Summary of the invention

[0004] The present invention aims to overcome the above-mentioned deficiencies in the existing technical solutions for determining the hydraulic gradient of seepage failure of a dislocation zone, and provides a test device and method for determining the hydraulic gradient of seepage failure of a dislocation zone based on a one-way flow in-situ test, which determines the hydraulic gradient of seepage failure of a dislocation zone according to the analytical solution of the unsteady flow formula in the dislocation zone under the condition of step boundary head.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention discloses a test device for determining the hydraulic gradient of seepage damage of a dislocation zone by a unidirectional flow in-situ test. The test device is used to perform a unidirectional flow test on an in-situ sample of an interlayer dislocation zone selected on the wall of a main cave, and comprises a water inlet bin, a water outlet bin, a pressure measuring tube, a pressure gauge and a water injection and pressurizing device. The water inlet bin and the water outlet bin are respectively arranged on both sides of the in-situ sample, and a portion of the surface of the in-situ sample between the water inlet bin and the water outlet bin is blocked by a concrete blocking layer. The water inlet bin is provided with a water inlet pipe, which is connected to the water injection and pressurizing device, and the water outlet bin is provided with a water outlet pipe. A gravel filter layer is filled in the water inlet bin, a steel mesh is provided on the side of the water outlet bin of the in-situ sample, and the steel mesh is filled with a gravel filter layer. The pressure measuring tube is evenly arranged in the in-situ sample and in the gravel filter layers on both sides, and the pressure gauge is connected to the pressure measuring tube.

[0007] Preferably, the water injection and pressurizing device includes a flow meter, a pressure-stabilizing water tank, a pressure regulating valve, a water pump and a water reservoir. The water reservoir is connected to the water pump, the pressure regulating valve, the pressure-stabilizing water tank and the water inlet pipe in sequence, and the pressure-stabilizing water tank is provided with a flow meter.

[0008] Preferably, the water outlet bin is provided with a transparent observation surface.

[0009] The present invention also provides a method for determining the hydraulic gradient of the seepage failure of the dislocation zone by a unidirectional flow in-situ test, the method comprising the following steps:

[0010] Step 1: Select a suitable test point in the main tunnel, cut off the interlayer dislocation zone from the surrounding area horizontally by drilling two branch holes and a connecting hole, install the above-mentioned test device, saturate the sample before the test, and start the test after the water flow stabilizes;

[0011] Step 2: Preliminary judgment is made on the form of penetration damage based on the filling material properties and fine particle content of the slip zone sample. The water injection and pressure device injects water into the water inlet bin and pressurizes it step by step. The test ends when the sample is damaged.

[0012] Step 3: After water injection and pressurization, record the water inlet flow, water outlet flow, water pressure and temperature of the pressure measuring tube every 0.5 minutes, and observe the changes at the outlet. When fine particles are brought out and the water becomes turbid, record the time of occurrence t in time. cr And the corresponding water head When the sample is damaged or the water head cannot be increased, record the time t f and the corresponding water head Termination of the trial;

[0013] Step 4: According to the permeability coefficient K and water storage rate μ of the in-situ sample of the dislocation zone s ,t cr and t f , calculate the critical hydraulic gradient J cr , destroy hydraulic gradient J f .

[0014] Preferably, the thickness of the in-situ sample of the dislocation zone in step 1 is 0.15-0.3 m, and a certain thickness of the original rock is retained vertically to form an in-situ sample with a seepage diameter of 2 m, a width of 1.5 m, and a height of 1.5 m.

[0015] Preferably, the water injection and pressurizing device in step 2 injects water into the water inlet bin and pressurizes it step by step in the following manner: the initial water pressure is 0.05MPa, and the boundary water pressure is increased step by step by 0.1MPa, 0.15MPa, 0.2MPa, 0.3MPa, 0.5MPa, 0.7MPa, 1.0MPa, 1.5MPa, 2.0MPa every 20 minutes or so, and then by 0.5MPa each time.

[0016] Preferably, the step 4 specifically comprises the following steps:

[0017] According to the unsteady flow hydraulic gradient formula in the sample under step boundary conditions:

[0018] In the formula a is the conductivity coefficient; J(x,t) is the change in hydraulic gradient at point x in the sample at time t; M is the number of test head pressure increases; is the water head applied in the i-th stage, in m; t is the test time, in s; t i is the head pressure time of the i-th stage, in seconds; l is the length of the sample displacement zone, in meters.

[0019] The time t at which fine particles will be carried out and the water will become turbid cr And the corresponding water head Substituting into the formula, the critical hydraulic gradient J is calculated. cr ; When the sample is destroyed or the water head cannot be increased, record the time t f and the corresponding water head Substitute into the formula to calculate the failure hydraulic gradient J f .

[0020] The experimental device and experimental process of the present invention are simple and easy to operate, the analytical solution theory is rigorous, and the seepage destruction hydraulic gradient is determined based on the analytical formula of unsteady flow. The key technical problem of in-situ determining the seepage destruction hydraulic gradient of the dislocation zone under unsteady flow conditions can be solved, and the error of testing in the laboratory after on-site sampling can be overcome; at the same time, the permeability coefficient, conductivity coefficient, water storage coefficient, critical hydraulic gradient and destruction hydraulic gradient of the dislocation zone can be obtained in one test, and many parameters can be obtained. Therefore, the method has a good value for promotion and application.

[0021] Compared with the existing method for determining hydraulic gradient of seepage failure in dislocation zone, the method provided by the present invention has the following advantages:

[0022] (1) The analytical solution derived is theoretically rigorous, so the method has a strict theoretical basis.

[0023] (2) The one-way flow in-situ test of the hydraulic gradient of seepage damage is realized, and the test device and test process are simple and easy to operate.

[0024] (3) The hydraulic gradient when the seepage damage occurs in the unsteady flow state can be accurately obtained, avoiding the error caused by the existing method that calculates the hydraulic gradient of the seepage damage according to the Darcy formula of steady flow.

[0025] (4) In one test, the permeability coefficient, conductivity coefficient, water storage coefficient, critical hydraulic gradient and failure hydraulic gradient of the dislocation zone can be obtained simultaneously, and many parameters can be obtained. Therefore, this method has a good value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of a one-way flow in-situ test site according to an embodiment of the present invention;

[0027] Figure 2 It is a cross-sectional view of the field test Ⅰ-Ⅰ of an embodiment of the present invention;

[0028] Figure 3 This is the boundary head change of the embodiment of the present invention.

[0029] In the figure:

[0030] 1. In-situ specimen; 2. Water inlet tank; 3. Water outlet tank; 4. Pressure measuring tube; 5. Pressure gauge; 6. Concrete sealing layer; 7. Water inlet pipe; 8. Water outlet pipe; 9. Gravel filter layer; 10. Wire mesh; 11. Flow meter; 12. Pressure-stabilizing water tank; 13. Pressure regulating valve; 14. Water pump; 15. Water reservoir; 16. Transparent observation surface; 17. Measuring bucket; 18. Main hole; 19. Branch hole; 20. Connecting hole. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0032] like Figure 1 , Figure 2As shown, a test device for determining the hydraulic gradient of the seepage failure of the dislocation zone by a one-way flow in-situ test of the present invention is used to perform a one-way flow test on the in-situ sample of the interlayer dislocation zone selected on the wall of the main cave. The in-situ sample 1 is selected at a suitable position on the wall of the main cave 18, and branch holes 19 are opened on both sides of the sample position, and then a connecting hole 20 is set at the inner end of the branch hole. Thereby, the interlayer dislocation zone is separated from the original rock around, and the thickness of the in-situ sample of the interlayer dislocation zone is 0.15 to 0.3m, and a certain thickness of the original rock is retained vertically, forming an in-situ sample with a seepage diameter of 2m, a width of 1.5m, and a height of 1.5m.

[0033] The test device includes a water inlet tank 2, a water outlet tank 3, a pressure measuring tube 4, a pressure gauge 5 and a water injection pressurizing device. The water inlet tank and the water outlet tank are respectively arranged on both sides of the in-situ sample. In this embodiment, the water inlet tank is arranged in the connecting hole, and the water outlet tank is arranged in the main hole.

[0034] The surface of the in-situ sample between the water inlet and outlet bins is blocked by a concrete blocking layer 6. The water inlet bin is provided with a water inlet pipe 7, which is connected to a water injection and pressure device. The water outlet bin is provided with a water outlet pipe 8. A water measuring bucket 17 is provided on one side of the water outlet pipe to measure the water outflow in a certain period of time and convert it into the seepage volume in the corresponding period of time.

[0035] The water inlet bin is filled with a gravel filter layer 9. The water outlet bin is provided with a transparent observation surface 16. The in-situ sample is provided with a wire mesh 10 on the side of the water outlet bin, and the wire mesh is filled with a gravel filter layer. The pressure measuring tubes are evenly arranged in the in-situ sample and the gravel filter layers on both sides, and the pressure gauge is connected to the pressure measuring tubes. The water injection and pressurization device includes a flow meter 11, a pressure-stabilizing water tank 12, a pressure regulating valve 13, a water pump 14 and a water reservoir 15. The water reservoir is connected to the water pump, the pressure regulating valve, the pressure-stabilizing water tank and the water inlet pipe in sequence, and the pressure-stabilizing water tank is provided with a flow meter.

[0036] The embodiment of the present invention also provides a method for determining the hydraulic gradient of the seepage failure of the dislocation zone by a one-way flow in-situ test based on the above test device, the method comprising the following steps:

[0037] Step 1: Select a suitable test point in the main tunnel, cut off the interlayer dislocation zone from the surrounding area horizontally by drilling two branch holes and a connecting hole, install the above-mentioned test device, saturate the sample before the test, and start the test after the water flow stabilizes.

[0038] In the step 1, the thickness of the in-situ sample of the interlayer dislocation zone is 0.15-0.3 m, and a certain thickness of the original rock is retained vertically to form an in-situ sample with a seepage diameter of 2 m, a width of 1.5 m, and a height of 1.5 m.

[0039] Step 2: Preliminary judgment is made on the form of penetration damage based on the filling material properties and fine particle content of the dislocation zone sample. The water injection and pressurization device injects water into the water inlet bin and pressurizes it step by step. The test is terminated when the sample is damaged.

[0040] The water injection and pressurizing device in step 2 injects water into the water inlet bin and pressurizes it step by step in the following manner: the initial water pressure is 0.05MPa, and the boundary water pressure is increased step by step by 0.1MPa, 0.15MPa, 0.2MPa, 0.3MPa, 0.5MPa, 0.7MPa, 1.0MPa, 1.5MPa, 2.0MPa every 20 minutes or so, and then by 0.5MPa each time.

[0041] Step 3: After water injection and pressurization, record the water inlet flow, water outlet flow, water pressure and temperature of the pressure measuring tube every 0.5 minutes, and observe the changes at the outlet. When fine particles are brought out and the water becomes turbid, record the time of occurrence t in time. cr And the corresponding water head When the sample is damaged or the water head cannot be increased, record the time t f and the corresponding water head Termination of the trial;

[0042] Step 4: According to the permeability coefficient K and water storage rate μ of the in-situ sample of the interlayer dislocation zone s ,t cr and t f , calculate the critical hydraulic gradient J cr , destroy hydraulic gradient J f .

[0043] The step 4 specifically comprises the following steps:

[0044] Considering the saturation of the dislocation zone sample, the water flow is horizontal unidirectional flow. Assuming that the water head at the water inlet rises by a certain value Taking the water inlet of the dislocation belt sample as the coordinate origin, the one-dimensional unsteady water flow model is:

[0045]

[0046] Where: u(x,t) is the water level change at point x in the sample at time t, m; t is the test head pressure time, s; K is the permeability coefficient of the dislocation zone, cm / s; μ s is the water storage rate of the slip zone, cm -1 ; is the water head increment at the water inlet of the sample, m; l is the length of the sample displacement zone, m.

[0047] make a is the conduction coefficient. By separating the variables and Fourier transforming the above equation, we can get:

[0048]

[0049] The formula for the change of hydraulic gradient at each location in the sample with time is:

[0050]

[0051] Unit flow rate q: the flow rate passing through the unit cross-sectional area at position x at time t

[0052]

[0053] By non-dimensionalizing equation (4), we can obtain

[0054]

[0055] The measured data can be plotted into a qt curve and the equation (5) Standard curve matching, make the two curves overlap, select any matching point, and write down the corresponding coordinate value [q] and [t], and substitute them into the corresponding formula to calculate the permeability coefficient K and water storage rate μ of the dislocation zone s .

[0056] When the boundary condition is a step-like head change, the entire change process is understood as the superposition of water level changes in each time period, and the water level changes in each time period can be regarded as changes under constant head boundary conditions.

[0057] Similarly, the formula for the unsteady flow hydraulic gradient in the sample under step boundary conditions is derived:

[0058]

[0059] In the formula a is the conductivity coefficient; J(x,t) is the change in hydraulic gradient at point x in the sample at time t; M is the number of test head pressure increases; is the water head applied in the i-th stage, in m; t is the test time, in s; t i is the head pressure time of the i-th stage, in seconds; l is the length of the sample displacement zone, in meters.

[0060] The time t at which fine particles will be carried out and the water will become turbid cr And the corresponding water head Substituting into the formula, the critical hydraulic gradient J is calculated. cr ; When the sample is destroyed or the water head cannot be increased, record the time t f and the corresponding water head Substitute into the formula to calculate the failure hydraulic gradient J f .

[0061] In a practical example, the YS2 specimen of the C2 interlayer dislocation zone in the flat tunnel of the Baihetan Hydropower Station was selected for a unidirectional flow in-situ test.

[0062] like Figure 3 When the water head increases to the third level (Δh = 1058cm), muddy water is observed to be carried out of the outlet. The test time of this stage is 240min to 360min. The hydraulic gradient of this stage can be regarded as the critical hydraulic gradient. When the water head is pressurized to 4264cm, it is found that the flow rate increases significantly and a large amount of mud is carried out, which is regarded as sample failure. The test time of this water head stage is 720min to 840min. The length of the sample is l = 210cm, and a is 40.29cm. 2 / s.

[0063] Since the flow measurement in the test process of this example is carried out when the water flow tends to be stable, the wiring using the non-steady flow formula cannot obtain better parameters, and the time when the signs of damage and the sample damage appear are not recorded in time, the algorithm proposed in the present invention gives the range of the critical hydraulic gradient and the destructive hydraulic gradient.

[0064] If the sample has muddy water outflow phenomenon when the third level water head is just pressurized, then t1 = 241min, and the critical hydraulic gradient J is calculated. cr1 =3.57; If the sample shows characteristic phenomenon at the end of the third level of head pressure, then let t2 = 360min and calculate J cr2 =4.65. Similarly, calculate the hydraulic gradient of failure: let t1 = 721min, J f1 =16.13; let t2 = 840min, J f2 =20.30.

[0065] It can be determined that the critical hydraulic gradient of the YS2 specimen is between 3.57 and 4.65, and the failure hydraulic gradient is between 16.13 and 20.30.

[0066] The test device and test process of the present invention are simple and easy to operate, the analytical solution theory is rigorous, and the seepage destruction hydraulic gradient is determined based on the analytical formula of non-steady flow. The key technical problem of in-situ determination of the seepage destruction hydraulic gradient of the dislocation zone under non-steady flow conditions can be solved, and the error of testing in the laboratory after on-site sampling can be overcome; at the same time, the permeability coefficient, conductivity coefficient, water storage coefficient, critical hydraulic gradient and destruction hydraulic gradient of the dislocation zone can be obtained in one test, and many parameters can be obtained. Therefore, the method has a good value for promotion and application.

[0067] Compared with the existing method for determining hydraulic gradient of seepage failure in dislocation zone, the method provided by the present invention has the following advantages:

[0068] (1) The analytical solution derived is theoretically rigorous, so the method has a strict theoretical basis.

[0069] (2) The one-way flow in-situ test of the hydraulic gradient of seepage damage is realized, and the test device and test process are simple and easy to operate.

[0070] (3) The hydraulic gradient when the seepage damage occurs in the unsteady flow state can be accurately obtained, avoiding the error caused by the existing method that calculates the hydraulic gradient of the seepage damage according to the Darcy formula of steady flow.

[0071] (4) In one test, the permeability coefficient, conductivity coefficient, water storage coefficient, critical hydraulic gradient and failure hydraulic gradient of the dislocation zone can be obtained simultaneously, and many parameters can be obtained. Therefore, this method has a good value for promotion and application.

Claims

1. A method for determining the hydraulic gradient of seepage failure in a dislocation zone by a one-way flow in-situ test, characterized in that: The method comprises the following steps: Step 1: Select a suitable test point in the main tunnel, cut off the interlayer dislocation zone from the surrounding area horizontally by drilling two branch holes and a connecting hole, install the test device, saturate the sample before the test, and start the test after the water flow stabilizes; Step 2: Preliminary judgment is made on the form of penetration damage based on the filling material properties and fine particle content of the slip zone sample. The water injection and pressure device injects water into the water inlet bin and pressurizes it step by step. The test ends when the sample is damaged. Step 3: After water injection and pressurization, record the water inlet flow, water outlet flow, water pressure and temperature of the pressure measuring tube every 0.5 minutes, and observe the changes at the outlet. When fine particles are brought out and the water becomes turbid, record the time of occurrence t in time. cr And the corresponding water head When the sample is damaged or the water head cannot be increased, record the time t f and the corresponding water head Termination of the trial; Step 4: According to the permeability coefficient K and water storage rate μ of the in-situ sample of the dislocation zone s ,t cr and t f , calculate the critical hydraulic gradient J cr , destroy hydraulic gradient J f ; The test device is used to perform a unidirectional flow test on an in-situ sample of an interlayer dislocation zone selected on the wall of a main tunnel, and includes a water inlet bin, a water outlet bin, a pressure measuring tube, a pressure gauge and a water injection and pressurizing device. The water inlet bin and the water outlet bin are respectively arranged on both sides of the in-situ sample, and the surface of the in-situ sample between the water inlet bin and the water outlet bin is blocked by a concrete blocking layer. The water inlet bin is provided with a water inlet pipe, which is connected to the water injection and pressurizing device, and the water outlet bin is provided with a water outlet pipe. The water inlet bin is filled with a sand and gravel filter layer. The in-situ sample is provided with a steel mesh on the side of the water outlet bin, and the steel mesh is filled with a sand and gravel filter layer. The pressure measuring tube is evenly arranged in the in-situ sample and the sand and gravel filter layers on both sides, and the pressure gauge is connected to the pressure measuring tube; The step 4 specifically comprises the following steps: According to the unsteady flow hydraulic gradient formula in the sample under step boundary conditions: In the formula a is the conductivity coefficient; J(x,t) is the change in hydraulic gradient at point x in the sample at time t; M is the number of test head pressure increases; is the water head applied in the i-th stage, in m; t is the test time, in s; t i is the water head pressure time of the i-th stage, in seconds; l is the length of the sample displacement zone, in meters; The time t at which fine particles will be carried out and the water will become turbid cr And the corresponding water head Substituting into the formula, the critical hydraulic gradient J is calculated. cr ; When the sample is destroyed or the water head cannot be increased, record the time t f and the corresponding water head Substitute into the formula to calculate the failure hydraulic gradient J f .

2. The method for determining the hydraulic gradient of the seepage failure of the dislocation zone by the one-way flow in-situ test according to claim 1 is characterized in that: The water injection and pressurizing device comprises a flow meter, a pressure-stabilizing water tank, a pressure regulating valve, a water pump and a water reservoir. The water reservoir is connected to the water pump, the pressure regulating valve, the pressure-stabilizing water tank and the water inlet pipe in sequence, and the pressure-stabilizing water tank is provided with a flow meter.

3. The method for determining the hydraulic gradient of the seepage failure of the dislocation zone by the one-way flow in-situ test according to claim 1 is characterized in that: The water outlet bin is provided with a transparent observation surface.

4. The method for determining the hydraulic gradient of the seepage failure of the dislocation zone by the one-way flow in-situ test according to claim 1 is characterized in that: The thickness of the in-situ sample of the interlayer dislocation zone in step 1 is 0.15-0.3 m, and a certain thickness of the original rock is retained vertically to form an in-situ sample with a seepage diameter of 2 m, a width of 1.5 m, and a height of 1.5 m.

5. The method for determining the hydraulic gradient of the seepage failure of the dislocation zone by the one-way flow in-situ test according to claim 4 is characterized in that: The water injection and pressurizing device in step 2 injects water into the water inlet bin and pressurizes it step by step in the following manner: the initial water pressure is 0.05MPa, and the boundary water pressure is increased step by step by 0.1MPa, 0.15MPa, 0.2MPa, 0.3MPa, 0.5MPa, 0.7MPa, 1.0MPa, 1.5MPa, 2.0MPa every 20 minutes or so, and then by 0.5MPa each time.

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