In-situ seepage test device for undisturbed soil body and permeability coefficient determination method

Abstract

The invention relates to an in-situ seepage test device for an undisturbed soil body and a permeability coefficient determination method. The device comprises a permeability test assembly, a sample cylinder pressing-in assembly, an infinite flow water pressure measurement and control assembly and a seepage determination assembly, the penetration test assembly comprises a sample cylinder and a sample cylinder sealing cover, a water through hole is formed in the side wall of the sample cylinder, and a water injection hole and an exhaust hole are formed in the sample cylinder sealing cover; the sample cylinder press-in assembly is used for vertically pressing the sample cylinder into the undisturbed soil body; the infinite flow water pressure measurement and control assembly is used for providing a water head for a to-be-tested soil sample in the sample cylinder through the water injection hole; the seepage measurement assembly comprises a pore pressure sensor, and is used for obtaining a seepage correlation parameter and obtaining a seepage coefficient of the to-be-measured soil sample in the sample cylinder based on the seepage correlation parameter. According to the invention, the in-situ accurate measurement of the permeability characteristics of the undisturbed soil body is realized, the reliability and continuity of test data are guaranteed, and a foundation is laid for accurately analyzing the real permeability characteristics of the soil sample.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and geotechnical testing technology, and in particular to an in-situ seepage test device for undisturbed soil and a method for determining the permeability coefficient. Background Technology

[0002] The permeability coefficient is one of the important parameters for measuring the permeability characteristics of soil. It is the basic input data for problems such as seepage analysis, slope stability, hydraulic structure design, and groundwater migration simulation in geotechnical engineering. Currently, the methods for determining the permeability coefficient are mainly divided into two categories: laboratory tests and in-situ tests.

[0003] Indoor permeability testing, including the constant head method and the variable head method, offers advantages such as controllable testing environment and standardized operating procedures. However, these methods often require drilling, transporting, and preparing undisturbed soil samples. This process inevitably disrupts the natural structure and stress state of the soil, causing the measured permeability coefficient to deviate from the actual value. Furthermore, indoor tests cannot accurately reproduce the structure, density, and boundary conditions of in-situ soil, and their results have significant limitations under complex geological conditions.

[0004] In-situ permeability testing, because it preserves the natural structure of the soil and does not disturb it, theoretically better reflects real-world working conditions. However, existing techniques such as injection / pumping tests, test pit methods, and cone penetration tests with pore water pressure measurement (CPTU) have significant limitations: first, the test boundaries are unclear, making it difficult to accurately define the soil sample area; second, the hydraulic gradient and seepage direction are difficult to control, making it impossible to establish the one-dimensional stable seepage field required by Darcy's law; and third, most methods rely on empirical formulas or semi-empirical graphical methods to calculate the permeability coefficient, resulting in insufficient measurement accuracy and reliability.

[0005] Therefore, there is currently no standardized seepage test device or method for measuring permeability that can accurately establish a unidirectional seepage state under in-situ conditions and achieve high-precision permeability coefficient measurement. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the problems in existing technologies, such as difficulty in accurately establishing Darcy's seepage conditions, fuzzy seepage boundaries, uncontrollable hydraulic gradients, and reliance on semi-empirical calculations, this invention provides an in-situ seepage test device and a method for determining the permeability coefficient of undisturbed soil. This device constructs a unidirectional stable seepage field in the in-situ soil layer that is consistent with the indoor Darcy's law test, enabling direct measurement and calculation of transient or steady-state permeability coefficients, thereby improving the authenticity, repeatability, and accuracy of the test results.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] In a first aspect, embodiments of the present invention provide an in-situ seepage test device for undisturbed soil, used in riverbanks and alluvial plains, coastal and tidal flats, and deltaic sedimentary areas, comprising: a seepage test component, a sample tube pressing component, an unlimited flow water pressure measurement and control component, and a seepage measurement component.

[0011] The permeation test assembly includes a sample cylinder and a sample cylinder sealing cap.

[0012] The sample tube is used to isolate the soil sample to be tested from the undisturbed soil mass. The side wall of the sample tube is provided with water passage holes for water to pass between the soil sample inside the sample tube and the undisturbed soil outside the sample tube to saturate the soil sample.

[0013] The sample tube sealing cap is provided with a water injection hole and a vent hole. The water injection hole is used to inject water into the soil sample to be tested in the sample tube from the outside or to provide water head. The vent hole is used to discharge the gas in the sample tube during the water saturation stage.

[0014] The sample tube pressing assembly is used to vertically press the sample tube into the undisturbed soil.

[0015] The unlimited flow water pressure measurement and control component is used to provide water head to the soil sample to be tested in the sample tube through the water injection hole.

[0016] The seepage measurement assembly includes a pore pressure sensor mounted on the side wall of the sample cylinder.

[0017] The seepage measurement component is used to acquire seepage correlation parameters and, based on these parameters, to obtain the permeability coefficient of the soil sample inside the sample tube.

[0018] Among them, the permeation-related parameters include the injection pressure and flow rate of the infinite flow water pressure measurement and control component, and the pore water pressure inside the sample tube collected by the pore pressure sensor.

[0019] The in-situ seepage test device of this invention presses the sample tube of the seepage test component into the undisturbed soil and constructs the seepage path using the water passage, water injection hole and air vent on the sealing cover. The sample tube pressing component ensures that the sample tube is pressed vertically to reduce soil disturbance. The unlimited flow water pressure measurement and control component provides water head from top to bottom. The seepage measurement component obtains parameters such as pore water pressure, injection pressure and flow rate through pore pressure sensors and calculates the permeability coefficient. Overall, it realizes the in-situ accurate measurement of the permeability characteristics of undisturbed soil, effectively ensuring the reliability and continuity of test data, and laying the foundation for accurate analysis of the true permeability characteristics of soil samples.

[0020] Preferably, multiple pore pressure sensors are provided and are installed at different heights on the side wall of the sample cylinder;

[0021] The permeation testing assembly also includes a sensor protective cover for protecting the pore pressure sensor.

[0022] The bottom of the sensor protective cover is provided with a cone-shaped or wedge-shaped penetration head to facilitate the pressing of the sample cylinder into the undisturbed soil.

[0023] Preferably, the sample cylinder pressing assembly includes a jack, a base plate, an upper plate parallel to the base plate, a vertically arranged guide shaft connecting the base plate and the upper plate, a guide sleeve slidably fitted with the guide shaft, a jack mounting plate located between the base plate and the upper plate, a pressed beam connected to the guide sleeve, a ground anchor, and a steel cable.

[0024] The fixed end of the jack is connected to the jack mounting plate, and the telescopic end of the jack is connected to the beam being pressed.

[0025] The jack mounting plate is connected to the upper plate via an adjusting shaft seat.

[0026] The compressed beam is connected to the sample cylinder.

[0027] Preferably, the seepage measurement component includes a host computer, which is used to perform the following steps:

[0028] S11. Obtain penetration correlation parameters;

[0029] S12. Based on the pore water pressure and injection pressure, the head loss of the soil sample to be tested is obtained;

[0030] S13. Based on the head loss and injection flow rate, the permeability coefficient of the soil sample to be tested is obtained. The permeability coefficient is equal to the product of the injection flow rate per unit time and the axial length of the soil sample to be tested in the sample tube, divided by the product of the head loss and the cross-section of the sample tube. The axial length of the soil sample to be tested and the cross-section of the sample tube are fixed values ​​obtained in advance.

[0031] Preferably, the seepage measurement assembly further includes a temperature sensor, an axial deformation sensor, a water injection pressure sensor, a flow sensor, and a host computer.

[0032] Among them, the temperature sensor is used to collect the real-time temperature inside the sample tube, the axial deformation sensor is used to collect the axial deformation of the soil sample to be tested inside the sample tube, the water injection pressure sensor is used to collect the real-time water injection pressure of the infinite flow water pressure measurement and control component, and the flow sensor is used to collect the real-time water injection flow of the infinite flow water pressure measurement and control component.

[0033] The host computer is used to perform the following steps:

[0034] S21. Obtain the permeation correlation parameters, which also include real-time temperature and axial deformation, and the water injection pressure and water injection flow rate in the permeation correlation parameters are real-time water injection pressure and real-time water injection flow rate.

[0035] S22. Based on the permeability correlation parameters, the seepage correlation correction parameters are obtained. The seepage correlation correction parameters include effective head loss, real-time dynamic viscosity, actual seepage path length, pressure fluctuation coefficient, effective injection flow rate, flow fluctuation coefficient, and pore connectivity coupling coefficient.

[0036] S23. Based on the seepage correlation correction parameters, the corrected permeability coefficient is obtained. Specifically, the corrected permeability coefficient is equal to the product of the effective injection flow rate, the actual seepage path length, the reference dynamic viscosity, and the pore connectivity coupling coefficient, divided by the product of the sample tube cross-sectional area, the effective head loss, the real-time dynamic viscosity, and the seepage fluctuation correction coefficient.

[0037] The reference dynamic viscosity and the cross-sectional area of ​​the sample cylinder are both fixed values ​​obtained in advance. The reference dynamic viscosity is the dynamic viscosity of water at standard temperature.

[0038] The seepage fluctuation correction factor is 1 plus the injection pressure fluctuation factor, and then minus 0.3 times the flow fluctuation factor.

[0039] Preferably, S2 includes:

[0040] The real-time water injection flow rate is weighted and averaged for a preset time period to obtain the effective water injection flow rate. The standard deviation of the water injection flow rate within the preset time period is calculated. The normalized ratio of the standard deviation of the water injection flow rate and the effective water injection flow rate is processed to obtain the flow fluctuation coefficient.

[0041] Based on the axial deformation, the axial length of the soil sample to be tested is corrected by deformation compensation to obtain the actual seepage path length.

[0042] Based on the axial deformation and real-time temperature, the initial pore connectivity parameters are corrected to obtain the pore connectivity coupling coefficient, where the initial pore connectivity parameters are pre-acquired fixed values.

[0043] The real-time injection pressure is weighted and averaged for a preset time to obtain the effective injection pressure. The standard deviation of the injection pressure within the preset time is calculated. Based on the difference between the effective injection pressure and the pore water pressure, combined with the density of water and the acceleration due to gravity, the effective head loss is obtained. The pressure fluctuation coefficient is obtained by normalizing the standard deviation of the injection pressure and the effective injection pressure.

[0044] Based on real-time temperature, the reference dynamic viscosity is corrected for temperature to obtain the real-time dynamic viscosity.

[0045] Secondly, embodiments of the present invention also provide a method for determining the in-situ permeability coefficient of undisturbed soil, comprising:

[0046] S100. Fix the in-situ seepage test device described in any of the first aspects at the test site, and press the sample tube vertically into the target soil layer of the undisturbed soil through the sample tube pressing component.

[0047] S200. Saturate the soil sample in the sample tube with water through the water injection hole;

[0048] S300: The infinite flow water pressure measurement and control component applies water head to the top of the soil sample in the sample tube from the water injection hole, forming a unidirectional vertical Darcy seepage condition from top to bottom.

[0049] S400: The permeability coefficient of the soil sample to be tested in the sample tube is obtained through the permeation measurement component.

[0050] Preferably, in step S100, the vertical pressing of the sample cylinder into the target soil layer of the undisturbed soil using the sample cylinder pressing assembly includes:

[0051] A layer of petrolatum with a thickness of 0.5 mm to 1 mm is evenly applied to the inner wall of the sample tube;

[0052] The sample tube is vertically pressed into the target soil layer of the undisturbed soil at a speed of 4.5 mm / s to 5 mm / s using the sample tube pressing assembly.

[0053] After the sample cylinder is pressed into the predetermined depth, it is left to stand for 8 to 10 minutes.

[0054] Preferably, the S200 adopts a stepped pressurization water injection method, specifically including:

[0055] S201. Water is injected into the soil sample in the sample tube through the water injection hole at an initial water pressure of 4 kPa to 6 kPa for 8 min to 10 min. The water injection hole and the vent hole are opened simultaneously, and the air is vented from the inside of the sample tube through the vent hole.

[0056] S202. Using a pressure increment of 4 kPa to 6 kPa as a step, with each step lasting 8 min to 10 min, continuously inject water into the soil sample in the sample tube. During the water injection, monitor the water output from the vent hole. When a continuous flow of bubble-free water appears from the vent hole for a duration longer than the preset time, stop the water injection and close the vent hole and the water inlet. The preset time is 28 s to 32 s.

[0057] Preferably, S300 includes:

[0058] After the water head is applied, the pore water pressure and injection flow rate are continuously monitored. When the fluctuation of the injection flow rate per unit time is less than the first preset threshold, and the duration of this state is greater than or equal to 5 minutes, and the fluctuation of the pore water pressure is less than the second preset threshold, the seepage is determined to have reached a steady state, and S400 is executed.

[0059] (III) Beneficial Effects

[0060] The beneficial effects of this invention are as follows: The in-situ seepage test device of this invention presses the sample tube of the seepage test component into the undisturbed soil and constructs the seepage path using the water passage, water injection hole and air vent on the sealing cover. The sample tube pressing component ensures that the sample tube is pressed vertically to reduce soil disturbance. The unlimited flow water pressure measurement and control component provides water head from top to bottom. The seepage measurement component obtains parameters such as pore water pressure, injection pressure and flow rate through pore pressure sensors and calculates the permeability coefficient. Overall, it realizes the in-situ accurate measurement of the permeability characteristics of undisturbed soil, effectively ensuring the reliability and continuity of test data, and laying the foundation for accurate analysis of the true permeability characteristics of soil samples.

[0061] This invention breaks through the bottleneck of not being able to directly measure the soil permeability coefficient outside the laboratory, and solves the problem that traditional methods cause soil structure disturbance and property changes due to sampling and transportation, resulting in inaccurate soil parameters, which in turn leads to large deviations between numerical analysis results and actual measurements, and excessive reliance on empirical judgment. At the same time, it overcomes the technical problem that existing in-situ permeability testing does not meet the test conditions of Darcy's law and relies on empirical / semi-empirical formulas to estimate the permeability coefficient.

[0062] Based on Darcy's law, this invention innovatively proposes a dedicated test device that meets the conditions for unidirectional seepage and a novel measurement method that conforms to Darcy's law. It can accurately determine the test soil sample, maintain the original stress state and history of the soil, and ensure that its composition and structure are undisturbed. It can directly obtain reliable permeability coefficient parameters, providing accurate basic data for geotechnical numerical analysis, providing a more accurate and reliable in-situ testing method for the field of geotechnical engineering, improving the accuracy and reliability of engineering analysis, and meeting the actual needs of high-quality seepage parameter testing. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the permeability test components and sample cylinder pressing components in an in-situ permeability test device for undisturbed soil, as described in Example 1.

[0064] Figure 2 This is a cross-sectional view of the sample cylinder in an in-situ seepage test device for undisturbed soil in Example 1.

[0065] Figure 3 This is a schematic diagram of the sample cylinder in an in-situ seepage test device for undisturbed soil, as described in Example 1.

[0066] Figure 4This is a schematic diagram of the in-situ seepage test device for undisturbed soil in Example 1.

[0067] Figure 5 This is a schematic diagram illustrating the principle of in-situ permeability testing when using an in-situ permeability testing device for undisturbed soil, as described in Example 1.

[0068] Figure 6 This is a flowchart of the steps executed by the host computer when using an in-situ seepage test device for undisturbed soil in Example 1.

[0069] Figure 7 This is a flowchart of the steps executed by the host computer when using an in-situ seepage test device for undisturbed soil in Example 2.

[0070] [Explanation of Labels in the Attached Image]

[0071] 1: Base plate; 2: Support base; 3: Guide shaft; 4: Sample tube; 5: Sample tube sealing cover; 6: Pressed beam; 7: Guide sleeve; 8: Top plate; 9: Jack; 10: Adjusting shaft seat; 11: Jack mounting plate; 12: Circular pressure head; 13: Sensor protective cover; 14: Penetration head; 15: Fixing hole; 16: Water passage hole; 17: Vent hole; 18: Filter plate; 19: Sealing ring groove; 20: Water injection hole; 21: Hole pressure sensor; 22: Ground anchor; 23: Water replenishment tank; 24: Unlimited flow water pressure controller; 25: Host computer; 26: Power supply; 27: Signal converter. Detailed Implementation

[0072] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0073] This invention provides a permeability coefficient testing device and method suitable for in-situ conditions. Specifically, it is an in-situ seepage testing device capable of establishing unidirectional Darcy flow conditions in in-situ soil layers, and a method for determining the permeability coefficient based on Darcy's law. This invention solves the problems of ambiguous seepage boundaries, uncontrollable hydraulic gradients, and reliance on empirical formulas in traditional in-situ tests, and is particularly suitable for determining permeability coefficients in the range of 10. -5 cm / s~10 -2 The data covers sand and clay in the range of cm / s, providing high-precision data support for geotechnical engineering design, numerical simulation, and geological disaster early warning.

[0074] Example 1

[0075] See Figures 1-3 This embodiment provides an in-situ seepage test device for undisturbed soil, which is used in riverbanks and alluvial plains, coastal and tidal flat areas, and deltaic sedimentary areas. The device includes: a seepage test component, a sample tube pressing component, an unlimited flow water pressure measurement and control component, and a seepage measurement component.

[0076] The permeability test assembly includes a sample tube 4 and a sample tube sealing cap 5. The sample tube 4 is used to isolate the soil sample to be tested from the undisturbed soil. The side wall of the sample tube 4 is provided with a water passage hole 16 for water to flow between the soil sample to be tested inside the sample tube 4 and the undisturbed soil outside the sample tube 4. The sample tube sealing cap 5 is provided with a water injection hole 20 and a vent hole 17. The water injection hole 20 is used to inject water into the soil sample to be tested inside the sample tube 4 from the outside or to provide water head. The vent hole 17 is used to discharge the gas inside the sample tube 4 during the water saturation stage.

[0077] Specifically, the diameter of sample cylinder 4 is 100 mm and the height is 200 mm.

[0078] The sample cylinder 4 is the core component, which can effectively separate the soil sample, isolate the soil sample to be tested in situ, and accurately measure the key parameters of the soil sample. The side wall of the sample cylinder 4 is provided with two water passages 16 for saturating the soil sample to be tested.

[0079] The sample tube sealing cap 5 is connected to the sample tube 4, and a filter plate 18 is provided at its bottom. The filter plate 18 allows the injected water to permeate evenly into the soil sample to be tested, thereby applying a constant water head to the top of the soil sample to ensure the stability and uniformity of the seepage. At the same time, the sample tube sealing cap 5 has a sealing ring groove 19, which is used to install a sealing ring, which can enhance the sealing between the sealing cap and the sample tube 4, prevent water leakage during the water injection process, ensure stable test pressure and flow rate, and improve the reliability of test data.

[0080] The sample tube pressing assembly is used to vertically press the sample tube 4 into the undisturbed soil.

[0081] The sample cylinder pressing assembly of the pressing module can press the sample cylinder 4 into a predetermined depth while preserving the original structure of the soil layer to the maximum extent. Specifically, the sample cylinder pressing assembly of the pressing module includes a jack 9, a base plate 1, an upper plate 8 arranged parallel to the base plate 1, a guide shaft 3 connected between the base plate 1 and the upper plate 8 and arranged vertically, a guide sleeve 7 that slides with the guide shaft 3, a jack mounting plate 11 located between the base plate 1 and the upper plate 8, a pressed beam 6 connected to the guide sleeve 7, a ground anchor 22 and a steel cable. The fixed end of the jack 9 is connected to the jack mounting plate 11, and the telescopic end of the jack 9 is connected to the pressed beam 6. The jack mounting plate 11 is connected to the upper plate 8 through an adjusting shaft seat 10, and the pressed beam 6 is connected to the sample cylinder 4.

[0082] The jack 9 is a hydraulic jack with a maximum loading force of 3t, providing stable and controllable vertical driving force to power the sample cylinder 4 as it is pressed into the target soil layer. Its hydraulic drive characteristics enable precise pressure adjustment to meet the differentiated pressing force requirements of different soil layers such as sand and clay. A circular pressing head 12 is fixed at the bottom of the jack 9, and its outline matches that of the sample cylinder 4. Through the close contact between the circular pressing head 12 and the top of the sample cylinder 4, the driving force of the jack 9 can be evenly transmitted to the sample cylinder 4, avoiding deformation of the sample cylinder 4 due to uneven local force. At the same time, the shape adaptation guides the sample cylinder 4 to enter the target soil layer vertically, reducing trajectory deviation caused by force offset during the pressing process.

[0083] The base plate 1, guide shaft 3, upper plate 8, jack mounting plate 11, and pressure beam 6 constitute the support mechanism. The base plate 1 serves as the bottom foundation of the entire device, bearing the weight of the upper structure and distributing the pressure to the ground. The upper plate 8 and the pressure beam 6 form the top load-bearing frame, which, together with the jack mounting plate 11, fixes the jack 9. The overall structure, through the transmission and distribution of force, realizes the function of applying vertical pressing force to the sample cylinder 4, while providing a stable installation and working platform for each component.

[0084] The guide shaft 3 is connected to the base plate 1 via the support base 2, and the guide shaft 3 passes through the guide sleeve 7, forming a sliding fit structure. The guide sleeve 7 constrains the lateral displacement of the guide shaft 3, thereby limiting the lateral offset of the sample cylinder 4 and providing it with precise vertical guidance; this fit can effectively counteract the tilting tendency of the sample cylinder 4 caused by the lateral resistance of the soil layer during the pressing process, ensuring the vertical stability of the pressing path.

[0085] The adjusting shaft seat 10 provides rigid support for the jack mounting plate 11. It works in conjunction with the guide shaft 3, which restricts lateral displacement, while the adjusting shaft seat 10 ensures the jack mounting plate 11 is fixed in position. Together, they constrain the movement trajectory of the sample cylinder 4, keeping it always in the vertical direction, thereby achieving precise control over the pressing depth and speed of the sample cylinder 4.

[0086] See Figure 4 The ground anchor 22 needs to be driven deep into the soil layer of the original site in advance to provide a stable anchor point by utilizing the anchoring force of the soil; one end of the steel cable is connected to the ground anchor 22, and the other end is fixed to the support mechanism, such as the bottom plate 1 or the upper plate 8. The tension generated by the tension will firmly fix the entire support mechanism in the original site, offsetting the reaction force generated when the jack 9 drives the sample cylinder 4 to press in, preventing the support mechanism from being lifted or displaced due to the reaction force, and providing a reliable reaction force guarantee for the stable pressing of the sample cylinder 4 into the target soil layer.

[0087] Through the coordinated cooperation of power supply, force transmission, trajectory control, and structural fixation, the various components of the sample cylinder pressing assembly enable the sample cylinder 4 to be pressed vertically, accurately, and stably into the target soil layer under in-situ conditions, providing a suitable in-situ soil sample environment for subsequent permeability coefficient tests.

[0088] The unlimited flow water pressure measurement and control component is used to provide water head from top to bottom to the soil sample to be tested in the sample tube 4 through the water injection hole 20.

[0089] Specifically, the unlimited flow water pressure measurement and control component includes an unlimited flow water pressure controller 24 and a water supply tank 23. The unlimited flow water pressure controller 24 consists of two water volume pressure controllers connected in parallel. Their coordinated operation improves water supply stability and expands the pressure regulation range. When one controller adjusts the pressure or replenishes water, the other can continuously supply water, avoiding interruptions. The unlimited flow water pressure controller 24 is connected to the water supply tank 23, ensuring continuous and uninterrupted water supply and providing the required pressure. This module can both achieve continuous water supply to maintain stable seepage conditions and precisely regulate the required pressure, meeting the dynamic water pressure requirements in experiments and providing reliable hydraulic support for permeability coefficient determination.

[0090] The seepage measurement component includes a pore pressure sensor 21 installed on the side wall of the sample cylinder 4. The seepage measurement component is used to acquire seepage correlation parameters and obtain the permeability coefficient of the soil sample to be tested in the sample cylinder 4 based on the seepage correlation parameters. The seepage correlation parameters include the injection pressure and injection flow rate of the infinite flow water pressure measurement and control component, and the pore water pressure in the sample cylinder 4 collected by the pore pressure sensor 21.

[0091] Specifically, multiple pore pressure sensors 21 can be installed, each located at a different height on the side wall of the sample cylinder 4. Correspondingly, the side wall of the sample cylinder 4 is provided with fixing holes 15 for installing the pore pressure sensors. The pore pressure sensors 21 are high-precision sensors with a range of 0 kPa to 20 kPa and an accuracy of 0.15% FS. The soil sample inside the sample cylinder 4 can be divided into several axial segments based on the installation positions of the multiple pore pressure sensors 21 at different heights on the side wall. By obtaining the pore water pressure at different heights, not only can the permeability coefficient of each segment of the soil sample inside the sample cylinder 4 be obtained, providing a refined monitoring basis for the layered analysis of the soil sample's permeability characteristics and the calculation of the permeability coefficient of each segment, but the total permeability coefficient can also be calculated by combining parameters such as injection pressure. Simultaneously, this method can more accurately reflect the axial seepage gradient changes within the soil sample, thereby improving the accuracy of the overall permeability coefficient measurement.

[0092] The permeability test assembly also includes a sensor cover 13 for protecting the pore pressure sensor 21. The bottom end of the sensor cover 13 is provided with a penetration head 14 to facilitate the pressing of the sample cylinder 4 into the undisturbed soil.

[0093] The sensor protective cover 13 can be made of high-strength wear-resistant material, which can prevent the pore pressure sensor 21 from being damaged by direct friction and collision with soil particles when the sample cylinder 4 is pressed into the soil, thus providing physical protection for it and ensuring that the pore pressure sensor 21 works stably in complex soil environment to obtain accurate data.

[0094] The penetration head 14 can be conical or wedge-shaped, with a sharp bottom end that matches the bottom profile of the sample tube 4. This reduces soil resistance during insertion, ensures a smooth insertion process, and minimizes disturbance to the soil structure.

[0095] The seepage measurement assembly also includes a control device and a host computer 25.

[0096] The control device receives analog signals and converts them into digital signals, while also acquiring and processing the raw data. It should be noted that the pore water pressure in the permeability correlation parameters is precisely the digital signal obtained after the control device converts the analog signal from the pore pressure sensor 21. The control device achieves digital processing of the raw data, providing an accurate and usable digital signal foundation for subsequent experimental analyses such as permeability coefficient calculations, ensuring the effectiveness of data processing and the reliability of experimental results.

[0097] The host computer 25 can be a computer, see [link / reference] Figure 6 This is used to perform the following steps:

[0098] S11. Obtain penetration correlation parameters.

[0099] S12. Based on the pore water pressure and injection pressure, the head loss of the soil sample to be tested is obtained.

[0100] Specifically, the head loss is calculated using the following formula.

[0101]

[0102] Where Δu is the pore water pressure difference of the soil sample to be tested, and γ ω The specific weight of water is generally a fixed value preset in the host computer 25. Δd is the height difference of the soil sample to be tested. In this embodiment, the height difference of the soil sample to be tested is also its axial length, which is L in the following text. 12 or k 23 or L 34 Or L.

[0103] It should be noted that the pore water pressure difference of the soil sample inside the sample cylinder 4 is determined by the injection pressure or pore water pressure at its upper and lower ends. Furthermore, the head loss in this embodiment is the total head loss, which includes both pressure head loss and height head loss.

[0104] S13. Based on the head loss and injection flow rate, the permeability coefficient of the soil sample to be tested is obtained. The permeability coefficient is equal to the product of the injection flow rate per unit time and the axial length of the soil sample to be tested in the sample tube 4, divided by the product of the head loss and the cross-section of the sample tube 4. The axial length of the soil sample to be tested and the cross-section of the sample tube 4 are fixed values ​​obtained in advance.

[0105] See Figure 4 The apparatus of this embodiment also includes a power supply 26 for power supply and a signal converter 27 for signal conversion.

[0106] To facilitate understanding, the following will be combined with Figure 5 Steps S12 and S13 will be further explained. In the apparatus shown in the figure, three pore pressure sensors 21 are provided, located at sampling points 2, 3, and 4 of the sample cylinder 4, respectively. Accordingly, the soil sample to be tested inside the sample cylinder 4 can be divided into three sections: the area between sampling point 1 and sampling point 2 is the upper section of the soil sample to be tested; the area between sampling point 2 and sampling point 3 is the middle section of the soil sample to be tested; and the area between sampling point 3 and sampling point 4 is the lower section of the soil sample to be tested.

[0107] The pore water pressure difference in the upper section of the soil sample is obtained by subtracting the pore water pressure at sampling point 2 from the pore water pressure at sampling point 1 (i.e., the injection pressure); the pore water pressure difference in the middle section of the soil sample is obtained by subtracting the pore water pressure at sampling point 3 from the pore water pressure at sampling point 2; the pore water pressure difference in the lower section of the soil sample is obtained by subtracting the pore water pressure at sampling point 4 from the pore water pressure at sampling point 3; and the total pore water pressure difference in the total soil sample in the sample cylinder 4 (corresponding to the area between sampling point 1 and sampling point 4) is obtained by subtracting the pore water pressure at sampling point 4 from the injection pressure.

[0108] Accordingly, the permeability coefficients of each soil sample and the total permeability coefficient of the total soil sample are obtained using the following formulas.

[0109]

[0110]

[0111] Where, k 12 Let dQ be the permeability coefficient of the soil sample to be tested in the upper section, dQ be the injection flow rate during the time interval dt, and L be the permeability coefficient of the soil sample to be tested in the upper section. 12 dH represents the axial length of the upper section of the soil sample to be tested, i.e., the height difference between sampling point 1 and sampling point 2. 12 The water head loss of the soil sample to be tested in the upper section is A, which is the cross-sectional area of ​​the sample tube 4, and can be obtained from the area formula by the diameter of the sample tube 4.

[0112] k 23 L represents the permeability coefficient of the soil sample in the middle section. 23dH represents the axial length of the soil sample in the middle section, i.e., the height difference between sampling point 2 and sampling point 3. 23 This refers to the head loss of the soil sample to be tested in the middle section;

[0113] k 34 Let L be the permeability coefficient of the soil sample to be tested in the next section. 34 dH represents the axial length of the soil sample to be tested in the next section, i.e., the height difference between sampling point 3 and sampling point 4. 34 This represents the head loss of the soil sample to be tested in the next section.

[0114] k is the total permeability coefficient of the total soil sample, L is the axial length of the total soil sample, i.e. the height difference between sampling point 1 and sampling point 4, and dH is the head loss of the total soil sample.

[0115] In this embodiment, the in-situ seepage test device presses the sample tube 4 of the seepage test component into the undisturbed soil and constructs a seepage path using the water passage 16, the water injection hole 20 on the sealing cover, and the vent hole 17. The sample tube pressing component ensures that the sample tube 4 is pressed vertically to reduce soil disturbance. The unlimited flow water pressure measurement and control component provides water head from top to bottom. The seepage measurement component obtains parameters such as pore water pressure, injection pressure, and flow rate through the pore pressure sensor 21 and other means, and calculates the permeability coefficient. Overall, it realizes the in-situ accurate measurement of the permeability characteristics of the undisturbed soil, effectively ensuring the reliability and continuity of the test data, and laying the foundation for accurate analysis of the true permeability characteristics of the soil sample.

[0116] Example 2

[0117] While Example 1 can achieve in-situ seepage testing of undisturbed soil, the complex and variable in-situ test environment, coupled with potential interference factors such as temperature fluctuations in the external environment, and the general lack of stable control over injection pressure and flow rate of traditional testing devices, makes it easy for the injection pressure to fluctuate during the test, and the injection flow rate to be difficult to maintain constant, affecting the reliability of the test data and adversely impacting the determination of the permeability coefficient. To address these complex interference factors, this example further improves upon Example 1 in terms of pressure and flow rate control stability and anti-interference capabilities.

[0118] The seepage measurement component in this embodiment also includes a temperature sensor, an axial deformation sensor, a water injection pressure sensor, and a flow sensor. The temperature sensor is used to collect the real-time temperature inside the sample tube, the axial deformation sensor is used to collect the axial deformation of the soil sample inside the sample tube, the water injection pressure sensor is used to collect the real-time water injection pressure of the infinite flow water pressure measurement and control component, and the flow sensor is used to collect the real-time water injection flow rate of the infinite flow water pressure measurement and control component.

[0119] Specifically, multiple temperature sensors can be arranged at intervals along the axial direction of the sample tube, the axial deformation sensor is a strain gauge installed inside the sample tube sealing cover, the water pressure sensor can be installed on the pipeline connecting the unlimited flow water pressure measurement and control component and the water injection hole of the sample tube sealing cover, and the flow sensor can be an electromagnetic flow meter, which can be connected in series in the same water injection pipeline.

[0120] See Figure 7 The host computer is used to execute the following steps:

[0121] S21. Obtain the permeation correlation parameters, which also include real-time temperature and axial deformation. The injection pressure and injection flow rate in the permeation correlation parameters are real-time injection pressure and real-time injection flow rate, respectively.

[0122] The real-time temperature is the arithmetic mean of the temperatures from all temperature sensors.

[0123] S22. Based on the seepage correlation parameters, the seepage correlation correction parameters are obtained. The seepage correlation correction parameters include effective head loss, real-time dynamic viscosity, actual seepage path length, pressure fluctuation coefficient, effective injection flow rate, flow fluctuation coefficient, and pore connectivity coupling coefficient.

[0124] Specifically, S22 includes performing a weighted average of the real-time water injection flow rate for a preset duration to obtain the effective water injection flow rate, calculating the standard deviation of the water injection flow rate within the preset duration, and performing normalization ratio processing on the standard deviation of the water injection flow rate and the effective water injection flow rate to obtain the flow fluctuation coefficient.

[0125] More specifically, the effective injection flow rate and flow fluctuation coefficient are obtained through the following formulas:

[0126]

[0127]

[0128] Among them, Q 有效 The effective water injection flow rate is given by T, which is the preset duration, t1 and t2 are the start and end times of the preset duration, respectively, and Q(t) is the real-time water injection flow rate. f represents the integral of Q(t) over the time interval [t1, t2]. Q σ is the flow fluctuation coefficient. Q This represents the standard deviation of the water injection flow rate.

[0129] Based on the axial deformation, the axial length of the soil sample to be tested is corrected by deformation compensation to obtain the actual seepage path length.

[0130] More specifically, the actual seepage path length is obtained using the following formula:

[0131] L 实际=L0-ΔL+β T ·L0·(T-T0)

[0132] Among them, L 实际 L0 is the actual seepage path length, L0 is the axial length of the soil sample to be tested, which is also the initial seepage path length of the soil sample to be tested, ΔL is the axial deformation of the soil sample to be tested, and β is the axial deformation of the soil sample to be tested. T T is the coefficient of thermal expansion of the soil sample to be tested, which is usually a fixed value preset in the host computer. T is the real-time temperature, and T0 is the reference temperature, which is usually the reference state temperature set at the beginning of the test.

[0133] Based on the axial deformation and real-time temperature, the initial pore connectivity parameters are corrected to obtain the pore connectivity coupling coefficient, where the initial pore connectivity parameters are pre-acquired fixed values.

[0134] More specifically, the pore connectivity coupling coefficient is obtained by the following formula:

[0135] Γ=Γ0·(1-ΔL / L0) 0.3 ·[1+0.01(T-20)]

[0136] Where Γ is the pore connectivity coupling coefficient, Γ0 is the initial pore connectivity parameter, ΔL is the axial deformation of the soil sample, L0 is the axial length of the soil sample, and T is the real-time temperature.

[0137] The real-time injection pressure is weighted and averaged for a preset time period to obtain the effective injection pressure. The standard deviation of the injection pressure within the preset time period is calculated. Based on the difference between the effective injection pressure and the pore water pressure, combined with the water density and gravitational acceleration, the effective head loss is obtained. The pressure fluctuation coefficient is obtained by normalizing the standard deviation of the injection pressure and the effective injection pressure.

[0138] More specifically, the effective head loss and pressure fluctuation coefficient are obtained through the following formulas:

[0139]

[0140] Among them, P 有效 To determine the effective water injection pressure, T represents the preset duration, t1 and t2 are the start and end times of the preset duration, respectively, and P(t) is the real-time water injection pressure. f represents the integral of P(t) over the time interval [t1, t2]. P σ is the pressure fluctuation coefficient. P dH represents the standard deviation of the injection pressure. 有效 To effectively reduce head, u 孔压 ρ is the pore water pressure at the lower end of the soil sample, g is the gravitational acceleration, and Δd is the height difference of the soil sample, which is also the axial length of the soil sample.

[0141] It should be noted that since the fluctuation of water injection pressure has a significant impact on the head loss of the total soil sample and the upper section soil sample, the head loss needs to be corrected based on the effective water injection pressure and calculated using formula (2); while the fluctuation of water injection pressure has a smaller impact on the head loss of the middle and lower sections soil samples, and no correction is needed. Therefore, the head loss of the middle and lower sections soil samples can be calculated using formula (1) in Example 1.

[0142] Based on real-time temperature, the reference dynamic viscosity is corrected for temperature to obtain the real-time dynamic viscosity.

[0143] More specifically, the real-time dynamic viscosity is obtained by the following formula:

[0144]

[0145] Where, μ T For real-time dynamic viscosity, μ 20 The reference dynamic viscosity is typically the dynamic viscosity at 20°C, where T is the real-time temperature.

[0146] S23. The corrected permeability coefficient is obtained based on the seepage correlation correction parameters. Specifically, the corrected permeability coefficient is equal to the product of the effective injection flow rate, the actual seepage path length, the reference dynamic viscosity, and the pore connectivity coupling coefficient, divided by the product of the sample tube cross-sectional area, the effective head loss, the real-time dynamic viscosity, and the seepage fluctuation correction coefficient. The reference dynamic viscosity and the sample tube cross-sectional area are fixed values ​​obtained in advance. The reference dynamic viscosity is the dynamic viscosity of water at the standard temperature. The seepage fluctuation correction coefficient is 1 plus the injection pressure fluctuation coefficient and then minus 0.3 times the flow rate fluctuation coefficient.

[0147] Specifically, the corrected permeability coefficient is obtained using the following formula.

[0148]

[0149] Where, k 修正 Q is the corrected permeability coefficient. 有效 To achieve an effective water injection flow rate, L 实际 μ is the actual seepage path length. 20 Let Γ be the reference dynamic viscosity, Γ be the pore connectivity coupling coefficient, A be the cross-sectional area of ​​the sample cylinder, and dH be the reference dynamic viscosity. 有效 To effectively reduce head, μ T For real-time dynamic viscosity, f P f is the pressure fluctuation coefficient. Q This is the flow fluctuation coefficient.

[0150] This embodiment introduces several anti-interference parameters based on Embodiment 1. These parameters are used to dynamically correct interference factors in the experiment. Among them, the effective injection flow rate and effective injection pressure are processed by weighted averaging to smooth instantaneous fluctuations and provide stable basic data for calculation; the flow fluctuation coefficient and pressure fluctuation coefficient quantify the degree of fluctuation and are used for seepage fluctuation correction; the actual seepage path length corrects for path deviations caused by deformation and temperature; the pore connectivity coupling coefficient reflects changes in pore structure due to environmental interference; the real-time dynamic viscosity eliminates the influence of temperature on water viscosity; the effective head loss corrects the influence of pressure fluctuation on head loss; and the seepage fluctuation correction coefficient comprehensively offsets the cumulative effect of pressure and flow fluctuations.

[0151] This embodiment systematically solves interference problems such as temperature fluctuations, water injection pressure and flow fluctuations, and soil deformation through the synergistic effect of multi-dimensional anti-interference parameters, significantly improving the anti-interference capability and measurement stability of the device in complex in-situ environments. The corrected permeability coefficient calculation strictly conforms to Darcy's law, effectively eliminating the deviation of uncorrected data and more closely matching the true permeability characteristics of the soil sample to be tested. It provides high-precision and reliable basic data for geotechnical engineering numerical analysis and engineering design, breaking through the technical bottleneck caused by interference in traditional devices.

[0152] Example 3

[0153] This embodiment provides a method for determining the in-situ permeability coefficient of undisturbed soil, including:

[0154] S100. Fix the in-situ seepage test device of Example 1 or Example 2 at the test site, and press the sample tube vertically into the target soil layer of the undisturbed soil through the sample tube pressing component.

[0155] Before step S100, select a test site, remove surface debris, and ensure the site is level to provide a foundation for the stable installation of the sample cylinder pressing assembly. When fixing the device, first fix the base plate of the sample cylinder pressing assembly to the test site using ground anchors and steel cables to ensure the stability of the support mechanism; then install the guide shaft, upper plate, jack mounting plate, and pressed beam, and check whether the connections of each component are firm. Finally, install the sample cylinder and the sample cylinder pressing assembly.

[0156] Specifically, in S100, the vertical pressing of the sample tube into the target soil layer of the undisturbed soil by the sample tube pressing assembly includes: uniformly applying a petroleum jelly layer with a thickness of 0.5 mm to 1 mm to the inner wall of the sample tube; pressing the sample tube vertically into the target soil layer of the undisturbed soil at a speed of 4.5 mm / s to 5 mm / s by the sample tube pressing assembly; and allowing the sample tube to stand for 8 min to 10 min after it has been pressed to the predetermined depth.

[0157] It should be noted that applying a layer of petroleum jelly to the inner wall of the sample tube can facilitate operation before the sample tube is installed. The preferred standing time after the sample tube is pressed into the predetermined depth is 9 minutes, and the preferred predetermined depth is 200 mm.

[0158] Step S100 achieves the sealing and isolation of the undisturbed soil, ensuring effective isolation of the soil sample and maintaining its natural original structure, providing a qualified in-situ soil environment for subsequent tests. In this step, a 0.5mm to 1mm thick layer of Vaseline is uniformly applied to the inner wall of the sample tube, which reduces frictional disturbance during injection and avoids contact permeation during the permeability test; injection at a rate of 4.5mm / s to 5mm / s reduces disturbance to the soil structure; and allowing the sample to stand for 8 to 10 minutes after injection to the predetermined depth allows the soil stress to recover, reducing the impact of instantaneous disturbance. The synergistic effect of these parameters ensures a tight fit between the sample tube and the undisturbed soil, while maintaining the original physical state of the soil, laying a reliable foundation for subsequent water saturation and permeability coefficient determination.

[0159] S200. Saturate the soil sample in the sample tube with water through the water injection hole.

[0160] Specifically, the S200 adopts a stepped pressurization water injection method, including:

[0161] S201. Water is injected into the soil sample in the sample tube through the water injection hole at an initial water pressure of 4 kPa to 6 kPa for 8 min to 10 min. The water injection hole and the vent hole are opened simultaneously, and the air is vented from the inside of the sample tube through the vent hole.

[0162] S202. Using a pressure increment of 4 kPa to 6 kPa as one step, with each step lasting 8 min to 10 min, continuously inject water into the soil sample in the sample tube. During the water injection, monitor the water output from the vent hole. When a continuous flow of bubble-free water appears from the vent hole for a duration longer than the preset time, stop the water injection and close the vent hole and water inlet at the same time. The preset time is 28 s to 32 s.

[0163] It should be noted that during water injection, the initial water pressure and pressure increment are preferably 5 kPa; the water injection duration and the maintenance time of each step are preferably 9 min; and the preset duration is preferably 30 s.

[0164] Step S200 involves gradually increasing the injection pressure by using an initial water pressure of 4 kPa to 6 kPa, with each increment of 4 kPa to 6 kPa, and maintaining each increment for 8 to 10 minutes. This gradually saturates the soil sample within the test tube, effectively expelling gas from the soil sample and the device, progressively displacing air from the soil pores, and establishing a uniform and stable saturated seepage environment, laying the foundation for a stable seepage field in the future. The initial water pressure and pressure increments prevent sudden pressure increases from disturbing the soil sample structure; the injection and step-by-step maintenance times ensure sufficient water penetration into the soil sample pores; and the injection is stopped when a continuous, bubble-free water flow appears at the vent for 28 to 32 seconds, ensuring complete saturation of the soil sample and complete gas removal, thus guaranteeing the accuracy of subsequent seepage tests.

[0165] S300: Apply water head to the top of the soil sample in the sample tube through the water injection hole using the infinite flow water pressure measurement and control component to form a unidirectional vertical Darcy seepage condition from top to bottom. After applying the water head, continuously monitor the pore water pressure and water injection flow rate. When the fluctuation amplitude of the water injection flow rate per unit time is less than the first preset threshold, and the duration of this state is greater than or equal to 5 minutes, and the fluctuation amplitude of the pore water pressure is lower than the second preset threshold, it is determined that the seepage has reached a steady state, and S400 is executed.

[0166] Step S300 applies water head through an infinite flow rate and pressure control component, forming a unidirectional vertical Darcy flow condition from top to bottom. This step determines whether the seepage has reached a steady state, providing a stable seepage environment for accurate permeability coefficient determination. The core of this step is establishing a unidirectional steady-state seepage condition that conforms to Darcy's law. In this step, a first preset threshold controls the fluctuation range of the injection flow rate per unit time, and a second preset threshold controls the fluctuation range of the pore water pressure. When the fluctuation ranges of both are less than their respective thresholds and remain so for at least 5 minutes, this is considered a criterion for determining that the seepage has reached a steady state. The first and second preset thresholds control flow rate stability and pressure uniformity, respectively, synergistically eliminating transient interference and ensuring that the collected data accurately reflects the soil sample's permeability characteristics, providing a theoretically sound steady-state seepage field for accurate permeability coefficient determination in step S400.

[0167] S400: The permeability coefficient of the soil sample to be tested in the sample tube is obtained through the permeation measurement component.

[0168] After the test, shut down the unlimited flow water pressure measurement and control component and stop water injection. Start the hydraulic jack and slowly lift the sample cylinder outside the soil layer. Check and record the soil sample condition. Disassemble each module, clean the sample cylinder and sensor, and ensure the equipment is in good condition for future use.

[0169] In this embodiment, the steps are closely coordinated. In S100, the sample cylinder is vertically pressed into the target soil layer to maintain the original structure of the soil, providing an undisturbed soil sample foundation for subsequent tests. In S200, the soil sample is fully saturated and gas is expelled through a stepped pressurization water injection method, eliminating the interference of pore gas on seepage and creating a prerequisite for establishing a stable seepage field. In S300, water head is applied to form unidirectional Darcy seepage conditions, and the steady-state judgment standard is used to ensure that the seepage state meets the calculation requirements, providing a reliable data basis for the accurate determination of the permeability coefficient in S400. The steps are sequentially connected, maintaining the natural stress state and structural integrity of the soil while strictly controlling the seepage conditions, jointly ensuring the scientific nature of the experiment and the validity of the data, forming a complete in-situ testing closed loop.

[0170] This embodiment constructs an in-situ unidirectional steady-state seepage testing system that conforms to Darcy's law. It overcomes the accuracy problems of traditional in-situ tests caused by soil sample disturbance, ambiguous seepage boundaries, and reliance on empirical formulas. It can directly obtain the reliable permeability coefficient of undisturbed soil. Through standardized operating procedures, such as injection rate, saturation parameters, and steady-state judgment criteria, it ensures the repeatability of the test and the accuracy of the results. It provides accurate basic data for numerical analysis of geotechnical engineering, significantly improves the reliability of engineering analysis, and is an effective method for high-quality permeability parameter determination in complex in-situ environments.

[0171] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0172] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions.

[0173] It should be noted that any reference numerals placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In claims that enumerate several means, several of these means may be embodied by the same hardware. The use of the terms first, second, third, etc., is merely for convenience of expression and does not indicate any order. These terms can be understood as part of the component names.

[0174] Furthermore, it should be noted that in the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0175] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims should be interpreted to include both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0176] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, then this invention should also include these modifications and variations.

Claims

1. An in-situ seepage test device for undisturbed soil, characterized in that, include: Permeability test assembly, sample cylinder injection assembly, unlimited flow water pressure measurement and control assembly, and permeation measurement assembly; The permeation test assembly includes a sample cylinder and a sample cylinder sealing cap. The sample tube is used to isolate the soil sample to be tested from the undisturbed soil mass. The side wall of the sample tube is provided with water passage holes for water to pass between the soil sample inside the sample tube and the undisturbed soil outside the sample tube to saturate the soil sample. The sample tube sealing cap is provided with a water injection hole and a vent hole. The water injection hole is used to inject water into the soil sample to be tested in the sample tube from the outside or to provide water head. The vent hole is used to discharge the gas in the sample tube during the water saturation stage. The sample tube pressing assembly is used to vertically press the sample tube into the undisturbed soil. The unlimited flow water pressure measurement and control component is used to provide water head to the soil sample to be tested in the sample tube through the water injection hole. The seepage measurement assembly includes a pore pressure sensor mounted on the side wall of the sample cylinder. The seepage measurement component is used to acquire seepage correlation parameters and, based on these parameters, to obtain the permeability coefficient of the soil sample inside the sample tube. Among them, the permeation-related parameters include the injection pressure and flow rate of the infinite flow water pressure measurement and control component, and the pore water pressure inside the sample tube collected by the pore pressure sensor.

2. The apparatus according to claim 1, characterized in that, Multiple pore pressure sensors are provided and are installed at different heights on the side wall of the sample cylinder. The permeation testing assembly also includes a sensor protective cover for protecting the pore pressure sensor. The bottom of the sensor protective cover is provided with a cone-shaped or wedge-shaped penetration head to facilitate the pressing of the sample cylinder into the undisturbed soil.

3. The apparatus according to claim 1, characterized in that, The sample cylinder pressing assembly includes a jack, a base plate, an upper plate parallel to the base plate, a vertically arranged guide shaft connecting the base plate and the upper plate, a guide sleeve slidably fitted with the guide shaft, a jack mounting plate located between the base plate and the upper plate, a pressed beam connected to the guide sleeve, a ground anchor, and a steel cable. The fixed end of the jack is connected to the jack mounting plate, and the telescopic end of the jack is connected to the beam being pressed. The jack mounting plate is connected to the upper plate via an adjusting shaft seat. The compressed beam is connected to the sample cylinder.

4. The apparatus according to claim 1, characterized in that, The seepage measurement component includes a host computer, which is used to perform the following steps: S11. Obtain penetration correlation parameters; S12. Based on the pore water pressure and injection pressure, the head loss of the soil sample to be tested is obtained; S13. Based on the head loss and injection flow rate, the permeability coefficient of the soil sample to be tested is obtained. The permeability coefficient is equal to the product of the injection flow rate per unit time and the axial length of the soil sample to be tested in the sample tube, divided by the product of the head loss and the cross-section of the sample tube. The axial length of the soil sample to be tested and the cross-section of the sample tube are fixed values ​​obtained in advance.

5. The apparatus according to claim 1, characterized in that, The seepage measurement assembly also includes a temperature sensor, an axial deformation sensor, a water injection pressure sensor, a flow sensor, and a host computer. Among them, the temperature sensor is used to collect the real-time temperature inside the sample tube, the axial deformation sensor is used to collect the axial deformation of the soil sample to be tested inside the sample tube, the water injection pressure sensor is used to collect the real-time water injection pressure of the infinite flow water pressure measurement and control component, and the flow sensor is used to collect the real-time water injection flow of the infinite flow water pressure measurement and control component. The host computer is used to perform the following steps: S21. Obtain the permeation correlation parameters, which also include real-time temperature and axial deformation, and the water injection pressure and water injection flow rate in the permeation correlation parameters are real-time water injection pressure and real-time water injection flow rate. S22. Based on the permeability correlation parameters, the seepage correlation correction parameters are obtained. The seepage correlation correction parameters include effective head loss, real-time dynamic viscosity, actual seepage path length, pressure fluctuation coefficient, effective injection flow rate, flow fluctuation coefficient, and pore connectivity coupling coefficient. S23. Based on the seepage correlation correction parameters, the corrected permeability coefficient is obtained. Specifically, the corrected permeability coefficient is equal to the product of the effective injection flow rate, the actual seepage path length, the reference dynamic viscosity, and the pore connectivity coupling coefficient, divided by the product of the sample tube cross-sectional area, the effective head loss, the real-time dynamic viscosity, and the seepage fluctuation correction coefficient. The reference dynamic viscosity and the cross-sectional area of ​​the sample cylinder are both fixed values ​​obtained in advance. The reference dynamic viscosity is the dynamic viscosity of water at standard temperature. The seepage fluctuation correction factor is 1 plus the injection pressure fluctuation factor, and then minus 0.3 times the flow fluctuation factor.

6. The apparatus according to claim 5, characterized in that, S2 includes: The real-time water injection flow rate is weighted and averaged for a preset time period to obtain the effective water injection flow rate. The standard deviation of the water injection flow rate within the preset time period is calculated. The normalized ratio of the standard deviation of the water injection flow rate and the effective water injection flow rate is processed to obtain the flow fluctuation coefficient. Based on the axial deformation, the axial length of the soil sample to be tested is corrected by deformation compensation to obtain the actual seepage path length. Based on the axial deformation and real-time temperature, the initial pore connectivity parameters are corrected to obtain the pore connectivity coupling coefficient, where the initial pore connectivity parameters are pre-acquired fixed values. The real-time injection pressure is weighted and averaged for a preset time to obtain the effective injection pressure. The standard deviation of the injection pressure within the preset time is calculated. Based on the difference between the effective injection pressure and the pore water pressure, combined with the density of water and the acceleration due to gravity, the effective head loss is obtained. The pressure fluctuation coefficient is obtained by normalizing the standard deviation of the injection pressure and the effective injection pressure. Based on real-time temperature, the reference dynamic viscosity is corrected for temperature to obtain the real-time dynamic viscosity.

7. A method for determining the in-situ permeability coefficient of undisturbed soil, characterized in that, include: S100. Fix the in-situ seepage test device according to any one of claims 1 to 6 at the test site, and press the sample tube vertically into the target soil layer of the undisturbed soil through the sample tube pressing component. S200. Saturate the soil sample in the sample tube with water through the water injection hole; S300: The infinite flow water pressure measurement and control component applies water head to the top of the soil sample in the sample tube from the water injection hole, forming a unidirectional vertical Darcy seepage condition from top to bottom. S400: The permeability coefficient of the soil sample to be tested in the sample tube is obtained through the permeation measurement component.

8. The method according to claim 7, characterized in that, In step S100, the vertical pressing of the sample cylinder into the target soil layer of the undisturbed soil using the sample cylinder pressing assembly includes: A layer of petroleum jelly with a thickness of 0.5 mm to 1 mm is evenly applied to the inner wall of the sample tube; The sample tube is vertically pressed into the target soil layer of the undisturbed soil at a speed of 4.5 mm / s to 5 mm / s using the sample tube pressing assembly. After the sample cylinder is pressed into the predetermined depth, it is left to stand for 8 to 10 minutes.

9. The method according to claim 5, characterized in that, The S200 adopts a stepped pressurization water injection method, specifically including: S201. Water is injected into the soil sample in the sample tube through the water injection hole at an initial water pressure of 4 kPa to 6 kPa for 8 min to 10 min. The water injection hole and the vent hole are opened simultaneously, and the air is vented from the inside of the sample tube through the vent hole. S202. Using a pressure increment of 4 kPa to 6 kPa as a step, with each step lasting 8 min to 10 min, continuously inject water into the soil sample in the sample tube. During the water injection, monitor the water output from the vent hole. When a continuous flow of bubble-free water appears from the vent hole for a duration longer than the preset time, stop the water injection and close the vent hole and the water inlet. The preset time is 28 s to 32 s.

10. The method according to claim 5, characterized in that, The S300 includes: After the water head is applied, the pore water pressure and injection flow rate are continuously monitored. When the fluctuation of the injection flow rate per unit time is less than the first preset threshold, and the duration of this state is greater than or equal to 5 minutes, and the fluctuation of the pore water pressure is less than the second preset threshold, the seepage is determined to have reached a steady state, and S400 is executed.

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