In-situ determination method and system for shear strength of soil body in saturated state

Abstract

The invention relates to the technical field of in-situ determination of shear strength of a soil body, in particular to an in-situ determination method and system for shear strength of the soil body in a saturated state, and a vane monitoring management module in the system is used for monitoring the shear strength of the soil body in situ after the in-situ soil body to be measured reaches the saturated state. Vertically penetrating the vane of the portable vane shear apparatus into a preset depth in the saturated soil body along the central axis of the inner ring of the double-ring permeation water injection test device at the same test point; shearing and breaking the in-situ soil body to be measured, and synchronously recording the peak torque and the residual torque. According to the invention, the double-ring permeation saturation process and the vane shear test process are creatively integrated at the same pilot point to form a continuous, in-situ and integrated test process for saturation determination; through an integrated testing process of first saturation and second shearing, the technical effects of clear testing state, high testing efficiency and high data reliability are achieved, and the industrial problem that the in-situ shearing strength in the saturation state cannot be clearly obtained by a traditional method is fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of in-situ measurement technology of soil shear strength, specifically to a method and system for in-situ measurement of soil shear strength under saturated conditions. Background Technology

[0002] In geotechnical engineering investigation, slope stability evaluation, and water conservancy engineering construction, the shear strength of soil under saturated conditions is a crucial core parameter. Accurately obtaining this parameter has a decisive impact on the safety and economy of engineering design. Currently, methods for obtaining the saturated shear strength of soil are mainly divided into two categories: laboratory tests and in-situ tests.

[0003] Laboratory tests (such as direct shear and triaxial shear tests) require the collection, transportation, and laboratory preparation of undisturbed soil samples. This process inevitably disturbs the soil samples, and the laboratory saturation process (such as vacuum saturation and counterpressure saturation) is time-consuming, often requiring several days or even weeks, resulting in low efficiency. More importantly, the stress history, structure, and boundary conditions of laboratory samples differ significantly from those of field soil, leading to test results that often fail to accurately reflect the actual engineering properties of the in-situ soil.

[0004] While portable vane shear testers in in-situ testing can quickly determine the undrained shear strength of soil, the results are highly dependent on the natural moisture content and saturation of the soil at the time of testing. Strength values ​​measured under unsaturated conditions are usually too high and cannot be directly used to evaluate the stability of soil under extreme conditions such as heavy rain or rising water levels (where the soil tends to be saturated and its strength significantly decreases). Current standards lack precise control and confirmation methods for soil saturation before vane testing, leading to significant uncertainty and risk in the application of test results. On the other hand, the double-ring permeability test is a classic method for determining the saturated permeability coefficient of in-situ soil, but its function is limited, only providing permeability parameters and not directly obtaining mechanical strength indicators. Therefore, existing technologies have significant shortcomings. Summary of the Invention

[0005] The purpose of this invention is to provide an in-situ method and system for determining the shear strength of soil under saturated conditions, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: an in-situ method for determining the shear strength of soil under saturated conditions, the method comprising: S1. Continuous water injection is carried out using a double-ring permeation water injection test device set on the surface of the soil to be tested. By controlling the constant water level of the outer ring of the double-ring permeation water injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. S2. Simultaneously monitor the change of the inner ring water level of the double-ring permeation injection test device over time, and dynamically calculate the permeability coefficient of the soil. When the permeability coefficient of the soil tends to stabilize, it is determined that the soil in the test site has reached saturation, and the permeability coefficient after the soil stabilizes is recorded as the saturation permeability coefficient. S3. After the soil in the test site reaches saturation, without moving the double-ring permeation injection test device or disturbing the established stable seepage field and soil structure, the cross plate of the portable cross plate shearing instrument is vertically inserted into the saturated soil to a predetermined depth along the inner ring center axis of the double-ring permeation injection test device at the same test point. The cross plate is rotated at a uniform rate until the soil is sheared and damaged, and the peak torque and residual torque are recorded simultaneously. In step S3 of this invention, the shear test is performed immediately at the same pilot site after the soil is confirmed to be saturated. This method effectively avoids changes in soil moisture content and sample disturbance to a certain extent, ensuring that the measured shear strength truly reflects the mechanical behavior of the in-situ soil under fully saturated conditions, thus making the obtained data more reliable. Simultaneously, this method shortens the lengthy indoor saturation process to efficient in-situ water injection saturation. The entire saturation and shear process can be completed within hours, greatly improving exploration efficiency and shortening the project cycle.

[0007] S4. Based on the recorded data obtained in step S3, the saturated undrained shear strength of the in-situ soil to be tested is calculated according to the vane shear theory model.

[0008] Furthermore, the instantaneous volumetric flow rate algorithm is used in the S2 dynamic calculation of the soil permeability coefficient, and the calculation formulas involved are as follows: Where, k(t) i ) indicates that at t i The soil permeability coefficient calculated at each time step; Δt represents the observation time interval; Δh(t) i H(t) represents the drop in water level in the inner ring during the time interval Δt; A represents the cross-sectional area of ​​the inner ring in the double-ring test; L represents the estimated saturation depth of the soil under water injection conditions, the value of L being determined based on the penetration depth of the inner ring; H(t) represents the height of ... i ) / L indicates that at t i The average hydraulic gradient acting on the soil at any given time, H(t) i H(t) represents the constant water depth maintained within the inner ring during the experiment, and H(t) represents the water depth maintained within the inner ring. i The value of ) is set manually.

[0009] Furthermore, the condition for determining that the permeability coefficient of the S2 soil tends to be stable is as follows: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0.

[0010] This invention determines the saturation state of soil by using the indicator that the soil permeability coefficient tends to stabilize, replacing the traditional fuzzy method that relies on experience or fixed time. This makes the confirmation of saturation state more objective, scientific, and traceable, providing a reliable prerequisite for subsequent strength testing. Furthermore, this step simultaneously obtains the soil's saturation permeability coefficient upon completion of soil saturation, providing basic data for subsequent seepage analysis and coupling studies, significantly improving the information output rate of a single test.

[0011] Furthermore, the vane shear theory model formula used in step S4 to calculate the saturated undrained shear strength of the in-situ soil to be tested is as follows: Where c represents the saturated undrained shear strength of the in-situ soil to be tested; Mmax represents the recorded peak torque; and K represents a theoretical constant related to the vane size. D represents the diameter of the crossplate used; HB represents the height of the crossplate used.

[0012] Furthermore, after step S4, the method further includes: replacing the peak torque in the vane shear theory model formula in step S4 with the residual torque recorded synchronously in step S3 to obtain the residual undrained shear strength of the in-situ soil to be tested, and calculating the sensitivity of the in-situ soil to be tested. The calculation formulas involved are as follows: Where SL represents the sensitivity of the in-situ soil to be tested; cr represents the residual undrained shear strength of the in-situ soil to be tested.

[0013] This invention, through a single test, can not only obtain the saturated undrained shear strength of the in-situ soil corresponding to the peak torque, but also further calculate the residual undrained shear strength of the in-situ soil corresponding to the residual torque, as well as the corresponding soil sensitivity. This method provides a direct basis for understanding the strength softening characteristics of saturated soil after shear failure, and is of great value for evaluating the flow risk after slope instability.

[0014] Furthermore, the saturated permeability coefficient obtained in step S2 is correlated with the saturated undrained shear strength obtained in step S4 and the soil sensitivity obtained in step S4 to construct a set of coupled parameters for comprehensively evaluating the engineering properties of soil. The resulting set of coupled parameters is then entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

[0015] This invention links permeability parameters (saturated permeability coefficient) with strength parameters (saturated undrained shear strength) and soil sensitivity parameters to form a coupled parameter set, breaking the limitations of traditional isolated parameters. This helps to establish regional empirical models and achieve a more comprehensive and in-depth evaluation of soil engineering properties. Furthermore, through integrated design, it ensures the concentricity of the two tests (by inserting the vane of the portable vane shear apparatus into the saturated soil to a predetermined depth perpendicular to the inner ring center axis of the double-ring permeation injection test device at the same pilot point), eliminating pilot point deviation and improving test accuracy.

[0016] An in-situ system for determining the shear strength of soil under saturated conditions, the system comprising: The stable seepage field construction module uses a double-ring permeation water injection test device set on the surface of the soil to be tested to continuously inject water. By controlling the constant water level of the outer ring of the double-ring permeation water injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. The permeability coefficient analysis module is used to synchronously monitor the change of the inner ring water level of the double-ring permeation injection test device over time, dynamically calculate the permeability coefficient of the soil, and determine the saturation state of the in-situ soil to be tested. The vane shearing module is used to, after the in-situ soil to be tested reaches saturation, insert the vane of the portable vane shearing device vertically into the saturated soil to a predetermined depth along the inner ring center axis of the double-ring permeation water injection test device at the same pilot point; shear and destroy the in-situ soil to be tested, and simultaneously record the peak torque and residual torque. The soil strength parameter calculation module calculates the saturated undrained shear strength of the in-situ soil under test based on the recorded peak torque and combined with the vane shear theory model. The soil sensitivity analysis module obtains the residual undrained shear strength of the in-situ soil to be tested based on the recorded residual torque, and calculates the saturated undrained shear strength of the in-situ soil to be tested by combining the solution, and calculates the sensitivity of the in-situ soil to be tested. The permeability strength coupling parameter construction module correlates the obtained saturated permeability coefficient, saturated undrained shear strength, and soil sensitivity to construct a set of coupling parameters for comprehensively evaluating soil engineering properties. These parameters are then entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

[0017] Furthermore, the condition for the permeability coefficient analysis module to determine the saturation state of the in-situ soil to be tested is as follows: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0.

[0018] Furthermore, the soil sensitivity analysis module includes a residual undrained shear strength analysis unit and a soil sensitivity calculation unit. The residual undrained shear strength analysis unit obtains the residual undrained shear strength of the in-situ soil to be tested based on the recorded residual torque. The soil sensitivity calculation unit calculates the sensitivity of the in-situ soil to be tested based on the saturated undrained shear strength and residual undrained shear strength of the in-situ soil to be tested obtained from the calculation.

[0019] A non-transitory computer-readable storage medium storing a computer program, which, when executed by a processor, controls the system to implement the steps of the in-situ determination method for the shear strength of soil under saturated conditions.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This invention creatively integrates the double-ring permeation saturation process and the vane shear test process into the same pilot test, forming a continuous, in-situ, integrated test process for saturation determination; (2) This invention achieves the technical effects of clear test status, high test efficiency, strong data reliability and rich information dimensions through the integrated test process of saturation first and shear later; at the same time, it fundamentally solves the industry problem that traditional methods cannot obtain the in-situ shear strength under clear saturation state. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of an in-situ measurement system for shear strength of soil under saturated state according to the present invention; Figure 2 This is a schematic flowchart of an in-situ method for determining the shear strength of soil under saturated conditions according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figures 1-2 The present invention provides a technical solution: such as Figure 1 As shown, this embodiment provides an in-situ system for determining the shear strength of soil under saturated conditions. The system includes: The stable seepage field construction module uses a double-ring permeation water injection test device set on the surface of the soil to be tested to continuously inject water. By controlling the constant water level of the outer ring of the double-ring permeation water injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. The permeability coefficient analysis module is used to synchronously monitor the change of the inner ring water level of the double-ring permeability injection test device over time, dynamically calculate the permeability coefficient of the soil, and determine the saturation state of the in-situ soil to be tested. The condition for the permeability coefficient analysis module to determine the saturation state of the in-situ soil to be tested is: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0. The vane shearing module is used to, after the in-situ soil to be tested reaches saturation, insert the vane of the portable vane shearing device vertically into the saturated soil to a predetermined depth along the inner ring center axis of the double-ring permeation water injection test device at the same pilot point; shear and destroy the in-situ soil to be tested, and simultaneously record the peak torque and residual torque. The soil strength parameter calculation module calculates the saturated undrained shear strength of the in-situ soil under test based on the recorded peak torque and combined with the vane shear theory model. The soil sensitivity analysis module includes a residual undrained shear strength analysis unit and a soil sensitivity calculation unit. The residual undrained shear strength analysis unit obtains the residual undrained shear strength of the in-situ soil to be tested based on the recorded residual torque. The soil sensitivity calculation unit calculates the sensitivity of the in-situ soil to be tested based on the saturated undrained shear strength and residual undrained shear strength of the in-situ soil to be tested obtained by calculation. The permeability strength coupling parameter construction module correlates the obtained saturated permeability coefficient, saturated undrained shear strength, and soil sensitivity to construct a set of coupling parameters for comprehensively evaluating soil engineering properties. These parameters are then entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

[0024] This embodiment takes a proposed reservoir located in the mountainous region of southwestern my country as an example. Its normal water level is designed at an elevation of 1250 meters. The reservoir bank slope is mainly composed of silty clay formed by Quaternary alluvial and colluvial deposits, interspersed with a small amount of gravel, with an average soil layer thickness of approximately 8-15 meters. During the periodic rise and fall of the reservoir water level and heavy rainfall, the slope soil undergoes repeated transitions between unsaturated and saturated states. Traditional survey methods typically involve sampling and conducting laboratory tests at natural moisture content, or using conventional in-situ testing. However, these methods struggle to accurately obtain the true shear strength of the soil under fully saturated and stable seepage conditions. This lack of data leads to significant uncertainty in the stability analysis of the slope under saturated conditions, potentially resulting in engineering safety hazards or excessively high treatment costs. To accurately assess the stability of this slope under reservoir water level fluctuations and rainfall infiltration conditions, it is necessary to obtain the in-situ shear strength of its surface silty clay under saturated conditions. like Figure 2 As shown in this embodiment, an in-situ method for determining the shear strength of soil under saturated conditions is provided. The method includes: S1. Continuous water injection is carried out using a double-ring permeation injection test device installed on the surface of the soil to be tested. By controlling the constant water level of the outer ring of the double-ring permeation injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. In this step, a pilot project is selected at a typical section of the reservoir bank slope, and a double-ring permeation injection device is installed. Water is continuously injected into the outer ring of the double-ring permeation injection test device, and a float valve or precision water level controller is used to maintain a constant water level in the outer ring (e.g., 5cm above the ground). This forces the formation of a one-dimensional vertically downward stable saturated seepage front in the soil to be tested. The inner ring is used for experimental observation. Through the physical separation of the two rings and independent control of the water level, the working condition of water being uniformly saturated downward from the surface of the slope during natural rainfall or reservoir water rise is accurately simulated, laying a real stress and pore water pressure state foundation for subsequent strength testing.

[0025] S2. Simultaneously monitor the change of the inner ring water level of the double-ring permeation injection test device over time, and dynamically calculate the permeability coefficient of the soil. When the permeability coefficient of the soil tends to stabilize, it is determined that the soil in the test site has reached saturation, and the permeability coefficient after the soil stabilizes is recorded as the saturation permeability coefficient. The instantaneous volumetric flow rate algorithm is used in the S2 dynamic calculation of the soil permeability coefficient. The calculation formulas involved are as follows: Where, k(t)i ) indicates that at t i The soil permeability coefficient calculated at each time step; Δt represents the observation time interval; Δh(t) i H(t) represents the drop in water level in the inner ring during the time interval Δt; A represents the cross-sectional area of ​​the inner ring in the double-ring test; L represents the estimated saturation depth of the soil under water injection conditions, the value of L being determined based on the penetration depth of the inner ring; H(t) represents the height of ... i ) / L indicates that at t i The average hydraulic gradient acting on the soil at any given time, H(t) i H(t) represents the constant water depth maintained within the inner ring during the experiment, and H(t) represents the water depth maintained within the inner ring. i The value of ) is set manually. In this embodiment, after the double-ring permeation water injection test device is vertically pressed into the in-situ soil to be tested, the penetration depth of the inner and outer rings is ensured to be 10cm. Furthermore, during the simultaneous injection of water into the inner and outer rings, the water level in the inner ring is maintained at a constant height of 10cm. If the observation time interval is 60 seconds, then... .

[0026] The condition for determining that the permeability coefficient of the S2 soil tends to be stable is: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0.

[0027] In this embodiment, during the process of determining the saturation state of the in-situ soil to be tested, the change in permeability coefficient typically exhibits a three-stage characteristic: an initial rapid rise, a fluctuation and adjustment period, and a final stabilization period. In the initial stage, the soil permeability coefficient rises rapidly and then gradually fluctuates. After approximately several hours (this interval varies depending on the soil type and the depth of the monitored soil; for highly permeable soil types such as sand, in an experiment on Quaternary loose sandy sediments in Beishan, Gansu, using a double-ring device with an outer ring diameter of 50cm and an inner ring diameter of 25cm, monitoring showed different depths...), The saturation time of sand layers varies. A surface sand layer at a depth of 0.2m reaches saturation in just 0.5 hours; this time increases to 3 hours at 0.4m depth, and to 3.5 hours at 0.6m depth. However, for less permeable soils such as cohesive soils (due to their high capillary force, small pores, and extremely slow water infiltration and diffusion, the saturation time is much longer than for sandy soils under the same conditions), the system detects that the coefficient of variation for 15 consecutive calculated soil permeability coefficients (N = 15 minutes) is less than 5%, indicating that the permeability coefficient has stabilized. At this point, the operator is notified that the soil has reached saturation, and the final saturated permeability coefficient is recorded.

[0028] S3. After the soil in the test site reaches saturation, without moving the double-ring permeation water injection test device or disturbing the established stable seepage field and soil structure, the cross plate of the portable cross plate shearing instrument is vertically and accurately inserted into the saturated soil to a predetermined depth at a constant low speed (e.g., 2 mm / s) along the inner ring center axis of the double-ring permeation water injection test device at the same pilot point. The cross plate is rotated at a uniform rate until the soil is sheared and damaged. Considering that the surface soil may form an abnormal zone due to preferential flow or slight erosion during continuous water injection, the test target depth is set in the lower middle part of the estimated saturation zone to ensure the representativeness of the test results for the main saturated soil. The peak torque and residual torque are recorded simultaneously. The corresponding shear test process in this embodiment is as follows: 31. Drive the vane and connecting rod vertically into the soil along the central axis of the inner ring at a constant low speed (e.g., 2 mm / s); stop driving when the tip of the vane blade reaches the predetermined test depth (e.g., 10-15 cm below the bottom of the inner ring to avoid potentially disturbed surface areas). 32. After the vane has penetrated to the test depth, replace the vane with a calibration rod of the same size and with a smooth surface. Rotate the calibration rod at the same speed and record the friction torque between the rod and the soil at that depth. 33. Replace with a vane plate. After the vane plate is inserted into place, let it stand for 2 minutes to allow the pore water pressure in the soil to redistribute and balance. 34. Rotate the crossplate at a standard uniform angular velocity (e.g., 0.1 degrees per second); 35. Through the built-in torque sensor and angle encoder, the torque and angle curves are recorded synchronously and at high frequency to accurately identify the peak torque and residual torque in this state; 36. Update the peak torque and residual torque. The updated peak torque is the difference between the peak torque monitored in step S35 and the friction torque at the corresponding depth in step S32. The updated residual torque is the difference between the residual torque monitored in step S35 and the friction torque at the corresponding depth in step S32. This step achieves a seamless in-situ connection from the soil saturation preparation stage to the strength testing stage, completely avoiding disturbances caused by sample removal, transportation, and reshaping. At the same time, this method avoids the influence of surface anomalous zones to a certain extent, and minimizes systematic errors by introducing a rod friction analysis mechanism. This ensures that the strength test results truly reflect the undrained shear strength of the in-situ saturated soil.

[0029] S4. Based on the recorded data obtained in step S3, the saturated undrained shear strength of the in-situ soil to be tested is calculated according to the vane shear theory model.

[0030] The vane shear theory model formula used in step S4 to calculate the saturated undrained shear strength of the in-situ soil to be tested is as follows: Where c represents the saturated undrained shear strength of the in-situ soil to be tested; Mmax represents the recorded peak torque; and K represents a theoretical constant related to the vane size. D represents the diameter of the crossplate used; HB represents the height of the crossplate used.

[0031] In this embodiment, if the recorded peak torque is 12.5 N·m, and the diameter and height of the cross-plate used are 50 mm and 100 mm respectively, The theoretical constants related to the dimensions of the vane. cubic meter; The saturated undrained shear strength of the in-situ soil to be tested kPa.

[0032] Following step S4, the method further includes: replacing the peak torque in the vane shear theoretical model formula in step S4 with the residual torque recorded synchronously in step S3 to obtain the residual undrained shear strength of the in-situ soil to be tested, and calculating the sensitivity of the in-situ soil to be tested. The calculation formulas involved are as follows: Where SL represents the sensitivity of the in-situ soil to be tested; cr represents the residual undrained shear strength of the in-situ soil to be tested.

[0033] The saturated permeability coefficient obtained in step S2 is correlated with the saturated undrained shear strength obtained in step S4 and the soil sensitivity obtained in step S4 to construct a set of coupled parameters for comprehensively evaluating the engineering properties of soil. The resulting set of coupled parameters is entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

[0034] A non-transitory computer-readable storage medium storing a computer program, which, when executed by a processor, controls the system to implement the steps of the in-situ determination method for the shear strength of soil under saturated conditions.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for in-situ determination of shear strength of soil under saturated state, characterized in that, The method includes: S1. Continuous water injection is carried out using a double-ring permeation water injection test device set on the surface of the soil to be tested. By controlling the constant water level of the outer ring of the double-ring permeation water injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. S2. Simultaneously monitor the change of the inner ring water level of the double-ring permeation injection test device over time, and dynamically calculate the permeability coefficient of the soil. When the permeability coefficient of the soil tends to stabilize, it is determined that the soil in the test site has reached saturation, and the permeability coefficient after the soil stabilizes is recorded as the saturation permeability coefficient. S3. After the soil in the test site reaches saturation, without moving the double-ring permeation injection test device or disturbing the established stable seepage field and soil structure, the cross plate of the portable cross plate shearing instrument is vertically inserted into the saturated soil to a predetermined depth along the inner ring center axis of the double-ring permeation injection test device at the same test point. The cross plate is rotated at a uniform rate until the soil is sheared and damaged, and the peak torque and residual torque are recorded simultaneously. S4. Based on the recorded data obtained in step S3, the saturated undrained shear strength of the in-situ soil to be tested is calculated according to the vane shear theory model.

2. The in-situ method for determining the shear strength of soil under saturated state according to claim 1, characterized in that: The instantaneous volumetric flow rate algorithm is used in the S2 dynamic calculation of the soil permeability coefficient. The calculation formulas involved are as follows: Where, k(t) i ) indicates that at t i The soil permeability coefficient calculated at each time step; Δt represents the observation time interval; Δh(t) i H(t) represents the drop in water level in the inner ring during the time interval Δt; A represents the cross-sectional area of ​​the inner ring in the double-ring test; L represents the estimated saturation depth of the soil under water injection conditions, the value of L being determined based on the penetration depth of the inner ring; H(t) represents the height of ... i ) / L indicates that at t i The average hydraulic gradient acting on the soil at any given time, H(t) i H(t) represents the constant water depth maintained within the inner ring during the experiment, and H(t) represents the water depth maintained within the inner ring. i The value of ) is set manually.

3. The in-situ method for determining the shear strength of soil under saturated state according to claim 1, characterized in that: The condition for determining that the permeability coefficient of the S2 soil tends to be stable is: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0.

4. The in-situ method for determining the shear strength of soil under saturated state according to claim 1, characterized in that: The vane shear theory model formula used in step S4 to calculate the saturated undrained shear strength of the in-situ soil to be tested is as follows: Where c represents the saturated undrained shear strength of the in-situ soil to be tested; Mmax represents the recorded peak torque; and K represents a theoretical constant related to the vane size. D represents the diameter of the crossplate used; HB represents the height of the crossplate used.

5. The in-situ method for determining the shear strength of soil under saturated state according to claim 4, characterized in that: Following step S4, the method further includes: replacing the peak torque in the vane shear theoretical model formula in step S4 with the residual torque recorded synchronously in step S3 to obtain the residual undrained shear strength of the in-situ soil to be tested, and calculating the sensitivity of the in-situ soil to be tested. The calculation formulas involved are as follows: Where SL represents the sensitivity of the in-situ soil to be tested; cr represents the residual undrained shear strength of the in-situ soil to be tested.

6. The in-situ method for determining the shear strength of soil under saturated state according to claim 5, characterized in that: The saturated permeability coefficient obtained in step S2 is correlated with the saturated undrained shear strength obtained in step S4 and the soil sensitivity obtained in step S4 to construct a set of coupled parameters for comprehensively evaluating the engineering properties of soil. The resulting set of coupled parameters is entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

7. An in-situ system for determining the shear strength of soil under saturated conditions, characterized in that, The system includes: The stable seepage field construction module uses a double-ring permeation water injection test device set on the surface of the soil to be tested to continuously inject water. By controlling the constant water level of the outer ring of the double-ring permeation water injection test device, a one-dimensional vertically downward stable seepage field is formed in the soil to be tested. The permeability coefficient analysis module is used to synchronously monitor the change of the inner ring water level of the double-ring permeation injection test device over time, dynamically calculate the permeability coefficient of the soil, and determine the saturation state of the in-situ soil to be tested. The vane shearing module is used to, after the in-situ soil to be tested reaches saturation, insert the vane of the portable vane shearing device vertically into the saturated soil to a predetermined depth along the inner ring center axis of the double-ring permeation water injection test device at the same pilot point; shear and destroy the in-situ soil to be tested, and simultaneously record the peak torque and residual torque. The soil strength parameter calculation module calculates the saturated undrained shear strength of the in-situ soil under test based on the recorded peak torque and combined with the vane shear theory model. The soil sensitivity analysis module obtains the residual undrained shear strength of the in-situ soil to be tested based on the recorded residual torque, and calculates the saturated undrained shear strength of the in-situ soil to be tested by combining the solution, and calculates the sensitivity of the in-situ soil to be tested. The permeability strength coupling parameter construction module correlates the obtained saturated permeability coefficient, saturated undrained shear strength, and soil sensitivity to construct a set of coupling parameters for comprehensively evaluating soil engineering properties. These parameters are then entered into a database to establish an empirical relationship model between permeability and mechanical properties of soil under saturated conditions in a regional context.

8. The in-situ testing system for shear strength of soil under saturated state according to claim 7, characterized in that: The condition for the permeability coefficient analysis module to determine the saturation state of the in-situ soil to be tested is as follows: within N consecutive observation time interval windows, the coefficient of variation of the permeability coefficient of the corresponding soil is less than a preset value; N is a human-preset constant; the coefficient of variation of the permeability coefficient of the soil is equal to the quotient of the difference between the maximum and minimum values ​​of the permeability coefficient of the soil at each time point within the corresponding time period, divided by the maximum permeability coefficient, and the maximum permeability coefficient is not 0.

9. The in-situ testing system for shear strength of soil under saturated state according to claim 7, characterized in that: The soil sensitivity analysis module includes a residual undrained shear strength analysis unit and a soil sensitivity calculation unit. The residual undrained shear strength analysis unit obtains the residual undrained shear strength of the in-situ soil to be tested based on the recorded residual torque. The soil sensitivity calculation unit calculates the sensitivity of the in-situ soil to be tested based on the saturated undrained shear strength and residual undrained shear strength of the in-situ soil to be tested obtained from the calculation.

10. A non-transitory computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it controls the system to implement the steps of the method as described in any one of claims 1 to 6.

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