A combined penetration vane shear testing device and method based on reconstruction of in-situ effective stress of borehole columnar sample

Abstract

The application discloses a kind of based on in-situ effective stress reconstruction of drilling columnar sample penetration vane combined shear testing device and method, belong to geotechnical engineering indoor test technical field.The device includes sealed pressure chamber, drilling columnar sample holding and pressure transmission component, confining pressure loading component, counter-pressure and drainage control component, axial loading component, penetration torsion composite driving component, sealing transmission component and data acquisition and control system.Flexible pressure transmission film is provided with windowed split sleeve, and axial gap is left between sleeve and upper and lower bearing pieces;Top force transmission cap and upper permeable stone are provided with coaxial central penetration hole and offset drainage channel.By confining pressure, counter-pressure and axial load, the target effective stress is approximately reconstructed, and undrained shear, disturbed remolding and remolding shear are continuously carried out under undrained condition, and the undrained shear strength and sensitivity are corrected and calculated using the idle torque.The application can reduce the disturbance of sample preparation and boundary influence, and improve the consistency of test results.

Description

Technical Field

[0001] This invention relates to the field of indoor testing instruments for geotechnical engineering, and in particular to a penetration vane combined shear test device and method based on in-situ effective stress reconstruction of borehole columnar samples. It is applicable to the undrained shear strength, remolded undrained shear strength and sensitivity testing of undisturbed soft soil columnar samples obtained from boreholes in terrestrial and seabed areas. Background Technology

[0002] The vane shear test is an important method for determining the undrained shear strength and sensitivity of soft clay, and it is widely used in marine geotechnical engineering, port engineering, soft soil foundation investigation, and other fields. Existing tests mainly include in-situ field tests and laboratory tests. Laboratory tests have advantages such as controllable environment, convenient operation, and easy parameter comparison, but their test results are easily affected by sample preparation disturbance, stress release, and changes in boundary conditions.

[0003] Conventional indoor vane shearing devices often employ open sample containers or rigid sample cylinders. Testing under normal pressure or low-constraint conditions makes it difficult to approximate the vertical effective stress, horizontal effective stress, and pore water pressure at the sampling depth of borehole columnar samples. During sampling, unloading, transportation, and unsealing, borehole columnar samples undergo stress release and structural relaxation, leading to reduced representativeness of indoor test results for the in-situ condition. Patent document CN118150370A proposes a stress recovery scheme for vertical loading, but it does not simultaneously address the coordinated control of confining pressure, counterpressure, and axial stress, and the rigid container struggles to simultaneously maintain the morphology of weak columnar samples and facilitate lateral pressure transmission.

[0004] While conventional triaxial tests can control confining pressure, counterpressure, and axial stress, they typically require the borehole column samples to be cut into cylindrical specimens of specified dimensions. For soft clay, silty soil, and highly sensitive marine sediments, cutting, moving, and repeated loading can easily cause cracking, collapse, sidewall disturbance, and changes in water content. Furthermore, triaxial tests primarily rely on axial compression and shear, and cannot directly perform vane penetration and torsional shear tests.

[0005] When performing vane tests in a sealed pressure chamber, the drive rod needs to simultaneously complete vertical movement and rotation around its axis while maintaining the chamber's seal. The sliding seal, rotary seal, coaxial guidance, and low-friction torque transmission are mutually constrained. Friction in the seals, friction in the drive rod, and guide resistance all contribute to the measured torque, which has a particularly significant impact on low-torque tests of low-strength soft soil.

[0006] Furthermore, undrained shear strength and remolded undrained shear strength are usually determined separately in different specimens or different devices. The natural dispersion of specimens, differences in sample preparation, and differences in stress recovery can reduce the consistency of sensitivity evaluation. Existing devices also rarely address issues such as direct fitting of borehole columnar specimens, lateral support and confining pressure transfer, axial load path isolation, sealed penetration torsion, and continuous undrained-remolded testing of the same sample.

[0007] Therefore, there is a need for a combined testing device and method that can directly receive borehole columnar samples, transmit confining pressure without forming axial load bypass, approximately reconstruct the target effective stress, and complete penetration, undisturbed shear, disturbance reshaping, and reshaping shear in a sealed environment. Summary of the Invention

[0008] To achieve the above objectives, the present invention adopts the following technical solution: To address the aforementioned deficiencies in the prior art, the present invention aims to provide a penetration vane combined shear test device and method based on in-situ effective stress reconstruction of borehole columnar samples, in order to solve the problems of large disturbance in standard sample preparation of borehole columnar samples, difficulty in balancing lateral support and confining pressure transmission, easy bypassing of axial loads, difficulty in approximate reconstruction of target effective stress, difficulty in coordinating penetration and torsion under sealed environment, and insufficient consistency of sensitivity testing.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a penetration vane combined shear test device based on in-situ effective stress reconstruction of a borehole columnar sample, comprising a rigid loading frame, a sealed pressure chamber, a borehole columnar sample holding and pressure transmission assembly, a confining pressure loading assembly, a back pressure and drainage control assembly, an axial loading assembly, a penetration torsion composite drive assembly, a sealed transmission assembly, an anti-eccentricity guide assembly, a replaceable test probe assembly, and a data acquisition and control system.

[0010] The borehole columnar sample is a relatively complete, approximately cylindrical, undisturbed soil sample obtained from land or seabed boreholes. After opening, only the obviously disturbed, dehydrated, or cracked parts at the ends are removed, and the sample is cut to the target height according to the effective height of the pressure chamber and the probe test depth. It does not need to be prepared into a standard-sized sample required by traditional triaxial testing.

[0011] The borehole columnar sample holding and pressure transmission assembly includes a bottom sample holder, a top force transmission cap, a flexible pressure transmission membrane, and a window-type splitting sleeve. The flexible pressure transmission membrane covers the borehole columnar sample and is sealed to the top force transmission cap and the bottom sample holder; the window-type splitting sleeve is located outside the flexible pressure transmission membrane and has a pressure transmission window, which is used to limit the sample bulging, cracking, or collapse during sample loading, and allows the confining pressure fluid to act on the flexible pressure transmission membrane through the pressure transmission window during loading.

[0012] The Window-type Splitting Sleeve is provided with axial movement gaps between the upper end and the top force transmission cap, and between the lower end and the bottom sample holder, or it can cooperate with adjacent components through a low-friction sliding structure so that the Window-type Splitting Sleeve only bears the radial shape maintenance function and does not bear the axial load transmitted by the top force transmission cap, thereby avoiding the axial load from being directly transmitted to the bottom sample holder through the rigid sleeve.

[0013] The top force-transmitting cap and the upper permeable stone are each provided with a coaxial central penetration hole, and the pressure chamber cover is provided with a transmission rod through hole coaxial with them. The top force-transmitting cap is provided with an annular drainage groove and an offset drainage hole that are isolated from the central penetration hole. The annular drainage groove is connected to the annular upper permeable stone, and the offset drainage hole is connected to the upper drainage pipe, so as to realize drainage and counter-pressure loading at the upper end of the sample without occupying the central penetration channel.

[0014] The bottom sample holder is equipped with a permeable stone, which is connected to the drainage pipe. At least one of the top force transmission cap, bottom sample holder, flexible pressure transmission membrane, and window-type splitting sleeve is designed as a replaceable component to adapt to different sampler diameters, different columnar sample heights, and different soft soil strength conditions.

[0015] The confining pressure loading assembly includes a confining pressure controller, a confining pressure sensor, and a confining pressure pipeline; the back pressure and drainage control assembly includes a back pressure controller, a pore pressure sensor, a volumetric deformation measurement unit, an upper drainage pipeline, a lower drainage pipeline, and a shut-off valve. The upper and lower back pressure branches can share a single back pressure controller, or they can each be equipped with an independent back pressure controller to meet the needs of bidirectional drainage, unidirectional drainage, or independent pore pressure monitoring.

[0016] The axial loading assembly includes a hollow annular axial loading piston, an axial force sensor, an axial displacement sensor, and a servo loader. The hollow annular axial loading piston is arranged around the transmission rod, and its annular loading surface acts on the top force transmission cap. The anti-eccentricity guide assembly is located in the hollow clearance area of ​​the hollow annular axial loading piston or is connected to the top force transmission cap by a low-friction sliding connection to avoid interference with the axial loading path.

[0017] The data acquisition and control system is configured with an isotropic stress recovery mode and a K0 approximate stress recovery mode. In the isotropic mode, the difference between the control confining pressure and the counterpressure is equal to the target effective confining pressure, and the corrected axial deviatoric stress is made close to zero. In the K0 approximate mode, the difference between the control confining pressure and the counterpressure is equal to the target horizontal effective stress, and the corrected additional axial load is applied through the axial loading component.

[0018] Under the K0 approximation mode, the target stress can be controlled according to the following relationship: the target horizontal effective stress σ′h0=pc-pb; the target vertical effective stress σ′v0=(pc-pb)+(Fa-Fc) / As. Where pc is the confining pressure, pb is the back pressure or the target initial pore water pressure, Fa is the axial load measured by the axial force sensor, Fc is the combined correction force of the confining pressure acting on the effective area of ​​the piston, sealing friction, self-weight, and the device's no-load resistance, and As is the current effective cross-sectional area of ​​the borehole columnar sample.

[0019] The penetration-torsion composite drive assembly includes a vertical servo drive mechanism and a torsion servo drive mechanism. The vertical servo drive mechanism controls the probe's penetration rate and depth, while the torsion servo drive mechanism controls the probe's rotation rate and angle. The transmission rod passes sequentially through the sealed transmission assembly, the anti-eccentricity guide assembly, the central penetration hole of the top force transmission cap, and the central penetration hole of the upper permeable stone before connecting to the test probe.

[0020] The sealing transmission assembly includes a vertical sliding sealing unit, a rotary sealing unit, a pressure-balanced sealing chamber, and a leakage observation port. The pressure-balanced sealing chamber is connected to a confining pressure controller or an independent compensation pressure controller via an external compensation pipeline, keeping the pressure difference between the confining pressure and the pressure within a preset range to reduce dynamic seal friction; the leakage observation port is used to monitor the leakage status of the sealing gap.

[0021] The replaceable test probes include at least a vane probe, and may also include a miniature conical probe, a T-bar probe, a spherical penetration probe, and a blank calibration rod. The blank calibration rod is used to obtain the no-load corrected torque under the same or equivalent confining pressure, rotational speed, drive rod axial position, and sealed guide condition as the actual shearing.

[0022] A temperature sensor is installed on the sealed pressure chamber. The probe of the temperature sensor extends into the confining liquid area or contacts the cylinder of the pressure chamber and is connected to the data acquisition module to record the test environment and the temperature of the confining liquid, as well as to correct for sensor temperature drift.

[0023] Secondly, the present invention provides a method for combined shear testing of a penetration vane based on in-situ effective stress reconstruction of a borehole columnar sample, including test preparation and no-load calibration, loading of the borehole columnar sample, sealing and venting of the pressure chamber, back pressure saturation, drainage consolidation, approximate reconstruction of the target effective stress, establishment of the undrained boundary, vane penetration, in-situ shearing, disturbance reshaping, reshaping shearing, and data calculation and unloading / sample removal.

[0024] In the saturation stage, the saturation state is determined by gradually increasing the confining pressure and back pressure while monitoring the pore pressure response, with the pore pressure coefficient B being the preferred criterion. In the drainage consolidation stage, the pore pressure, volumetric strain, and axial deformation reach a preset stability criterion as the termination condition. In the non-drained stage, the shut-off valves of the upper and lower drainage pipes are closed to isolate the sample from the back pressure controller, maintaining the confining pressure and axial load at set values, and recording the changes in pore water pressure caused by penetration and shear.

[0025] During the disturbance reshaping stage, the vane probe is continuously rotated until the torque reaches a stable residual plateau; preferably, the average torque change rate within a preset number of revolutions not exceeding a preset threshold is used as the criterion for reshaping completion. After reshaping, it is sheared again at a specified angular velocity, and the stable reshaping torque or the peak reshaping shear torque is used to calculate the reshaping undrained shear strength.

[0026] The net shear torque is calculated as Tnet = Tmeas - T0, where T0 = Tseal + Trod + Tidle; the undrained shear strength is calculated as Su = Tnet / Kv, and the soil sensitivity is calculated as St = Su0 / Sur. For a probe with a vane diameter of D and a height of H, the vane geometric coefficient Kv can be determined as Kv = πD²H / 2 + πD³ / 6.

[0027] To reduce boundary effects, sufficient spacing should be maintained between the outer edge of the vane blade and the sidewall of the specimen, and between the upper and lower ends of the vane and the end face of the specimen to form a complete shear plane. The specimen size and vane size should be determined based on preliminary tests and soil properties. When conducting multi-depth tests, the shear influence range of adjacent test areas should not overlap, and the axial distance between the centers of adjacent vanes should preferably be no less than H+D.

[0028] Compared with the prior art, the advantages of the technical solution of this application include at least the following: 1. It can directly load relatively complete columnar samples obtained from land or seabed drilling after only trimming the ends and cutting off the height, reducing secondary disturbances caused by cutting, moving and repeated loading; 2. The open-window splitting sleeve and the flexible pressure-transmitting membrane work together to maintain the radial shape of the weak columnar sample and transmit lateral pressure. The upper and lower ends of the sleeve are provided with axial movement gaps, which can reduce the influence of the rigid sleeve on the axial load path and shear boundary. 3. The coordinated control of confining pressure, counter pressure, and modified axial load can approximately reconstruct the target vertical effective stress, target horizontal effective stress, and initial pore water pressure at the sampling depth, thereby improving the representativeness of indoor test results to the in-situ stress state. 4. The penetration torsion composite drive, dynamic seal, pressure-balanced sealing cavity, and anti-eccentric guide structure work together to ensure penetration, positioning, and torsional shearing in the sealing pressure environment; the blank calibration rod can be used to correct the additional torque of the seal, transmission, and guide. 5. The same borehole columnar sample can continuously complete undisturbed shearing, disturbed reshaping, and reshaping shearing under the same target stress state, reducing the sensitivity evaluation error corresponding to the natural differences between different samples; the replaceable probe and multi-parameter synchronous acquisition structure can also support micro-penetration and full-flow penetration tests. Attached Figure Description

[0029] The above-described features and advantages, as well as other features and advantages, and the ways in which they are implemented, of these embodiments will become more apparent and the embodiments of this application will be better understood by referring to the following description in conjunction with the accompanying drawings, in which: Figure 1 This is a schematic diagram of the overall structure of the device of the present invention; Figure 2 This is a schematic diagram of the sealed pressure chamber and the borehole columnar sample holding and pressure transmission assembly of the present invention. Figure 3 This is a schematic diagram of the structure and cross-section of the window-type split sleeve of the present invention; Figure 4 This is a schematic diagram of the structure of the penetrating torsion composite drive component of the present invention; Figure 5 This is a partially enlarged structural schematic diagram of the sealed transmission assembly of the present invention; Figure 6 This is a schematic diagram of the replaceable test probe assembly of the present invention; Figure 7 This is a schematic diagram of the connection of the confining pressure, counter pressure, axial pressure and data acquisition control system of the present invention; Figure 8 This is a flowchart illustrating the testing method of the present invention.

[0030] In the diagram: 1 - Rigid loading frame; 101 - Base; 102 - Column; 103 - Upper crossbeam; 104 - Adjustable support; 2 - Sealed pressure chamber; 201 - Pressure chamber base; 202 - Pressure chamber cylinder; 203 - Pressure chamber top cover; 204 - Tie rod; 205 - Sealing ring; 3 - Confining pressure fluid inlet; 4 - Confining pressure fluid outlet; 5 - Vent hole; 6 - Safety relief valve; 7 - Drilled columnar sample; 8 - Flexible pressure transmitting membrane; 9 - Window-type split sleeve; 901 - Arc-shaped cylindrical plate; 902 - Pressure transmitting window; 903 - Connecting ear plate; 904 - Locking bolt; 10 - Bottom sample holder; 11 - Top force transmitting cap; 12 - Lower permeable stone; 13 - Upper permeable stone; 14 - Lower drainage pipe; 15 - Upper drainage pipe; 16 - 17 - Pore pressure sensor; 18 - Back pressure controller; 19 - Volumetric variation measurement unit; 20 - Shut-off valve; 21 - Confining pressure controller; 22 - Confining pressure sensor; 23 - Axial loading piston; 24 - Axial force sensor; 25 - Axial displacement sensor; 26 - Servo loader; 27 - Vertical servo motor; 28 - Lead screw; 29 - Guide rod; 30 - Slide table; 31 - Torque servo motor; 32 - Reducer; 33 - Torque sensor; 34 - Angular displacement encoder; 35 - Penetration force sensor; 36 - Drive rod; 37 - Sealing transmission assembly; 38 - Vertical sliding sealing unit; 39 - Rotary sealing unit; 30 - Pressure balanced sealing chamber; 31 - Leakage observation port; 32 - Cross plate probe; 33 - Probe connector; 34 - Center rod; 35 - Cross plate blade; 36 - Miniature conical probe; 39 - T-bar probe; 40 - Spherical penetration probe; 41 - Blank calibration rod; 42 - Anti-eccentricity guide assembly; 43 - Control host; 44 - Touch screen; 45 - Data acquisition module; 46 - Servo control module; 47 - Pressure control module; 48 - Temperature sensor; 49 - Confining pressure pipeline; 50 - Back pressure pipeline. Detailed Implementation

[0031] Example 1: Overall Structure of the Device like Figure 1 As shown, the penetration vane combined shear test device includes a rigid loading frame 1, a sealed pressure chamber 2, a borehole columnar sample holding and pressure transmission assembly, a confining pressure loading assembly, a back pressure and drainage control assembly, an axial loading assembly, a penetration torsion composite drive assembly, a sealed transmission assembly 36, an anti-eccentricity guide assembly 42, a replaceable test probe assembly, and a data acquisition and control system.

[0032] The rigid loading frame 1 is a portal reaction frame, including a base 101, a column 102, an upper crossbeam 103, and an adjustable support 104. A sealed pressure chamber 2 is located in the middle of the base 101, including a pressure chamber base 201, a pressure chamber cylinder 202, and a pressure chamber cover 203. The pressure chamber cylinder 202 is sealed to the pressure chamber base 201 and the pressure chamber cover 203 via a sealing ring 205 and a tie rod 204. A confining pressure fluid inlet 3 and a confining pressure fluid outlet 4 are located on the pressure chamber base 201, and an exhaust port 5 and a safety relief valve 6 are located on the pressure chamber cover 203.

[0033] The pressure chamber cover 203 has a central through hole through which the transmission rod 35 passes, and a sealing transmission assembly 36 is installed at the central through hole. The top force transmission cap 11 and the upper permeable stone 13 are respectively provided with coaxial central penetration holes. The cross plate probe 37, driven by the transmission rod 35, passes through the sealing transmission assembly 36, the anti-eccentric guide assembly 42, the top force transmission cap 11 and the upper permeable stone 13 in sequence and then penetrates the drilled columnar sample 7.

[0034] Example 2: Drilled Columnar Sample Holding and Pressure Transmission Assembly As shown in Figures 2 and 3, the borehole columnar sample holding and pressure transmission assembly includes a bottom sample holder 10, a top force transmission cap 11, a flexible pressure transmission membrane 8, and a window-type splitting sleeve 9. After the borehole columnar sample 7 is smoothly pushed out from the sampling tube or liner, only the obviously disturbed, dehydrated, or cracked parts at the end are removed, and it is cut off to the height of the fitting device. The bottom sample holder 10 is embedded with a lower permeable stone 12, which is connected to the lower drainage pipe 14. The top force transmission cap 11 is embedded with an annular upper permeable stone 13. The top force transmission cap 11 is provided with an annular drainage groove and an offset drainage hole. The upper drainage pipe 15 is connected to the annular drainage groove through the offset drainage hole, so that the upper drainage and the central penetration channel are isolated from each other. The flexible pressure transmission membrane 8 covers the outside of the borehole columnar sample 7, and its upper and lower ends are respectively embedded in the membrane fixing grooves of the top force transmission cap 11 and the bottom sample holder 10, and sealed by a hoop. The flexible pressure-transmitting membrane 8 can be made of latex, rubber, silicone, or polyurethane. The window-type splitting sleeve 9 consists of at least two arc-shaped cylindrical plates 901, with connecting lugs 903 on both sides of the arc-shaped cylindrical plates 901 connected by locking bolts 904. Pressure-transmitting windows 902 are arranged at intervals along the circumferential and height directions. The opening ratio is defined as the ratio of the total area of ​​the pressure-transmitting windows to the effective unfolded area of ​​the sleeve's sidewalls, and can be selected according to the soil sample strength, stability, and confining pressure transmission requirements. Axial movement clearances are maintained between the upper end of the window-type splitting sleeve 9 and the top force-transmitting cap 11, and between the lower end and the bottom sample holder 10; in another embodiment, low-friction sliding washers can be provided at these locations. Thus, the sleeve provides radial support during sample loading and pressurization, but does not directly bear the axial load transmitted by the axial loading piston 22. The bottom sample holder 10, top force transmission cap 11, flexible pressure transmission diaphragm 8, and window-type splitting sleeve 9 can be manufactured in multiple specifications, adapting to drilled cylindrical samples of different diameters and heights by changing the specifications of the parts. The sample size and vane size should meet the requirement that the shear plane of the vane does not intersect with the sidewalls and upper and lower boundaries of the sample.

[0035] Example 3: Stress Control and Target Effective Stress Reconstruction like Figure 1 and Figure 7 As shown, the confining pressure loading assembly includes a confining pressure controller 20, a confining pressure sensor 21, and a confining pressure pipeline 49. The confining pressure controller 20 injects degassed water into the sealed pressure chamber 2 through the confining pressure pipeline 49 and applies confining pressure. The confining pressure sensor 21 is used for closed-loop feedback.

[0036] The back pressure and drainage control assembly includes a back pressure controller 17, a pore pressure sensor 16, a volumetric deformation measurement unit 18, an upper drainage pipe 15, a lower drainage pipe 14, a back pressure pipe 50, and a shut-off valve 19. The upper and lower back pressure branches can share a single back pressure controller 17, or they can each have an independent controller. The back pressure pipe 50 uses a solid-line fluid circuit to connect the back pressure controller 17 to the upper drainage pipe 15 and the lower drainage pipe 14; electrical control and sensor signals are represented by dashed lines. The axial loading assembly includes a hollow annular axial loading piston 22, an axial force sensor 23, an axial displacement sensor 24, and a servo loader 25. The annular loading surface of the hollow annular axial loading piston 22 acts on the top force transmission cap 11, and the transmission rod 35 is located in its hollow portion. An anti-eccentricity guide assembly 42 is arranged in the hollow clearance area and restricts the offset of the transmission rod 35 through a low-friction structure. In the isotropic stress recovery mode, the pc-pb is controlled to equal the target effective confining pressure, and the corrected eccentric stress is brought close to zero through axial loading control. In the K0 approximate stress recovery mode, pc-pb is controlled to equal the target horizontal effective stress σ′h0, and the axial load is adjusted according to σ′v0=(pc-pb)+(Fa-Fc) / As. Fc is determined through no-load loading test or sub-item calibration, and As is corrected according to the initial size of the specimen and axial deformation and volumetric strain data. Temperature sensor 48 is set in the pressure chamber cylinder 202 or the confining liquid area and connected to data acquisition module 45 to record the test temperature and perform sensor temperature drift correction.

[0037] Example 4: Penetration Torsional Composite Drive and Sealed Transmission As shown in Figures 4 and 5, the vertical servo drive mechanism includes a vertical servo motor 26, a lead screw 27, a guide rod 28, and a slide table 29. The vertical servo motor 26 drives the slide table 29 to move vertically along the guide rod 28 via the lead screw 27, realizing probe penetration and depth positioning. The torsional servo drive mechanism is mounted on the slide table 29 and includes a torsional servo motor 30, a reducer 31, a torque sensor 32, an angular displacement encoder 33, and a penetration force sensor 34. The torsional servo motor 30 drives the test probe to rotate via the reducer 31 and the transmission rod 35. The torque sensor 32 and the angular displacement encoder 33 record the torque and rotation angle, respectively. The sealing transmission assembly 36 includes a vertical sliding sealing unit 361, a rotary sealing unit 362, a pressure balancing sealing chamber 363, and a leakage observation port 364. The pressure balancing sealing chamber 363 is connected to the confining pressure controller 20 or an independent compensation pressure controller via an external compensation pipeline, maintaining the difference between its pressure and the confining pressure within a preset range. The leakage observation port 364 communicates with the sealing gap and is used to observe the leakage of sealing fluid and determine the condition of the seal. The anti-eccentricity guide assembly 42 includes a guide sleeve and a self-lubricating self-aligning ring, located above the top force transmission cap 11 and sleeved on the outside of the transmission rod 35. The anti-eccentricity guide assembly 42 allows the top force transmission cap 11 and the axially loaded piston 22 to move axially within a set range, while limiting the lateral offset of the transmission rod 35.

[0038] Example 5: Replaceable Probe and Data Acquisition System like Figure 6 As shown, the test probe is detachably connected to the transmission rod 35 via the probe connector 371. The vane probe 37 includes a central rod 372 and vane blades 373, the blade height H and diameter D of which can be selected according to the sample size and soil strength. The miniature conical probe 38 is used for miniature penetration testing, the T-bar probe 39 and the spherical penetration probe 40 are used for full-flow penetration testing, and the blank calibration rod 41 is used to determine the no-load correction torque.

[0039] The no-load calibration is preferably performed under the same or equivalent confining pressure, rotational speed, axial position of the transmission rod, sealed tightness, anti-eccentric guide contact state, and temperature conditions as the actual shear test. The blank calibration rod 41 does not contact the soil sample, and the torque obtained therefrom serves as a comprehensive correction value for the additional torque of sealing, transmission, and guidance.

[0040] The data acquisition and control system includes a control host 43, a touch screen 44, a data acquisition module 45, a servo control module 46, and a pressure control module 47. It can simultaneously acquire data on confining pressure, back pressure, pore pressure, axial force, axial displacement, penetration force, penetration depth, torque, rotation angle, volumetric deformation, temperature, and time, and execute saturation, consolidation, stress reconstruction, penetration, and shear control according to a preset process.

[0041] Example 6: Test Method Flow As shown in Figure 8, the specific steps for performing a combined shear test on a drilled cylindrical sample using the above-mentioned device are as follows: Step 1: Test preparation and no-load calibration.

[0042] The leveling device is used to calibrate the sensor at zero point; a blank calibration rod 41 is installed, and the sensor is rotated under no-load conditions without contacting the soil sample, with the same or equivalent confining pressure, rotation speed, axial position of the transmission rod, and sealed guide state as the actual shearing, and the stable torque T0 is recorded.

[0043] Step 2: Drilling and loading of cylindrical samples.

[0044] Smoothly push out the drilled columnar sample 7, cut off the obviously disturbed section at the end and cut it to the target height; place it on the bottom sample support 10, cover it with the flexible pressure transmission membrane 8, install the top force transmission cap 11 and seal the membrane end; close the window-type split sleeve 9 and confirm that there is an axial movement clearance between the upper and lower ends of the sleeve and the adjacent bearing.

[0045] Step 3: Sealing and venting the pressure chamber.

[0046] Move the pressure transmission assembly into the sealed pressure chamber 2, connect the upper drain pipe 15 and the lower drain pipe 14, close the pressure chamber and lock the pull rod 204; slowly inject the degassed confining fluid from the confining fluid inlet 3, open the vent 5, and close the vent 5 after the continuous flow of bubble-free liquid.

[0047] Step 4, back pressure saturation and drainage consolidation.

[0048] The confining pressure and counterpressure are gradually increased. With the drainage channel temporarily closed, small increments of confining pressure are applied and the pore pressure increment is measured to calculate the pore pressure coefficient B. When B reaches a preset value, preferably not less than 0.95, the sample is deemed to have reached the target saturation state. Subsequently, the drainage channel is opened, and confining pressure and axial load are applied according to the target stress path until the pore pressure, volumetric strain, and axial deformation all reach the preset stability criteria.

[0049] Step 5: Approximate reconstruction of the target effective stress.

[0050] Determine σ′v0, σ′h0 and the target initial pore water pressure based on sampling depth, soil weight, groundwater level and lateral pressure coefficient. Select the isotropic mode or K0 approximation mode, and adjust the loading parameters according to the confining pressure, counter pressure, axial force correction value and effective cross-sectional area of ​​the sample to stabilize the pressure until the stress and deformation tend to be stable.

[0051] Step 6: Establish a non-drainage boundary.

[0052] Close the shut-off valves 19 of the upper and lower drainage pipes to isolate the sample from the back pressure controller 17; maintain the confining pressure and axial load according to the set values, and record the changes in pore water pressure during penetration and shearing.

[0053] Step 7: Insert the cross-shaped plate.

[0054] The vertical servo motor 26 is driven to make the cross-plate probe 37 penetrate to the target depth at a set rate; the penetration force, depth and hole pressure are recorded simultaneously during the penetration process.

[0055] Step 8: Cut the original cross-shaped blade.

[0056] After the insertion is completed, the device is left to stand for a preset waiting time. Then, the cross-plate probe 37 is rotated at a set angular velocity to record the torque-rotation angle curve and determine the peak torque of the original shear.

[0057] Step 9, Disturbance reshaping and reshaping shearing.

[0058] Continue rotating the cross-plate probe 37 until the torque reaches a stable residual plateau; the average torque change rate within two or more consecutive preset revolutions not exceeding a preset threshold can be used as the criterion for completion of reshaping. Then, shear again at the specified angular velocity and record the reshaping shear torque.

[0059] Step 10: Calculation and sample breakdown.

[0060] The original and remolded undrained shear strength and sensitivity are calculated by subtracting the no-load correction torque from the measured torque. After the test, the axial load, confining pressure and counter pressure are removed in stages, the confining pressure fluid is drained, the pressure chamber is opened and the components are cleaned.

[0061] Example 7: Data Calculation and Multi-Depth Testing The no-load corrected torque satisfies T0 = Tseal + Trod + Tidle, and the net shear torque is calculated as Tnet = Tmeas - T0. When T0 is directly measured using the blank calibration rod, it is not necessary to measure each component separately; when it is necessary to analyze the source of error, Tseal, Trod, and Tidle can be determined by component calibration.

[0062] When the diameter of the vane blade is D and the height is H, the geometric coefficient Kv of the vane is determined by Kv=πD²H / 2+πD³ / 6, the undrained shear strength Su is calculated by Su=Tnet / Kv; the undrained shear strength in its original state is denoted as Su0, the undrained shear strength in its remolded state is denoted as Sur, and the soil sensitivity St is calculated by St=Su0 / Sur.

[0063] When conducting multi-depth tests, the vane probe should be moved to an undisturbed area outside the previous shear influence range, and the shear influence ranges of adjacent test areas should not overlap; the axial distance between the centers of adjacent vanes should preferably be no less than H+D, and should be adjusted according to the sample height and boundary effect verification results.

[0064] Example 8: Extended Testing Method When replacing the miniature conical probe 38, the change in cone tip resistance with depth can be obtained under the same effective target stress conditions; when replacing the T-bar probe 39 or the spherical penetration probe 40, full-flow penetration testing can be carried out. When testing with different probes, the lateral and end boundary spacing of the specimen should be recalibrated according to the probe size.

[0065] The above embodiments can be combined or substituted according to the sample diameter, soil strength, target stress level, and testing purpose. All equivalent substitutions or conventional adjustments made within the scope of the inventive concept should fall within the protection scope of this invention.

Claims

1. A penetration vane combined with shear testing device based on in-situ effective stress reconstruction of drilled cylindrical samples, comprising a rigid loading frame, a sealed pressure chamber, and a vane probe, characterized in that, It also includes a borehole columnar sample holding and pressure transmission assembly, a confining pressure loading assembly, a back pressure and drainage control assembly, an axial loading assembly, a penetration torsion composite drive assembly, a sealing transmission assembly, an anti-eccentricity guide assembly, and a data acquisition and control system. The borehole columnar sample holding and pressure transmission assembly is disposed in the sealed pressure chamber and includes a bottom sample holder, a top force transmission cap, a flexible pressure transmission diaphragm, and a window-type splitting sleeve. The borehole columnar sample is placed between the bottom sample holder and the top force transmission cap. The flexible pressure transmission diaphragm covers the outside of the borehole columnar sample and its upper and lower ends are respectively sealed to the top force transmission cap and the bottom sample holder. The window-type splitting sleeve is sleeved on the outside of the flexible pressure transmission diaphragm and is formed by splicing at least two arc-shaped cylindrical plates. The arc-shaped cylindrical plates have pressure transmission windows. The upper end of the window-type splitting sleeve is provided with an axial movement gap between it and the top force transmission cap, and the lower end is provided with it and the bottom sample holder, so that the window-type splitting sleeve provides radial support to the borehole columnar sample without forming an axial load transfer bypass. The top force transmission cap and the upper permeable stone set inside the top force transmission cap are respectively provided with coaxial central penetration holes. The upper permeable stone is connected to the upper drainage pipe through an annular drainage groove and an offset drainage hole set inside the top force transmission cap and isolated from the central penetration holes. The confining pressure loading component is connected to the sealed pressure chamber and is used to apply confining pressure to the confining fluid; the back pressure and drainage control component is connected to the upper and lower ends of the borehole columnar sample, respectively, and is used to apply back pressure, control drainage consolidation, and switch between drainage and non-drainage boundaries. The axial loading assembly includes a hollow annular axial loading piston arranged around the transmission rod, the hollow annular axial loading piston acting on the top force transmission cap and applying an axial load to the drilled columnar sample; The penetration-torsion composite drive assembly includes a vertical servo drive mechanism and a torsion servo drive mechanism, which are connected to the cross-plate probe through the transmission rod and are used to drive the cross-plate probe to penetrate vertically and to rotate and shear. The sealing transmission assembly is disposed between the pressure chamber cover of the sealing pressure chamber and the transmission rod, and includes a vertical sliding sealing unit and a rotary sealing unit; the anti-eccentricity guide assembly is located above the top force transmission cap and sleeved on the outside of the transmission rod, and is used to limit the horizontal offset of the transmission rod and the cross plate probe; The data acquisition and control system is connected to the confining pressure loading component, the counterpressure and drainage control component, the axial loading component, and the penetration torsion composite drive component, respectively, and is used to control the confining pressure, counterpressure, axial load, penetration parameters, and torsion parameters and to acquire test data.

2. The testing apparatus according to claim 1, characterized in that, The arc-shaped cylindrical plate is provided with connecting lugs on both sides, and the connecting lugs of adjacent arc-shaped cylindrical plates are detachably connected by locking components; the pressure transmission window is one or more of rectangular holes, oblong holes, round holes, and grid holes; the ratio of the total area of ​​the pressure transmission window to the effective sidewall unfolded area of ​​the window-type split sleeve is the opening ratio.

3. The testing apparatus according to claim 1, characterized in that, The bottom sample holder is provided with a lower permeable stone, which is connected to the lower drainage pipe; the top force transmission cap is provided with an annular upper permeable stone, which is connected to the annular drainage groove; the flexible pressure transmission membrane is a latex membrane, rubber membrane, silicone membrane or polyurethane membrane, and its upper and lower ends are respectively sealed and fixed in the membrane fixing grooves of the top force transmission cap and the bottom sample holder by hoop rings.

4. The testing apparatus according to claim 1, characterized in that, At least one of the bottom sample holder, top force transmission cap, flexible pressure transmission diaphragm, and window-type splitting sleeve is a replaceable specification part to adapt to drilled columnar samples of different diameters and heights.

5. The testing apparatus according to claim 1, characterized in that, The confining pressure loading assembly includes a confining pressure controller, a confining pressure sensor, and a confining pressure pipeline; the back pressure and drainage control assembly includes a back pressure controller, a pore pressure sensor, a volumetric deformation measurement unit, an upper drainage pipeline, a lower drainage pipeline, and a shut-off valve; the axial loading assembly also includes an axial force sensor, an axial displacement sensor, and a servo loader; the data acquisition and control system is configured with an isotropic stress recovery mode and a K0 approximate stress recovery mode.

6. The testing apparatus according to claim 1, characterized in that, The sealing transmission assembly also includes a pressure balancing sealing chamber and a leakage observation port; the pressure balancing sealing chamber is located between the vertical sliding sealing unit and the rotary sealing unit, and is connected to the confining pressure controller or independent compensation pressure controller through an external compensation pipeline, so that the difference between the pressure in the pressure balancing sealing chamber and the confining pressure in the sealing pressure chamber is kept within a preset range; the leakage observation port is connected to the sealing gap.

7. The testing apparatus according to claim 1, characterized in that, The vertical servo drive mechanism includes a vertical servo motor, a lead screw, a guide rod, and a slide. The vertical servo motor drives the slide to move vertically along the guide rod via the lead screw. The torsional servo drive mechanism includes a torsional servo motor, a reducer, a torque sensor, and an angular displacement encoder. The torsional servo motor is fixed on the slide and connected to the transmission rod via the reducer. A penetration force sensor is also provided on the transmission rod.

8. The testing apparatus according to claim 1, characterized in that, The vane probe is detachably connected to the transmission rod via a quick-change connector; the replaceable test probes also include a miniature conical probe, a T-bar probe, a spherical penetration probe, and a blank calibration rod; the blank calibration rod is used to determine the no-load correction torque under the same or equivalent confining pressure, rotational speed, axial position of the transmission rod, and sealed guiding state as the actual shearing; a temperature sensor connected to the data acquisition and control system is installed on the sealed pressure chamber.

9. A method for combined shear testing of a penetration vane based on in-situ effective stress reconstruction of a drilled cylindrical sample, characterized in that, The testing apparatus according to any one of claims 1 to 8 comprises the following steps: S1, Test preparation and no-load calibration: The device is leveled and the sensor zero point is calibrated. Without contacting the soil sample, the blank calibration rod is rotated under no-load conditions with the same or equivalent confining pressure, speed, axial position of the transmission rod and sealed guide state as the actual shearing to obtain the no-load correction torque. S2, Borehole columnar sample loading: The obviously disturbed section at the end of the relatively complete borehole columnar sample obtained from the land or seabed borehole is cut off and cut to the target height. It does not need to be cut into a standard size sample. It is placed directly on the bottom sample holder, covered with a flexible pressure transmission membrane and sealed and fixed at both ends. The window-type split sleeve is closed and its upper and lower ends are kept axially movable with the top force transmission cap and the bottom sample holder, respectively. S3, Pressure Chamber Sealing and Venting: Move the borehole column sample holder and pressure transmission assembly into the sealing pressure chamber, connect the upper and lower drainage pipes, seal the sealing pressure chamber and inject confining pressure fluid to vent the air in the pressure chamber. S4, Saturation and Drainage Consolidation: Open the upper and lower drainage pipes, apply back pressure step by step and determine saturation; then apply confining pressure and axial load, and consolidate under drainage conditions until pore pressure, volumetric strain and axial deformation reach the preset stability criteria. S5, Approximate reconstruction of target effective stress: Based on the target vertical effective stress, target horizontal effective stress and target initial pore water pressure at the sampling depth, the confining pressure, back pressure and modified axial load are coordinated to make the borehole columnar sample reach the target stress level. S6, Establish a non-drainage boundary: Close the shut-off valves on the upper and lower drainage pipes to isolate the borehole columnar sample from the back pressure controller, maintain the confining pressure and axial load according to the set values, and collect changes in pore water pressure. S7, Vane Penetration: Drive the vane probe to penetrate the drilled columnar sample at a set rate to the target test depth; S8, Original Cross Shear: Drive the cross probe to rotate at a set angular velocity and record the torque and rotation angle to obtain the peak torque of the original shear; S9, Disturbance Reshaping and Reshaping Shear: Continue rotating the cross-plate probe until the torque reaches the preset stable residual platform criterion, and then shear again at a set angular velocity to obtain the reshaping shear torque; S10, Data Calculation and Post-processing: The measured torque is corrected using the no-load correction torque, and the original undrained shear strength, remolded undrained shear strength and soil sensitivity are calculated. Then, the soil is unloaded in stages and the samples are removed.

10. The test method according to claim 9, characterized in that, The unloaded corrected torque T0 obtained in step S1 satisfies T0=Tseal+Trod+Tidle, and the net shear torque is calculated according to Tnet=Tmeas-T0; where Tseal is the friction torque of the seal, Trod is the friction torque of the transmission rod and guide, Tidle is the unloaded transmission torque, and Tmeas is the measured torque; the undrained shear strength is calculated according to Su=Tnet / Kv, where Kv is the geometric coefficient of the vane; the soil sensitivity is calculated according to St=Su0 / Sur, where Su0 is the original undrained shear strength and Sur is the remolded undrained shear strength.

Images