Rock-soil body in-hole shearing instrument based on bidirectional shearing principle and testing method

Abstract

The invention provides a rock-soil body in-hole shearing instrument based on a bidirectional shearing principle and a testing method, and relates to the technical field of measurement. The shearing instrument comprises a shearing mechanism and shearing force loading mechanisms, the shearing mechanism and the shearing force loading mechanisms are symmetrically arranged, a middle shearing force loading oil cylinder applies shearing stress to drilling surrounding rock, and a front oil cylinder and a rear oil cylinder apply normal stress to the drilling surrounding rock. Identical shear plates are fixed on the loading oil cylinders to form symmetrical bilateral compression-shear test models; the shear apparatus can ensure that rock masses on the two sides of a shear surface are synchronously damaged at the same strain rate, and the boundary effect is eliminated. When the shear apparatus is used for testing, a press-in load-displacement curve and a shear load-displacement curve of a bidirectional shear tooth can be acquired in real time, a double-variable simultaneous equation is established, and the stress state of a synchronous failure point is optimally fitted by applying a least square method, so that measurement parameters are accurately calculated, and the measurement accuracy is improved. And high-fidelity loading simulation in a deep hole environment is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of deep sea and deep earth geotechnical engineering measurement, and in particular to a rock and soil body in-hole shear instrument and a testing method based on the bidirectional shear principle. Background Art

[0002] With the rapid development of deep-sea exploration and development, as well as deep-earth resource extraction, the precise acquisition of geotechnical parameters has become a core technical challenge for ensuring the safety of major engineering projects. Traditional borehole shear testing, a key in-situ testing method for geotechnical engineering, dates back to the development of the RBST system in the 1970s. This method, through a combined test mode of single-point normal loading and tangential pull, provides a fundamental solution for determining rock mass parameters in shallow boreholes.

[0003] In the prior art, the key test process of the RBST test system and similar test devices is to use a connecting rod to push the shear device probe into the borehole and record the test depth, then install the flange, oil pump, etc., then apply normal stress to the pair of probe teeth on the probe, then pull the connecting rod to apply tangential stress, then unload the oil pump, retract the probe teeth, and repeat the test. Although this test method can provide certain data, it has certain limitations. The problems of the prior art include: (1) The operation is complicated and requires joint arrangement inside and outside the borehole, which increases the complexity and limitations of the application; (2) Loading through the connecting rod outside the hole is only applicable to shallow hole detection, and its application in deep holes or deep holes in extreme environments is limited, and it is often difficult to meet the requirements of high precision and high efficiency testing; (3) It is impossible to accurately obtain normal displacement and shear displacement, and it is impossible to give the load-displacement curve change, so it is impossible to invert parameters such as modulus and hardness; (4) The stability is poor and the operation efficiency is low. Due to human factors and equipment limitations during the operation, the data may be inaccurate. In order to solve the above problems, it is necessary to further improve the existing shear device and test method. Summary of the Invention

[0004] In order to improve the efficiency and quality of borehole shear tests under complex working conditions and more accurately obtain rock and soil mechanical parameters such as cohesion, internal friction angle, shear strength, and modulus, the present invention provides a rock and soil in-hole shear instrument and testing method based on the bidirectional shear principle. The specific technical solution is as follows.

[0005] The cam is provided with a plurality of guide rails, and the guide rail is provided with a plurality of guide rails, and a plurality of guide rails are provided with a plurality of guide rails.

[0006] Preferably, the bidirectional pressure piston of the fixed oil cylinder moves in opposite directions under the push of hydraulic oil, pushing the piston to fix the tooth seat and the shear plate to move, and the shear teeth cut into the surrounding rock of the hole wall.

[0007] Preferably, the hydraulic oil of the shear cylinder pushes the shear piston to move, thereby moving the rear guide pad, and the reaction force acts on the front guide pad, so that the shear teeth on the shear plate shear the surrounding rock of the borehole.

[0008] It is also preferred that the displacement sensor converts the displacement signal of the shear plate into an electrical signal, and the electrical signal output realizes real-time monitoring of the displacement.

[0009] It is also preferred that pressure sensors are provided on the bidirectional pressure piston and the shear piston, and the sensors convert pressure signals into electrical signals, and the electrical signal output realizes real-time monitoring of normal stress and shear force.

[0010] It is also preferred that two shear plates are symmetrically arranged along the midpoint of the outer cylinder at both ends of the outer cylinder, and the two shear plates are also symmetrically arranged on the outer cylinder along the axis of the outer cylinder; the shear teeth on the shear plates are the same in shape and size.

[0011] It is also preferred that the shearing teeth synchronously apply shear loads of equal magnitude and opposite direction to form a mechanical balance system with mutually reacting forces.

[0012] A rock and soil in-hole shear testing method based on the bidirectional shear principle, using the rock and soil in-hole shear instrument based on the bidirectional shear principle, is characterized by the following steps:

[0013] S1. Determine the location, spacing, and depth of drill holes based on geological exploration information;

[0014] S2. Inspect the borehole wall and debug the rock and soil in-hole shear instrument based on the bidirectional shear principle to test signal transmission;

[0015] S3. Vertical stress loading and shear stress loading;

[0016] S4. Collect displacement and stress monitoring data;

[0017] S5. Based on the indentation load-displacement curve and shear load-displacement curve of the bidirectional shear teeth and the Mohr-Coulomb strength criterion, a set of simultaneous equations with two variables was established. The stress state at the synchronous failure point was optimally fitted using the least squares method to calculate the cohesion, internal friction angle, shear strength, and modulus.

[0018] S6. Recovering the in-hole shear instrument based on the bidirectional shear principle of rock and soil through the guide rod;

[0019] Repeat steps S1 to S6 to test different positions.

[0020] It is further preferred that the geological exploration information includes detection information of geological radar and seismic wave detection; and the inspection of the borehole wall includes inspection of the verticality of the borehole and the integrity of the borehole wall.

[0021] Further preferably, in the in-hole bidirectional shear test, the area of ​​the rock sheet embedded between the shear teeth is A, the normal pressure acting on the rock sheet generated by the front and rear fixed cylinders is P, and the shear force acting on the rock sheet generated by the shear cylinder is T. Then, the normal stress σ and shear stress τ acting on the rock sheet are respectively:

[0022] σ=P / A

[0023] τ=T / 2A

[0024] During the test, the normal force can be adjusted by adjusting the oil pressure in the fixed cylinder. According to the Mohr-Coulomb strength criterion:

[0025]

[0026] Then, the shear stress under different normal stress conditions is linearly fitted by the least square method to obtain the rock cohesion c and internal friction angle.

[0027] The beneficial effect of the in-hole shear instrument and testing method for rock and soil based on the bidirectional shear principle provided by the present invention is that, by synchronously applying equal reverse loads through bidirectional symmetrical shear teeth, a self-balancing mechanical system in the hole is constructed, eliminating the stress field distortion and boundary effect caused by traditional unilateral loading; the use of a bidirectional synergistic action mode not only breaks through the mechanical limitations of traditional single-point loading, but also realizes high-fidelity loading simulation in a deep hole environment; the supporting shear test system realizes the integration of loading and testing by constructing a bidirectional hydraulic drive system and a multi-sensor array, and obtains the shear tooth's indentation load-displacement curve and the shear tooth's shear load-displacement curve in one measurement, thereby more accurately obtaining key mechanical parameters of rock and soil such as cohesion, internal friction angle, shear strength, and modulus. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of the in-hole shear test method for rock and soil based on the bidirectional shear principle;

[0029] Figure 2 This is a schematic diagram of the structure of the in-hole bidirectional shear instrument;

[0030] Figure 3 It is a top view of the in-hole bidirectional shear instrument;

[0031] Figure 4 It is a schematic diagram of the AA section of the bidirectional shear apparatus;

[0032] Figure 5 is the stress-strain curve of biaxial shear;

[0033] Figure 6 This is a schematic diagram of the working scene of the in-hole bidirectional shear instrument;

[0034] Figure 7 This is a cross-sectional diagram of the working scene of the in-hole bidirectional shear instrument;

[0035] Figure 8 This is the front view of the working scene of the in-hole bidirectional shear instrument;

[0036] Figure 9 is an enlarged schematic diagram of region 100 of the biaxial shear instrument before vertical stress loading;

[0037] Figure 10 It is a schematic diagram during vertical stress loading;

[0038] Figure 11 It is a schematic diagram after vertical stress loading is stabilized;

[0039] Figure 12 is a schematic diagram of shear failure;

[0040] Figure 13 Shear stress-normal stress fitting curve diagram of bidirectional shear;

[0041] In the figure: 1-outer cylinder; 2-rear end baffle; 3-guide rod; 4-fixed steel plate; 5-shear plate; 6-piston fixed gear seat; 7-shear cylinder; 8-guide pad; 9-guide shaft; 10-positioning hole; 15-fixed cylinder; 17-front end baffle; 18-connecting pressure ring; 23-bidirectional pressure piston; 29-fixed cylinder cover; 31-pressure relief spring; 36-shear piston; 50-front end displacement sensor; 51-rear end displacement sensor; 55-shearing tooth; 101-rock mass; 102-shear instrument; 103-shear failure line. DETAILED DESCRIPTION

[0042] Combine Figures 1 to 13 As shown, the specific implementation of the rock and soil in-hole shear instrument and testing method based on the bidirectional shear principle provided by the present invention is as follows.

[0043] This in-hole shear instrument for rock and soil based on the bidirectional shear principle utilizes the principle of bidirectional collaborative shear testing. By drilling a hole in the rock and soil and installing a shear device, shear forces are applied in opposite directions to the rock and soil closely spaced at either end of the shear instrument. The rock masses at both ends are simultaneously destroyed and their displacements are evenly distributed. The mechanical parameters and deformation characteristics are then obtained based on the Mohr-Coulomb strength criterion and the least squares fitting method. The shear instrument specifically includes a shear mechanism and a shear force loading mechanism. The shear mechanism and shear force loading mechanism are designed to be symmetrical in front and back. When loaded, the front and rear cylinders apply normal stress to the rock surrounding the borehole, while the middle shear force loading cylinder primarily applies shear stress to the rock surrounding the borehole. The shearing mechanism includes a rear end baffle 2, a guide rod 3, a shear plate 5, a piston fixed tooth seat 6, a guide shaft 9, a fixed oil cylinder 15, a bidirectional pressure piston 23, a front end baffle 17, a pressure relief spring 31, and a displacement sensor. The displacement sensor includes a front end displacement sensor 50 and a rear end displacement sensor 51. The front end baffle 17 and the rear end baffle 2 are respectively arranged at both ends of the outer tube. The end of the guide rod 3 is fitted on the rear end baffle. The guide rod 3 is provided with a pressure relief spring 31. The fixed oil cylinder 15 is arranged in the outer tube and connected to the guide rod 3. The fixed oil cylinder 15 is provided with a bidirectional pressure piston. The outer tube 1 is provided with multiple positioning holes and four fixed steel plates 4. A shear plate 5 is respectively arranged on each fixed steel plate. The fixed steel plate 4 is also provided with a piston fixed tooth seat. A displacement sensor is also provided on each shear plate 5. The shear force loading mechanism includes a fixed cylinder cover 29, a connecting pressure ring 18, a shear cylinder 7, and a shear piston 36. The fixed cylinder cover 29 is arranged at one end of the shear cylinder, and the connecting pressure ring 18 is arranged between the trapezoidal ferrule and the trapezoidal ferrule. The shear piston 36 is pushed by hydraulic oil. The shear instrument adopts a symmetrical hydraulic drive system and does not rely on an external reaction force device or pull rod loading. It achieves self-balancing loading through a built-in bidirectional pressure piston. Combined with PTFE / ceramic composite sealing technology with a pressure resistance of 60MPa, the sensor element is sealed and can operate stably in deep sea 3000 meters or high temperature (150℃) deep boreholes, and the success rate of extreme environment testing has been increased to more than 90%.

[0044] The hydraulic oil in the fixed cylinder 15 drives the bidirectional pressure piston in opposite directions, pushing the piston fixed tooth holder 6 and shear plate 5 to move, causing the shear teeth to cut into the surrounding rock of the hole. The hydraulic oil in the shear cylinder 7 drives the shear piston, which in turn moves the rear guide pad. The reaction force acts on the front guide pad, causing the shear teeth on the shear plate to shear the surrounding rock of the hole.

[0045] The displacement sensor converts the displacement signal of the shear plate into an electrical signal, and the electrical signal output enables real-time displacement monitoring. Pressure sensors are installed on the bidirectional pressure piston and the shear piston. The sensors convert the pressure signal into an electrical signal, and the electrical signal output enables real-time monitoring of normal stress and shear force. The integrated indentation-shear composite sensor array can synchronously capture the normal indentation load-displacement curve in a single test with an accuracy of ±0.01mm. With a sampling rate of over 100Hz, the synchronous inversion of cohesion, internal friction angle, shear modulus, and strain hardening index is achieved, and the test efficiency is more than doubled compared to traditional step-by-step testing.

[0046] Two shear plates 5 are symmetrically arranged along the midpoint of the outer cylinder 1 at both ends of the outer cylinder 1, and the two shear plates 5 are also symmetrically arranged on the outer cylinder 1 along the axis of the outer cylinder; the shear teeth on the shear plates 5 have the same shape and size, forming a completely symmetrical double-sided compression shear test model.

[0047] The shear teeth simultaneously apply shear loads of equal magnitude and opposite direction, forming a mechanical equilibrium system with mutually reacting forces. This mechanism ensures that the rock masses on both sides of the shear surface are synchronously destroyed at the same strain rate by precisely controlling the displacement coordination of the bidirectional actuators, and eliminates the boundary effect caused by traditional unilateral loading based on the assumption of equal displacement distribution.

[0048] A rock and soil in-hole shear testing method based on the bidirectional shear principle, using the rock and soil in-hole shear instrument based on the bidirectional shear principle, is characterized by the following steps:

[0049] S1. Determine the location, spacing, and depth of drill holes based on geological exploration information;

[0050] Geological survey information includes information collected by geological radar, seismic wave detection and other means, which comprehensively understands the geological structure, rock mass distribution and potential joint and fissure trends of the project site; based on the project design requirements and rock mass characteristics, the drilling location, spacing and depth are accurately planned to ensure that the drilling can cover the key rock mass areas.

[0051] S2. Inspect the borehole wall and debug the rock and soil in-hole shear instrument based on the bidirectional shear principle to test signal transmission;

[0052] Conduct a comprehensive inspection of the main body of the in-hole bidirectional shear instrument to check whether the outer shell is damaged or deformed, ensure the integrity of the instrument structure, check the performance of the sensor to ensure its sensitivity is normal, and check whether its output signal is accurate. If any deviation is found in the sensor, it needs to be adjusted or replaced in time.

[0053] Use a borehole imager or inclinometer to check the verticality and integrity of the borehole. If the verticality deviation exceeds the allowable range, analyze the cause and abandon and re-drill if necessary. If the borehole wall has obvious cracks, collapse, or other defects, take appropriate measures, such as injecting cement slurry to repair the wall. Wait until the hole wall stabilizes before proceeding with subsequent operations. Slowly lower the debugged in-situ drilling bidirectional shear instrument into the bottom of the borehole, using installation auxiliary devices to ensure that the instrument is concentric with the borehole.

[0054] S3. Vertical stress loading and shear stress loading;

[0055] Among them, when vertical stress is loaded, the hydraulic oil in the oil pump flows into the front and rear fixed cylinders, and the hydraulic oil pushes the bidirectional pressure piston to move in the upward and downward directions, thereby pushing the piston fixed tooth seat and shear plate to move, so that the shear teeth cut into the surrounding rock of the hole wall.

[0056] The hydraulic oil in the shear stress loading oil pump flows into the shear cylinder through the connecting pressure ring, trapezoidal ferrule and trapezoidal ferrule. The hydraulic oil pushes the shear piston to move, thereby pushing the rear guide pad to move. Since the front shear mechanism and the rear shear mechanism have been loaded and fixed before loading, the reaction force will act on the front guide pad, so that the shear teeth on the front and rear pairs of shear plates shear the surrounding rock of the borehole.

[0057] S4. Collect displacement and stress monitoring data;

[0058] Since the two pairs of shear plates on both sides of the shear instrument are identical, according to comprehensive analysis of elastic-plastic theory and numerical simulation, under normal circumstances, the sheared rocks on the front and rear sides will be destroyed at the same time, and the shear displacement on both sides is evenly divided.

[0059] When the in-hole bidirectional shear instrument is working, the front-end displacement sensor and the rear-end displacement sensor located on the shear plate will convert the displacement signal into an electrical signal and transmit it to the display instrument outside the hole, realizing real-time monitoring of the displacement; the pressure sensor located on the bidirectional pressure piston and the shear piston will convert the pressure signal into an electrical signal and transmit it to the display instrument outside the hole, realizing real-time monitoring of the normal force and shear force.

[0060] S5. Based on the indentation load-displacement curve and shear load-displacement curve of the bidirectional shear teeth and the Mohr-Coulomb strength criterion, a set of simultaneous equations with two variables was established. The stress state at the synchronous failure point was optimally fitted using the least squares method to calculate the cohesion, internal friction angle, shear strength, and modulus.

[0061] In the in-hole bidirectional shear test, the area of ​​the rock sheet embedded between the shear teeth is A, the normal pressure exerted on the rock sheet by the front and rear fixed cylinders is P, and the shear force exerted on the rock sheet by the shear cylinder is T. Then, the normal stress σ and shear stress τ acting on the rock sheet are:

[0062] σ=P / A

[0063] τ=T / 2A

[0064] During the test, the normal force can be adjusted by adjusting the oil pressure in the fixed cylinder. According to the Mohr-Coulomb strength criterion:

[0065]

[0066] Then, the shear stress under different normal stress conditions is linearly fitted by the least square method to obtain the rock cohesion c and internal friction angle. The least squares fitting algorithm based on the displacement equal distribution assumption and bivariate simultaneous equations reduces the error in cohesion calculation to ±2.0 kPa and improves the accuracy of the internal friction angle to ±0.5°, which is more than twice the accuracy of traditional methods.

[0067] The stress-strain curve of the in-situ shear test of the rock mass is below the yield point, and the deformation curve is similar to the compression deformation. After the yield point, a structural surface and a structural body in the rock mass may be sheared first, followed by a stress drop, and multiple stress drops may occur before the peak. When the stress increases to a certain level, the parts that are not sheared appear in the form of instantaneous destruction, accompanied by a large stress drop, and then stable slip may occur. The shear stress-normal stress fitting curve of the rock mass is roughly a straight line, the intercept of the fitting line is the cohesion c, and the slope is the internal friction angle

[0068] S6. Recovering the in-hole shear instrument based on the bidirectional shear principle of rock and soil through the guide rod;

[0069] When the normal force is unloaded, the hydraulic oil flows into the fixed cylinder through the upper and lower pairs of connecting pressure rings, pushing the bidirectional pressure piston to move toward the middle of the cylinder, thereby driving the shear plate to retract; when the shear force is unloaded, the pressure relief spring will push the shear piston back to its original position.

[0070] Repeat steps S1 to S6 to test different positions.

[0071] During the test, the integrated sensor array collected the indentation load-displacement and shear load-displacement curves of the bidirectional shear teeth in real time. Using the Mohr-Coulomb strength criterion, a set of simultaneous equations with two variables was established. The least squares method was then used to optimally fit the stress state at the simultaneous failure point, allowing for accurate calculation of parameters such as cohesion, internal friction angle, shear strength, and modulus. This bidirectional synergistic approach not only overcomes the mechanical limitations of traditional single-point loading but also enables high-fidelity loading simulation in deep-hole environments.

[0072] Furthermore, the operational testing process is relatively standardized. The fully symmetrical shear design ensures uniform loading stress distribution, and the dual-constraint mechanism of the guide rod and slide shaft controls the system's eccentric load rate to within 1.5%. The integrated structure eliminates external components such as flanges and connecting rods required in traditional methods, shortening deep-hole test preparation time to 15 minutes and reducing operational errors by 80%, resulting in more stable and repeatable results.

[0073] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A rock and soil in-hole shear instrument based on the bidirectional shear principle, characterized in that: The cam is provided with a plurality of guide holes, and the guide holes are provided with a plurality of piston rods, and the piston rods are provided with a plurality of piston rods, and the piston rods are provided with a plurality of piston rods.

2. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 1, characterized in that: The fixed oil cylinder moves the bidirectional pressure piston in opposite directions under the push of hydraulic oil, pushing the piston fixed tooth seat and the shear plate to move, and the shear teeth cut into the surrounding rock of the hole wall.

3. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 1, characterized in that: The hydraulic oil in the shear cylinder pushes the shear piston to move, thereby moving the rear guide pad to move, and the reaction force acts on the front guide pad, and the shear teeth on the shear plate shear the surrounding rock of the borehole.

4. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 1, characterized in that: The displacement sensor converts the displacement signal of the shear plate into an electrical signal, and the electrical signal output realizes real-time monitoring of the displacement.

5. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 4, characterized in that: The bidirectional pressure piston and the shearing piston are provided with pressure sensors, which convert pressure signals into electrical signals. The electrical signal output realizes real-time monitoring of normal stress and shear force.

6. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 1, characterized in that: The shear plates are symmetrically arranged along the midpoint of the outer cylinder at both ends of the outer cylinder, and the two shear plates are also symmetrically arranged on the outer cylinder along the axis of the outer cylinder; the shear teeth on the shear plates have the same shape and size.

7. The rock and soil in-hole shear instrument based on the bidirectional shear principle according to claim 1, characterized in that: The shear teeth synchronously apply shear loads of equal magnitude and opposite direction to form a mechanical balance system with mutually reactive forces.

8. A method for testing rock and soil in-hole shear based on the bidirectional shear principle, using the rock and soil in-hole shear instrument based on the bidirectional shear principle according to any one of claims 1 to 7, characterized in that the steps include: S1. Determine the location, spacing, and depth of drill holes based on geological exploration information; S2. Inspect the borehole wall and debug the rock and soil in-hole shear instrument based on the bidirectional shear principle to test signal transmission; S3. Vertical stress loading and shear stress loading; S4. Collect displacement and stress monitoring data; S5. Based on the indentation load-displacement curve and shear load-displacement curve of the bidirectional shear teeth and the Mohr-Coulomb strength criterion, a set of simultaneous equations with two variables was established. The stress state at the synchronous failure point was optimally fitted using the least squares method to calculate the cohesion, internal friction angle, shear strength, and modulus. S6. Recovering the in-hole shear instrument based on the bidirectional shear principle of rock and soil through the guide rod; Repeat steps S1 to S6 to test different positions.

9. The method for in-hole shear testing of rock and soil based on the bidirectional shear principle according to claim 8, characterized in that: The geological exploration information includes detection information from geological radar and seismic wave detection; the inspection of the borehole wall includes inspection of the verticality of the borehole and the integrity of the borehole wall.

10. The rock and soil in-hole shear testing method based on the bidirectional shear principle according to claim 8, characterized in that: In the in-hole bidirectional shear test, the area of ​​the rock sheet embedded between the shear teeth is A, the normal pressure exerted on the rock sheet by the front and rear fixed cylinders is P, and the shear force exerted on the rock sheet by the shear cylinder is T. Then, the normal stress σ and shear stress τ acting on the rock sheet are: σ=P / A τ=T / 2A During the test, the normal force can be adjusted by adjusting the oil pressure in the fixed cylinder. According to the Mohr-Coulomb strength criterion: Then, the shear stress under different normal stress conditions is linearly fitted by the least square method to obtain the rock cohesion c and internal friction angle.

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