Cemented sand gravel in-situ testing device and deformation modulus and shear strength testing method

Abstract

The invention provides a cemented sand gravel in-situ testing device and a deformation modulus and shear strength testing method.The cemented sand gravel in-situ testing device comprises a force transmission base plate, a plurality of pull rods are hinged to the force transmission base plate and evenly distributed around the force transmission base plate, and anchoring assemblies are hinged to the lower ends of the pull rods and anchored to the ground; a force transmission column, a vertical jack, a first base plate and a pressure bearing plate for pressurizing the top of a test piece are sequentially and downwards arranged on the lower side of the force transmission seat plate; a plurality of vertical displacement sensors are distributed on the top of the bearing plate, and the vertical jack is connected with a vertical pressure sensor for measuring the pressure of the vertical jack. According to the invention, the in-situ test of the cemented sand gravel is realized, and the cost is low; material disturbance and stress release in the sampling and sample preparation process are avoided, the result is real, and data are accurate; and a reliable technical support is provided for evaluating the mechanical property of the large-particle-size cemented sand gravel.

Description

Technical Field

[0001] This invention relates to the technical field of mechanical property testing devices for dam construction materials, specifically to an in-situ testing device for cemented sand and gravel, and a method for testing deformation modulus and shear strength. Background Technology

[0002] Cemented gravel is a new type of dam construction material in the field of hydraulic engineering. It is typically made by mixing a small amount of cement, fly ash, and other cementing materials with unscreened and unwashed natural gravel from the construction site. The mixture is then simply mixed, spread, and vibrated and compacted (or poured and vibrated) to form a cemented body with specific compressive strength, shear strength, and resistance to deformation. Currently, this material has been successfully applied in more than forty reservoir dams, cofferdams, and embankment projects in my country, and accurate testing of its in-situ mechanical properties has become a crucial step in ensuring the safety and quality of these projects.

[0003] However, cemented gravel, as a novel material with structural and material properties between concrete and soil / rock materials, presents significant challenges to traditional in-situ testing methods due to its unique weak cementation characteristics and wide particle size distribution. Using the horizontal shearing method based on rigid shear boxes, common in soil / rock materials, would severely disrupt its original cementation structure and aggregate interlocking effect by forcibly pre-setting the shear surface, leading to test results that deviate significantly from the true strength. Conversely, directly applying the direct shearing method for precast concrete specimens is problematic because cemented gravel has large aggregate sizes (often exceeding 150mm), a wide gradation range, and high dispersion; conventionally sized specimens cannot represent the gradation, resulting in large data dispersion, prominent size effects, and an inability to reflect the combined failure mechanism of aggregate shearing and cementation. Both of these traditional in-situ testing methods, one for granular soil / rock materials and the other for strongly cemented concrete, have inherent limitations due to their incompatibility with the transitional mechanical behavior of cemented gravel.

[0004] In summary, the lack of specialized equipment and standard methods for testing the shear strength and deformation modulus of in-situ cemented gravel has become a key technical bottleneck restricting the safety evaluation and engineering promotion of this material. Therefore, the absence of a device and method for rapidly, accurately, and cost-effectively determining its in-situ shear strength and deformation modulus is particularly problematic when dealing with coarse-grained gravel with aggregate diameters exceeding 150mm and widely sourced materials. There is an urgent need to develop dedicated testing theories and methods that can balance structural integrity and material heterogeneity, and to provide equipment and methods suitable for field conditions that can obtain accurate mechanical parameters in situ. This has become a pressing need to promote the safe and reliable application of this material. Summary of the Invention

[0005] To solve at least one of the above technical problems, the present invention provides an in-situ testing device for cemented gravel and a method for testing deformation modulus and shear strength.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: This invention provides an in-situ testing device for cemented gravel, comprising a force transmission base plate, on which multiple tie rods are hinged and evenly distributed around the force transmission base plate. An anchoring assembly is hinged to the lower end of each tie rod and anchored to the ground. A force transmission column, a vertical jack, a first pad, and a pressure plate for applying pressure to the top of the specimen are sequentially arranged downwards on the lower side of the force transmission base plate. Multiple vertical displacement sensors are distributed on the top of the pressure plate, and a vertical pressure sensor for measuring its own pressure is connected to the vertical jack.

[0007] The beneficial effects of this invention are: This invention enables in-situ testing of cemented gravel, avoiding the need for repeated equipment handling, setup, and calibration. This reduces the total testing time for a single point by over 50%, resulting in highly efficient and cost-effective testing. Furthermore, it can be used not only for deformation modulus testing but also for shear strength testing, replacing two sets of traditional dedicated equipment. This significantly reduces equipment procurement, maintenance, and labor costs, demonstrating outstanding engineering economics. In addition, this invention directly tests the in-situ, undisturbed engineering entity, fundamentally avoiding material disturbance and stress release during sampling, transportation, and indoor sample preparation. This ensures that the test results accurately reflect the mechanical behavior of the foundation under in-situ stress, resulting in reliable and precise data. Moreover, considering the characteristics of cemented gravel aggregates—large particle size, wide gradation range, and strong heterogeneity—this invention, through a full-scale in-situ testing method, fully encompasses the material's actual maximum particle size and representative gradation, effectively solving the size effect problem of traditional indoor testing. This provides reliable technical support for evaluating the mechanical properties of large-particle-size cemented gravel. Furthermore, the force transmission base plate and the anchoring structure constitute an expandable design platform. Its size can be designed according to the actual material conditions on the engineering site, which has good scalability and breaks through the inherent limitations of traditional equipment on specimen size, and can adapt to the testing needs of materials with different particle sizes.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the anchoring assembly includes an anchor seat, on which an anchor rod is fixed, the lower end of which is anchored into the ground; the lower end of the tie rod is hinged to the anchor seat.

[0010] When the vertical jack applies a stable vertical load to the specimen, the force transmission plate transmits the force from the other end of the vertical jack to the anchor group through the tie rod. The anchor rod provides pull-out resistance through its own bond strength with the foundation or mechanical interlocking, which facilitates providing a stable and reliable tension support point for the tie rod and improves the stability of the force transmission plate. At the same time, the entire system can be quickly disassembled, transported and assembled on site, combining structural stability and construction convenience, making it particularly suitable for use in field construction sites.

[0011] Furthermore, a first ball joint plate is provided on the lower side of the force transmission base plate, and the first ball joint plate and the force transmission base plate are in spherical contact; the first ball joint plate is fixedly connected to the upper end of the force transmission column.

[0012] Under the load applied by the vertical jack, the first ball joint plate transmits pressure to the force transmission seat plate through the ball joint, thereby achieving universal adjustment. This universal adjustment can automatically compensate for the angle changes caused by uneven contact surfaces between the pressure plate and the specimen or installation deviations, ensuring that the vertical load is always uniformly applied to the upper surface of the specimen, effectively eliminating measurement errors caused by eccentric compression and stress concentration.

[0013] Furthermore, a pad is provided between the force transmission column and the vertical jack. The upper end of the pad has a boss that extends into the lower end of the force transmission column, and the lower end of the pad has a groove into which the upper end of the vertical jack extends.

[0014] By matching the boss with the lower end of the force transmission column and the vertical jack with the groove at the lower end of the pad, instability at the connection between the vertical jack and the force transmission column is avoided, thus improving the stability of force transmission between the two.

[0015] Furthermore, it also includes a horizontal jack, which is located on one side of the specimen. A second pad is provided between the first end of the horizontal jack and the soil, and a side force transmission plate for applying pressure to the side of the specimen is provided between the second end of the horizontal jack and the specimen. Multiple horizontal displacement sensors are also distributed on the side of the specimen away from the side force transmission plate. A horizontal pressure sensor for measuring its own pressure is connected to the horizontal jack.

[0016] With the support of the second pad, the horizontal jack applies pressure to the side of the specimen through the side force transmission plate. At the same time, the horizontal pressure sensor can collect pressure changes, and the horizontal displacement sensor can collect the shear displacement of the specimen, which facilitates the in-situ shear strength test of the specimen.

[0017] Furthermore, a second ball joint plate is provided between the second end of the horizontal jack and the side force transmission plate. The second ball joint plate and the side force transmission plate are in spherical contact, and the second ball joint plate is fixedly connected to the second end of the horizontal jack.

[0018] Under the load of the horizontal jack, the second ball joint plate transmits pressure through the ball surface to the side force transmission plate, thereby achieving universal adjustment. This universal adjustment can automatically compensate for the angle changes caused by uneven contact surfaces between the side force transmission plate and the specimen or installation deviations, ensuring that the horizontal load is always applied evenly to the side of the specimen, effectively eliminating measurement errors caused by eccentric compression and stress concentration.

[0019] Furthermore, a roller array is provided between the first pad and the pressure plate.

[0020] By converting the friction between the first pad and the bearing plate into rolling friction through the roller array, the horizontal friction force is significantly reduced, thus offsetting the horizontal thrust of the horizontal jack. This ensures that the horizontal load is used to overcome the shear strength of the specimen itself to the maximum extent, guaranteeing the authenticity of the test results.

[0021] Furthermore, it also includes an instrument frame, which is a gantry frame with both ends extending to the outside of the anchoring components and fixed to the ground; the pressure plate is located directly below the instrument frame, and the reference ends of the vertical displacement sensor and the horizontal displacement sensor are both fixed on the instrument frame.

[0022] Using an independent instrument frame as a reference, which extends beyond the anchoring components, it is independently and stably supported on a solid foundation outside the test area. This allows for complete isolation of the reference from the reaction force and loading system, avoiding errors caused by soil stress and deformation, and improving the accuracy of the test results.

[0023] This invention also provides a method for testing the in-situ deformation modulus of cemented gravel, based on the above-mentioned in-situ testing device for cemented gravel, comprising the following steps: I. Test Point Preparation and Site Leveling: Select a flat, dense and representative cemented gravel test area at the project site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; level the test area to ensure that its flatness meets the installation requirements of the bearing plate. 2. Device placement: Place the pressure plate precisely at the center of the leveled test surface. The area covered by the pressure plate is the test specimen. Complete the overall installation of the in-situ test device for cemented gravel. 3. Apply a preload using vertical jacks, and then unload to the initial load; IV. Graded Loading and Data Acquisition: The vertical jack is subjected to graded loading. For each grade of load Pi applied, the initial reading of the vertical displacement sensor under that load is recorded, and the settlement value Si is recorded at predetermined intervals. V. Staged unloading and rebound observation: After the load reaches the estimated maximum pressure Pmax and stabilizes, staged unloading begins; VI. Data Processing and Deformation Modulus Calculation: Organize the data, plot the complete load-settlement PS curve, select the initial linear segment of the PS curve, and calculate the deformation modulus E0 of the cemented gravel according to the elastic theory formula.

[0024] Through the above steps, this invention achieves accurate determination of the deformation characteristics of cemented gravel in large-size, in-situ conditions, providing key deformation parameters for engineering design and safety evaluation. Furthermore, the testing is efficient and cost-effective; it fundamentally avoids material disturbance and stress release during sampling, transportation, and indoor sample preparation, ensuring that the test results truly reflect the mechanical behavior of the foundation under in-situ stress conditions, resulting in accurate and reliable data; it effectively solves the size effect problem of traditional indoor tests, providing reliable technical support for the mechanical property evaluation of large-diameter cemented gravel.

[0025] This invention also provides a method for testing the in-situ shear strength of cemented gravel, based on the aforementioned in-situ testing device for cemented gravel, comprising the following steps: I. Test point preparation and site leveling: Select a flat, dense and representative cemented gravel test area at the engineering site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; cut and trim regular cuboid specimens, and trim the top surface, the side surface that bears the horizontal thrust, and the bottom surface of the specimens. II. Installation of the device: Complete the overall installation of the in-situ testing device for cemented sand and gravel, and lay a roller array at the bottom of the prepared specimen; slowly apply the first design load using vertical jacks; III. Vertical pressure stabilization and data initialization: Slowly increase the vertical pressure step by step to the predetermined test value, clear the readings of all horizontal displacement sensors and horizontal pressure sensors, and prepare to start the shear test; IV. Applying Horizontal Thrust and Simultaneous Data Acquisition: Activate the horizontal jack to apply a horizontal thrust to the specimen at a constant displacement rate; simultaneously, collect the following data: Time t, vertical stress σ, horizontal shear stress τ, shear displacement δh, vertical displacement δv; V. Test Termination and Specimen Failure Recording: When any of the following conditions occur, the specimen is deemed to have suffered shear failure, the test is terminated, and the final failure mode of the specimen is recorded: 1) The horizontal shear stress τ peaks and then steadily decreases; 2) The shear displacement δh continues to increase while the rate of change of the horizontal shear stress τ is significantly flat; 3) The shear displacement has reached 1 / 15 to 1 / 10 of the specimen's side length; VI. Data Processing and Parameter Calculation: Plot the horizontal shear stress τ-shear displacement δh relationship curve, and determine the shear strength of the specimen under the vertical stress σ from the curve.

[0026] Through the above steps, this invention enables accurate and reliable determination of the shear strength parameters of large-sized, in-situ cemented gravel specimens, providing crucial shear strength parameters for engineering design and safety evaluation. Furthermore, the testing is efficient and cost-effective; it fundamentally avoids material disturbance and stress release during sampling, transportation, and indoor sample preparation, ensuring that the test results accurately reflect the mechanical behavior of the foundation under in-situ stress conditions. The results are reliable and the data is precise; it effectively solves the size effect problem of traditional indoor tests, providing reliable technical support for the mechanical property evaluation of large-diameter cemented gravel. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention.

[0028] Figure 2 for Figure 1 Top view.

[0029] Figure 3 This is a schematic diagram of the specimen's structure.

[0030] In the accompanying drawings, the technical features represented by each reference numeral are as follows: 1-Force transmission base plate; 2-Tie rod; 3-Force transmission column; 4-Vertical jack; 5-First pad plate; 6-Pressure plate; 7-Vertical displacement sensor; 8-Vertical pressure sensor; 9-Anchor seat; 10-Anchor rod; 11-First ball joint plate; 12-Padded block; 13-Horizontal jack; 14-Second pad plate; 15-Side force transmission plate; 16-Second ball joint plate; 17-Horizontal displacement sensor; 18-Horizontal pressure sensor; 19-Roller array; 20-Instrument frame. Detailed Implementation

[0031] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] See also: This invention Figure 1-3 .

[0033] This invention provides an in-situ testing device for cemented gravel, comprising a force transmission base plate 1, on which multiple tie rods 2 are hinged, evenly distributed around the force transmission base plate 1, and the lower ends of the tie rods 2 are hinged to anchoring components, which are anchored to the ground; on the lower side of the force transmission base plate 1, a force transmission column 3, a vertical jack 4, a first pad 5, and a pressure plate 6 for applying pressure to the top of the specimen are arranged sequentially downwards; multiple vertical displacement sensors 7 are distributed on the top of the pressure plate 6, and a vertical pressure sensor 8 for measuring its own pressure is connected to the vertical jack 4.

[0034] principle: The following steps were taken to test the in-situ deformation modulus of cemented gravel using this device: I. Test Point Preparation and Site Leveling: Select a flat, dense, and representative cemented gravel test area at the project site. Remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer. Level the test area to ensure its flatness meets the installation requirements of the bearing plate 6. Preferably, the unevenness is typically required to be less than 1% of the diameter of the bearing plate 6.

[0035] Preferably, the area should be adjacent to but not overlap with the shear strength test point.

[0036] II. Device Placement: Precisely place the pressure plate 6 at the center of the leveled test surface. The area covered by the pressure plate 6 becomes the test specimen. Complete the overall installation of the in-situ testing device for cemented gravel. Preferably, the pressure plate 6 should have sufficient rigidity and be circular. Its diameter D should be determined based on the maximum aggregate particle size Dmax and the test requirements, typically (2-3) × Dmax. Furthermore, four vertical displacement sensors 7 are evenly distributed around the vertical jack 4.

[0037] 3. Apply a preload using vertical jack 4, then reduce to the initial load. This step aims to eliminate any small gaps inside the device and between the pressure plate 6 and the specimen surface, ensuring tight contact between all components. Check that all sensor readings are stable and that the data acquisition system is functioning correctly. Zero the vertical displacement sensor readings to prepare for formal loading.

[0038] Preferably, the preload is typically 5%-10% of the maximum preload, such as 0.05 MPa. The initial load is preferably 0.01 MPa.

[0039] IV. Graded Loading and Data Acquisition: The vertical jack 4 is subjected to graded loading. For each grade of load Pi applied, the initial reading of the vertical displacement sensor under that load is recorded, and the settlement value Si is recorded at predetermined intervals.

[0040] Preferably, the load increment ΔP for each level is typically taken as 1 / 5 to 1 / 8 of the estimated maximum pressure Pmax; the estimated maximum pressure Pmax is a manually set estimate. Immediately after each load level Pi is applied, the initial reading of the vertical displacement sensor under that load level is recorded, and then timing begins. Then, at predetermined time intervals (e.g., 1, 2, 5, 10, 15, 30 minutes, etc.), the load Pi and the corresponding settlement values ​​Si of each vertical displacement sensor 7 are recorded. The displacement measured by the vertical displacement sensor 7 is the settlement value.

[0041] Note: The pressure P mentioned above represents the pressure per unit area of ​​the test specimen's bearing surface, in MPa. It can be calculated by multiplying the hydraulic pressure of the jack by the piston area and dividing by the area of ​​the test specimen's bearing surface. The conversion program can be built into the pressure sensor.

[0042] The next level of load may be applied only if one of the following stability criteria is met: a) The settlement increment in 1 hour is less than 0.1 mm; b) The settlement rate decreases continuously in two consecutive observations (30 minutes apart).

[0043] V. Staged unloading and rebound observation: After the load reaches the estimated maximum pressure Pmax and stabilizes, staged unloading begins.

[0044] Preferably, the unloading amount at each stage can be the same as or double the loading stage difference. After each stage of load is unloaded, it is maintained for a period of time, and the rebound displacement is recorded at predetermined intervals until the load is completely unloaded.

[0045] VI. Data Processing and Deformation Modulus Calculation: Organize the data, plot the complete load-settlement PS curve, select the initial linear segment of the PS curve, and calculate the deformation modulus E0 of the cemented gravel according to the elastic theory formula.

[0046] Preferably, after processing the data, the time-settlement curves for each load level are plotted to verify stability. The initial linear segment is the segment where the load-settlement value shows a near-linear relationship, typically ranging from 1 / 3 to 1 / 2 of the maximum load.

[0047] For the circular rigid bearing plate 6, the elastic theory formula is: E0 = (1-u) 2 )·(π·D / 4)·(ΔP / ΔS) Where: E0: deformation modulus of the specimen (MPa); u: Poisson's ratio of cemented gravel (selected based on experience or similar materials, usually between 0.2 and 0.3); D: diameter of bearing plate (m); ΔP / ΔS: slope of the linear segment of the PS curve (MPa / m).

[0048] Through the above steps, this invention achieves accurate measurement of the deformation characteristics of cemented gravel in large-size, in-situ conditions, providing key deformation parameters for engineering design and safety evaluation.

[0049] In summary, this invention enables in-situ testing of cemented gravel, avoiding the need for repeated equipment handling, setup, and calibration. This reduces the total testing time for a single point by more than 50%, resulting in highly efficient and cost-effective testing. Furthermore, it can be used not only for deformation modulus testing but also for shear strength testing, replacing two sets of traditional dedicated equipment. This significantly reduces equipment procurement, maintenance, and labor costs, demonstrating outstanding engineering economics. In addition, this invention directly tests the in-situ, undisturbed engineering entity, fundamentally avoiding material disturbance and stress release during sampling, transportation, and indoor sample preparation. This ensures that the test results accurately reflect the mechanical behavior of the foundation under in-situ stress, resulting in reliable and accurate data. Moreover, considering the characteristics of cemented gravel aggregates—large particle size, wide gradation range, and strong heterogeneity—this invention, through a full-scale in-situ testing method, fully encompasses the material's actual maximum particle size and representative gradation, effectively solving the size effect problem of traditional indoor testing. This provides reliable technical support for the mechanical property evaluation of large-particle-size cemented gravel. In addition, the force transmission base plate 1 and the anchoring structure constitute an expandable design platform. Its size can be designed according to the actual material conditions on the engineering site. It has good scalability and breaks through the inherent limitations of traditional equipment on specimen size, and can adapt to the testing needs of materials with different particle sizes.

[0050] Furthermore, the anchoring assembly includes an anchor seat 9, on which an anchor rod 10 is fixed, with the lower end of the anchor rod 10 anchored into the ground; the lower end of the tie rod 2 is hinged to the anchor seat 9.

[0051] Preferably, there are four tie rods 2 arranged at the four corners of the force transmission base plate 1, and four anchor seats 9.

[0052] When the vertical jack 4 applies a stable vertical load to the specimen, the force transmission plate 1 transmits the force from the other end of the vertical jack 4 to the anchor bolt group 10 through the tie rod 2. The anchor bolt 10 provides pull-out resistance through its own bonding strength with the foundation or mechanical interlocking, which facilitates providing a stable and reliable tension support point for the tie rod 2 and improves the stability of the force transmission plate 1. At the same time, the entire system can be quickly disassembled, transported and assembled on site, combining structural stability and construction convenience, making it particularly suitable for use in field construction sites.

[0053] Furthermore, a first ball joint plate 11 is provided on the lower side of the force transmission base plate 1, and the first ball joint plate 11 and the force transmission base plate 1 are in spherical contact; the first ball joint plate 11 is fixedly connected to the upper end of the force transmission column 3.

[0054] Preferably, the lower side of the force transmission base plate 1 is provided with a spherical protrusion, and the upper side of the first ball hinge plate 11 is provided with a spherical groove, and the spherical protrusion matches and contacts the spherical groove.

[0055] Under the load applied by the vertical jack 4, the first ball hinge plate 11 transmits pressure to the force transmission seat plate 1 through the ball, thereby achieving universal adjustment. This universal adjustment can automatically compensate for the angle change caused by uneven contact surface between the pressure plate 6 and the specimen or installation deviation, ensuring that the vertical load is always uniformly applied to the upper surface of the specimen, effectively eliminating measurement errors caused by eccentric compression and stress concentration.

[0056] Furthermore, a pad 12 is provided between the force transmission column 3 and the vertical jack 4. The upper end of the pad 12 is provided with a boss that extends into the lower end of the force transmission column 3, and the lower end of the pad 12 is provided with a groove that extends into the groove.

[0057] Preferably, the force transmission column 3 is a steel pipe and its lower end is sleeved on the protrusion of the pad block 12.

[0058] By matching the boss with the lower end of the force transmission column 3, and matching the groove at the lower end of the vertical jack 4 with the pad block 12, instability at the connection between the vertical jack 4 and the force transmission column 3 is avoided, and the stability of force transmission between the two is improved.

[0059] Furthermore, it also includes a horizontal jack 13, which is located on one side of the specimen. A second pad 14 is provided between the first end of the horizontal jack 13 and the soil. A side force transmission plate 15 for applying pressure to the side of the specimen is provided between the second end of the horizontal jack 13 and the specimen. Multiple horizontal displacement sensors 17 are also distributed on the side of the specimen away from the side force transmission plate 15. A horizontal pressure sensor 18 for measuring its own pressure is connected to the horizontal jack 13.

[0060] Supported by the second pad 14, the horizontal jack 13 applies pressure to the side of the specimen through the side force transmission plate 15. At the same time, the horizontal pressure sensor 18 can collect pressure changes, and the horizontal displacement sensor 17 can collect the shear displacement of the specimen, which facilitates the in-situ shear strength test of the specimen.

[0061] Specifically: The following steps were taken to test the in-situ shear strength of cemented gravel using this device: I. Test Point Preparation and Site Leveling: Select a flat, dense and representative cemented gravel test area at the engineering site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; cut and trim regular cuboid specimens, and trim the top surface, the side surface that bears the horizontal thrust, and the bottom surface of the specimens.

[0062] Note: The rectangular specimen should be cut and trimmed using cutting equipment or manually. The specimen size must be determined based on the maximum aggregate size Dmax of the material, ensuring that its minimum side length is not less than 3-5 Dmax to encompass the representative gradation of the material. When trimming the top, sides, and bottom of the specimen, ensure that the top and bottom surfaces are parallel and the sides are perpendicular to the top surface to create conditions for uniform load transfer.

[0063] II. Installation of the device: Complete the overall installation of the in-situ testing device for cemented gravel, and lay rollers 19 at the bottom of the prepared specimen; slowly apply the first design load using vertical jacks 4.

[0064] Preferably, during the overall installation of the cemented gravel in-situ testing device, holes are drilled at the design points according to the specimen's location and size, and anchor bolts 10 are inserted to ensure their anchoring depth reaches the stable stratum. Then, tie rods 2, force transmission base plates 1, etc., are installed to form a stable reaction frame. Next, roller rows 19 are laid on the bottom of the prepared specimen, ensuring they are flat and cover the entire potential shear area. Then, a bearing plate 6, a first pad 5, a vertical jack 4, a force transmission column 3, etc., are installed on the top surface of the specimen. Furthermore, after installing the vertical jack 4, the first-level design load is slowly applied using the vertical jack 4, and after stabilization, the horizontal jack 13 is installed. The first-level design load can be set to 25% of the design pressure, which is the manually set pressure environment of the specimen in the in-situ shear test.

[0065] III. Vertical pressure stabilization and data initialization: Slowly increase the vertical pressure step by step to the predetermined test value, clear the readings of all horizontal displacement sensors 17 and horizontal pressure sensors 18, and prepare to start the shear test.

[0066] Note: The test value is the design pressure; for each additional load level, stabilize the pressure until the specimen deformation stabilizes (e.g., settlement rate is less than 0.01 mm / min) before adding the next load level. Then, check all sensor readings to confirm that the data acquisition system is working properly, and reset all displacement sensor readings to zero before starting the shear test.

[0067] IV. Applying Horizontal Thrust and Simultaneous Data Acquisition: Activate horizontal jack 13 to apply a horizontal thrust to the specimen at a constant displacement rate; simultaneously, collect the following data: Time t, vertical stress σ, horizontal shear stress τ, shear displacement δh, vertical displacement δv.

[0068] Note: The constant displacement rate is usually controlled at 0.5 - 1.0 mm / min. When collecting the above data, the data acquisition system supporting the sensors can be used to record automatically and synchronously. Among them, the vertical stress σ is calculated from the readings of the vertical pressure sensor 8; the horizontal shear stress τ is calculated from the readings of the horizontal pressure sensor 18; the shear displacement δh is read by the horizontal displacement sensor 17 (the average value of multiple horizontal displacement sensors 17 is taken); the vertical displacement δv is read by the vertical displacement sensor 7 (the average value of multiple vertical displacement sensors 7 is taken).

[0069] V. Test Termination and Recording of Specimen Failure State: When any of the following situations occurs, it is determined that the specimen has shear failure, the test is terminated, and the final failure mode of the specimen is recorded: 1) After the horizontal shear stress τ reaches the peak value, it decreases steadily; 2) The shear displacement δh continues to increase while the change rate of the horizontal shear stress τ becomes significantly gentle; 3) The shear displacement has reached 1 / 15 to 1 / 10 of the side length of the specimen.

[0070] Note: When situation 2) occurs, the change rate of the horizontal shear stress τ becomes significantly gentle, that is, the residual strength is reached. Record the final failure mode of the specimen, including the position of the shear plane, whether the large aggregates are cut off, whether it fails along the bonding surface, etc., and take pictures for archiving.

[0071] VI. Data Processing and Parameter Calculation: Plot the relationship curve of the horizontal shear stress τ - shear displacement δh, and determine the shear strength of the specimen under this vertical stress σ from the curve.

[0072] Note: The shear strength includes the peak shear strength and the residual shear strength, and either one can be selected according to the requirements. Generally, the peak shear strength is taken.

[0073] Preferably, after the above tests and calculations, the test points can be changed, and steps one to six are repeated under different vertical stresses σ (usually at least 3 - 4 different vertical stress σ levels) to obtain a set of data pairs of (vertical stress σ, shear strength τf). Plot the data points in the σ - τf coordinate system, perform linear regression, fit the Coulomb strength envelope, and determine the cohesion c (the intercept of the straight line on the vertical axis is c) and the internal friction angle φ (the inclination angle of the straight line is φ) of the material from the fitted straight line. Thus, the Coulomb formula can be described as a linear relationship between σ and τf. According to this Coulomb formula, the shear strength τf at any vertical stress σ level can be estimated.

[0074] Through the above steps, the present invention realizes the accurate and reliable determination of the in-situ and large-size specimen shear strength parameters of cemented gravel.

[0075] Furthermore, a second ball joint plate 16 is provided between the second end of the horizontal jack 13 and the side force transmission plate 15. The second ball joint plate 16 and the side force transmission plate 15 are in spherical contact, and the second ball joint plate 16 is fixedly connected to the second end of the horizontal jack 13.

[0076] Preferably, one side of the side force transmission plate 15 is provided with a spherical protrusion, and one side of the second ball hinge plate 16 is provided with a spherical groove, with the spherical protrusion matching and contacting the spherical groove.

[0077] Under the load of the horizontal jack 13, the second ball joint plate 16 transmits pressure to the side force transmission plate 15 through the ball joint, thereby achieving universal adjustment. This universal adjustment can automatically compensate for the angle change caused by uneven contact surface between the side force transmission plate 15 and the specimen or installation deviation, ensuring that the horizontal load is always uniformly applied to the side of the specimen, effectively eliminating measurement errors caused by eccentric compression and stress concentration.

[0078] Furthermore, a roller row 19 is provided between the first pad 5 and the pressure plate 6.

[0079] Note: Roller row 19 refers to multiple rollers arranged in a row. Preferably, roller row 19 is made of high-carbon chromium bearing steel with a surface hardness of HRC58-62. Each roller has a diameter of 30mm and a length that matches the specimen. The rollers are arranged at equal intervals using a cage, which reduces the sliding friction coefficient from 0.3-0.5 to 0.01-0.02, thus reducing the influence of bottom surface friction resistance on the test results to a negligible range.

[0080] By converting the friction between the first pad 5 and the bearing plate 6 into rolling friction through the roller row 19, the horizontal friction force on the horizontal thrust of the horizontal jack 13 is significantly reduced, ensuring that the horizontal load is used to overcome the shear strength of the specimen itself to the maximum extent and guaranteeing the authenticity of the test results.

[0081] Furthermore, it also includes an instrument frame 20, which is a gantry frame with both ends extending to the outside of the anchoring components and fixed to the ground; the pressure plate 6 is located directly below the instrument frame 20, and the reference end of the vertical displacement sensor 7 and the reference end of the horizontal displacement sensor 17 are both fixed on the instrument frame 20.

[0082] Note: The reference end of the displacement sensor, i.e., the probe, is fixed to the instrument frame 20 via a magnetic base and can sense the displacement of its trigger end; its trigger end is the test marker, fixed near the specimen and displaced as the specimen deforms. This type of displacement sensor can be the 0-30 mm model from Guilin Guanglu, product number 312-103-10.

[0083] Using an independent instrument frame 20 as a reference, which extends beyond the anchoring components, it is independently and stably supported on a solid foundation outside the test area. This facilitates complete isolation of the reference from the reaction force and loading system, avoids errors caused by soil stress and deformation, and improves the accuracy of the test results.

[0084] This invention also provides a method for testing the in-situ deformation modulus of cemented gravel, based on the above-mentioned in-situ testing device for cemented gravel, comprising the following steps: 1. Test point preparation and site leveling: Select a flat, dense and representative cemented gravel test area at the project site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; level the test area to ensure that its flatness meets the installation requirements of bearing plate 6. 2. Device placement: Place the pressure plate 6 precisely at the center of the flattened test surface. The area covered by the pressure plate 6 is the test specimen. Complete the overall installation of the in-situ test device for cemented gravel. 3. Apply preload using vertical jack 4, and then unload to the initial load; IV. Graded loading and data acquisition: The vertical jack 4 is loaded in stages. For each grade of load Pi applied, the initial reading of the vertical displacement sensor under that load is recorded, and the settlement value Si is recorded once at a predetermined time interval. V. Staged unloading and rebound observation: After the load reaches the estimated maximum pressure Pmax and stabilizes, staged unloading begins; VI. Data Processing and Deformation Modulus Calculation: Organize the data, plot the complete load-settlement PS curve, select the initial linear segment of the PS curve, and calculate the deformation modulus E0 of the cemented gravel according to the elastic theory formula.

[0085] In step one, the leveling process typically requires the unevenness to be less than 1% of the diameter of the bearing plate. This area should be adjacent to but not overlap with the shear strength test point.

[0086] In step two, the bearing plate 6 should have sufficient rigidity and be circular. Its diameter D should be determined according to the maximum aggregate particle size Dmax of the material and the test requirements, and is usually (2-3)×Dmax. In addition, there are four vertical displacement sensors 7, which are evenly distributed around the vertical jack 4.

[0087] Step three aims to eliminate minute gaps inside the device and between the pressure plate 6 and the specimen surface, ensuring tight contact between all components. Additionally, it is necessary to check that all sensor readings are stable and that the data acquisition system is functioning correctly. Zero the displacement sensor readings to prepare for formal loading. Furthermore, the preload is typically 5%-10% of the maximum preload, such as 0.05 MPa. The initial load is preferably 0.01 MPa.

[0088] In step four, the load increment ΔP for each level is typically taken as 1 / 5 to 1 / 8 of the estimated maximum pressure Pmax; the estimated maximum pressure Pmax is a manually set estimate. Furthermore, after each load Pi is applied, the initial readings of the vertical displacement sensors under that load level are immediately recorded, and then timing begins. Then, at predetermined time intervals (e.g., 1, 2, 5, 10, 15, 30 minutes, etc.), the load Pi and the corresponding settlement values ​​Si of each vertical displacement sensor 7 are recorded. The displacement measured by the vertical displacement sensor 7 is the settlement value. The next load level can only be applied when one of the following stability criteria is met: a) The settlement increment in 1 hour is less than 0.1 mm; b) The settlement rate continuously decreases in two consecutive observations (30 minutes apart).

[0089] In step five, the unloading amount for each stage can be the same as or double the loading stage difference. After each stage of load is unloaded, maintain the load for a period of time, and record the rebound displacement at predetermined intervals until the load is completely unloaded.

[0090] In step six, after processing the data, the time-settlement curves for each load level are plotted to verify stability. The initial linear segment, where the load-settlement values ​​show a near-linear relationship, is typically within the range of 1 / 3 to 1 / 2 of the maximum load. For the circular rigid bearing plate 6, the elastic theory formula is: E0 = (1-u) 2 )·(π·D / 4)·(ΔP / ΔS) Where: E0: deformation modulus of the specimen (MPa); u: Poisson's ratio of cemented gravel (selected based on experience or similar materials, usually between 0.2 and 0.3); D: diameter of bearing plate (m); ΔP / ΔS: slope of the linear segment of the PS curve (MPa / m).

[0091] Through the above steps, this invention achieves accurate determination of the deformation characteristics of cemented gravel in large-size, in-situ conditions, providing key deformation parameters for engineering design and safety evaluation. Furthermore, the testing is efficient and cost-effective; it fundamentally avoids material disturbance and stress release during sampling, transportation, and indoor sample preparation, ensuring that the test results truly reflect the mechanical behavior of the foundation under in-situ stress conditions, resulting in accurate and reliable data; it effectively solves the size effect problem of traditional indoor tests, providing reliable technical support for the mechanical property evaluation of large-diameter cemented gravel.

[0092] This invention also provides a method for testing the in-situ shear strength of cemented gravel, based on the aforementioned in-situ testing device for cemented gravel, comprising the following steps: I. Test point preparation and site leveling: Select a flat, dense and representative cemented gravel test area at the engineering site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; cut and trim regular cuboid specimens, and trim the top surface, the side surface that bears the horizontal thrust, and the bottom surface of the specimens. II. Installation of the device: Complete the overall installation of the in-situ testing device for cemented sand and gravel, and lay rollers 19 at the bottom of the prepared specimen; slowly apply the first design load through vertical jacks 4. III. Vertical pressure stabilization and data initialization: Slowly increase the vertical pressure step by step to the predetermined test value, clear the readings of all horizontal displacement sensors 17 and horizontal pressure sensors 18, and prepare to start the shear test. IV. Applying Horizontal Thrust and Simultaneous Data Acquisition: Activate horizontal jack 13 to apply a horizontal thrust to the specimen at a constant displacement rate; simultaneously, collect the following data: Time t, vertical stress σ, horizontal shear stress τ, shear displacement δh, vertical displacement δv; V. Test Termination and Specimen Failure Recording: When any of the following conditions occur, the specimen is deemed to have suffered shear failure, the test is terminated, and the final failure mode of the specimen is recorded: 1) The horizontal shear stress τ peaks and then steadily decreases; 2) The shear displacement δh continues to increase while the rate of change of the horizontal shear stress τ is significantly flat; 3) The shear displacement has reached 1 / 15 to 1 / 10 of the specimen's side length; VI. Data Processing and Parameter Calculation: Plot the horizontal shear stress τ-shear displacement δh relationship curve, and determine the shear strength of the specimen under the vertical stress σ from the curve.

[0093] In step one, a rectangular specimen is cut and trimmed, which can be done using cutting equipment or manually. The specimen size needs to be determined based on the maximum aggregate size Dmax of the material, ensuring that its minimum side length is not less than 3-5 Dmax to encompass the representative gradation of the material. When trimming the top, sides, and bottom of the specimen, ensure that the top and bottom surfaces are parallel and the sides are perpendicular to the top surface to create conditions for uniform load transfer in the future.

[0094] In Step 2, preferably, when the whole installation of the in-situ testing device for cemented gravel is carried out, according to the position and size of the test piece, drill holes at the designed points and implant anchor rods 10 to ensure that their anchoring depth enters the stable stratum. Then, install tension rods 2, force transfer seat plates 1, etc. to form a stable reaction force frame. Then, lay a roller row 19 at the bottom of the trimmed test piece to ensure its flatness and coverage of the entire potential shear area. Then, install a bearing plate 6, a first cushion plate 5, a vertical jack 4, a force transfer column 3, etc. on the top surface of the test piece. In addition, after installing the vertical jack 4, slowly apply it to the first-stage designed load through the vertical jack 4, and then install the horizontal jack 13 after pressure stabilization. The first-stage designed load can be set to 25% of the designed pressure, and the designed pressure is the compression environment of the test piece for the in-situ shear test set manually.

[0095] In Step 3, the test value is the designed pressure; for each increase in one level of load, stabilize the pressure until the deformation of the test piece is stable (such as the settlement rate is less than 0.01 mm / min), and then increase the next level of load. Then, check the readings of all sensors, confirm that the data acquisition system is working properly, and clear the readings of all displacement sensors to prepare for the shear test.

[0096] In Step 4, the constant displacement rate is usually controlled at 0.5 - 1.0 mm / min. When collecting the above data, it can be automatically and synchronously recorded by the data acquisition system supporting the sensors. Among them, the vertical stress σ is calculated from the readings of the vertical pressure sensor 8; the horizontal shear stress τ is calculated from the readings of the horizontal pressure sensor 18; the shear displacement δh is read by the horizontal displacement sensor 17 (the average value of multiple horizontal displacement sensors 17 is taken); the vertical displacement δv is read by the vertical displacement sensor 7 (the average value of multiple vertical displacement sensors 7 is taken).

[0097] In Step 5, when the situation 2) occurs, the change rate of the horizontal shear stress τ is significantly gentle, that is, the residual strength is reached. Record the final failure mode of the test piece, including the position of the shear surface, whether the large aggregate is cut off, whether it fails along the cemented surface, etc., and take photos for archiving.

[0098] In Step 6, the shear strength includes the peak shear strength and the residual shear strength, and either one can be selected according to requirements. Generally, the peak shear strength is taken.

[0099] After step six, preferably, after performing the above tests and calculations, the test points can be changed, and steps one through six can be repeated under different vertical stresses σ (usually at least 3-4 different vertical stress σ levels) to obtain a set of (vertical stress σ, shear strength τf) data pairs. The data points are plotted in the σ-τf coordinate system, and linear regression is performed to fit the Coulomb strength envelope. According to the Coulomb formula τf = c + σ·tanφ, the material's cohesion c (the intercept of the line on the vertical axis is c) and the internal friction angle φ (the inclination angle of the line is φ) are determined from the fitted straight line. Thus, the Coulomb formula can be described as a linear relationship between σ and τf. Based on this Coulomb formula, the shear strength τf under any vertical stress σ level can be estimated.

[0100] Through the above steps, this invention enables accurate and reliable determination of the shear strength parameters of large-sized, in-situ cemented gravel specimens, providing crucial shear strength parameters for engineering design and safety evaluation. Furthermore, the testing is efficient and cost-effective; it fundamentally avoids material disturbance and stress release during sampling, transportation, and indoor sample preparation, ensuring that the test results accurately reflect the mechanical behavior of the foundation under in-situ stress conditions. The results are reliable and the data is precise; it effectively solves the size effect problem of traditional indoor tests, providing reliable technical support for the mechanical property evaluation of large-diameter cemented gravel.

[0101] In the description of this invention, it should be understood that if descriptive terms indicating orientation, direction, or positional relationship appear, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc., the orientation or positional relationship indicated in this specification is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of understanding this invention and simplifying the description, and does not indicate or imply that the part, element, or whole referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0102] Furthermore, if sequential descriptive terms such as "first," "second," etc., appear, their purpose in this specification is for ease of understanding or simplification. For example, to distinguish multiple technical features of the same type or function, which must be mentioned separately, this specification may use prefixes or suffixes to differentiate them. Therefore, they should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. In the description of this invention, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0103] In this invention, if descriptive terms describing structural relationships are used, such as "installation," "connection," "joining," and "fixation," they should be interpreted broadly unless otherwise explicitly specified and limited. For example, "installation," "connection," and "joining" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two components or the interaction between two components. "Fixation" can refer to an integral fixation or a detachable fixation using fasteners; it can be a direct fixation or a fixation through an intermediate medium. For those skilled in the art, the specific meaning of the above descriptive terms in this invention can be understood based on the specific circumstances, the context, and the coherence of the preceding and following text.

[0104] In this invention, if descriptive terms containing subordinate or connecting meanings appear, such as "above" or "below" the second feature, they should not be interpreted restrictively unless otherwise explicitly specified and limited. For example, "above" or "below" could mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Those skilled in the art can understand the specific meaning of the above descriptive terms in this invention based on the specific circumstances, the context, and the coherence of the preceding and following text.

[0105] Furthermore, "above," "on top of," and "above" the first feature in relation to the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "under," and "below" the first feature in relation to the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0106] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. The illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments, examples, and features described in this specification, and such combinations or integrations should all fall within the scope of the present invention.

[0107] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Variations, modifications, substitutions, and modifications made by those skilled in the art to the above embodiments within the scope of information available through public channels and in conjunction with the technical teachings given in this application are still covered within the protection scope of this application.

Claims

1. An in-situ testing device for cemented gravel, characterized in that: The test specimen includes a force transmission base plate (1), on which multiple tie rods (2) are hinged. The tie rods (2) are evenly distributed around the force transmission base plate (1). The lower end of each tie rod (2) is hinged to an anchoring assembly, which is anchored to the ground. The lower side of the force transmission base plate (1) is provided with a force transmission column (3), a vertical jack (4), a first pad (5), and a pressure plate (6) for applying pressure to the top of the specimen. Multiple vertical displacement sensors (7) are distributed on the top of the pressure plate (6). A vertical pressure sensor (8) for measuring its own pressure is connected to the vertical jack (4).

2. The in-situ testing device for cemented gravel according to claim 1, characterized in that: The anchoring assembly includes an anchor seat (9), on which an anchor rod (10) is fixed, with the lower end of the anchor rod (10) anchored into the ground; the lower end of the tie rod (2) is hinged to the anchor seat (9).

3. The in-situ testing device for cemented gravel according to claim 1, characterized in that: The lower side of the force transmission base plate (1) is also provided with a first ball joint plate (11), and the first ball joint plate (11) and the force transmission base plate (1) are in spherical contact; the first ball joint plate (11) is fixedly connected to the upper end of the force transmission column (3).

4. The in-situ testing device for cemented gravel according to claim 3, characterized in that: A pad (12) is provided between the force transmission column (3) and the vertical jack (4). The upper end of the pad (12) is provided with a boss that extends into the lower end of the force transmission column (3). The lower end of the pad (12) is provided with a groove and the upper end of the vertical jack (4) extends into the groove.

5. The in-situ testing device for cemented gravel according to any one of claims 1-4, characterized in that: It also includes a horizontal jack (13), which is located on one side of the specimen. A second pad (14) is provided between the first end of the horizontal jack (13) and the soil. A side force transmission plate (15) for applying pressure to the side of the specimen is provided between the second end of the horizontal jack (13) and the specimen. Multiple horizontal displacement sensors (17) are also distributed on the side of the specimen away from the side force transmission plate (15). A horizontal pressure sensor (18) for measuring its own pressure is connected to the horizontal jack (13).

6. The in-situ testing device for cemented gravel according to claim 5, characterized in that: A second ball joint plate (16) is provided between the second end of the horizontal jack (13) and the side force transmission plate (15). The second ball joint plate (16) and the side force transmission plate (15) are in spherical contact. The second ball joint plate (16) is fixedly connected to the second end of the horizontal jack (13).

7. The in-situ testing device for cemented gravel according to claim 5, characterized in that: A roller row (19) is also provided between the first pad (5) and the pressure plate (6).

8. The in-situ testing device for cemented gravel according to claim 5, characterized in that: It also includes an instrument frame (20), which is a gantry frame with both ends extending to the outside of the anchoring components and fixed to the ground; the pressure plate (6) is located directly below the instrument frame (20), and the reference end of the vertical displacement sensor (7) and the reference end of the horizontal displacement sensor (17) are both fixed on the instrument frame (20).

9. A method for testing the in-situ deformation modulus of cemented gravel, characterized in that: The in-situ testing device for cemented gravel according to any one of claims 1-8 includes the following steps:

1. Test point preparation and site leveling: Select a flat, dense and representative cemented gravel test area at the project site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; level the test area to ensure that its flatness meets the installation requirements of the bearing plate (6).

2. Device placement: Place the pressure plate (6) precisely in the center of the flat test surface. The area covered by the pressure plate (6) is the test specimen. Complete the overall installation of the cemented gravel in-situ test device.

3. Apply preload by using vertical jacks (4), and then unload to the initial load; IV. Gradual loading and data acquisition: The vertical jack (4) is used for gradual loading. For each level of load Pi applied, the initial reading of the vertical displacement sensor under that level of load is recorded, and the settlement value Si is recorded once at a predetermined time interval. V. Staged unloading and rebound observation: After the load reaches the estimated maximum pressure Pmax and stabilizes, staged unloading begins; VI. Data Processing and Deformation Modulus Calculation: Organize the data, plot the complete load-settlement PS curve, select the initial linear segment of the PS curve, and calculate the deformation modulus E0 of the cemented gravel according to the elastic theory formula.

10. A method for testing the in-situ shear strength of cemented gravel, characterized in that: Based on the in-situ testing device for cemented gravel according to any one of claims 5-8, the method includes the following steps: I. Test point preparation and site leveling: Select a flat, dense and representative cemented gravel test area at the engineering site, remove all loose particles and dust from the test point surface to expose the undisturbed cemented gravel layer; cut and trim regular cuboid specimens, and trim the top surface, the side surface that bears the horizontal thrust, and the bottom surface of the specimens.

2. Installation of the device: Complete the installation of the cemented gravel in-situ testing device, and lay rollers (19) on the bottom of the prepared specimen; apply the first design load slowly through the vertical jack (4); III. Vertical pressure stabilization and data initialization: Slowly increase the vertical pressure to the predetermined test value, clear the readings of all horizontal displacement sensors (17) and horizontal pressure sensors (18), and prepare to start the shear test; IV. Applying Horizontal Thrust and Simultaneous Data Acquisition: Activate the horizontal jack (13) to apply a horizontal thrust to the specimen at a constant displacement rate; simultaneously, collect the following data: Time t, vertical stress σ, horizontal shear stress τ, shear displacement δh, vertical displacement δv; V. Test Termination and Specimen Failure Recording: When any of the following conditions occur, the specimen is deemed to have suffered shear failure, the test is terminated, and the final failure mode of the specimen is recorded: 1) The horizontal shear stress τ peaks and then steadily decreases; 2) The shear displacement δh continues to increase while the rate of change of the horizontal shear stress τ is significantly flat; 3) The shear displacement has reached 1 / 15 to 1 / 10 of the specimen's side length; VI. Data Processing and Parameter Calculation: Plot the horizontal shear stress τ-shear displacement δh relationship curve, and determine the shear strength of the specimen under the vertical stress σ from the curve.

Images