Patent ID: 12241876

Reference Numerals:1. load applying assembly;2. soil shearing assembly;3. data acquisition assembly;4. shear plate;5. drilling rig;6. drill rod;7. servo motor;8. shear cylinder;9. spinning shaft;10. drill rod joint;11. circular receiving groove;12. connecting piece;13. fitting groove;14. notch;15. guide rail strip;16. limit bar;17. limit slot;18. limit flange;19. rebound assembly;20. spring sleeve;21. return spring;22. push plate;23. rotating base;24. threaded cylindrical pin; and25. thrust bearing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The specific embodiment of the present disclosure will be described below so that those skilled in the art can understand the present disclosure, but it should be clear that the present disclosure is not limited to the scope of the specific embodiment. For those of ordinary skill in the art, as long as various changes fall within the spirit and scope of the present disclosure defined and determined by the appended claims, these changes are apparent, and all inventions and creations using the concept of the present disclosure are protected.

As shown inFIG.1, the present disclosure provides a borehole wall spin-shearing device for an in-situ borehole shear test, including load applying assembly1, soil shearing assembly2, and data acquisition assembly3.

The load applying assembly1is configured to apply a vertical load and an axial rotational load to the soil shearing assembly2.

The soil shearing assembly2includes a plurality of shear plates4. The plurality of shear plates4are configured to be ejected and penetrate into undisturbed soil after being subjected to the vertical load. The plurality of shear plates4penetrating into the undisturbed soil further shear the undisturbed soil after being subjected to the axial rotational load.

The data acquisition assembly3is configured to acquire torque values of the plurality of shear plates4during a process of shearing the undisturbed soil.

The load applying part can use drilling rig5, a jack, or other devices. In this embodiment, preferably, the load applying assembly1uses drilling rig5. Specifically, the load applying assembly1includes drilling rig5. The drilling rig5includes drill rod6and servo motor7located at a top of the drill rod6.

The soil shearing assembly2is connected to a bottom of the drill rod6through drill rod joint10. An output end of the servo motor7is connected to the top of the drill rod6. The drill rod6and the servo motor7are respectively configured to apply the vertical load and the axial rotational load to the soil shearing assembly2.

In this embodiment, as shown inFIGS.2and3, as a specific design of the soil shearing assembly2, the soil shearing assembly2further includes shear cylinder8in a hollow cylindrical structure. Spinning shaft9is provided in the shear cylinder8and is vertically movable. An upper half of the spinning shaft9forms a cylindrical structure, and a top on the upper half of the spinning shaft9is provided with the drill rod joint10. A lower half of the spinning shaft9forms a conical structure with a tip facing downwards.

A bottom circumferential outer wall of the shear cylinder8is provided with circular receiving groove11. The four shear plates4centered on an axis of the shear cylinder8are circumferentially evenly spaced in the circular receiving groove. Each of the shear plates4is in a curved plate structure, and a length direction of the shear plate4is identical to a length direction of the shear cylinder8. The four shear plates enclose a cylindrical structure, and an axis of the cylindrical structure coincides with the central axis of the shear cylinder8.

As shown inFIG.5, an inner curved surface of each shear plate4facing the central axis of the shear cylinder8protrudes to form connecting piece12. The connecting piece12has a trapezoid-like structure with a small upper end and a large lower end. An inner side of the connecting piece12is provided with fitting groove13with a T-shaped cross-section along a length direction of the connecting piece. A gradient of the inner side of the connecting piece12is equal to a generatrix inclination of the lower half of the spinning shaft9.

Four notches14are arranged at a bottom of the circular receiving groove11for partial passage of the four connecting pieces12. The inner side of the connecting piece12passes through the notch14to be located inside the shear cylinder8.

As shown inFIG.4, a conical surface on the lower half of the spinning shaft9is provided with four guide rail strips15that are circularly spaced around an axis of the spinning shaft9. A length direction of each guide rail strip15is oriented from a major-diameter end on the lower half of the spinning shaft9towards a minor-diameter end on the lower half of the spinning shaft9.

Each guide rail strip15is provided with a T-shaped cross-section, and each guide rail strip15is matched with one connecting piece12. The guide rail strip15is slidably provided in the fitting groove13.

Before a borehole wall spin-shearing test is started, first, the spinning shaft9is fixedly connected to the bottom of the drill rod6through the drill rod joint10, and the top of the drill rod6is connected to a power output shaft of the servo motor7. Then, the entire soil shearing assembly2is lowered to a designated depth inside a borehole through the drilling rig5and the drill rod6. A bottom of the soil shearing assembly2is in contact with soil at the bottom of the borehole. The drilling rig5drives the drill rod6to press downwards. The downwards pressing drill rod6transmits a force to the spinning shaft9through the drill rod joint10. The spinning shaft9moves vertically and downwards relative to the shear cylinder8. When the spinning shaft9moves vertically and downwards, the guide rail strips15on the conical surface on the lower half of the spinning shaft9are matched with the fitting grooves13of the connecting pieces12on the shear plates4. As the spinning shaft9continues to move vertically and downwards, the shear plates4are ejected in a radial direction of the spinning shaft9until the shear plates4penetrate into undisturbed soil. Finally, the servo motor7is started to conduct the spin-shearing test. The servo motor7automatically stops rotating after the shear plates4rotate 90°, and the drilling rig5stops applying the vertical load. At this point, the data acquisition assembly3records, saves, and exports the complete torque value data saved in the data acquisition system during the shearing process.

Specifically, the data acquisition assembly3includes a controller, a torque sensor, and a pressure sensor that are connected to each other electrically. The torque sensor is located on the servo motor7to acquire the torque value applied by the servo motor7to the shear plate4. The pressure sensor is located between the drill rod6and the soil shearing assembly2to acquire maximum normal force acting on the shear plate4. The connection relationship and model of the electrical elements in the data acquisition assembly3are based on existing mature technologies, so the circuit structure and working principle of the electrical elements will not be elaborated herein.

Preferably, but not limited to, as shown inFIGS.4,6, and7, a plurality of limit bars16are circularly evenly spaced on a circumferential outer wall on the upper half of the spinning shaft9within the shear cylinder8. The plurality of limit bars16are detachably connected to the circumferential outer wall on the upper half of the spinning shaft9. The shear cylinder8is provided with two open ends. A circumferential inner wall of the shear cylinder8is provided with a plurality of limit slots17that are slidably matched with the plurality of limit bars16. The limit bars16and the limit slots17are arranged along an axial direction of the spinning shaft9.

The limit bars16and the limit slots17are matched to limit the rotational freedom of the spinning shaft9, such that the spinning shaft9can only be vertically displaced within the shear cylinder8, thereby avoiding the rotation of the spinning shaft9relative to the shear cylinder8.

In order to fix the spinning shaft9inside the shear cylinder8to avoid the spinning shaft9from detaching from the shear cylinder8during the shearing test, preferably, a top opening of the shear cylinder8is provided with limit flange18. An inner ring diameter of the limit flange18is greater than a diameter of the upper half of the spinning shaft9and smaller than an inner diameter of the shear cylinder8.

Preferably, but not limited to, a bottom opening of the shear cylinder8is provided with rebound assembly19. The rebound assembly19includes spring sleeve20. The spring sleeve20includes a top end with an opening and a closed bottom end. Atop of the spring sleeve20is connected to a bottom of the shear cylinder8. A reset spring is provided in the spring sleeve20. A bottom end of the reset spring is fixedly connected to an inner bottom side of the spring sleeve20. A top of the reset spring is fixed to push plate22. When the drill rod6presses downwards, the lower half of the spinning shaft9is driven to pass through the top opening of the spring sleeve20to contact an upper end face of the push plate22and compress return spring21.

After the shearing test is completed, the drill rod6drives the soil shearing assembly2to pull upwards. At this point, the spinning shaft9moves upwards relative to the shear cylinder8. Meanwhile, the return spring21pushes the spinning shaft9upwards. The upwards moving spinning shaft9contracts the four shear plates4back into the circular receiving groove11, playing an active role in storing the shear plates4. Due to the setting of the rebound assembly19, the shear plate4has a certain distance from the soil at the bottom of the borehole, eliminating the impact of borehole wall collapse on the test accuracy.

Preferably, a bottom of the spring sleeve20is provided with rotating base23in a cylindrical structure. An axis of the rotating base23coincides with an axis of the spring sleeve20. Threaded cylindrical pin24is provided in the spring sleeve20. An axis of the threaded cylindrical pin24coincides with the axis of spring sleeve20. A threaded end of the threaded cylindrical pin24passes through the bottom end of the spring sleeve20and is matched with a center thread of the rotating base23. A plain shaft portion of the threaded cylindrical pin24is rotatably matched with the bottom end of the spring sleeve20. Thrust bearing25is provided between the rotating base23and the spring sleeve20. Through the above design, the rotating base23is rotatable relative to the bottom of the spring sleeve20without transmitting the torque to the spring sleeve20. Therefore, during the shearing test, the impact of the frictional force between the soil at the bottom of the borehole and the soil shearing assembly2is eliminated, further improving the test accuracy.

The present disclosure further provides a testing method for the borehole wall spin-shearing device for an in-situ borehole shear test, including the following steps. Step 1. A borehole is drilled by the drilling rig5.

Step 2. The soil shearing assembly2is calibrated on a ground. That is, the drill rod6applies a vertical load, and the data acquisition assembly3measures load values required to eject the plurality of shear plates4.

Step 3. The drill rod6drives the soil shearing assembly2to a preset test depth in the borehole, such that a bottom of the soil shearing assembly2comes into contact with soil at a bottom surface of the borehole.

Step 4. The drill rod6continues to press downwards and apply a vertical load to the plurality of shear plates4in the soil shearing assembly2. Due to the vertical load, the plurality of shear plates4are ejected and penetrate into undisturbed soil.

Step 5. The vertical load is kept constant. The servo motor7is started, and the plurality of shear plates4rotate to conduct a borehole wall spin-shearing test. The test stops after the plurality of shear plates4rotate 90°.

Step 6. The data acquisition assembly3includes a torque sensor and a pressure sensor.

The torque sensor acquires the maximum torque applied to the plurality of shear plates4during the borehole wall spin-shearing test, while the pressure sensor acquires the maximum normal force received by the plurality of shear plates4, and calculates a shear strength parameter of the undisturbed soil based on the maximum torque and the maximum normal force.

Further, in the step 6, the shear strength parameter of the undisturbed soil is calculated as follows:

τmax=4⁢MTmaxπ⁢D2⁢hwhere, τmaxdenotes a maximum shear stress of the undisturbed soil, kPa; MTmaxdenotes a maximum torque applied to a single shear unit, kN·m; and D and h respectively denote a diameter and height of a circular arc formed by the rotation of the plurality of shear plates4ejected, m.

At a same depth in four adjacent boreholes, maximum shear stresses of the undisturbed soil at the same depth in four different boreholes are expressed as τmax1−τmax4, and maximum normal forces acquired by the pressure sensor are expressed as σnmax1−σnmax4.
τmax=c+σnmaxtan φ

The maximum normal forces σnmax1−σnmax4are measured in kPa. A curve is plotted with the maximum normal force σnmaxas an x-axis and the maximum shear stress τmaxas a y-axis. c and φ are acquired through curve fitting. C denotes cohesion, kPa. φ denotes an internal friction angle. The cohesion and the internal friction angle are the shear strength parameters of the undisturbed soil.

In summary, the testing method can quickly carry out an in-situ borehole shear test while drilling, and automatically and accurately acquire the shear strength parameters of the undisturbed soil, meeting the requirements of quickly and accurately acquiring the shear strength parameters of the undisturbed soil.