Indoor soil body high-speed shear apparatus considering shear rate effect

Abstract

The invention discloses an indoor test device for measuring the undrained shear strength of cohesive soil under the action of different higher shear rates. The invention aims to provide a device capable of quickly and accurately measuring the undrained shear strength of cohesive soil under the action of different higher shear rates. The invention relates to the technical field of shear tests, in particular to a novel device for measuring undrained shear strength values of cohesive soil under the action of different high shear rates. The device comprises a high-speed rotating base, an upper shearing box, a lower shearing box, a torque sensor, a shearing plate head and a reinforcing plate head. And the high-speed rotating base drives the lower shearing box and the soil body to rotate at a high speed. The upper shear box is kept still, and a shear plate head in the inner wall of the upper shear box cuts the outer edge of the soil sample at a high speed to form a shear zone. The torque sensor is used for collecting the resistance torque borne by the shear plate head in the shearing process, and the undrained shear strength and the soil body sensitivity during high-speed shear failure of the soil body can be obtained through conversion according to a proposed formula. The shearing plate head is located on the inner wall of the lower portion of the upper shearing box, and the shearing linear speed can be further increased by enlarging the diameter of a shearing belt. The reinforcing plate head is located in the lower shearing box and used for preventing the soil body from displacing in the high-speed shearing process. The method is suitable for measuring the undrained shear strength and sensitivity of the cohesive soil. And moreover, the method is simple to operate and can be used for measuring the undrained shear strength of the cohesive soil under the action of different higher shear rates indoors. And a new device and thought are provided for the test method for measuring the undrained shear strength of the cohesive soil.

Description

Technical Field

[0001] The invention relates to the field of measuring the undrained shear strength of clay by shear test, and in particular to a shear device for measuring the undrained shear strength of clay under different higher shear rates. Background Art

[0002] Undrained shear strength refers to the ability of soil to withstand shear stress perpendicular to the shear plane and resist damage without considering seepage. Undrained shear strength is one of the important parameters for evaluating the load and deformation capacity of soil. This index is related to factors such as the properties of the soil and comprehensive engineering conditions. At the same time, it is also affected by factors such as the internal structure of the soil, moisture content and porosity. In catastrophic environments such as earthquakes and explosions, the shear strength of the soil has a significant impact on the safety of the structure.

[0003] The undrained shear strength of clay is usually obtained by indoor test methods or in-situ test measurements. The commonly used indoor test method is mainly triaxial test. Although the triaxial test can provide relatively accurate experimental parameters. However, during the triaxial test, it is necessary to apply confining pressure. If the confining pressure is uneven, it may affect the accuracy of the test results. In addition, the test results are greatly affected by the shear rate. The commonly used in-situ test is the cross-plate shear test. The cross-plate shear test can directly test the soil on site, thereby reducing the influence of sampling disturbance on the undrained shear strength of the soil. The test takes into account the stress state of the soil in actual engineering, thereby more accurately reflecting the shear strength of the soil. However, during the cross-plate shear test, the rotation speed needs to be strictly controlled and should not be too fast.

[0004] In summary, although the existing test devices and methods can measure the undrained shear strength of clay soil more accurately, they all have a more obvious defect. The above test methods all require strict control of the shear rate, and can only measure the undrained shear strength of the soil under a lower shear rate. The undrained shear strength of the soil is closely related to the shear rate. When the shear rate is low, the undrained shear strength of the soil is low, and vice versa. Moreover, in most working conditions, the soil will be affected by a higher shear rate. Therefore, using the undrained shear strength of the soil measured under a lower shear rate as an evaluation indicator for related projects has a certain error. Therefore, for the test method of the undrained shear strength of clay soil, it is necessary to invent a test device that considers the soil under high-speed shear and measures its undrained shear strength. Summary of the invention

[0005] Aiming at the deficiencies of the existing devices, the present invention provides a shearing device with reasonable design and low engineering cost, which is suitable for measuring the undrained shear strength of clay soil under different high shear rates.

[0006] The technical solution adopted by the present invention to solve its technical problem is a shearing device for measuring the undrained shear strength of clay soil under different high shear rates.

[0007] Preferably, the indoor test device is mainly composed of an upper and lower shear box, characterized in that the diameter of the lower shear box is D and the wall thickness is 4 mm. A groove is provided at the bottom of the lower shear box. The lower shear box is fixed on the rotating base through the groove, so that the lower shear box can drive the soil to rotate at high speed with the platform. Then, the shear plate head on the inner wall of the upper shear box is twisted at a constant speed to perform high-speed shearing on the soil. Finally, a failure surface is formed at the outer edge of the soil sample, and the undrained shear strength of the soil is obtained by converting the resisting torque during the test.

[0008] Preferably, the indoor test device is characterized in that the undrained shear strength of clay under a higher shear rate can be measured by enlarging the size of the shear box and increasing the rotation angular velocity of the lower shear box. The undrained shear strength of clay under different higher shear rates can be obtained by changing the size of the shear box and the rotation angular velocity of the lower shear box. The minimum size of the shear box is 100 mm, the minimum rotation angular velocity is 10° / min, and the minimum shear speed is 50 cm / min.

[0009] Preferably, 4 reinforcing plate heads are evenly arranged around the center of the lower shear box, with a height of 25 mm and a width of 30 mm, for reinforcing the soil to prevent displacement of the soil during high-speed rotary shearing, further ensuring that a regular shearing surface can be formed during the shearing process, and effectively improving the accuracy of the test results.

[0010] Preferably, the upper shear box has a variable cross-section cylinder shape, with a lower diameter of D+4mm and a height of 25mm, an upper diameter of (D+4mm) / 2 and a height of 15mm. Six shear plate heads are evenly arranged on the lower inner wall, with a height H of 25mm and a width d of 12mm. The shear plate heads are evenly arranged in the circumferential direction, and there is always a gap between the outer end and the reinforcement plate head. When the lower shear box drives the soil sample in the box to rotate at a high speed, the shear plate heads at the lower inner wall of the upper shear box will shear the soil at the outer edge of the soil sample to form a shear band. When the shear band is located at the outer edge of the soil sample, the shear line speed can be further increased.

[0011] Preferably, the resisting torque M is the resisting torque M of the shear plate head. 1 and bottom resistance torque M 2 According to formula (4), the undrained shear strength S of clay soil is u The resisting torque M can be obtained by a torque collector connected to the transmission shaft.

[0012] Preferably, the rotation of the rotating platform is controlled by a recoilless driving motor to provide the required shearing speed for the shear box. The upper part of the upper shear box is connected to a torque sensor to record the resisting torque of the shear plate head during the high-speed shearing of the soil. By changing the rotational angular velocity and size of the lower shear box, and then converting the resisting torque obtained, the relationship between the undrained shear strength and the shear rate of the clay soil can be obtained.

[0013] The present invention uses a unique structural design and is based on the cross-plate shear test principle to effectively measure the undrained shear strength of clay under different high-speed shear rates. This improves the defect that the existing test device can only measure the undrained shear strength of clay under low-speed shear. The overall device of the present invention uses simple materials, has a low overall structural cost, and can obtain test data with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a front view of the present invention;

[0015] Figure 2 A top view of the lower shear box of the present invention;

[0016] Figure 3 A bottom view of the shear box of the present invention;

[0017] Figure 4 It is a front view of the shear box of the present invention;

[0018] Figure 5 A top view of the shear box of the present invention;

[0019] Figure 6 It is a top view of the shear band side stress analysis of the present invention;

[0020] Figure 7 This is a bottom view of the stress analysis of the shear zone bottom of the present invention.

[0021] The reference numerals in the figure are: lower shear box 1, upper shear box 2, reinforcement plate head 3, shear plate head 4, rotating base 5, torque sensor 6, soil sample 7, recoilless drive motor 8, displacement sensor 9, computer 10, shear belt 11. Specific implementation methods

[0023] A shearing device for measuring the undrained shear strength of clay under different high shear rates. The implementation method of the present invention is clearly described below in conjunction with the accompanying drawings of the present invention. A shearing device considering high-speed shearing of clay mainly includes a lower shear box 1, an upper shear box 2, a reinforcement plate head 3, a shear plate head 4 and a rotating base 5. The indoor test measurement method includes the following steps.

[0024] 1. According to the required shearing speed and formula (1), select a shearing box of appropriate size and set an appropriate rotational angular velocity.

[0025] 2. Before using the device to measure the undrained shear strength of the soil, the clay soil to be tested is first made into a cylindrical soil sample with a height of 30 mm and a width of D.

[0026] 3. Use a paper towel to wipe the inside of the shear box clean to prevent impurities from affecting the accuracy of the test results.

[0027] 4. First place the lower shear box on the rotating platform and fix it through the slot.

[0028] 5. Press the soil sample into the lower shear box and then let it stand for 2 to 3 minutes to reduce the impact of soil disturbance on the test results.

[0029] 6. Place the upper shear box on top of the lower shear box and slowly lower it. Allow the shear plate head on the inner wall of the upper shear box to slowly insert into the soil sample. When the bottom of the upper shear box is flush with the lower shear box, let it stand for 2 to 3 minutes to reduce the impact of soil disturbance on the test results.

[0030] 7. Start the recoilless drive motor to make the lower shear box drive the soil to rotate at high speed. At this time, the shear plate head at the inner wall of the upper shear box shears the soil at a uniform speed. Record the torque for every 1° twist. When the torque reaches a peak or stabilizes, continue shearing for 1 minute to confirm the peak or stable torque. According to formula (4), the undrained shear strength S of the original soil can be calculated. u .

[0031] 8. After the peak strength or stability test is completed, rotate it for 6 consecutive times to fully disturb the soil around the shear plate head. Then the undrained shear strength S' of the remolded soil under the shearing action of velocity V can be measured. u .

[0032] Therefore, the sensitivity of the test soil sample can be calculated according to formula (5).

[0033]

[0034] 9. Turn off the recoilless drive motor to stop the shear box from shearing.

[0035] 10. Take out the shear box, take out the soil sample in the lower shear box, and clean the shear box. At this point, the determination of the undrained shear strength of the soil under the action of velocity V is completed.

[0036] 11. Change the size of the shear box and reset the rotation angular velocity of the lower shear box, repeat steps 1 to 10, and you can get the undrained shear strength of clay under different higher shear rates.

[0037] 12. Repeat steps 1 to 11 at least three times and sort the data to obtain the relationship between the undrained shear strength of clay and the shear rate.

[0038] In summary, the present invention provides a shearing device for measuring the undrained shear strength of clay soil under different high shear rates, and compares it with the traditional test measuring device. The present invention makes up for the defect that the traditional shearing device has a slow shear rate and cannot measure the undrained shear strength of soil under high-speed shear.

Claims

1. An indoor test device for measuring the undrained shear strength of clay soil at different higher shear rates, characterized in that: The lower shear box and the soil rotate at high speed with the rotating base, the upper shear box is fixed, and the shear plate head is located on the inner wall of the upper shear box, so that the shear surface is located outside the soil sample. By expanding the diameter of the shear zone, the shear linear speed is further increased.

2. The indoor test device according to claim 1, characterized in that The lower shear box and the soil rotate at high speed along with the rotating base. The shear plate head located on the inner wall of the upper shear box twists at a constant speed to shear the soil at high speed. The shear linear velocity can be calculated according to formula (1): In formula (1), D is the diameter of the lower shear box, and ω is the angular velocity of the lower shear box. The purpose of high-speed shearing is achieved by enlarging the size of the lower shear box and using a recoilless motor to increase the angular velocity of the lower shear box. By selecting shear boxes of different sizes and adjusting the angular velocity of the lower shear box, the shear test of clay under different higher shear rates can be completed. The minimum size of the shear box is 100 mm, the minimum angular velocity of rotation is 10° / min, and the minimum shear speed is 50 cm / min.

3. The indoor test device according to claim 1 is composed of an upper shear box and a lower shear box, characterized in that The shape of the lower shear box is consistent with the disc cushion, with a diameter of D and a wall thickness of 4mm. It has a groove at the bottom and can be fixed on the rotating base and rotate with the base. This drives the soil to rotate at high speed, realizing the feature of the shear plate head shearing the soil at high speed. The upper shear box is a variable-section cylinder with a lower diameter of D+4mm and a height of 30mm, and an upper diameter of (D+4mm) / 2 and a height of 15mm.

4. The lower shear box according to claim 3, characterized in that There are 4 reinforcement plates at the center of the shear box, with a height of 25 mm and a width of 30 mm, which are used to reinforce the soil and prevent the soil from shifting during high-speed rotary shearing.

5. The upper shear box according to claim 3, characterized in that: Six shear plate heads are arranged on the lower inner wall of the upper shear box, with a height H of 25 mm and a width d of 12 mm. The shear plate heads are evenly arranged along the circumferential direction, and there is always a gap between their outer ends and the reinforcement plate heads.

6. The indoor test device according to claim 1, characterized in that The torque sensor can collect the resisting torque M of the shear plate head during the shearing process. Then the undrained shear strength S of the test soil sample under a specific shear speed can be calculated. u The resistance torque is obtained by adding the resistance torque M1 of the shear surface and the resistance torque M2 of the bottom surface of the shear plate head. The resistance torque M1 of the shear surface is shown in formula (2), and the resistance torque of the bottom surface of the shear plate head is shown in formula (3). In formula (2), C c is the stress on the side of the shear surface. In formula (3), R1 is D / 2, R2 is R1-10, C d The stress on the bottom of the board head when the board head is extended to the center of the bottom circle. In fact, the width of the board head does not reach the center of the bottom circle. At this time, the stress on the bottom of the board head is According to equations (2) and (3), the maximum resistance moment M generated by the soil during the shear process can be obtained. Among them, the undrained shear strength S of the soil u =C c =C d The undrained shear strength of soil is shown in formula (4).

7. The indoor test device according to claim 1, characterized in that The upper shear box is connected to a torque sensor to record the resisting torque M during shearing.

8. The indoor test device according to claim 1, characterized in that By changing the size of the lower shear box and the angular velocity of rotation, the resistance torque of the clay under different higher shear rates can be obtained. By calculating and sorting out formula (4), the relationship between the undrained shear strength of the clay and the shear rate can be obtained.

9. The rotating base according to claim 3, characterized in that The base is connected to a displacement sensor for recording the shear displacement L.

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