Improved direct shear apparatus for balancing heights of samples on two sides of shear surface

Abstract

The invention relates to the technical field of geotechnical tests, and provides an improved direct shear apparatus for balancing the heights of samples on two sides of a shear plane, which comprises a modified shear box, a displacement adjustment input panel, a hydraulic pump controller and the like. The improved shear box comprises an upper shear box body and a lower shear box body, the lower shear box body comprises a lower shear box peripheral wall, a movable lower bottom plate and vertical displacement adjusting columns, the movable lower bottom plate is arranged in the lower shear box peripheral wall, and the four vertical displacement adjusting columns are symmetrically connected to the lower portions of the four vertex angles of the movable lower bottom plate. And the displacement adjustment input panel is used for inputting a required vertical displacement value and controlling the adjustment height of the vertical displacement adjustment column through the hydraulic pump controller. According to the invention, the lower shear box is improved, the height balance of samples at two sides of a direct shear surface in a direct shear test is realized through the movable lower bottom plate and the bottom plate vertical displacement adjusting column, the shear strength of soil engineering materials such as clay, sandy soil and reinforced soil can be accurately measured, the principle is easy to understand, and the operation is simple and convenient.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical testing. Background Art

[0002] The shear strength of soil refers to the ultimate strength of soil to resist shear failure, including the internal friction angle and cohesion, and for clay soil, it also includes cohesion. When one part of the soil moves relative to another part, causing the shear stress generated by the external force at a certain point in the soil to reach the shear strength of the soil, the soil is considered to have sheared. Once the soil has sheared, it will cause a variety of catastrophic consequences, such as large-scale sliding of soil slopes due to shear failure. Therefore, in traditional civil engineering and its interdisciplinary extension fields, the shear strength of soil has always been a key indicator for understanding the basic physical and chemical properties of rock and soil.

[0003] The test methods commonly used in engineering to determine the shear strength of soil include indoor tests and field tests. The indoor test methods include triaxial shear test, direct shear test and unconfined compression test. Among them, the direct shear test, also known as the direct shear test, is a shear strength determination method that was developed earlier and is widely used in the engineering community. It has the advantages of simple equipment and easy operation. The soil sample of the direct shear test is placed in the fixed upper box and the movable lower box of the direct shear instrument. During the test, vertical pressure is first applied to the soil sample, and then a horizontal thrust is applied to the lower box to make the sample directly sheared along the plane between the upper and lower boxes. Although the direct shear test has a history of more than 100 years, there are also some defects in actual use. For example, the shear surface is artificially fixed, while the actual soil is often uneven. The properties of the soil on the fixed shear surface are not necessarily representative, and this shear surface is continuously reduced during the shear process, resulting in uneven stress and strain in the sample and difficult to determine. In addition, during the direct shear test, there is a significant difference in the height of the samples in the upper and lower shear boxes, which makes the stress distribution of the samples on both sides of the shear surface uneven. Domestic and foreign researchers have balanced the height difference of the samples in the upper and lower shear boxes by placing a plate of a certain height in the lower shear box to reduce the initial height of the sample inside the lower shear box. However, this operation method reduces the overall height of the sample, and the thickness of the lower plate is not clear, and the operability and precision control are poor. This phenomenon is particularly serious when the soil sample is soft, resulting in large deviations in the test results. Summary of the invention

[0004] In view of the problem of large height difference of samples in the upper and lower shear boxes when using a conventional direct shear apparatus, the present invention provides an improved direct shear apparatus which balances the sample heights on both sides of the shear surface. The present invention is achieved through the following technical solutions: An improved direct shear shearing instrument for balancing the height of samples on both sides of a shearing surface comprises a modified shearing box 12, a displacement adjustment input panel 11, a hydraulic pump controller 13, a pushing mechanism 3, a rotating hand wheel 10, a vertical pressure frame 2, a lever 8, and a weight 9, wherein: The modified shear box 12 includes an upper shear box and a lower shear box, which are used to load and shear the sample 5; the upper shear box is located above the lower shear box; The lower shear box includes a lower shear box peripheral wall 12-1, a movable lower bottom plate 12-3 and a vertical displacement adjustment column 12-2, wherein: the movable lower bottom plate 12-3 is placed inside the lower shear box peripheral wall 12-1; there are four vertical displacement adjustment columns 12-2, which are symmetrically connected to the lower parts of the four top corners of the movable lower bottom plate 12-3; The displacement adjustment input panel 11 is connected to the hydraulic pump controller 13 through a wire, and the hydraulic pump controller 13 is connected to the four vertical displacement adjustment columns 12-2 through wires, respectively. The entire control circuit is used to control the adjustment height of the vertical displacement adjustment column 12-2; The pushing mechanism 3 is connected to the lower shear box and is used to apply a horizontal thrust to the lower shear box to achieve displacement between the upper and lower shear boxes; The rotating hand wheel 10 is connected to the pushing mechanism 3 and is used to adjust the shear rate of the pushing mechanism 3; The vertical pressure frame 2 is located above the modified shear box 12, and is used to apply a vertical load to the upper surface of the sample in the modified shear box; the lever 8 is connected to the vertical pressure frame 2, and by arranging weights 9 of different masses at the end of the lever 8, the vertical pressure frame 2 applies different vertical loads to the upper surface of the sample 5 in the modified shear box 12.

[0005] Beneficial effects of the present invention: The present invention ensures that the heights of the upper and lower shear box samples are consistent and the shear surface is stable during the direct shear test through a movable lower base plate and an electrically controlled vertical displacement adjustment column, thereby achieving effective balancing of the sample heights on both sides of the direct shear surface in the consolidation quick shear test. The principle is easy to understand, the operation is simple, and the accuracy is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 Schematic diagram of the structure of a traditional direct shear apparatus.

[0007] Figure 2 Schematic diagram of the structure of an improved direct shear shearing instrument in an embodiment of the present invention.

[0008] Figure 3 Schematic diagram of the lower shear box structure in an embodiment of the present invention.

[0009] Figure 4 Schematic diagram of the vertical displacement adjustment column structure in an embodiment of the present invention.

[0010] Figure 5 The shear surface of the soil sample in the traditional direct shear apparatus in the embodiment is compared with that in the improved direct shear apparatus of the present invention.

[0011] Reference numerals: 1-vertical deformation dial indicator, 2-vertical pressure frame, 3-driving mechanism, 4-traditional shear box, 5-specimen, 6-load sensor, 7-table, 8-lever, 9-weight, 10-rotating hand wheel, 11-displacement adjustment input panel; 12- Modified shear box; 12-1-lower shear box peripheral wall, 12-2-vertical displacement adjustment column, 12-3-movable lower bottom plate; 12-2-1-adjustable support column, 12-2-2-cylinder housing, 12-2-3-hydraulic oil, 12-2-4-support chassis, 12-2-5-electric control wire, hydraulic pump module 12-2-6; lifting platform 12-2-7; oil storage tank 12-2-8; solenoid valve 12-2-9; 13-Hydraulic pump controller; 14-shear plane, 15-thick plate. DETAILED DESCRIPTION

[0012] The technical solution provided by the present application will be further described below in conjunction with specific embodiments and accompanying drawings. The advantages and features of the present application will become more apparent with the following description.

[0013] Example: The present invention is Figure 1 Based on the traditional direct shear shearing instrument shown in the figure, the structure is improved. The specific description is as follows: like Figure 2 , Figure 3 As shown, an improved direct shear shearing instrument for balancing the height of the specimens on both sides of the shearing surface includes a modified shearing box 12, a displacement adjustment input panel 11, a hydraulic pump controller 13, a pushing mechanism 3, a rotating hand wheel 10, a vertical pressure frame 2, a lever 8, a weight 9, and also includes a vertical deformation percentage indicator 1 and a load sensor 6. Among them: The modified shear box 12 includes an upper shear box and a lower shear box, which are used to load and shear the sample 5; the upper shear box is located above the lower shear box; The lower shear box includes a lower shear box peripheral wall 12-1, a movable lower bottom plate 12-3 and a vertical displacement adjustment column 12-2, wherein: the movable lower bottom plate 12-3 is placed inside the lower shear box peripheral wall 12-1; there are four vertical displacement adjustment columns 12-2, which are symmetrically connected to the lower parts of the four top corners of the movable lower bottom plate 12-3; the displacement adjustment input panel 11 is connected to the hydraulic pump controller 13 through a wire, and the hydraulic pump controller 13 is connected to the four vertical displacement adjustment columns 12-2 through wires respectively, and the entire control circuit is used to control the adjustment height of the vertical displacement adjustment column 12-2; The pushing mechanism 3 is connected to the lower shear box and is used to apply horizontal thrust to the lower shear box to achieve displacement between the upper and lower shear boxes. The pushing mechanism 3 is arranged on the table 7; The rotating hand wheel 10 is connected to the pushing mechanism 3 and is used to adjust the shear rate of the pushing mechanism 3; The vertical pressure frame 2 is located above the modified shear box 12 and is used to apply a vertical load to the upper surface of the sample 5 in the modified shear box 12; the lever 8 is connected to the vertical pressure frame 2, and the end of the lever 8 is located below the table 7. By arranging weights 9 of different masses at the end of the lever 8, the vertical pressure frame 2 applies different vertical loads to the upper surface of the sample 5 in the modified shear box 12; The vertical deformation dial gauge 1 is placed on the vertical pressure frame 2 and is used to measure the vertical displacement of the sample 5 under the vertical load; The load sensor 6 is connected to the upper shear box and is used to measure the horizontal shear stress on the soil sample 5 when the pushing mechanism 3 shears the soil sample 5 .

[0014] Furthermore, the modified shear box 12 also includes a water tank (not shown in the figure), which is placed under the movable lower bottom plate 12-3 of the lower shear box and is used to collect pore water that may be compressed by the sample 5 under the vertical load.

[0015] Further, a fixing pin is provided between the upper and lower shear boxes, and the fixing pin is used to fix the upper and lower shear boxes to prevent displacement. Before the upper and lower shear boxes are horizontally displaced, the fixing pin is taken out.

[0016] Further, such as Figure 4As shown (the right side of the figure is a structural schematic diagram, and the left side is a schematic diagram of the cross-sectional structure of the vertical displacement adjustment column), the vertical displacement adjustment column 12-2 adopts an electrically controlled hydraulic adjustment, including an adjustable support column 12-2-1, a cylinder housing 12-2-2, hydraulic oil 12-2-3, a support chassis 12-2-4, an electronically controlled wire 12-2-5, a hydraulic pump module 12-2-6, and a lift platform 12-2-7. The cylinder housing 12-2-2 is fixedly connected to the support chassis 12-2-4, and the lower part of the adjustable support column 12-2-1 is arranged in the cylinder housing 12-2-2. Sealing measures are adopted at the connection. The enclosed space formed by the cavity of the cylinder housing 12-2-2 and the adjustable support column 12-2-1 is filled with hydraulic oil 12-2-3. The enclosed space is connected to an external oil storage tank 12-2-8 through a high-pressure oil pipe. The high-pressure oil pipe is provided with a solenoid valve 12-2-9. The hydraulic pump module 12 -2-6 controls the solenoid valve 12-2-9 through electrical signals to realize the transmission and exchange of internal and external oil; the lifting platform 12-2-7 is combined with the hydraulic pump module 12-2-6 as a whole, and is connected to the lower end of the adjustable support column 12-2-1; the electric control wire 12-2-5 is led out from the hydraulic pump module 12-2-6, passes through the supporting chassis 12-2-4, is connected to the hydraulic pump controller 13, and continues to lead out the wire from the hydraulic pump controller 13 to the displacement adjustment input panel 11.

[0017] Furthermore, a limiting structure is provided in the cylinder housing 12-2-2 to assist the up and down displacement of the adjustable support column 12-2-1.

[0018] The working principle of the vertical displacement adjustment column 12-2 is as follows: the displacement adjustment input panel 11 receives the displacement required for adjustment, transmits the electrical signal to the hydraulic pump controller 13, and the hydraulic pump controller 13 transmits the control signal to the hydraulic pump module 12-2-6, and the hydraulic pump module 12-2-6 controls the hydraulic pump solenoid valve 12-2-9 to realize the oil transmission and exchange between the hydraulic oil 12-2-3 in the closed space formed by the cylinder shell 12-2-2 cavity and the adjustable support column 12-2-1 and the oil storage tank 12-2-8, and the pressure change of the hydraulic oil 12-2-3 brings about the longitudinal displacement of the lifting platform 12-2-7, thereby driving the longitudinal displacement of the adjustable support column 12-2-1. Furthermore, the pressure adjustment of the hydraulic oil 12-2-3 is precisely controlled by the hydraulic pump controller 13 through the hydraulic pump module 12-2-6, thereby realizing the displacement control of the adjustable support column 12-2-1, and then realizing the precise adjustment of the height of the sample on the movable lower bottom plate 12-3. Furthermore, the longitudinal displacement rate of the adjustable support column 12-2-1 is controlled to be constant at 1 mm / min.

[0019] The improved direct shear shearing apparatus with balanced sample heights on both sides of the shearing surface can be used to measure the shear strength of soil, and its operation method includes the steps of: Step 1: Preparation and installation of samples; Step 2: Application of vertical load; Step 3: Adjustment of the vertical displacement of the movable lower bottom plate of the lower shear box; Step 4: Shear the sample; Step 5: End of the experiment and organization.

[0020] The step 1, preparation and installation of the sample, specifically comprises the following steps: Cut the original soil sample from the original soil sample or prepare the disturbed soil sample with given dry density and moisture content. Insert the fixing pins to fix the upper and lower shear boxes, put the permeable board in the lower box, put the sample into the shear box, fill the upper and lower shear boxes, put a hardwood board on the sample, and use a small hammer to gently level and compact the soil, then take out the hardwood board.

[0021] The step 2, application of vertical load, comprises the following specific steps: Set the number of weights 9 on the lever 8 so that the sample obtains the set vertical load, i.e., vertical pressure; start the vertical deformation percentage meter 1 at the same time, and record the reading and the applied vertical load when the reading is stable. The vertical deformation percentage meter reading indicates the downward displacement value of the sample under the vertical load. During implementation, the vertical load can be applied according to the actual project and the hardness of the soil sample. The vertical loads of multiple groups of samples are roughly equal. Generally, the vertical loads are often taken as 100 kPa, 200 kPa, 300 kPa, 400 kPa, etc. Different set vertical loads can be applied lightly at one time. If the soil is soft, they can also be applied in stages to prevent the sample from being squeezed out.

[0022] The step 3, adjusting the vertical displacement of the movable lower bottom plate of the lower shear box, comprises the following specific steps: Remove the weight 9 to remove the vertical load of the sample. According to the reading recorded when the vertical deformation percentage gauge 1 is stable in step 2, enter half of the reading in the displacement adjustment input panel 11 as the preset displacement. Under the control of the hydraulic pump controller 13, synchronously start the vertical displacement of each vertical displacement adjustment column 12-2. When each vertical displacement adjustment column 12-2 synchronously completes the preset displacement upward, the next shear surface of the sample is the vertical bisector in the thickness direction (vertical direction), thereby achieving a balance in height between the upper and lower sides of the sample. After the vertical displacement adjustment column 12-2 stops running, re-place the weight to restore the vertical load of step 2.

[0023] Among them, the displacement adjustment column 12-2 adopts electric-controlled hydraulic adjustment, which is stable during operation, and the four displacement adjustment columns always keep in sync to ensure that the bottom surface of the lower shear box is always level.

[0024] The step 4, shearing the sample, comprises the following specific steps: Remove the fixing pins that fix the upper and lower shear boxes, return to zero and start the stopwatch. According to the set shear displacement rate, use the rotating handwheel 10 and the pushing mechanism 3 to push the lower shear box horizontally to shear the sample. Generally, the shearing rate is 0.8 mm / min~1.2 mm / min, and the handwheel 10 is rotated at a uniform speed of 4~6 turns per minute to shear the sample within 3min~5min. When the shear stress reading reaches stability or has a significant retreat, it means that the sample has been sheared. Usually, the shear deformation reaches 4mm. When the shear stress reading continues to increase, the shear deformation should reach 6mm. Each time the handwheel 10 is rotated, the shear stress displayed by the load sensor 6 reading when the soil is sheared is recorded.

[0025] The step 5, end of the test and arrangement, has the following specific steps: After the test is completed, remove the specimen and clean the test equipment; use multiple specimens to conduct multiple sets of tests at different vertical Load The corresponding shear strength is measured under the action of the load, and the stress-strain graph is drawn through the vertical load and horizontal shear force data recorded during each test. The internal friction angle and cohesion of the soil sample are analyzed according to formula (1): (1) Where 𝜎 is the normal stress, that is, the magnitude of the vertical load selected for each test; 𝜏 is the shear stress, that is, the magnitude of the shear stress displayed by the reading of load sensor 6 when the soil is destroyed each time the test is carried out with different vertical loads; 𝑐 is the cohesion; 𝜙 is the internal friction angle.

[0026] A coordinate system is established with 𝜎 as the horizontal coordinate and 𝜏 as the vertical coordinate. The (𝜎, 𝜏) points measured in each of the multiple tests are marked in the coordinate system and connected by a fitting straight line. Combining the form of formula (1), it can be seen that the intercept of the fitting straight line on the vertical axis is the cohesion c, and the slope is .

[0027] Furthermore, the effect of the present invention on the height balance of the specimens on both sides of the shear plane 14 can be verified in the following manner: First, after completing the adjustment of the vertical displacement of the movable lower bottom plate of the lower shear box in step 3, use a depth gauge to gently insert it into the sample until it touches the movable lower bottom plate 12-3. Repeat the measurement multiple times and take the average value, which is used as the overall height of the sample in the upper and lower shear boxes and recorded. Then, after the sample is sheared in step 4, the upper and lower shear boxes are staggered, and a depth gauge is gently inserted into the exposed sample in the lower shear box until it touches the movable lower bottom plate 12-3, and the measurement is repeated several times to obtain the average value, which is used as the height of the sample in the lower shear box and recorded. The height of the sample in the lower shear box is half of the total height of the samples in the upper and lower shear boxes recorded in step 3, which can verify that the present invention has indeed accurately balanced the sample heights on both sides of the shear surface 14.

[0028] Application comparison: like Figure 5 As shown, in the conventional shear box 4 of the conventional direct shear shearing instrument, as shown in (a), a thick plate 15 with a certain height is placed to reduce the initial height of the sample inside the lower shear box. The accuracy is difficult to grasp, and the thickness of the thick plate is not clear, the operability is poor, and the height of the samples in the upper and lower shear boxes on both sides of the shear surface 14 still has a large difference. In the modified shear box of the present invention, as shown in (b), due to the provision of a movable lower bottom plate 12-3 and a vertical displacement adjustment column 12-2, the height of the movable lower bottom plate 12-3 can be flexibly adjusted, thereby more accurately balancing the height of the samples on both sides of the shear surface 14.

[0029] The above description is only a description of the preferred embodiments of the present application, and is not intended to limit the scope of the present application. Any changes or modifications made by any person skilled in the art based on the above disclosed technical contents shall be deemed as equivalent effective embodiments and shall fall within the scope of protection of the technical solution of the present application.

Claims

1. An improved direct shear shearing apparatus for balancing the sample heights on both sides of the shearing surface, characterized in that: It comprises a modified shear box (12), a displacement adjustment input panel (11), a hydraulic pump controller (13), a pushing mechanism (3), a rotating hand wheel (10), a vertical pressure frame (2), a lever (8), and a weight (9), wherein: The modified shear box (12) comprises an upper shear box and a lower shear box, and is used to load and shear the sample (5); the upper shear box is located above the lower shear box; The lower shear box comprises a lower shear box peripheral wall (12-1), a movable lower bottom plate (12-3) and a vertical displacement adjustment column (12-2), wherein: the movable lower bottom plate (12-3) is placed inside the lower shear box peripheral wall (12-1); there are four vertical displacement adjustment columns (12-2) which are symmetrically connected to the lower parts of the four top corners of the movable lower bottom plate (12-3); The displacement adjustment input panel (11) is connected to the hydraulic pump controller (13) via a wire, and the hydraulic pump controller (13) is connected to the four vertical displacement adjustment columns (12-2) via wires, respectively. The entire control circuit is used to control the adjustment height of the vertical displacement adjustment columns (12-2); The pushing mechanism (3) is connected to the lower shear box and is used to apply a horizontal thrust to the lower shear box to achieve displacement between the upper and lower shear boxes; The rotating hand wheel (10) is connected to the driving mechanism (3) and is used to adjust the shear rate of the driving mechanism (3); The vertical pressure frame (2) is located above the modified shear box (12) and is used to apply a vertical load to the upper surface of the sample in the modified shear box; the lever (8) is connected to the vertical pressure frame (2), and weights (9) of different masses are arranged at the end of the lever (8) to enable the vertical pressure frame (2) to apply different vertical loads to the upper surface of the sample (5) in the modified shear box (12).

2. An improved direct shearing shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 1, characterized in that: It also includes a vertical deformation dial gauge (1) and a load sensor (6), wherein: The vertical deformation dial gauge (1) is placed on the vertical pressure frame (2) and is used to measure the vertical displacement of the sample (5) under the action of the vertical load; The load sensor (6) is connected to the upper shear box and is used to measure the horizontal shear stress exerted on the soil sample when the pushing mechanism (3) shears the soil sample (5).

3. An improved direct shearing shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 1, characterized in that: A fixing pin is arranged between the upper and lower shear boxes, and the fixing pin is used to fix the upper and lower shear boxes to prevent displacement.

4. An improved direct shearing shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 1, characterized in that: The vertical displacement adjustment column (12-2) adopts electric-controlled hydraulic adjustment.

5. An improved direct shearing shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 4, characterized in that: The vertical displacement adjustment column (12-2) comprises an adjustable support column (12-2-1), a cylinder shell (12-2-2), hydraulic oil (12-2-3), a support chassis (12-2-4), an electric control wire (12-2-5), a hydraulic pump module (12-2-6), and a lift platform (12-2-7), wherein: the cylinder shell (12-2-2) is fixedly connected to the support chassis (12-2-4), the lower part of the adjustable support column (12-2-1) is arranged in the cylinder shell (12-2-2), a sealing measure is adopted at the connection, and the closed space formed by the cavity of the cylinder shell (12-2-2) and the adjustable support column (12-2-1) is filled with hydraulic oil (12-2-3). The enclosed space is connected to an external oil storage tank (12-2-8) through a high-pressure oil pipe, and the high-pressure oil pipe is provided with a solenoid valve (12-2-9). The hydraulic pump module (12-2-6) controls the solenoid valve (12-2-9) through an electrical signal to achieve internal and external oil transmission and exchange; the lift platform (12-2-7) and the hydraulic pump module (12-2-6) are combined into one body and connected to the lower end of the adjustable support column (12-2-1); the electric control wire (12-2-5) is led out from the hydraulic pump module (12-2-6), passes through the support chassis (12-2-4), is connected to the hydraulic pump controller (13), and continues to lead out wires from the hydraulic pump controller (13) to connect to the displacement adjustment input panel (11).

6. An improved direct shearing shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 1, characterized in that: The operation method for measuring the shear strength of soil based on the improved direct shear shearing instrument comprises the following steps: Step 1: Preparation and installation of samples; Step 2: Application of vertical load; Step 3: Adjustment of the vertical displacement of the movable lower bottom plate of the lower shear box; Step 4: Shear the sample; Step 5: End of the experiment and organization.

7. An improved direct shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 6, characterized in that: Step 2: The number of weights (9) on the lever (8) is set so that the specimen obtains a set vertical load, i.e., a vertical pressure; at the same time, the vertical deformation percentage indicator (1) is started, and the reading and the applied vertical load are recorded when the reading is stable. The vertical deformation percentage indicator reading indicates the downward displacement value of the specimen under the vertical load.

8. An improved direct shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 6, characterized in that: Step 3: The weight (9) is removed to remove the vertical load of the sample. According to the reading recorded when the vertical deformation percentage meter (1) is stable in step 2, half of the reading is input into the displacement adjustment input panel (11) as the preset displacement. Under the control of the hydraulic pump controller (13), each vertical displacement adjustment column (12-2) is synchronously started to vertically displace. When each vertical displacement adjustment column (12-2) synchronously completes the preset displacement upward, the next shear surface of the sample is a vertical bisector in the thickness direction, thereby achieving a balance in height between the upper and lower sides of the sample. After the vertical displacement adjustment column (12-2) stops running, the weight is replaced to restore the vertical load of step 2.

9. An improved direct shearing apparatus for balancing the sample height on both sides of the shearing plane as claimed in claim 6, characterized in that: Step 4: Remove the fixing pins that fix the upper and lower shear boxes, return to zero and start the stopwatch. According to the set shear displacement rate, use the rotating hand wheel (10) and the pushing mechanism (3) to push the lower shear box horizontally to shear the sample. When the shear stress reading reaches a stable state or significantly retreats, it indicates that the sample has been sheared. Record the shear stress value displayed by the load sensor (6) when the soil is sheared.

10. An improved direct shearing instrument for balancing the sample height on both sides of the shearing plane as claimed in claim 6, characterized in that: Step 5: After the test is completed, the specimens are removed and the test equipment is cleaned. Multiple groups of tests are carried out using multiple specimens to measure the corresponding shear strength under different vertical loads. The stress-strain graph is drawn based on the vertical load and horizontal shear force data recorded during each test, and the internal friction angle and cohesion of the soil sample are analyzed according to formula (1): (1) Where 𝜎 is the normal stress, that is, the magnitude of the vertical load selected for each test; 𝜏 is the shear stress, that is, the magnitude of the shear stress shown by the load sensor reading when the soil is destroyed each time the test is carried out with different vertical loads; 𝑐 is the cohesion; 𝜙 is the internal friction angle.

Images