A shear stress control device for direct shear creep instrument

Abstract

The present invention provides a shear stress control device for a direct shear creep instrument, which mainly includes a liquid container, a weight container, and a plurality of stress control containers. The weight container is placed inside the liquid container, and the bottom of the liquid container is connected in series with the plurality of stress control containers through a pipeline. A cutting and connecting mechanism is provided between adjacent stress control containers and between the liquid container and the stress control container to change the sum of the inner bottom area of ​​the liquid container and the inner bottom area of ​​each stress controller connected in series. The present invention is used as an auxiliary device of the direct shear creep instrument. With the occurrence of shear, the weight container will produce relative displacement with the liquid container, and the effective shear force will decrease. By controlling the connection between different stress control containers and the liquid container, different liquid level rising rates are controlled to meet the requirement that the increase in buoyancy (i.e., the decrease in effective shear force) is equal to the product of the decrease in effective area and the shear stress under different shear stresses, thereby controlling the constant shear stress of the soil sample during the shearing process.

Description

Technical Field

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

[0002] The direct shear creep test is a test in which a soil sample is sheared on a specific plane, the shear stress is kept constant, and the shear displacement is measured over time. The currently commonly used direct shear creep tester studies the creep properties of soil by applying weights on a specific shear plane to test the change in soil strain over time under a certain shear force F. However, creep refers to the change in strain over time under a constant shear stress (shear stress = shear force / shear area: τ = F / S). Therefore, the traditional direct shear creep tester is based on the premise that the effective shear area remains unchanged. The test device is mainly composed of a shear box, a force system, and a measurement system. The principle is clear and the operation is simple. Test instruments such as Figure 1 shown.

[0003] However, in actual situations, as shear occurs, the upper and lower shear boxes are offset from each other, and the effective shear area of ​​the soil sample will gradually decrease. The shear force is provided by the mass of the weight and will not change with the occurrence of shear displacement. The shear stress will continue to increase with the occurrence of shear displacement. Therefore, the traditional direct shear creep instrument strictly does not meet the premise of creep test. Summary of the invention

[0004] The object of the present invention is to provide a test device which can ensure that the shear stress remains constant during the test and accurately measure the shear displacement.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a shear stress control device of a direct shear creep instrument, which includes a liquid container, a weight container and a plurality of stress control containers, the liquid container is filled with liquid, and the shear stress weight used in the creep test is placed in the weight container, the weight container is placed in the liquid of the liquid container and floats and sinks upright under the action of gravity and buoyancy, the bottom of the liquid container is connected in series with a plurality of stress control containers through a pipeline, and a cutting and connecting mechanism is provided between adjacent stress control containers and between the liquid container and the stress control container, and the cutting or connecting state of the mechanism is changed so that the inner bottom area of ​​the liquid container and the sum of the inner bottom areas of the series-connected stress control containers S 有效 satisfy

[0006]

[0007] S 砝码 is the outer bottom area of ​​the weight container; L is the side length of the square shear box perpendicular to the shear direction in the creep test; τ is the shear stress; ρ is the liquid density; g is the gravitational acceleration.

[0008] As a preferred embodiment, the liquid contained in the liquid container is silicone oil.

[0009] The weight container is placed inside the liquid container, and a plurality of guide wheels are evenly distributed around the upper part of the outer wall of the weight container. The guide wheels are in rolling contact with the inside of the liquid container to limit the weight container to remain upright during the floating and sinking process.

[0010] Rubber tubes are arranged between adjacent stress control containers and between the liquid container and the stress control container for communication, and clamps are arranged on the rubber tubes for cutting off the pipelines.

[0011] The present invention is used as an auxiliary device of a direct shear creep instrument. The weight container is used to provide shear force for the shear test. As shear occurs, the weight container will sink in the liquid container, and the silicone oil level in the liquid container will rise accordingly. The buoyancy of the weight container will increase accordingly, and the effective shear force will decrease. By controlling the connection between different stress control containers and liquid containers, different liquid level rise rates are controlled to meet the requirement that the increase in buoyancy (i.e., the decrease in effective shear force) under different shear forces is equal to the product of the decrease in effective area and the shear stress, thereby controlling the constant shear stress of the soil sample during the shear process. The present invention solves the defect of the non-constant shear stress of the traditional direct shear creep instrument by means of an additional device, which is simple to operate and highly feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The technical solution of the present invention is now further described in conjunction with the accompanying drawings.

[0013] Figure 1 It is the side view of the traditional direct shear creep instrument;

[0014] Figure 2 It is a structural schematic diagram of the shear stress control device of the direct shear creep instrument of the present invention;

[0015] Figure 3 It is a side view of a direct shear creep instrument with the shear stress control device of the direct shear creep instrument of the present invention added;

[0016] Figure 4 This is a schematic diagram of the silicone oil level rising;

[0017] Figure 5 Top view of a shear stress control device for a direct shear creep instrument.

[0018] Among them: 1. Lower shear box, 2. Axial pressure rod, 3. Pressure cover, 4. Soil sample, 5. Upper shear box, 6. Steel ring, 7. Dial indicator, 8. Dial indicator, 9. Pulley, 10. Steel strand, 11. Weight, 212. Weight container, 213. Liquid container, 214. Guide wheel, 215. Stress control container, 216. Shear force weight, 217. Clamp, 218. Silicone oil, 219. Rubber tube DETAILED DESCRIPTION

[0019] The following are merely examples of implementation of the present invention and are not intended to limit the scope of the present invention. That is, any insubstantial changes and modifications made within the scope of the present invention should still fall within the scope of the present invention.

[0020] like Figure 2 The figure shows a shear stress control device of a direct shear creep instrument of the present invention, which includes a liquid container 213, a weight container 212 and a plurality of stress control containers 215. The liquid container 213 contains liquid, and its function is to make the weight container float and sink therein. In order to ensure that the weight container floats and sinks upright in the liquid container, guide wheels 214 are evenly distributed on the upper part of the outer wall of the weight container to roll in contact with the inner wall of the liquid container. The liquid contained in the liquid container can be water or other reagents, but care should be taken to avoid evaporation of the liquid (such as covering the surface of the water with a layer of oil that is not easy to evaporate), and silicone oil 218 is preferably used. The bottom of the liquid container 213 is connected in series with a plurality of stress control containers 215 through a pipeline, and rubber tubes 219 are arranged between adjacent stress control containers and between the liquid container and the stress control container for communication. The rubber tube is cut off or connected by clamping and loosening the clamp 217.

[0021] like Figure 3 As shown, the shear stress control device of the direct shear creep instrument of the present invention is installed on the direct shear creep instrument, and the soil sample shear box uses a square soil sample shear box, then the effective shear area is linearly reduced, and there is no need to simplify. The shear box adopts a square shape, and the side length perpendicular to the shear direction is L. When the shear displacement is x, the effective shear area of ​​the soil sample will decrease by Δ S =xL, to ensure that the shear stress τ remains unchanged, the shear force needs to be reduced by Δ F =τΔ S The device is now simplified into two parts. One part is the weight container that provides shear force. Suppose the outer bottom area of ​​the weight container is S. 砝 , part of it is an effective liquid container, and the bottom area of ​​the effective liquid container is S 有效 , as shear occurs, the weight container drops by x, and the liquid level rises by h, as Figure 3 As shown: According to the constant volume of silicone oil,

[0022]

[0023] To control the shear stress constant, then: Δ F =Δ 浮力 =(x+h)S 砝 ρg, where ρ is the density of silicone oil and g is the acceleration due to gravity. Substitute Δ F =τΔ S , Δ S =xL, we can eliminate x and get Where ρ and g are constants, S 砝Once determined, an S can be calculated in a shear stress creep test. 有效 To ensure that the shear stress remains constant during the shear test.

[0024] In order to meet the test requirements under multiple shear stresses, S 有效 It is divided into two parts, one is the liquid container and the other is the stress control container, which are connected in series through the rubber tube at the bottom. The sum of the inner bottom areas of the connected stress control containers is S 控制 =S 有效 -S 液 , S 液 Refers to the bottom area of ​​the liquid container. Different shear stress creep tests only require clamping the corresponding rubber tube to block a part of the connection.

[0025] Change the clamping or loosening state of the rubber tube to make the inner bottom area of ​​the liquid container and the sum of the inner bottom areas of the series-connected stress control containers S 有效 satisfy

[0026]

[0027] S 砝 is the outer bottom area of ​​the weight container; L is the side length of the square shear box in the creep test, τ is the shear stress; ρ is the liquid density; g is the gravitational acceleration.

[0028] The implementation steps of the present invention are as follows:

[0029] 1) Determine the bottom area of ​​the stress control container: According to the shear stress required by the experiment, from large shear stress to small shear stress, combined with the formula (Where S 砝 is the outer bottom area of ​​the weight container (cm 2 );S 有效 is the sum of the inner bottom area of ​​the liquid container and the inner bottom area of ​​the stress control container in series (cm 2 ); τ is shear stress (kPa); ρ is silicone oil density (kg / m 3 ); g is the acceleration due to gravity (m / s 2 )) to calculate the S required for each shear stress 有效 Finally, the inner bottom area that needs to be increased is calculated in sequence from large shear stress to small shear stress, and then the inner bottom area of ​​each stress control container is determined.

[0030] 2) Easy connection stress control: According to the shear stress required by the experiment, connect each stress control container and the liquid container in series from large to small.

[0031] 3) Sampling: Place the soil sample into the shear box and apply the corresponding axial pressure.

[0032] 4) Fill with silicone oil: Place the weight container in the liquid container, pour into the liquid container until the silicone oil contacts the bottom of the weight container, check whether the stress control containers are connected and whether the silicone oil flows in.

[0033] 5) Loading: Place weights in the weight container to load and conduct creep test.

[0034] 6) Record: Record the shear deformation within the corresponding time according to the test requirements.

[0035] For example: creep tests with shear stresses of 50 kPa, 100 kPa, 150 kPa, 200 kPa, 250 kPa, and 300 kPa are carried out, and the external area of ​​the fixed weight container is S 砝 =1600cm 2 The side length of the shear box perpendicular to the shear direction is 6 cm, and the density of silicone oil is 0.963 g / cm 3 , the acceleration due to gravity is 10N / kg, and the formula Calculation can be obtained S 有效 They should be 3289.5cm respectively 2 、2152.9cm 2 、1930.5cm 2 、1835.7cm 2 、1783.2cm 2 、1749.8cm 2 The inner bottom area of ​​the liquid container is 1700cm 2 , when conducting a 300 kPa creep test, a stress control container needs to be connected, and its inner bottom area is 1749.8 cm 2 -1700cm 2 =49.8cm 2 When conducting a 250 kPa creep test, a second stress control container needs to be added on the basis of the first stress control container. The inner bottom area of ​​the second stress control container is 1783.2 cm 2 -1749.8cm 2 =33.4cm 2 When conducting a 200 kPa creep test, a third stress control container is required to be added on the basis of connecting the first and second stress control containers. The inner bottom area of ​​the third stress control container is 1835.7 cm 2 -1783.2cm 2 =52.5cm 2 By analogy, the inner bottom areas of other stress-controlled containers are 94.8 cm 2 、222.4cm 2 、1136.6cm 2 See Table 1 for details.

[0036] Table 1

[0037]

[0038] From this, it can be calculated that the inner bottom area used by each stress control container is shown in Table 2:

[0039] Table 2

[0040]

[0041] At the beginning of the test, starting from 50 kPa shear stress, all stress control vessels are connected in series so that S 控制 =49.8+33.4+52.5+94.8+222.4+1136.6=1589.5,

[0042] That is S 有效 =S 液 +S 控制 =1589.5+1700=3289.5, which satisfies When conducting a 100 kPa shear stress test, clamp the outermost stress control container with a clamp and interrupt its connection. 控制 =49.8+33.4+52.5+94.8+222.4=452.9, that is, S 有效 =S 液 +S 控制 =452.9+1700=2152.9, which satisfies The same applies when conducting other shear stress tests.

Claims

1. A shear stress control device for a direct shear creep instrument, characterized in that: The invention comprises a liquid container, a weight container and a plurality of stress control containers. The liquid contained in the liquid container is silicone oil. The weight used as the shear stress weight in the creep test is placed in the weight container. The weight container is placed in the liquid inside the liquid container. A plurality of guide wheels are evenly distributed on the upper part of the outer wall of the weight container. The guide wheels are in rolling contact with the inside of the liquid container to limit the weight container to float and sink upright under the action of gravity and buoyancy. The bottom of the liquid container is connected in series with the plurality of stress control containers through a pipeline. Rubber tubes are provided between adjacent stress control containers and between the liquid container and the stress control container for communication. A clamp is provided on the rubber tube for cutting off the pipeline, so that the inner bottom area of ​​the liquid container and the sum of the inner bottom areas of the series-connected stress control containers S 有效 satisfy S 码 is the outer bottom area of ​​the weight container; L is the side length of the square shear box perpendicular to the shear direction in the creep test; τ is the shear stress; ρ is the liquid density; g is the gravitational acceleration.

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