A vertical variable shear force direct shear creep instrument

Abstract

The present invention provides a vertical variable shear force direct shear creep instrument, which includes an instrument table, a shear box, a dial indicator and a pressurizing system. The shear box is composed of a first box body and a second box body. The second box body slides down relative to the first box body under the action of gravity and a second weight group. The pressurizing system includes a horizontal axial pressure weight system and a vertical shear force weight system. The horizontal axial pressure weight system includes a first weight group; the vertical shear force weight system includes a second weight group, and the second weight group is placed in a weight container. The weight container is placed in a liquid container. The bottom of the liquid container is connected in series with multiple 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. The present invention can avoid the force loss of the traditional direct shear instrument when converting vertical gravity into horizontal shear force, and can control the shear stress of the soil sample to be constant 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 refers to a test that shears a soil sample on a specific surface, keeps the shear stress constant, and measures the shear displacement over time. The current direct shear creep tester uses a basic force mode of applying axial pressure vertically and shearing horizontally. The vertical gravity is converted into horizontal force by hooking a weight on a pulley to provide shear force for the sample. Since the shear force is usually much larger than the axial pressure, there will be a certain loss after the pulley converts the direction of the force, and the actual shear force needs to be tested through a steel ring.

[0003] In addition, the commonly used direct shear creep tester studies the creep properties of soil by applying weights on a specific shear plane and testing the change of soil strain over time under a certain shear force F. However, creep refers to the change of strain over time while the shear stress remains unchanged (shear stress = shear force / shear area: τ = F / S). 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 weights and will not change with the occurrence of shear displacement. The shear stress will continue to increase with the occurrence of shear displacement. Therefore, strictly speaking, the traditional direct shear creep tester does not meet the premise of creep testing. Summary of the invention

[0004] The purpose of the present invention is to make up for the deficiencies of the prior art and to provide an improved direct shear test creep instrument, which can overcome the defects of the prior art in that the axial pressure is lost and the shear stress cannot be kept constant during the test.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a vertical variable shear force direct shear creep instrument, characterized in that it includes: an instrument table, a shear box, a dial indicator and a pressurization system,

[0006] The instrument table is provided with a vertical baffle, and the table near the vertical baffle has a through hole that runs through the table from top to bottom.

[0007] The shear box is composed of a first box body and a second box body to form an inner cavity for containing soil samples. The first box body is an annular shell with two open ends. The first box body is placed on the instrument table so that one open end is connected to the opening of the second box body, and the other open end is closed by a pressure cover pulled by a steel hinge wire. The open end of the second box body is connected to the first box body, and the closed end opposite to the open end is provided with a pulley block in sliding contact with a vertical baffle.

[0008] The dial of the dial indicator is relatively fixedly connected to the instrument table, and the spring contact head of the dial indicator contacts the top of the second box body.

[0009] The pressurization system includes a horizontal axial pressure weight system and a vertical shear force weight system. The horizontal axial pressure weight system includes a fixed pulley mounted on the instrument table, a steel hinge wire that is fixedly connected to the pressure cover and then passes around the fixed pulley and hangs down, and a first weight group that is directly or indirectly connected to the hanging end of the steel hinge wire; the vertical shear force weight system includes a hanging rod that is fixed to the bottom surface of the second box body and passes through the perforated hole on the instrument table surface, and a second weight group that is hung at the bottom of the hanging rod; the second box body slides down relative to the first box body under the action of gravity and the second weight group.

[0010] The second weight group is placed in a weight container, and the weight container is placed in a 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. The liquid in the liquid container remains upright and floats and sinks under the buoyancy of the liquid. The bottom of the liquid container is connected in series with multiple 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. 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

[0011]

[0012] S 砝 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.

[0013] The horizontal axial pressure weight system also includes a lever, the fulcrum of the lever is hinged to the side of the instrument table, the end of the steel hinge is fixedly connected to the lever body, and the first weight group is suspended at one end of the lever away from the fulcrum.

[0014] The lever is a U-shaped lever consisting of two longitudinal bars and a cross bar connected between the ends of the two longitudinal bars. The head end of the longitudinal bar is hinged to the side of the instrument table, and the first weight group is suspended in the middle of the cross bar.

[0015] A detachable axial connecting bolt is provided between the first box body and the second box body. When the axial connecting bolt is removed, the second box body can slide down relative to the first box body under the action of force.

[0016] 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.

[0017] 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.

[0018] The liquid contained in the liquid container is silicone oil.

[0019] The pressure cover extends to both sides to form extended ends, each extended end is connected to the head end of the steel strand on the same side, and the end of the steel strand is connected to the two longitudinal rod bodies of the lever.

[0020] The instrument table top is supported by four legs, kept horizontal, and perpendicular to the upright baffle.

[0021] The dial of the dial indicator is fixed on the upright baffle.

[0022] The creep instrument of the present invention firstly adopts the vertical shearing method, changes the axial pressure direction to the horizontal direction, and changes the shear force direction to the vertical direction, so as to avoid the force loss of the traditional direct shear instrument when converting the vertical gravity into the horizontal shear force. The applied weight gravity can directly become the shear force, and the steel ring force measurement is also omitted. At the same time, the soil sample shear box of the present invention adopts a square shape, and the effective shear area is linearly reduced, and there is no need to simplify it. A shear stress control device is added to the shear stress weight, and the effective shear force is reduced while the effective shear area is reduced, thereby ensuring the constant shear stress. The needs of different shear stress tests can be met by connecting with a rubber tube, solving the defect of the non-constant shear stress of the traditional direct shear creep instrument, and can also meet the requirements of multi-stage direct shear creep tests on the same soil sample. At the same time, the present invention also adjusts the shear force through an additional stress control device, so that the change of the shear force is synchronized with the change of the shear area, thereby ensuring the constant shear stress and the accuracy of the shear force test. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The technical solution of the present invention is now further described in conjunction with the accompanying drawings.

[0024] Figure 1 It is a schematic elevation diagram of a vertical variable shear force direct shear creep instrument of the present invention;

[0025] Figure 2 This is a schematic diagram of the silicone oil level rising;

[0026] Figure 3 It is the top view of the shear stress control system container;

[0027] Figure 4 It is a top view of the vertical variable shear force direct shear creep instrument of the present invention;

[0028] Figure 5 This is a schematic diagram of the shear box structure before shearing;

[0029] Figure 6 Schematic diagram of the shear box displacement after shearing.

[0030] Wherein: baffle 101, dial indicator 102, second box body 103, suspension rod 103.1, first box body 104, pulley block 105, pressure cover 106, steel strand 107, instrument table 108, first weight group 109, second weight group 110, soil sample 111, fixed pulley 112, lever 113, longitudinal rod 113.1, cross rod 113.2, connecting bolt 114, 212. weight container, 213. liquid container, 214. guide wheel, 215. stress control container, 217. clamp, 218. silicone oil, 219. rubber tube DETAILED DESCRIPTION

[0031] 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.

[0032] like Figure 1 As shown, the vertical variable shear force direct shear creep instrument of the present invention includes an instrument platform 108, a shear box, a dial indicator 102 and a pressurization system.

[0033] The instrument table 108 is provided with a vertical baffle 101, and the table surface near the vertical baffle has a through hole running through it from top to bottom. The instrument table surface is supported by four legs to maintain horizontality and be perpendicular to the vertical baffle. The dial of the dial indicator 102 is fixed on the vertical baffle, and the spring contact head of the dial indicator contacts the top of the shear box.

[0034] The shear box is composed of a first box body 104 and a second box body 103, which are used to hold the inner cavity of the soil sample. The first box body 104 is an annular shell with two open ends. The first box body is placed on the instrument table so that one open end is connected to the opening of the second box body on its right side, and the other open end is closed by a pressure cover on the left side that is pulled by the steel strand 107. The open end of the second box body is connected to the first box body, and the closed end opposite to the open end is provided with a pulley block and a vertical baffle for sliding contact. A detachable axial connecting bolt 114 is provided between the first box body and the second box body. When the axial connecting bolt is removed, the second box body can slide down relative to the first box body under the action of force. The pressure cover extends to both sides to form an extended end, and each extended end is connected to the head end of the steel strand on the same side.

[0035] The pressurization system includes a horizontal axial pressure weight system and a vertical shear force weight system. The horizontal axial pressure weight system includes a fixed pulley 112, a steel hinge 107, a first weight group 109 and a lever 113 mounted on the side of the instrument table. In this example, the lever 113 is a U-shaped lever consisting of two longitudinal rods 113.1 and a cross bar 113.2 connected between the ends of the two longitudinal rods. The head end of the longitudinal rod 113.1 is hinged to the instrument table as the fulcrum of the lever. The first weight group 109 is suspended at the midpoint of the cross bar 113.2. The head end of the steel hinge is connected to the extended end of the pressure cover, and the end is connected to the rod body of the lever 113 after passing the fixed pulley 112. The length of the extended ends on both sides of the pressure cover is equivalent to the distance between the fixed pulleys 105 on both sides of the baffle, and is greater than the width of the shear box body.

[0036] Of course, the present invention can also eliminate the lever and connect the first weight set directly to the end of the steel hinge wire.

[0037] The vertical shear force weight system includes a suspension rod 103.1 fixed to the lower bottom surface of the second box body and passing through the perforation of the instrument table top, and a second weight group 110 suspended at the bottom of the suspension rod. The second weight group 110 is placed in a weight container 212, and the weight container 212 is placed in a liquid container 213. A plurality of guide wheels 214 are evenly distributed on the upper part of the outer wall of the weight container. The guide wheels are in rolling contact with the inner wall of the liquid container to limit the weight container to remain upright during the floating and sinking process. The liquid contained in the container for providing buoyancy can be water or other reagents, but it is advisable to use a liquid with low volatility or adopt measures to reduce volatility. Silicone oil 218 is selected in this example. The bottom of the liquid container 213 is connected in series with multiple stress control containers 215 through a rubber tube 219. Clips for cutting and connecting are provided between adjacent stress control containers 215 and between the liquid container 213 and the stress control container 215. When the clips are clamped or loosened, the connection between the liquid container and each stress control container will be changed.

[0038] like Figure 4 As shown in the figure, the second weight, weight container, liquid container and stress control container are connected, and the second weight is hung at the bottom of the hanging rod 103.1. If the soil sample shear box uses a square soil sample shear box, the effective shear area is linearly reduced and does not need to be simplified. The shear box is square, 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,

[0039] 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, in a shear stress creep test, an S 有效 To ensure that the shear stress remains constant during the shear test.

[0040] 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.

[0041] 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

[0042]

[0043] S 砝 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.

[0044] The implementation steps of the present invention are as follows:

[0045] 1) Determine the bottom area of ​​each stress control container: According to the shear stress required by the experiment, 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 ), L is the side length of the square shear box perpendicular to the shear direction in the creep test, ), 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.

[0046] 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 width of the shear box 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.

[0047] Table 1

[0048]

[0049]

[0050] From this, it can be calculated that the inner bottom area used by each stress control container is shown in Table 2:

[0051] Table 2

[0052]

[0053] 2) Connect stress control containers: According to the shear stress required by the experiment, connect each stress control container and the liquid container in series from large to small.

[0054] 3) Sampling: Place the soil sample into the shear box and apply the corresponding axial pressure.

[0055] 4) Fill with silicone oil: Place the weight container in the liquid container, pour the silicone oil into the liquid container, and check whether the stress control containers are connected and whether the silicone oil flows in.

[0056] 5) Loading: Place weights in the weight container to load and conduct creep test.

[0057] 6) Record: Record the shear deformation within the corresponding time according to the test requirements.

[0058] For example, when conducting a 50 kPa shear stress test, S 有效 =S 液 +S 控制 =1700+1589.5=3289.5, which satisfies When conducting the 100 kPa shear stress test, clamp the outermost stress control container 215.6 with a clamp to interrupt its connection. At this time, S 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 vertical variable shear force direct shear creep instrument, characterized in that include: Instrument table, shear box, dial indicator and pressurization system, The instrument table is provided with a vertical baffle, and the table near the vertical baffle has a through hole that runs through the table from top to bottom. The shear box is composed of a first box body and a second box body, and is used to hold an inner cavity of a soil sample. The first box body is an annular shell with two open ends. The first box body is placed on the table of an instrument so that one open end is connected to the opening of the second box body, and the other open end is closed by a pressure cover pulled by a steel hinge wire. The open end of the second box body is connected to the first box body, and a pulley block is provided at the closed end opposite to the open end to slide in contact with a vertical baffle. A detachable axial connecting bolt is provided between the first box body and the second box body. When the axial connecting bolt is removed, the second box body can slide down relative to the first box body under the action of force. The dial of the dial indicator is relatively fixedly connected to the instrument table, and the spring contact head of the dial indicator contacts the top of the second box body. The pressurization system includes a horizontal axial pressure weight system and a vertical shear force weight system. The horizontal axial pressure weight system includes a fixed pulley mounted on the instrument table, a steel hinge wire that is fixedly connected to the pressure cover and then passes around the fixed pulley and hangs down, and a first weight group that is directly or indirectly connected to the hanging end of the steel hinge wire; the vertical shear force weight system includes a hanging rod that is fixed to the bottom surface of the second box body and passes through the perforated hole on the instrument table surface, and a second weight group that is hung at the bottom of the hanging rod; the second box body slides down relative to the first box body under the action of gravity and the second weight group. The second weight group is placed in a weight container, and the weight container is placed in a liquid container and remains upright to float and sink under the buoyancy of the liquid in the 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 remain upright during the floating and sinking process. The bottom of the liquid container is connected in series with a 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. By changing the cutting or connecting state of the mechanism, 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 砝 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.

2. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: The horizontal axial pressure weight system also includes a lever, the fulcrum of the lever is hinged to the side of the instrument table, the end of the steel hinge is fixedly connected to the lever body, and the first weight group is suspended at one end of the lever away from the fulcrum.

3. The vertical variable shear force direct shear creep instrument according to claim 2, characterized in that: The lever is a U-shaped lever consisting of two longitudinal bars and a cross bar connected between the ends of the two longitudinal bars. The head end of the longitudinal bar is hinged to the side of the instrument table, and the first weight group is suspended in the middle of the cross bar.

4. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: 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.

5. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: The liquid contained in the liquid container is silicone oil.

6. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: The pressure cover extends to both sides to form extended ends, each extended end is connected to the head end of the steel strand on the same side, and the end of the steel strand is connected to the two longitudinal rod bodies of the lever.

7. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: The instrument table top is supported by four legs, kept horizontal, and perpendicular to the upright baffle.

8. The vertical variable shear force direct shear creep instrument according to claim 1, characterized in that: The dial of the dial indicator is fixed on the upright baffle.

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