AU2021101004A4 - Tensile-shear tester for frozen soil - Google Patents

Abstract

The invention discloses a tensile-shear tester for frozen soil, which relates to the technical field of civil engineering and comprises a low-temperature test cover and an internal loading device, wherein the loading device is provided with a drawing clamp and a shearing clamp; Sample 1 and sample 2 both include frozen soil samples and concrete structural blocks in surface contact, and a horizontal tensile force perpendicular to the contact surface between frozen soil samples and concrete structural blocks is applied to sample 1 in the drawing fixture by a loading device to complete the drawing test for measuring the tensile strength of the interface area between frozen soil and solid structures,The shear test for measuring the shear strength of the interface area between frozen soil and solid structure is completed by applying the pressure perpendicular to the interface between frozen soil sample and concrete structure block and the horizontal shear force parallel to the interface between frozen soil sample and concrete structure block to the sample 2 in the shear fixture through the loading device. According to the invention, a low-temperature environment is provided by the low-temperature test cover, so that tensile and shear tests can be completed in a small operating space, and the mechanical behavior of a contact surface between frozen soil and a solid structure can be accurately simulated. 136 20 52 5 51 51 12 8 9 11 14 15 4147 4 4445 4842 4 Figure 1 7 41 47 1 2 48 52 3 \FT 42 431 70 432 Figure 2 43 2 431 42 51 104 o ooD 3 47 70 44 45 46 4849 10

Description

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Tensile-shear tester for frozen soil

Field of technology

The invention relates to the technical field of civil engineering tests, in particular to a frozen soil tensile-shear tester.

Background art

Tensile test and shear test of soil at normal temperature study the tensile strength and shear strength of soil, while the mechanical properties of the interface between frozen soil and solid structure are very complex, and the tensile and shear strength are the main reasons that affect the foundation freezing and overturning of solid structure in frozen soil area.

At present, the conventional geotechnical test equipment is not suitable in low temperature environment. Most of the existing tensile strength test equipment adopts vertical tension, and there is a certain deviation of tensile strength due to the dead weight of the sample. Moreover, the tensile experimental devices of soil sample layer are all modified from other experimental devices. If used in low temperature environment, they often face problems such as limited operating space, high cost and difficult control of precision, which greatly limits the operational range of the test; Furthermore, the tensile strength and shear strength tests are realized by using different test equipment, which has large capital investment, large occupied space and tedious operation. Therefore, it is urgent to develop a test device which is suitable for integrating tensile and shear strength of soil and solid structures in low temperature environment, which can improve the accuracy of tensile strength test.

Summary of the invention

The technical problem to be solved by the present invention is to provide a frozen soil tensile shear tester, which can measure both the tensile strength and the shear strength of the contact surface between frozen soil samples and solid structures, and has low manufacturing cost and can complete tensile strength and shear strength tests in a small operating space.

To solve the above technical problems, the technical scheme adopted by the invention is as follows:

A tensile shear tester for frozen soil comprises a low-temperature test cover and a loading device in the low-temperature test cover, wherein the loading device is provided with a drawing clamp for clamping a sample I and a shearing clamp for clamping a sample II; The first sample and the second sample both comprise frozen soil samples and concrete structural blocks which are in surface contact, and a horizontal tensile force is applied to the first sample in the drawing fixture through a loading device, and the applied tensile force is perpendicular to the contact surface between the frozen soil samples and the concrete structural blocks, so as to complete the drawing test for measuring the tensile strength of the interface area between the frozen soil and the solid structure; The loading device applies vertical pressure and horizontal shear force to the second sample in the shear fixture, the applied pressure is perpendicular to the contact surface between frozen soil sample and concrete structure block, and the applied shear force is parallel to the contact surface between frozen soil sample and concrete structure block, so as to complete the shear test for measuring the shear strength of the interface area between frozen soil and solid structure.

Preferably, the low-temperature test cover comprises a base, a hollow shell and an inner liner, wherein the shell is arranged on the base, and one end of the shell is rotatably connected with one end of the base for opening the shell to install a first sample and a second sample; The liner is arranged on the inner wall of the shell, and a refrigeration pipe connected with refrigeration equipment is arranged in the shell.

Preferably, the loading device comprises a horizontal counterforce frame, a vertical counterforce frame, a vertical loading mechanism and a horizontal loading mechanism, wherein the horizontal loading mechanism, the drawing fixture and the shearing fixture are all arranged on the horizontal counterforce frame; The applied end of the horizontal loading mechanism is provided with a displacement sensor and a horizontal load sensor; the horizontal loading mechanism is connected with a drawing clamp and a shearing clamp through a force applying frame; and the applied end of the vertical loading mechanism is connected with the shearing clamp through a vertical load sensor.

Preferably, the base is provided with a linear guide rail, and the horizontal reaction frame, the drawing fixture and the shearing fixture are all matched with the linear guide rail through a slider; The horizontal counterforce frame comprises a front counterforce beam, a force applying frame, a rear counterforce beam and a pull rod, wherein the force applying frame comprises a fixed clamp block, a moving clamp block, a push rod, a drawing push plate and a shearing push plate; Two ends of the pull rods are respectively connected with a front reaction beam and a rear reaction beam; the fixed clamping block and the mobile clamping block are arranged in parallel; more than two pull rods are symmetrically arranged at two sides of the mobile clamping block; The drawing fixture is arranged in the middle of thefixed clamping block and the movable clamping block; The horizontal loading mechanism is fixed on the front reaction beam, the loading end of the horizontal loading mechanism is connected with the drawing push plate through a displacement sensor, and there are two push rods which respectively penetrate through both sides of the fixed clamp block, one end of the push rod is connected with the drawing push plate, the other end penetrates through the moving clamp block and is connected with the shearing push plate, and the push rod is fixedly connected with the moving clamp block and used for applying horizontal tension to the first sample in the drawing clamp; And the shear push plate is connected with the shear clamp through a horizontal ejector rod and used for applying a horizontal shear force to the sample 2 in the shear clamp.

Preferably, the drawing jig has a split structure, including a fixed part and a movable part at the top, wherein both sides of the fixed part are respectively fixedly connected with the left and right halves of the fixed and mobile blocks, and both sides of the movable part are respectively slidably connected with the left and right halves of the fixed and mobile blocks; The middle parts of the fixed part and the movable part are provided with horizontally penetrating through holes for accommodating the first sample; The first sample has a dumbbell-shaped structure with two large ends and a small middle, and the matching surface between the frozen soil sample and the concrete structure block of the first sample is the vertical plane in the middle. Among them, the sample preparation device used for manufacturing sample 1 comprises two semicircular hoops, the mating surfaces of the two semicircular hoops are connected by bolts, a rib is arranged in the middle of the inner holes of the two semicircular hoops, and symmetrical taper holes are arranged on both sides of the rib.

Furthermore, both sides of the fixed part and the movable part are provided with vertical clamping grooves, and the inner sides of the left half and the right half of the fixed clamping block and the moving clamping block are provided with protrusions matched with the clamping grooves.

Preferably, the shearing fixture comprises a lower shearing box and an upper shearing box, wherein the inner cavity enclosed by the lower shearing box and the upper shearing box contains a sample 2, the matching surface of frozen soil sample and concrete structure block of the sample 2 is located at the gap between the lower shearing box and the upper shearing box, and the force applying end of the horizontal loading mechanism abuts against the side surface of the lower shearing box; A pressure plate is arranged on the top of the sample 2 in the upper shear box, and the force applying end of the vertical loading mechanism abuts against the pressure plate through an axial compression bar.

Preferably, the lower shearing box and its internal sample 2 are arranged in a pressure chamber connected with an air pressure system, the lower shearing box is arranged on a shearing bottom plate, a through hole matched with a push rod is arranged on the side wall of the pressure chamber, and the push rod is in sealing fit with the through hole; The side wall of the upper shearing box is provided with a convex eaves which is hermetically connected with the top of the side wall of the pressure chamber, the edge of the convex eaves protrudes out of the side wall of the pressure chamber, and four corners of the convex eaves are connected with four corners of the bottom plate of the pressure chamber through upright posts; The top of the upper shearing box is hermetically connected with the upper cover, and the axial compression bar penetrates through the middle part of the upper cover and is hermetically matched with the upper cover.

Preferably, a roller plate is arranged between the shear bottom plate and the pressure chamber bottom plate, the pressure chamber is cylindrical, and the upper shear box, the lower shear box and the internal sample 2 are all rectangular parallelepiped structures; Limit bearings are arranged between the outer walls on both sides of the lower shear box adjacent to the ejector rod and the side walls of the pressure chamber.

Preferably, the air pressure system comprises an air inlet pipe communicated with the pressure chamber, the air inlet pipe is connected with a buffer tank, and the air inlet pipe is provided with a pressure reducing valve and an electromagnetic valve; The buffer tank is arranged in a low temperature chamber, and the air compressor is connected with the buffer tank through an air outlet pipe.

Preferably, the bottom of the base is provided with a roller, and the side wall of the shell is provided with an observation window for observing the motion state during the tension-shear test.

Compared with the prior art, the invention provides a low-temperature environment for the first sample and the second sample in the low-temperature test cover, and utilizes the loading device to apply a horizontal pulling force to the first sample in the drawing fixture to complete the drawing test for measuring the tensile strength of the interface area between frozen soil and solid structure; Apply vertical pressure and horizontal shear force to sample 2 in the shear fixture to complete the shear test for measuring the shear strength of the interface area between frozen soil and solid structure. The invention has the advantages of simple structure, low cost and high precision, can complete tensile and shear strength tests in a small operating space, and can accurately simulate the mechanical behavior of the contact surface between frozen soil and solid structures. The method provides data support for the research of freezing and pulling the foundation of solid structures in frozen soil areas.

Brief description of drawings

Fig,1 is a structural schematic diagram of a tensile-shear tester for frozen soil provided by an embodiment of the present invention;

Fig,2 is a top view of the loading device in fig,1;

Fig,3 is a schematic diagram showing the arrangement of the drawing jig and the shearing jig in fig,2 on the horizontal reaction frame;

Fig,4 is a left side view of the fixing block in fig,3;

Fig,5 is a sectional view taken along line B-B in fig,4;

Fig,6 is a schematic structural diagram of the drawing jig of the present invention;

Fig,7 is an exploded schematic diagram of a sample maker for making sample 1;

Fig,8 is a structural schematic diagram of the shearing jig in fig,1;

Fig,9 is a sectional view taken along A-A in fig,8;

Fig,10 is an outline view of the tensile-shear tester for frozen soil provided by another embodiment of the present invention;

In the drawing: 001- concrete structure block, 002- frozen soil sample, 003- semicircular hoop, 004- rib; 01- sample 1, 02- sample 2;

1- low temperature test cover, 11- base, 12- shell, 13- refrigeration pipe, 14- linear guide rail, - slider, 16- roller, 17- observation window, 18- leg, 19- handle, 20- lining;

2- Drawing fixture, 21- Fixed part, 22- Moving part, 23- Clamping groove;

3- shear fixture, 30- convex eaves, 31- lower shear box, 32- upper shear box, 33- pressure plate, 34- axial compression bar, 35- shear bottom plate, 36- upright post, 37- force applying block and 38- top block;

4- Horizontal counterforce frame, 41- Front counterforce beam, 42- Rear counterforce beam, 43- Pull rod, 44- Fixed block, 45- Moving block, 46- Push rod, 47- Pulling push plate, 48- Shear push plate and 49- Ejector rod;

5- Vertical reaction frame, 51- pillar, 52-beam;

6- Vertical loading mechanism; 7- horizontal loading mechanism, 70- horizontal load sensor; 8- Displacement sensor; 9- Vertical load sensor;

10- pressure chamber, 101- pressure chamber bottom plate, 102- upper cover, 103- roller plate, 104- limit bearing.

Detailed description of the invention

In order to make the object, technical scheme and advantages of the present invention clearer, the present invention will be further explained in detail with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

As shown in figs,1 and 2, a frozen soil tensile-shear tester provided by an embodiment of the present invention includes a low-temperature test cover 1 and its internal loading device, and the loading device is provided with a drawing jig 2 for holding a sample 1 01 and a shearing jig 3 for holding a sample 2 02; The first sample 01 and the second sample 02 both include a frozen soil sample 002 and a concrete structure block 001 which are in surface contact, and a horizontal tensile force is applied to the first sample 01 in the drawing fixture 2 through a loading device, and the applied tensile force is perpendicular to the contact surface between the frozen soil sample 002 and the concrete structure block 001, so as to complete the drawing test for measuring the tensile strength of the interface area between the frozen soil and the solid structure; The loading device applies vertical pressure and horizontal shear force to the sample 2 02 in the shear fixture 3,The applied pressure is perpendicular to the contact surface between the frozen soil sample 002 and the concrete structure block 001, and the applied shear force is parallel to the contact surface between the frozen soil sample 002 and the concrete structure block 001, so as to complete the shear test for measuring the shear strength of the interface area between the frozen soil and the solid structure. The low temperature environment is provided by means of the low temperature test cover, and the tensile strength pull-out test and shear strength shear test of the interface zone between frozen soil and solid structure in the low temperature environment are realized by the loading device, which provides data support for the frozen pull-out research of solid structure foundation in frozen soil area.

In a specific embodiment of the present invention, as shown in figs,1 and 2, the low temperature test cover 1 comprises a base 11, a hollow shell 12 and an inner liner, wherein the shell 12 is arranged on the base 11, and one end of the shell 12 is rotatably connected with one end of the base 11 for opening the shell 12 to install a sample 1 01 and a sample 2 02; The liner is arranged on the inner wall of the shell 12, and a refrigeration pipe 13 connected with refrigeration equipment is arranged in the shell 12 .

In a specific embodiment of the present invention, as shown in figs,1 and 2, the loading device includes a horizontal reaction frame 4, a vertical reaction frame 5, a vertical loading mechanism 6 and a horizontal loading mechanism 7,The horizontal loading mechanism 7, the drawing jig 2 and the shearing jig 3 are all arranged on the horizontal reaction frame 4, the vertical reaction frame 5 is arranged outside the shearing jig 3, and the vertical loading mechanism 6 is arranged on the vertical reaction frame 5 for applying pressure to the sample 2 02 in the shearing jig 3 A displacement sensor 8 and a horizontal load sensor 70 are arranged at the applied end of the horizontal loading mechanism 7,The horizontal loading mechanism 7 is connected with the drawing jig 2 and the shearing jig 3 through a force applying frame, and the applied end of the vertical loading mechanism 6 is connected with the shearing jig 3 through a vertical load sensor 9 . Among them, the vertical counterforce frame includes struts on both sides of the shear fixture and beams on the tops of the two struts, and the struts on both sides are inclined relative to the shearfixture, which is convenient for installing sample 2 . The horizontal reaction force during drawing test is provided by the horizontal reaction frame, and the horizontal tensile force applied to the first sample and the horizontal shear force applied to the second sample are controlled by the horizontal load sensor. The vertical reaction force during the direct shear test is supported by the vertical reaction frame, and the vertical pressure exerted on the second sample is controlled by the vertical load sensor.

In a specific embodiment of the present invention, as shown in figs,1-3, the base 11 is provided with a linear guide rail 14, and the horizontal reaction frame 4, the drawing jig 2 and the shearing jig 3 are all matched with the linear guide rail 14 through a slider 15; The horizontal reaction frame 4 comprises a front reaction beam 41, a force applying frame, a rear reaction beam 42 and a pull rod 43, wherein the force applying frame comprises a fixed block 44, a moving block , a push rod 46, a drawing push plate 47 and a shearing push plate 48; There are more than two pull rods 43, both ends of which are respectively connected with the front reaction beam 41 and the rear reaction beam 42; the fixed block 44 is arranged in parallel with the moving block 45; more than two pull rods 43 are symmetrically arranged on both sides of the moving block 45; the fixed block 44 penetrates through the pull rods 43 and can be fixed on the pull rods 43; The drawing jig 2 is arranged in the middle of the fixed block 44 and the moving block 45. The horizontal loading mechanism 7 is fixed on the front reaction beam 41, and the loading end of the horizontal loading mechanism 7 is connected with a drawing push plate 47 through a displacement sensor 8,There are two push rods 46, which respectively penetrate through both sides of the fixed clamp block 44. One end of the push rod 46 is connected with the drawing push plate 47, and the other end is connected with the shearing push plate 48 through the moving clamp block 45. The push rod 46 is fixedly connected with the moving clamp block 45, and is used for testing the first sample in the drawing fixture 2 The shear push plate 48 is connected with the shear clamp 3 through a horizontal ejector pin 49, and is used for applying a horizontal shear force to the sample 2 02 in the shear clamp 3 .

Among them, there are two linear guides 14, which are arranged in parallel on the base 11. The shearing jig 3 is matched with two linear guides 14 through two sliders 15, and the two sliders bear the loading force when loading vertically. The remaining sliders 15 are used to install and fix the front reaction beam 41, the rear reaction beam 42 and the drawing jig 2. A single slider 15 can bear a maximum load of 16.97KN, and the combined maximum bearing capacity of the two sliders 15 can reach about 34KN. The shearing fixture 3, the front reaction beam 41 and the rear reaction beam 42 are all fixed with the slide block 15 on the linear guide rail 14 by screws, and the horizontal reaction frame 4 can move freely on the linear guide rail 14, and is fixed with screws after the position is adjusted.

The tie rod 43 has a split structure, including a front tie rod 431 and a rear tie rod 432,As shown in Figure 2, one end of the front tie rod 431 is connected with the front reaction beam 41 and the other end is connected with the fixed block 44, while the other end of the rear tie rod 432 is connected with the rear reaction beam 42 .

Further optimizing the above technical scheme, as shown in fig,4-6, the drawing jig 2 has a split structure, including a fixed part 21 and a movable part 22 on its top, both sides of the fixed part 21 are respectively connected with the left and right halves of the fixed and movable blocks 44 and , and both sides of the movable part 22 are respectively connected with the left of the fixed and movable blocks 44 and 45,The middle parts of the fixed part 21 and the movable part 22 are provided with horizontal through holes for accommodating the first sample 01,The first sample 01 is a dumbbell-shaped structure with large ends and small middle, and the mating surface between the frozen soil sample 002 of the first sample 01 and the concrete structure block 001 is the vertical plane in its middle. The two sides of the fixed part 21 and the movable part 22 are provided with vertical clamping grooves 23, and the inner sides of the left half and the right half of the fixed clamping block 44 and the moving clamping block 45 are provided with protrusions matching with the clamping grooves. The drawing jig 2 adopts a split structure with an inner circle and an outer circle, and two half rings of the fixed part 21 and the movable part 22 are connected into a whole by screws. The clamping grooves 23 and threaded holes on both sides are used for connecting with the fixed clamping block and the sliding clamping block. The fixed part 21, as the lower die, is connected with the slider 15 on the linear guide rail 14 at the same time, so as to ensure that no deflection occurs during the drawing test. When installing the sample 1 01, only the movable part 22, as the upper die, can be taken out, and the lower die can be fixed.

As shown in fig,7, the sample maker for manufacturing sample 101 includes two semicircular hoops 003, the mating surfaces of the two semicircular hoops 003 are connected by bolts, a rib 004 is arranged in the middle of the inner hole of the two semicircular hoops 003, and both sides of the rib 004 are symmetrical taper holes.

During the drawing test, the slots 23 at both ends of the drawing jig 2 are respectively clamped on the fixed clamp block 44 and the movable clamp block 45,Under the push of the horizontal loading mechanism 7, the drawing push plate 47, push rod 46 and the movable clamp block 45 move along the linear guide rail 14, and the distance between the fixed clamp block 44 and the movable clamp block 45 increases. Under the action of the drawing jig 2, the sample 1 01 is stretched to both ends until it is destroyed. At this time, the front reaction beam 41, the front pull rod 421 and the fixing block 44 bear the reaction force when the sample 1 01 is drawn.

The shear push plate 48 is connected with the moving block 45. During the shear test, the shear push plate 48 applies horizontal shear force to the lower shear box 31. At this time, the front reaction beam 41, the front and rear tie rods 43, and the rear reaction beam 42 bear the shear reaction force. Two sides of the fixing block 44 are provided with threaded holes, and the front pull rod 431 and the rear pull rod 432 are connected into a whole through threaded connection.

In a specific embodiment of the present invention, as shown in figs,1, 8, and 9, the shear clamp 3 includes a lower shear box 31 and an upper shear box 32, wherein the inner cavity enclosed by the lower shear box 31 and the upper shear box 32 contains a sample 2 02, and the mating surface between the frozen soil sample 002 of the sample 2 02 and the concrete structural block 001 is located at the gap between the lower shear box 31 and the upper shear box 32 A pressure plate 33 is arranged on the top of the sample 2 02 in the upper shear box 32, and the pressing end of the vertical loading mechanism 6 abuts against the pressure plate 33 through an axial pressing rod 34

. The edge of the lower shearing box 31 is provided with a protruding force applying block 37 for abutting against the end of the ejector rod 49 . The other side of the lower shearing box 31 is provided with a top block 38 corresponding to the force applying block 37, so as to limit the shearing jig 3 . The gap between the lower shear box 31 and the upper shear box 32 is 10mm, and there are no obstructions on both sides, which is convenient for observing and recording images. The theoretical center line of the horizontal thrust exerted by the ejector rod 49 coincides with the center line of the shear seam of sample 2 02. The size of the upper pressing plate 33 is slightly smaller than that of the second sample 02, and the vertical normal force is directly loaded on the surface of the second sample 02,In order to prevent the upper shear box 32 from falling, screw holes can be machined on the side surface of the top block 38 to facilitate connection with the rear reaction beam 42 . When installing sample 2 02, the rear reaction frame 42 needs to be dragged out to one end; Two ends of the linear guide rail 14 are respectively provided with limiting blocks for positioning and preventing the sliding block 15 from sliding out.

Further optimizing the above technical scheme, as shown in fig,8, the lower shear box 31 and its internal sample 2 02 are arranged in the pressure chamber 10 connected with the pneumatic system, the lower shear box 31 is arranged on the shear bottom plate 35, and the side wall of the pressure chamber 10 is provided with a through hole matched with the ejector rod 49, and the ejector rod 49 is hermetically matched with the through hole; The side wall of the upper shearing box 32 is provided with a flange 30 which is hermetically connected with the top of the side wall of the pressure chamber 10, the edge of the flange 30 protrudes out of the side wall of the pressure chamber 10, and four corners of the flange 30 are connected with four corners of the pressure chamber bottom plate 101 through columns 36,The top of the upper shearing box 32 is hermetically connected with the upper cover 102, and the axial pressing rod 34 penetrates through the middle of the upper cover 102, and the axial pressing rod 34 is hermetically matched with the upper cover 102 . The vertical column 36 plays a limiting role on the shear bottom plate 35 to prevent the lower shear box 31 from twisting. The matching surface between frozen soil sample 002 and concrete structure block 001 in the lower shear box 31 and the upper shear box 32 is in the gap between them, which leads to a part of soil in free exposed state. At present, the shear test of exposed part of soil is carried out, and the exposed free soil is not stressed. It is quite different from the ordinary direct shear test in which the whole soil is in a shear box, so the pressure chamber can provide a confining pressure system, which can make the exposed free soil stress variable, which is more in line with the actual situation and can meet more demands.

In a specific embodiment of the present invention, as shown in fig,8, a roller plate 103 is arranged between the shear bottom plate 35 and the pressure chamber bottom plate 101, the pressure chamber 10 is cylindrical, and the upper shear box 32, the lower shear box 31 and the internal sample 2 02 are all rectangular parallelepiped structures. The sample making box used to make sample 2 02 adopts assembled structure, and the side plates are bolted, which is convenient for disassembly and assembly. Limit bearings 104 are provided between the outer walls of both sides of the lower shear box 31 adjacent to the ejector rod 49 and the side walls of the pressure chamber 10 . The shear bottom plate 31 is further limited by the limit bearing 104, and the roller plate 103 is placed between the lower shear box 31 and the pressure chamber bottom plate 101 to reduce the friction resistance.

In a specific embodiment of the present invention, the air pressure system includes an air inlet pipe (not shown) communicating with the pressure chamber 10, which is connected with a buffer tank (not shown) and provided with a pressure reducing valve and an electromagnetic valve; The buffer tank is arranged in a low-temperature room (not shown in the figure), and the air compressor is connected with the buffer tank through an air outlet pipe. The pressure chamber 10 adopts a transparent plexiglass cylinder, which can be filled with high-pressure gas with a rated working pressure of IMPa, and the charging port is located at one side of the bottom plate of the pressure chamber. The normal-temperature air compressor is installed outside the low-temperature greenhouse, and the buffer tank is placed in a low-temperature environment. The pressure of the buffer tank is equal to that of the compressed air in the air compressor. If the pressure drops, the air compressor can make up the pressure automatically. The low-temperature and high-pressure gas in the buffer tank is charged into the pressure chamber after passing through the pressure reducing valve and electromagnetic valve. A digital pressure gauge is installed on the intake pipe, which can measure the gas pressure in the pressure chamber in real time. When the pressure is lower than the set lower limit, the electromagnetic valve opens and the high-pressure gas in the buffer tank is injected into the pressure chamber; When the air pressure in the pressure chamber is higher than the set upper limit, the electromagnetic valve is closed to maintain the air pressure; If the air pressure drops and the actual air pressure value is between the upper and lower limits, the solenoid valve will not act, and when it drops to the lower limit, the solenoid valve will open again to pressurize the pressure chamber. This repeated cycle keeps the air pressure in the pressure chamber fluctuating within a certain range. The controllable confining pressure system provided by this structure can not only meet the requirements of direct shear test, but also carry out shear test with changing confining pressure.

As shown in fig,10, the bottom of the base 11 is provided with a roller 16, which is convenient for moving the equipment to any working place. An observation window 17 is provided on the side wall of the housing 12 for observing the motion state during the tension-shear test. The observation window is rectangular, and is arranged corresponding to sample 2 . In addition, a leg 18 with a lifting structure is installed at the bottom of the base 11, which can be firmly fixed by the leg after moving in place.

The design parameters of the invention are as follows:

The horizontal loading mechanism and the vertical loading mechanism both adopt the screw loading mechanism, and the servo motor drives the screw to rotate through the reducer, thereby driving the nut on the screw to move, and the thrust cylinder connected with the nut realizes loading. The load of horizontal loading and vertical loading shall be controlled at 4kN; ; The measuring

range of the horizontal displacement sensor is 25.4mm, and the accuracy is 0.1%FS.

Both horizontal load sensor and vertical load sensor used for detecting axial load adopt S-type load sensor. The internal circuit structure of this sensor is strain-type full-bridge structure, which has high measurement accuracy and good stability, and is widely used for measurement at present.

LVDT displacement sensor is used as the displacement sensor, because the sensor works at low temperature for a long time, frost, condensation and icing will affect the sensor. In conventional integrated displacement sensor, electronic devices and mechanical devices are integrated, which has a great impact on the working reliability of electronic components, so MEAS split sensor is selected.

The specification of sample 1 is: the cones at both ends are 100mm x 50mm x5 degrees (small end x height x taper); Sample 2 has a specification of100x100x90 mm.

The temperature control range in the low temperature test enclosure is from normal temperature to MINUS 30°C.

During the concrete production, the low-temperature test cover is made of 304 stainless steel, the inner lining is made of thermal insulation material, the refrigeration pipe installed at the top is copper pipe, and the copper pipe is laid flat on the top of the inner wall of the low-temperature test cover by coil structure; The refrigerant liquid cools the air inside the low-temperature test cover after passing through the copper pipe. One end of the short side of the low-temperature test cover is connected with the base through a hinge, which can be turned over by about 90 degrees during the test, so as to facilitate the installation of sample 1 and sample 2 . At the same time, the low temperature test cover is equipped with an automatic constant temperature system, which can ensure the long-term stable operation of the equipment in the low-temperature environment of °C. The front end of the monitoring camera uses a low-temperature resistant Shi Ying lens to

block heat conduction, while the light transmission is required to ensure the light transmission of the camera. The internal use of a 2 million high-definition micro-focus camera ensures that the equipment can collect ultra-high-definition images within a visual range of 30-150mm (the images are clearer than those of conventional 2 million high-definition monitoring cameras).

The observation window is made of transparent plexiglass, with a thickness of about 40mm (if the thickness affects shooting, the double layer can be about 6mm, but the thermal insulation performance will be slightly reduced). The motion state during the shear test can be observed through the observation window, and the camera can also record the test process through the observation window. The surveillance camera can be used in low temperature environment after adopting thermal insulation design. Because the camera is in the ultra-low temperature environment of the low-temperature test chamber, the camera shell needs to be insulated at low temperature to effectively reduce the speed of heat conduction and heat exchange. At the same time, an automatic constant temperature system needs to be installed inside the equipment (constant temperature heating is started below 5C through sensor control, heating is turned off when it is higher than

°C, and the temperature of the heating device should be controlled at 60°C in consideration of local high temperature) to ensure the long-term stable operation of the equipment in the low temperature environment.

Because the inner space of the low temperature test cover is limited, it is necessary to make the overall size of the monitoring camera as small as possible. There is no light inside the test chamber and the distance from the monitoring camera is very close. The camera needs to install low-power adjustable diffuse reflection supplementary lighting to meet the experimental requirements. Use black and white images to improve contrast.

The horizontal load sensor, vertical load sensor, horizontal displacement sensor, pressure gauge, monitoring camera and temperature sensor in the low temperature test cover are all connected with the computer for data acquisition and data analysis.

To sum up, the method has the advantages of simple structure, low cost and high precision, and can accurately simulate the mechanical behavior of the contact surface between frozen soil and solid structures in a small operating space. The loading accuracy is improved by horizontal load sensor and vertical load sensor, and real-time detection is realized by horizontal displacement sensor. The low temperature environment is provided by using the low temperature test cover, and the test temperature is more strictly controlled; Combine the two functions of measuring the tensile strength and shear strength of the interface area between frozen soil and solid structure; The confining pressure system is simulated by the pressure chamber, so that it can meet the requirements of direct shear test and can also carry out shear test with changing confining pressure Compared with the general vertical tensile strength test device, the instrument can realize the transverse direct tensile test, and can effectively avoid the deviation of the measured tensile strength caused by the dead weight of the sample during vertical tensile test.

In this paper, a specific example is applied to illustrate the principle and implementation of the present invention, and the explanation of the above embodiments is only used to help understand the method and core idea of the present invention. It should be pointed out that, for those of ordinary skill in the technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (1)

1, A tensile-shear tester for frozen soil is characterized by comprising a low-temperature

test cover and a loading device in the low-temperature test cover, wherein the loading

device is provided with a drawing clamp for clamping a sample I and a shearing clamp

for clamping a sample II; The first sample and the second sample both comprise

frozen soil samples and concrete structural blocks which are in surface contact, and a

horizontal tensile force is applied to the first sample in the drawing fixture through a

loading device, and the applied tensile force is perpendicular to the contact surface

between the frozen soil samples and the concrete structural blocks, so as to complete

the drawing test for measuring the tensile strength of the interface area between the

frozen soil and the solid structure; The loading device applies vertical pressure and

horizontal shear force to the second sample in the shear fixture, the applied pressure is

perpendicular to the contact surface between frozen soil sample and concrete structure

block, and the applied shear force is parallel to the contact surface between frozen soil

sample and concrete structure block, so as to complete the shear test for measuring the

shear strength of the interface area between frozen soil and solid structure.

2, The tensile-shear tester for frozen soil according to claim 1, which is characterized in

that: the low-temperature test cover comprises a base, a hollow shell and an inner liner,

wherein the shell is arranged on the base, and one end of the shell is rotatably

connected with one end of the base for opening the shell to install sample 1 and

sample 2; The liner is arranged on the inner wall of the shell, and a refrigeration pipe

connected with refrigeration equipment is arranged in the shell.

3, The tensile-shear tester for frozen soil according to claim 2, characterized in that the

loading device comprises a horizontal counterforce frame, a vertical counterforce

frame, a vertical loading mechanism and a horizontal loading mechanism, wherein the

horizontal loading mechanism, the drawing fixture and the shearing fixture are all

arranged on the horizontal counterforce frame, the vertical counterforce frame is

arranged outside the shearing fixture, and the vertical loading mechanism is arranged on the vertical counterforce frame and used for exerting pressure on the second sample in the shearing fixture; The applied end of the horizontal loading mechanism is provided with a displacement sensor and a horizontal load sensor; the horizontal loading mechanism is connected with a drawing clamp and a shearing clamp through a force applying frame; and the applied end of the vertical loading mechanism is connected with the shearing clamp through a vertical load sensor.

4, The tensile-shear tester for frozen soil according to claim 3 is characterized in that a

linear guide rail is arranged on the base, and the horizontal reaction frame, the drawing

fixture and the shearing fixture are all matched with the linear guide rail through a

slider; The horizontal counterforce frame comprises a front counterforce beam, a force

applying frame, a rear counterforce beam and a pull rod, wherein the force applying

frame comprises a fixed clamp block, a moving clamp block, a push rod, a drawing

push plate and a shearing push plate; Two ends of the pull rods are respectively

connected with a front reaction beam and a rear reaction beam; thefixed clamping

block and the mobile clamping block are arranged in parallel; more than two pull rods

are symmetrically arranged at two sides of the mobile clamping block; The drawing

fixture is arranged in the middle of the fixed clamping block and the movable

clamping block; The horizontal loading mechanism is fixed on the front reaction beam,

the loading end of the horizontal loading mechanism is connected with the drawing

push plate through a displacement sensor, and there are two push rods which

respectively penetrate through both sides of the fixed clamp block, one end of the push

rod is connected with the drawing push plate, the other end penetrates through the

moving clamp block and is connected with the shearing push plate, and the push rod is

fixedly connected with the moving clamp block and used for applying horizontal

tension to the first sample in the drawing clamp; And the shear push plate is connected

with the shear clamp through a horizontal ejector rod and used for applying a

horizontal shear force to the sample 2 in the shear clamp.

, The tensile-shear tester for frozen soil according to claim 4, characterized in that: the

drawing fixture has a split structure, including a fixed part and a movable part at the

top, wherein both sides of the fixed part are respectively fixedly connected with the

left and right halves of the fixed and movable blocks, and both sides of the movable

part are respectively slidably connected with the left and right halves of the fixed and

movable blocks; The middle parts of the fixed part and the movable part are provided

with horizontally penetrating through holes for accommodating the first sample; The

first sample has a dumbbell-shaped structure with two large ends and a small middle,

and the matching surface between the frozen soil sample and the concrete structure

block of the first sample is the vertical plane in the middle.

6, The tensile-shear tester for frozen soil according to claim 4, characterized in that: the

shear clamp comprises a lower shear box and an upper shear box, wherein the inner

cavity enclosed by the lower shear box and the upper shear box contains sample 2, the

matching surface of frozen soil sample and concrete structure block of sample 2 is

located at the gap between the lower shear box and the upper shear box, and the

applied end of the horizontal loading mechanism abuts against the side surface of the

lower shear box; A pressure plate is arranged on the top of the sample 2 in the upper

shear box, and the force applying end of the vertical loading mechanism abuts against

the pressure plate through an axial compression bar.

7, The tensile-shear tester for frozen soil according to claim 6, which is characterized in

that the lower shear box and its internal sample 2 are arranged in a pressure chamber

connected with an air pressure system, the lower shear box is arranged on a shear

bottom plate, the side wall of the pressure chamber is provided with a through hole

matched with a push rod, and the push rod is hermetically matched with the through

hole; The side wall of the upper shearing box is provided with a convex eaves which is

hermetically connected with the top of the side wall of the pressure chamber, the edge

of the convex eaves protrudes out of the side wall of the pressure chamber, and four

comers of the convex eaves are connected with four corners of the bottom plate of the pressure chamber through upright posts; The top of the upper shearing box is hermetically connected with the upper cover, and the axial compression bar penetrates through the middle part of the upper cover and is hermetically matched with the upper cover.

8, The tensile-shear tester for frozen soil according to claim 7, characterized in that a

roller plate is arranged between the shear bottom plate and the pressure chamber

bottom plate, the pressure chamber is cylindrical, and the upper shear box, the lower

shear box and its internal sample 2 are all rectangular parallelepiped structures; Limit

bearings are arranged between the outer walls on both sides of the lower shear box

adjacent to the ejector rod and the side walls of the pressure chamber.

9, The tensile-shear tester for frozen soil according to claim 7, which is characterized in

that the air pressure system comprises an air inlet pipe communicated with the

pressure chamber, the air inlet pipe is connected with a buffer tank, and the air inlet

pipe is provided with a pressure reducing valve and an electromagnetic valve; The

buffer tank is arranged in a low temperature chamber, and the air compressor is

connected with the buffer tank through an air outlet pipe.

, The frozen soil tensile-shear tester according to any one of claims 2-9, which is

characterized in that a roller is arranged at the bottom of the base, and an observation

window is arranged on the side wall of the shell for observing the motion state during

the tensile-shear test.