CN212722332U

CN212722332U - Direct shear test device suitable for unsaturated expansive soil

Info

Publication number: CN212722332U
Application number: CN202021239863.1U
Authority: CN
Inventors: 姚永胜; 罗深平; 肖宏彬; 尹健; 李珍玉; 宁远思; 王聚山; 李涛; 谢江胜
Original assignee: Central South University of Forestry and Technology; China Railway 20th Bureau Group Corp; Chongqing Railway Hub East Ring Line Construction Headquarters of China Railway Chengdu Group Co Ltd
Current assignee: Central South University of Forestry and Technology; China Railway 20th Bureau Group Corp; Chongqing Railway Hub East Ring Line Construction Headquarters of China Railway Chengdu Group Co Ltd
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2021-03-16
Anticipated expiration: 2030-06-30

Abstract

The utility model provides a direct shear test device suitable for unsaturated expansive soil, which comprises a strain type direct shear system, a relative humidity control device, a rubber membrane and a data acquisition terminal; the strain type direct shearing system comprises an inner shearing box and an outer shearing box; the outer shearing box is arranged at the outer side of the inner shearing box; the rubber film is tightly wrapped outside the strain type direct shear system; the relative humidity control device comprises a hygrometer and a saturated saline solution container for containing saturated saline solutions of different types; the saturated saline solution container is oppositely and horizontally placed in a space formed by the outer side of the inner shearing box and the inner side of the outer shearing box. The utility model discloses a direct shear test device suitable for unsaturated swelling soil makes the unsaturated swelling soil shear strength parameter of survey after cuting, is the shear strength who records under "normal water content" condition, can accurately, objectively react the mechanical properties of unsaturated swelling soil, has actual engineering meaning.

Description

Direct shear test device suitable for unsaturated expansive soil

Technical Field

The utility model belongs to the technical field of geotechnical test measures, a direct shear test device suitable for unsaturated swelling soil is related to.

Background

The expansive soil is widely distributed in more than ten provinces and cities of China, and the characteristics of water loss shrinkage and water absorption expansion softening are difficult problems to be treated urgently during engineering construction. The existing geotechnical structures (such as railways, highways, dams and the like) built on expansive soil foundations have the engineering problems of structural instability and the like caused by softening and deformation of expansive soil, and the reason is mainly that under the action of natural environment, the water content in the expansive soil body tends to change continuously, so that the strength characteristic of the expansive soil body is influenced.

Shear strength is an important parameter for evaluating the strength characteristic of expansive soil, and the shear strength of a soil body is usually tested by a direct shear test. However, for unsaturated expansive soil, when the traditional direct shear test equipment is used for shearing, the moisture content of the shearing surface of the unsaturated expansive soil is in a constantly changing state, namely, the direct shear test is carried out under the condition of very high moisture content, and in order to enable the shear strength to be capable of accurately and objectively evaluating the strength characteristic of the unsaturated expansive soil, the direct shear test must be carried out under the condition of very high moisture content, so that the measured shear strength of the unsaturated expansive soil has reference significance and value.

To this technical problem who exists widely in unsaturated inflation soil mechanics category, the water content relatively stable of unsaturated inflation soil body is unchangeable even when realizing cuting, surveys unsaturated inflation soil's shear strength under "normal water content" condition, the utility model discloses a direct shear test device suitable for unsaturated inflation soil.

Disclosure of Invention

In order to achieve the above object, the utility model provides a direct shear test device suitable for unsaturated expansive soil has effectively, has reacted unsaturated expansive soil mechanics characteristic fast, with high accuracy, and the direct shear test of the unsaturated expansive soil who has solved the existence among the prior art is in the problem that shear strength can not be accurate, the unsaturated expansive soil mechanics characteristic of objective reaction that the condition leads to surveying is very "very water content".

The technical scheme adopted by the utility model is that the direct shear test device suitable for unsaturated expansive soil comprises a strain type direct shear system, a relative humidity control device, a rubber membrane and a data acquisition terminal; the strain type direct shearing system comprises an inner shearing box and an outer shearing box; the outer shearing box is arranged at the outer side of the inner shearing box; a loading block is horizontally arranged at the central position of the top of the internal shearing box; a stress meter is arranged at the upper end of the loading block; the lower end of the loading block is fixedly provided with an L-shaped steel sheet; one end of the L-shaped steel sheet is provided with a displacement sensor; the fixing ring is arranged on the outer side of the top end of the inner shearing box, and the inner diameter of the fixing ring is larger than the outer diameter of the inner shearing box; the rubber film is tightly wrapped outside the strain type direct shear system; the two fixing bolts are fixed on the inner shearing box through the rubber film and the fixing ring in sequence; the rubber membrane is fixed on the outer side of the outer shearing box through 3 sealing O-shaped rings; the relative humidity control device comprises a hygrometer, a first saturated salt solution container and a second saturated salt solution container, wherein the first saturated salt solution container and the second saturated salt solution container are used for containing different kinds of saturated salt solutions; the first saturated salt solution container and the second saturated salt solution container are oppositely and horizontally placed in a space formed by the outer side of the inner shearing box and the inner side of the outer shearing box.

Further, the displacement sensor is an LVDT sensor.

Further, the sealing "O" ring is circular in cross-section and 2.70mm in diameter.

Furthermore, the first saturated salt solution container and the second saturated salt solution container are both in a round table shape, the radius of the lower bottom is 50mm, the radius of the upper bottom is 100mm, and the height is 200 mm.

Further, a hygrometer was placed on the upper end of the first saturated salt solution container through a rubber membrane.

Further, the hygrometer is an RH390 high precision hygrometer.

Furthermore, the data acquisition terminal is respectively connected with the stress meter and the displacement sensor through data transmission lines and is used for automatically acquiring the data of the stress meter and the displacement sensor in the variable direct shear system in real time.

The utility model has the advantages that:

(1) the utility model discloses use the rubber mould closely to wrap up in the outside of STRAIGHT-SHEARING SYSTEM, can prevent interior shearing box, outer shearing box space and outside steam exchange that takes place, can make the inside waterproof airtight space of formation of STRAIGHT-SHEARING system, test the shear strength of soil sample promptly under "normal water content" condition.

(2) The utility model discloses an inside relative humidity of different saturated salt solution control enclosure makes the inside initial stage of enclosure form steam pressure differential to drive and carry out the aqueous vapor exchange cycle with unsaturated expansive soil sample, until reaching balanced state, thereby the water content and the suction of control unsaturated expansive soil sample combine the technological means who adopts "the rubber membrane closely wraps up", verify through the contrast test, its effect is superior to: only adopting a rubber film for tight wrapping; only a single saturated salt solution is adopted to control the relative humidity in the closed space; the test data can accurately and objectively reflect the mechanical characteristics of the unsaturated expansive soil sample.

(3) The utility model discloses a hygrometer reading is as the judgement foundation of experimental termination state, easy operation, after the hygrometer reading is stable, judges promptly in the box of shearing unsaturated expansive soil sample the water content have reached steady state, can terminate the experiment this moment and record stable water content to reach the direct shear test purpose of controlling unsaturated expansive soil sample for normal water content.

(4) The utility model is suitable for a direct shear test device of unsaturated swelling soil has cost economy, rational in infrastructure, preparation convenience, easy operation's advantage.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of the direct shear test device for unsaturated expansive soil of the present invention.

Fig. 2 is a schematic structural diagram of a relative humidity control device in a direct shear test device for unsaturated expansive soil of the present invention.

Fig. 3 is a schematic diagram of the position of the fixing ring in the direct shear test device for unsaturated expansive soil of the present invention.

In the figure: the system comprises a 1-strain type direct shear system, a 2-loading block, a 3- 'L' -shaped steel sheet, a 4-strain gauge, a 5-displacement sensor, a 6-inner shear box, a 7-outer shear box, an 8-relative humidity control device, a 9.1-first saturated salt solution container, a 9.2-second saturated salt solution container, a 10-hygrometer, an 11-fixing ring, a 12-sealing 'O' -shaped ring, a 13-rubber film, a 14-data acquisition terminal and a 15-fixing bolt.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

Referring to fig. 1-3, a direct shear test device suitable for unsaturated expansive soil comprises a strain type direct shear system 1, a relative humidity control device 8, a rubber membrane 13 and a data acquisition terminal 14; the strain type direct shear system 1 comprises a loading block 2, an L-shaped steel sheet 3, a strain gauge 4, a displacement sensor 5, an inner shear box 6, an outer shear box 7 and a fixing ring 11; the relative humidity control device 8 comprises a hygrometer 10, a first saturated saline solution container 9.1 and a second saturated saline solution container 9.2 for placing saturated saline solutions with different kinds; the first saturated salt solution container 9.1 and the second saturated salt solution container 9.2 are oppositely and horizontally placed in a space formed by the outer side of the inner shearing box 6 and the inner side of the outer shearing box 7; the outer cutting box 7 is arranged at the outer side of the inner cutting box 6; the loading block 2 is horizontally arranged at the center of the top of the inner shearing box 6; the upper end of the loading block 2 is provided with a stress meter 4; the lower end of the loading block 2 is fixedly provided with an L-shaped steel sheet 3, one end of the L-shaped steel sheet 3 is provided with a displacement sensor 5, and the displacement sensor 5 is used for measuring the overlying stress and the vertical displacement of the unsaturated expansive soil sample; the displacement of the L-shaped steel sheet 3 is consistent with that of the unsaturated expansive soil sample, the displacement sensor 5 can directly measure the displacement of the L-shaped steel sheet 3, rough errors and accidental errors which possibly exist in the process of directly measuring the displacement of the unsaturated expansive soil sample are avoided, and the L-shaped steel sheet 3 is of a rigid structure, so that the influence can be reduced, and the accuracy is improved; the stress meter 4 and the displacement sensor 5 are respectively connected with the data acquisition terminal 14 through data transmission lines; the fixing ring 11 is arranged on the outer side of the top end of the inner shearing box 6, and the inner diameter of the fixing ring 11 is slightly larger than the outer diameter of the inner shearing box 6; the rubber film 13 is tightly wrapped outside the strain type direct shear system 1, so that a watertight closed space is formed inside the strain type direct shear system 1; the two fixing bolts 15 are fixed on the inner shearing box 6 sequentially through the rubber membrane 13 and the fixing ring 11, the fixing bolts 15 are fixed at the two ends of the fixing ring 11 in the arrangement mode, the purpose is that the fixing rubber membrane 13 is not loosened in the test process, gaps are reserved at the rest positions, the rubber membrane 13 only isolates the inner shearing box from the outside, but the inner shearing box and the outer shearing box are still in an intercommunicated state due to the existence of the gaps, and therefore water and gas exchange between the inner shearing box and the outer shearing box can be achieved; the rubber membrane 13 is fixed on the outer side of the outer shear box 7 through 3 sealing O-shaped rings 12; the section of the sealing O-shaped ring 12 is circular, and the diameter is 2.70 mm; the rubber membrane 13 is provided with through holes corresponding to the positions where the stress meter 4, the displacement sensor 5 and the hygrometer 10 penetrate out, the diameter of each through hole is slightly smaller than that of the positions where the stress meter 4, the displacement sensor 5 and the hygrometer 10 penetrate out of the rubber membrane 13, the rubber membrane 13 can strain the through holes after the through holes are penetrated out, the sealing performance of the rubber membrane 13 is not affected, and rubber sealing rings can be sleeved on the outer sides of the through holes to achieve the sealing effect; wherein, the first saturated salt solution container 9.1 and the second saturated salt solution container 9.2 are both in a round table shape, the radius of the lower bottom is 50mm, the radius of the upper bottom is 100mm, and the height is 200 mm; the hygrometer 10 is arranged at the upper end of the first saturated salt solution container 9.1 through a rubber membrane 13; a small hole is formed in a rubber membrane 13 at the upper end of a first saturated salt solution container 9.1, the diameter of the small hole is slightly smaller than that of a probe of a hygrometer 10, the probe of the hygrometer 10 is inserted into the small hole, the rubber membrane 13 tensions the small hole, the rubber membrane 13 has light weight, the friction force of the rubber membrane 13 on the hygrometer 10 is enough to enable the hygrometer 10 to be clamped at a preset position, and a rubber sealing ring can be sleeved on the probe of the hygrometer 10 at the small hole; the data acquisition terminal 14 is respectively connected with the stress gauge 4 and the displacement sensor 5 through data transmission lines and is used for automatically acquiring the data of the stress gauge 4 and the displacement sensor 5 in the variable direct shear system 1 in real time.

Among them, the hygrometer 10 is preferably an RH390 high-precision hygrometer.

Among them, the displacement sensor 5 is preferably an LVDT sensor.

The utility model is suitable for a direct shear test device of unsaturated swelling soil includes following step during the implementation:

step S1, drying the unsaturated expansive soil sample according to the specification requirement, and preparing the soil sample; the inner cutting box 6, the outer cutting box 7, the first saturated saline solution container 9.1 and the second saturated saline solution container 9.2 are washed and wiped dry, and the permeable stone and the filter paper are prepared.

Step S2, a permeable stone is padded at the lower part of the inner shearing box 6, the unsaturated expansive soil sample is placed after the filter paper is placed, the filter paper and the permeable stone are sequentially placed above the soil sample, the loading block 2 is placed at the upper part of the uppermost permeable stone of the inner shearing box 6, and the position of the loading block 2 is kept to be right above the unsaturated expansive soil sample and horizontal;

step S3, installing a stress meter 4 at the upper end of the loading block 2; an L-shaped steel sheet 3 is fixedly arranged at the lower end of the loading block 2, and a displacement sensor 5 is arranged at one end of the L-shaped steel sheet 3 and used for measuring the overlying stress and the vertical displacement of the unsaturated expansive soil sample;

step S4, preparing two different kinds of saturated salt solutions according to the water content requirement of the test, respectively pouring the two different kinds of saturated salt solutions into a first saturated salt solution container 9.1 and a second saturated salt solution container 9.2, and respectively and horizontally placing the first saturated salt solution container 9.1 and the second saturated salt solution container 9.2 between the inner shearing box 6 and the outer shearing box 7 in an opposite direction;

step S5, arranging a fixing ring 11 at the outer side of the top end of the inner shearing box 6, wherein the inner diameter of the fixing ring 11 is slightly larger than the outer diameter of the inner shearing box 6; the rubber film 13 is tightly wrapped outside the strain type direct shear system 1, so that a watertight closed space is formed inside the strain type direct shear system 1; the two fixing bolts 15 are fixed on the inner shear box 6 sequentially through the rubber film 13 and the fixing ring 11; the rubber membrane 13 is fixed on the outer side of the outer shear box 7 through 3 sealing O-shaped rings 12; as shown in fig. 2, the relative humidity control device 8 was checked for tightness, and the rubber mold 13 and the inner shear box 6 were not loosened.

Step S6, switching on a power supply, calibrating the working state of the instrument, performing a pre-test, performing a direct shear test on the soil sample by using a loading device of the direct shear instrument, and ensuring that the data acquisition terminal 14 is in a normal tool state and the instrument displays normally; calibrating readings of the stress meter 4 and the displacement sensor 5; checking whether the value of the hygrometer 10 meets the humidity requirement for starting the test; starting an instrument, performing a pre-test, checking whether the rubber mold 13 is loosened in the test, and reinstalling and fixing the rubber mold if the rubber mold is loosened; checking the reading of the hygrometer 10 in the test process, and judging whether the pre-test result test is performed under the condition of constant water content;

step S7, after the instrument is checked and calibrated, performing formal test; starting the instrument, adjusting the shearing rate of a loading device of the direct shear instrument, checking whether the shearing rate of the data acquisition terminal 14 is consistent with the shearing rate set by the direct shear instrument, and if so, keeping the test to continue; when the reading of the hygrometer 10 is unchanged, the unsaturated expansive soil sample is judged to reach a stable state, at the moment, the curve trend of the data acquisition terminal 14 tends to be stable, and the test result is recorded, namely, a direct shear test of the soil sample is completed; and repeating the steps, and respectively applying different load pressures to the soil body according to the test types until the test is completed.

The utility model discloses when the direct shear test device of unsaturated expansive soil starts the initial stage, different kinds of saturated salt solution forms different vapor pressure in airtight space, two kinds of saturated salt solution constantly evaporate, vapor pressure after the evaporation has formed the pressure differential with vapor pressure after the moisture evaporation in the unsaturated expansive soil sample to promote multidirectional aqueous vapor circulation, such aqueous vapor circulation goes on always, reaches the circulation equilibrium state at last, can let the moisture evenly distributed of unsaturated expansive soil sample, reach "normal water content" condition. The utility model discloses a place different kinds of saturated salt solution, reach the control to unsaturated inflation soil sample moisture content, because the vapor pressure that different kinds of saturated salt solution correspond is different, can select saturated salt solution kind according to the demand. The two different kinds of saturated salt solutions can help to form a closed annular circulation, and the device space cannot be excessively occupied, so that the water-gas circulation is not influenced. The utility model discloses the mode of multidirectional aqueous vapor exchange can guarantee aqueous vapor removal rate, makes the aqueous vapor distribute evenly in whole airtight space, and the aqueous vapor circulation can reach balanced state fast, and the time that reaches the equilibrium than the mode of one-way aqueous vapor exchange reduces 10-15 days at least.

The utility model discloses a moisture content and relative humidity when unsaturated inflation soil sample reaches balance can be calculated to the demonstration reading of hygrometer 10, and this kind of water content and relative humidity when setting up the mode and simply, conveniently, show unsaturated inflation soil sample and reach balance directly perceivedly.

The utility model discloses make the shear strength parameter of the unsaturated expansive soil sample of survey after cuting, be the shear strength who records under "normal water content" condition, can accurately, objectively react the mechanical properties of unsaturated expansive soil, have actual engineering meaning. Overall, the utility model has the advantages of reasonable structure, convenient manufacture and simple operation.

It is to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. A direct shear test device suitable for unsaturated expansive soil is characterized by comprising a strain type direct shear system (1), a relative humidity control device (8), a rubber membrane (13) and a data acquisition terminal (14); the strain type direct shear system (1) comprises an inner shear box (6) and an outer shear box (7); the outer shearing box (7) is arranged on the outer side of the inner shearing box (6); the loading block (2) is horizontally placed at the center of the top of the inner shearing box (6); the upper end of the loading block (2) is provided with a stress meter (4); the lower end of the loading block (2) is fixedly provided with an L-shaped steel sheet (3); one end of the L-shaped steel sheet (3) is provided with a displacement sensor (5); the fixing ring (11) is arranged on the outer side of the top end of the inner shearing box (6), and the inner diameter of the fixing ring (11) is larger than the outer diameter of the inner shearing box (6); the rubber film (13) is tightly wrapped outside the strain type direct shear system (1); two fixing bolts (15) are fixed on the inner shearing box (6) through a rubber film (13) and a fixing ring (11) in sequence; the rubber membrane (13) is fixed on the outer side of the outer shearing box (7) through 3 sealing O-shaped rings (12); the relative humidity control device (8) comprises a hygrometer (10), a first saturated salt solution container (9.1) and a second saturated salt solution container (9.2) for placing different kinds of saturated salt solutions; the first saturated saline solution container (9.1) and the second saturated saline solution container (9.2) are oppositely and horizontally placed in a space formed by the outer side of the inner shearing box (6) and the inner side of the outer shearing box (7).

2. The direct shear test device for unsaturated expansive soil according to claim 1, wherein the displacement sensor (5) is an LVDT sensor.

3. A direct shear test device for unsaturated expansive soil according to claim 1, wherein the sealing "O" ring (12) is circular in cross-section and 2.70mm in diameter.

4. The direct shear test device suitable for unsaturated expansive soil according to claim 1, wherein the first saturated salt solution container (9.1) and the second saturated salt solution container (9.2) are both in a shape of a truncated cone, the radius of the lower bottom is 50mm, the radius of the upper bottom is 100mm, and the height is 200 mm.

5. A direct shear test apparatus for unsaturated expansive soil according to claim 1, wherein the hygrometer (10) is placed at the upper end of the first saturated salt solution container (9.1) through a rubber membrane (13).

6. The direct shear test device for unsaturated expansive soil according to claim 1 or 5, wherein the hygrometer (10) is an RH390 high precision hygrometer.

7. The direct shear test device suitable for unsaturated expansive soil according to claim 1, wherein the data acquisition terminal (14) is respectively connected with the stress gauge (4) and the displacement sensor (5) through data transmission lines, and is used for automatically acquiring data of the stress gauge (4) and the displacement sensor (5) in the variable direct shear system (1) in real time.