CN114279818B - Bidirectional flexible loading and unloading ring shear device and test method thereof - Google Patents
Bidirectional flexible loading and unloading ring shear device and test method thereof Download PDFInfo
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Abstract
The invention discloses a bidirectional flexible loading and unloading ring shear device and a test method thereof, wherein the bidirectional flexible loading and unloading ring shear device comprises a working platform, a vertical pressurizing system for applying vertical pressure to a soil sample, a circumferential pressurizing system for applying circumferential pressure to the soil sample, a shear loading system for applying torque to the soil sample, a dry-wet circulating system for injecting water or dry air to the soil sample and a measuring system for measuring the parameter change of the soil sample.
Description
Technical Field
The invention relates to the technical field of test equipment, in particular to a bidirectional flexible loading and unloading ring shear device and a test method thereof.
Background
In the construction process of excavation of foundation pit and excavation of cutting side slope, the unloading process is quite common. After excavation is completed, the exposed rock and soil mass will undergo a wet and dry process due to the effects of rainfall and evaporation. Under the combined action of excavation unloading and dry and wet processes, engineering problems such as large deformation, damage and the like occur in the engineering such as foundation pit, cutting slope and the like.
Conventional test means for geotechnical engineering problems mainly comprise a direct test, an unconfined compression test, a triaxial test and the like. The direct shear test is used for measuring the strength parameters of the rock-soil materials, and has the advantages of simple equipment and convenient operation. However, the direct test has the problems that the shearing area in the soil sample is continuously changed along with the development of shearing strain, the normal stress is uneven, and the like. The unconfined compression test only applies vertical axial pressure, and the lateral direction is not limited during the test, so that the unconfined compression test is mainly used for measuring the cohesive force of the clay. The triaxial test realizes control of vertical and confining pressure, but is limited by a test method, and has certain limitation on shear displacement. There are conventional approaches that have limitations in studying the problems of large shear deformation and failure. The ring shear test has the characteristic of constant shear surface under the condition of continuous shear deformation, can observe the whole deformation and damage process of the rock-soil material, and has good application prospect in the research of large shear deformation and strength problems.
In view of the actual engineering needs, students at home and abroad are always devoted to the research and development of ring shearing equipment, and develop different types of ring shearing equipment, so that the technical problems of soil body water seepage, large friction between an upper shearing box and a lower shearing box, inconvenient test control and the like are solved, and the existing ring shearing equipment is continuously developed to a high-precision and automatic direction. At present, most shearing boxes in ring shearing equipment adopt a rigid structure, and a ring shearing test is carried out after one-dimensional consolidation under a side limit condition. Zhu Zeji and the like (patent number: CN 106092756A) of the institute of the mechanical and rock and the Wuhan of the national academy of sciences of 2016 use an oil cavity surrounded by an elastic membrane to apply confining pressure to an inner side soil body, and apply vertical pressure through a rigid top cover, so that hollow ring shear equipment capable of applying confining pressure is developed. Ning Yibing, etc. in 2018, adopts the structure of an inner and outer shearing box, and is still loaded by adopting an oil cavity formed by surrounding an elastic membrane and a rigid top cover in a pressurizing manner (patent number: CN 108801804A). When the elastic membrane in the device is laterally deformed, the elastic membrane and the rigid top cover have larger mutual influence, and the measurement result is influenced to a certain extent. For the excavation unloading of the expansive soil foundation pit and the path of the dry and wet process, the soil body has larger stress change and expansion and shrinkage body change, and the influence of the mutual influence between the rigid top cover and the elastic membrane is more obvious. Furthermore, these two devices cannot achieve an action path of unloading and wet-dry coupling. The soil body dry-wet circulation annular shear apparatus (patent number: CN 106018126A) with measurable humidity is developed by the Ind of the science and technology engineering limited liability company of the West An in 2016, and the moisture content in the soil body is changed by injecting steam or dry air into the soil body through the ventilation pipes at the top and the bottom of a soil sample, and the humidity in the soil body is measured through the hygrometer probe of the top disc. The arrangement of the top and bottom vent pipes has certain constraint and limiting effects on the circumferential shear deformation, and influences and limits the operation of the ring shear test.
In summary, in the ring shearing device in the prior art, during the ring shearing test, the problems of inaccurate measurement results, incapability of realizing an action path of unloading and dry-wet coupling, inconvenience in operation due to constraint and limitation on circumferential shearing deformation and the like caused by loading in a mode of pressurizing an oil cavity and a rigid top cover which are enclosed by an elastic membrane can occur.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a bidirectional flexible loading and unloading ring shear device and a test method thereof, and aims to solve the problems that the measurement result of the existing ring shear device is inaccurate, bidirectional unloading cannot be realized, the action path of dry-wet coupling cannot be simulated and the operation is inconvenient.
In order to achieve the above purpose, the invention adopts the following technical scheme: the bidirectional flexible loading and unloading ring shear device comprises a working platform, a vertical pressurizing system, a circumferential pressurizing system, a shear loading system, a dry-wet circulating system and a measuring system;
an upper shearing box with an opening at the top and a lower shearing box with an opening at the bottom are arranged on the working platform, a detachable top cover is arranged at the top of the upper shearing box, and a detachable bottom cover is arranged on the lower shearing box; a steel protection cylinder is arranged in the upper shearing box, the top of the steel protection cylinder is fixedly connected with the top cover, and the bottom of the steel protection cylinder is in rotary sealing connection with the bottom cover; the upper shearing box, the lower shearing box, the top cover, the bottom cover and the steel casing are enclosed to form a shearing box body for accommodating the soil sample to be tested;
the vertical pressurizing system comprises a vertical pressure bag which applies vertical pressure to the soil sample in the shearing box body when the vertical pressurizing system is full; the annular pressurizing system comprises an annular pressure bag which applies annular pressure to the soil sample in the shearing box body when filling; the shear loading system is used for applying torque to the soil sample in the shear box body; the dry-wet circulation system is used for injecting water or dry air into the soil sample in the shear box body;
the measuring system is used for measuring the vertical pressure of the soil sample, the confining pressure of the soil sample, the shear stress on the shear surface of the soil sample, the shear displacement of the soil sample, the volume change of the vertical pressure bag and the volume change of the circumferential pressure bag.
Further, as a concrete setting mode of top cap and workstation fixed connection, the symmetry is provided with two vertical fixed bolster on the workstation, is provided with the fixed cross beam between the top of two fixed bolsters, is provided with the mounting on the fixed cross beam, cuts the box body setting between two fixed bolsters, mounting and top cap fixed connection.
Further, as a concrete implementation mode of the vertical pressurizing system, the vertical pressurizing system further comprises a hydraulic power source device, the cross section of the vertical pressure bag is of a circular ring structure and is provided with an outer ring rigid ring, the vertical pressure bag is fixedly connected with the lower surface of the top cover through the outer ring rigid ring, a vertical liquid inlet pipe is arranged between the hydraulic power source device and the vertical pressure bag, one end of the vertical liquid inlet pipe is communicated with the hydraulic power source device, and the other end of the vertical liquid inlet pipe penetrates through the top cover to be communicated with the vertical pressure bag.
Further, as a specific implementation mode of the annular pressurizing system, the annular pressurizing system further comprises an annular liquid inlet pipe, one end of the annular liquid inlet pipe is communicated with the hydraulic power source device, and the other end of the annular liquid inlet pipe penetrates through the top cover and is communicated with the annular pressure bag;
the cross section of the annular pressure bag is in a circular ring structure, the inner wall of the annular pressure bag is fixedly connected with the outer wall of the steel casing, and the two ends of the annular pressure bag are respectively contacted with the lower end face of the top cover and the upper end face of the bottom cover.
Further, as a specific connection mode of the vertical pressure bag, an inner ring elastic ring is arranged on the inner side wall of the vertical pressure bag, and the inner wall of the vertical pressure bag is contacted with the outer wall of the annular pressure bag through the inner ring elastic ring.
Further, the shearing loading system comprises a rotary power driving device arranged at the bottom of the shearing box body, two torque dowel bars are arranged on the rotary power driving device, one ends of the two torque dowel bars are fixedly connected with the rotary power driving device, and the other ends of the two torque dowel bars are fixedly connected with the lower end face of the bottom cover.
Further, a drainage tube is arranged in the middle of the bottom cover, one end of the drainage tube is communicated with the inside of the steel casing, the other end of the drainage tube is communicated with the outside, a three-way valve is arranged on the drainage tube, and two ports in the three-way valve are respectively communicated with two ends of the drainage tube; a soil sample dry-wet pipeline is arranged in the bottom cover, one end of the soil sample dry-wet pipeline is communicated with the interior of the shearing box body, and the other end of the soil sample dry-wet pipeline is communicated with the interior of the steel casing through a left port of the three-way valve;
the dry-wet circulation system comprises a humidifying and air-drying device arranged on the workbench and a water injection and air-ventilation pipeline communicated with the humidifying and air-drying device, and the water injection and air-ventilation pipeline penetrates through the top cover and is communicated with the inside of the steel casing; the water-filling ventilation pipeline is provided with a water-filling ventilation switch.
Further, the measuring system comprises a first flowmeter, a vertical pressure gauge and a vertical pressure transmitter which are arranged on the vertical liquid inlet pipe, a second flowmeter, a circumferential pressure gauge and a circumferential pressure transmitter which are arranged on the circumferential liquid inlet pipe, a humidity sensor arranged on the inner wall of the shearing box body, a signal collector arranged on the workbench and electrically connected with the humidity sensor, and a rotation angle and torque measuring element arranged in the rotary power driving device.
The invention also provides a test method of the bidirectional flexible loading and unloading ring shear device, which comprises the following steps:
step 1, obtaining a soil sample to be detected, and placing the soil sample to be detected in a shearing box body;
step 4, carrying out unloading test on the soil sample to be tested, and recording physical parameters of the soil sample to be tested;
and 9, according to the physical parameters of the step 3, the step 4, the step 5 and the step 6, obtaining the relationship between the shear displacement and the shear stress of the soil sample to be tested after consolidation, after an unloading test or after a rainfall simulation test.
Specifically, the step 3 further includes:
applying vertical pressure to the soil sample to be tested by adopting a vertical pressure bag until the vertical pressure to be tested in the shearing box body is the same as the vertical pressure to be tested before excavation of the foundation pit, stopping the circumferential pressure bag, and recording the liquid volume v in the vertical pressure bag h ；
Applying circumferential pressure to the soil sample to be detected by the circumferential pressure bag until the circumferential pressure to be detected in the shearing box body is the same as the circumferential pressure to be detected before excavation of the foundation pit, stopping the circumferential pressure bag, and recording the liquid volume v in the circumferential pressure bag r ；
Calculating the inner diameter r of the soil sample to be measured after being pressed 0L And height h after compression L ：
wherein ,h0 、r 0 r 1 Respectively the initial height, the inner diameter and the outer diameter of the soil sample to be measured;
the step 4 further comprises: the circumferential pressure of the soil sample to be detected is kept unchanged, and the hydraulic pressure of the vertical pressure bag is reduced until the vertical pressure of the soil sample to be detected is reduced to a preset pressure;
simulation baseUnloading effect of pit excavation, recording liquid discharge volume Deltav of vertical pressure bag h1 Liquid discharge volume Deltav of circumferential pressure bladder r1 ；
Calculating the inner diameter r of the soil sample to be measured after the soil sample to be measured unloading test 0u And height h u ：
Said step 5 further comprises: opening a three-way valve, enabling water to enter a shearing box body through a steel casing soil and soil sample dry-wet pipeline, adjusting the water content of the soil sample to be detected to a preset water content, and keeping the pressure of the annular pressure bag and the vertical pressure bag equal to the preset pressure in the process;
recording the humidity value of the soil sample to be measured every preset time until the humidity value is unchanged, and recording the liquid discharge volume Deltav of the vertical pressure bag h2 Liquid discharge volume Deltav of circumferential pressure bladder r2 ；
Calculating the inner diameter r of the soil sample to be measured after water seepage 0w And height h w ：
The step 6 further comprises: the water content of the soil sample to be measured is kept unchanged, the volumes of the vertical pressure bag and the annular pressure bag are kept unchanged, the rotary power driving device applies annular shearing force to the soil sample to be measured through the torque dowel bar until the soil sample to be measured is damaged, and the rotary power driving device and the torque value measured by the measuring device are kept unchanged, and the rotary angle theta and the torque T are recorded;
the step 7 further comprises: according to the change amount of the size of the soil sample to be detected in the step 3 and the step 4, calculating the circumferential deformation epsilon of the soil sample caused by unloading ru Vertical deformation epsilon hu Deformation epsilon of volume vu ：
The step 8 further comprises: according to the change amount of the soil sample size to be measured in the step 3 and the step 6, calculating the circumferential deformation epsilon to be measured after the water content is increased rw Vertical deformation epsilon hw Volume deformation epsilon vw ：
According to the circumferential deformation epsilon rw Vertical deformation epsilon hw Volume deformation epsilon vw Evaluating deformation conditions of the foundation pit in which rainwater infiltrates after the foundation pit is excavated;
said step 9 further comprises: according to the change amount of the size of the soil sample to be detected in any one of the steps 3 to 5 and the rotation angle theta and the torque T in the step 6, calculating the shear displacement s and the shear stress tau of the soil sample:
wherein ,r0f The inner diameter value of the soil sample before the start of the ring shear is r 0f Can be r according to different tests 0 、r0u、r 0w Any one of them; and drawing a relation curve between the shear stress tau and the shear displacement s, and evaluating the slip deformation of the foundation pit.
The beneficial effects of the invention are as follows: 1. the vertical pressurizing system and the annular pressurizing system are arranged in the scheme, so that the loading and unloading paths of the vertical and annular pressures of the soil sample are realized, the change of the water content in the soil sample can be realized, and the shearing deformation is not restrained, so that the complex stress path and the dry-wet process can be realized to meet the requirements of actual engineering.
2. The dry-wet circulation system is arranged in the scheme, so that the change of physical and mechanical parameters of the soil sample after rainfall infiltrates into the soil sample to be detected can be simulated, and further the soil mass shearing large deformation damage rule under the complex stress path condition and the action of a plurality of dry-wet processes can be studied, and test support is provided for further theoretical research.
3. The outside of the annular pressure bag is contacted with the soil sample, only annular deformation can occur in the test, and annular pressure is applied to the inside of the soil sample. The lower part of the vertical pressure bag is contacted with the soil sample, vertical pressure is applied to the top of the soil sample in the test, the inner ring of the vertical pressure bag correspondingly deforms in the circumferential direction along with the deformation of the circumferential pressure bag, the contact area can be adjusted along with the deformation of the soil sample, and the mutual influence of the two direction pressure application processes is avoided. The vertical pressure bag and the circumferential pressure bag are correspondingly deformed under the action of internal pressure and under the condition that an external soil sample is deformed, and the flexible loading mode ensures that the stress applied to the soil sample has better uniformity.
4. The vertical pressurizing system, the annular pressurizing system and the dry-wet circulating system in the scheme are mutually independent, and in the shearing process, the steel casing, the annular pressure bag, the upper shearing box and the vertical pressure bag do not rotate, so that the annular shearing process is ensured not to influence the operation of annular, vertical pressurizing and dry-wet circulating control on the workbench.
Drawings
FIG. 1 is a schematic structural view of a bidirectional flexible ring shear device.
Fig. 2 is a schematic structural view of the bottom cover.
Fig. 3 is a schematic structural view of the circumferential pressure bladder.
Fig. 4 is a schematic diagram of the connection between the vertical pressure bladder of the circumferential pressure bladder, the steel casing and the bottom cover.
Wherein, 1, soil sample; 2. a lower shear box; 3. a humidity sensor; 4. an upper shear box; 5. a circumferential pressure bladder; 6. a vertical pressure bladder; 7. a vertical liquid inlet pipe; 8. a circumferential liquid inlet pipe; 9. shearing the box body; 10. a steel pile casing; 11. a water injection ventilation pipe; 12. a fixing member; 13. a top cover; 14. a bottom cover; 15. a drainage tube; 16. soil sample dry and wet pipelines; 17. a three-way valve; 18. a signal collector; 19. a foot rest; 20. a working platform; 21. a hydraulic power source device; 22. a circumferential pressure gauge; 23. a vertical pressure gauge; 24. a hoop pressure transmitter; 25. a vertical pressure transmitter; 26. fixing the cross beam; 27. a fixed bracket; 28. a water-through ventilation switch; 29. a humidifying and air-drying device; 30. a torque dowel bar; 31. a rotary power driving device; 32. an outer ring rigid ring; 33. an inner ring elastic ring.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and all the inventions which make use of the inventive concept are protected by the spirit and scope of the present invention as defined and defined in the appended claims to those skilled in the art.
As shown in fig. 1 to 4, the invention provides a bidirectional flexible loading and unloading ring shear device, which comprises a working platform 20, a vertical pressurizing system, a circumferential pressurizing system, a shear loading system, a dry-wet circulating system and a measuring system;
an upper shearing box 4 with an opening at the top and a lower shearing box 2 with an opening at the bottom are arranged on the working platform 20, a detachable top cover 13 is arranged at the top of the upper shearing box 4, and a detachable bottom cover 14 is arranged on the lower shearing box 2; the upper shearing box 4 is internally provided with a steel casing 10, the top of the steel casing 10 is fixedly connected with a top cover 13, and the bottom of the steel casing 10 is in rotary sealing connection with a bottom cover 14; the upper shearing box 4, the lower shearing box 2, the top cover 13, the bottom cover 14 and the steel casing 10 are enclosed into a shearing box body 9 for accommodating the soil sample 1 to be tested. The arrangement of the upper shearing box 4 and the lower shearing box 2 is convenient to install and detach, the soil sample 1 is convenient to put in and take out the shearing box body 9, and meanwhile, after the shearing loading system applies torque to the soil sample 1, the soil sample 1 generates shearing slip planes between the upper shearing box 4 and the lower shearing box 2.
As a concrete setting mode of top cap 13 and workstation fixed connection, be provided with two vertical fixed bolster 27 on the workstation symmetry, be provided with fixed cross beam 26 between the top of two fixed bolster 27, be provided with mounting 12 on the fixed cross beam 26, shearing box body 9 sets up between two fixed bolster 27, mounting 12 and top cap 13 fixed connection. The stable operation of the whole bidirectional flexible loading and unloading ring shear device in the test process is ensured.
In order to facilitate the fixed installation of the working platform 20, a foot rest 19 is provided on the bottom surface of the working platform 20.
The vertical pressurizing system comprises a vertical pressure bag 6 which applies vertical pressure to the soil sample 1 in the shearing box body 9 when filling; as a specific implementation mode of the vertical pressurizing system, the vertical pressurizing system further comprises a hydraulic power source device 21, the cross section of the vertical pressure bag 6 is of a circular ring structure and is provided with an outer ring rigid ring 32, the vertical pressure bag 6 is fixedly connected with the lower surface of the top cover 13 through the outer ring rigid ring 32, a vertical liquid inlet pipe 7 is arranged between the hydraulic power source device 21 and the vertical pressure bag 6, one end of the vertical liquid inlet pipe 7 is communicated with the hydraulic power source device 21, and the other end of the vertical liquid inlet pipe passes through the top cover 13 and is communicated with the vertical pressure bag 6. The hydraulic power source device 21 charges liquid to the vertical pressure bag 6 through the vertical liquid inlet pipe 7, and the vertical pressure bag 6 after the liquid charging applies vertical pressure to the soil sample 1.
The circumferential pressurizing system comprises a circumferential pressure bag 5 which applies circumferential pressure to the soil sample 1 in the shearing box body 9 when filling; as a specific implementation mode of the annular pressurizing system, the annular pressurizing system further comprises an annular liquid inlet pipe 8, one end of the annular liquid inlet pipe 8 is communicated with the hydraulic power source device 21, and the other end of the annular liquid inlet pipe passes through the top cover 13 and is communicated with the annular pressure bag 5; the cross section of the annular pressure bag 5 is in a circular ring structure, the inner wall of the annular pressure bag 5 is fixedly connected with the outer wall of the steel casing 10, and two ends of the annular pressure bag 5 are respectively contacted with the lower end face of the top cover 13 and the upper end face of the bottom cover 14. The hydraulic power source device 21 fills the annular pressure bag 5 through the annular liquid inlet pipe 8, and the annular pressure bag 5 after filling applies annular pressure to the soil sample 1.
Preferably, but not limited to, as a specific connection manner of the vertical pressure bladder 6, as shown in fig. 1 and 4, an inner ring elastic ring 33 is disposed on an inner side wall of the vertical pressure bladder 6, and an inner wall of the vertical pressure bladder 6 is in contact with an outer wall of the circumferential pressure bladder 5 through the inner ring elastic ring 33. The outside of the circumferential pressure bag 5 is in contact with the soil sample 1, and only circumferential deformation can occur in the test, and circumferential pressure is applied to the inside of the soil sample 1. The lower part of the vertical pressure bag 6 is in contact with the soil sample 1, vertical pressure is applied to the top of the soil sample 1 in the test, the inner ring of the vertical pressure bag correspondingly deforms in the circumferential direction along with the deformation of the circumferential pressure bag 5, the contact area can be adjusted along with the deformation of the soil sample 1, and the mutual influence of the two direction pressure application processes is avoided. The vertical pressure bags 6 and the circumferential pressure bags 5 deform correspondingly under the action of internal pressure and under the condition that the external soil sample 1 deforms, and the flexible loading mode ensures that the compressive stress acting on the soil sample 1 has better uniformity.
The shear loading system is used for applying torque to the soil sample 1 in the shear box body 9; the shearing loading system comprises a rotary power driving device 31 arranged at the bottom of the shearing box body 9, two torque dowel bars 30 are arranged on the rotary power driving device 31, one ends of the two torque dowel bars 30 are fixedly connected with the rotary power driving device 31, and the other ends of the two torque dowel bars 30 are fixedly connected with the lower end face of the bottom cover 14. The ring shear test is performed by applying torque to the bottom cap 14 through torque transmission. In the annular shearing process, the bottom cover 14 and the lower shearing box 2 rotate, shearing stress is applied to soil in the lower shearing box 2, and a shearing slip surface is generated between the upper shearing box 2 and the lower shearing box 2 by the soil sample 1. In the ring shearing process, the steel casing 10, the annular pressure bag 5, the upper shearing box 4 and the vertical pressure bag 6 do not rotate, so that the operation of annular, vertical pressurization and dry-wet cycle control on a workbench is not influenced in the ring shearing process. The vertical pressurizing system and the annular pressurizing system are arranged in the scheme, so that the loading and unloading paths of the vertical and annular pressures of the soil sample 1 are realized, the change of the water content in the soil sample 1 can be realized, and the shearing deformation is not restrained, so that the complex stress path and the dry-wet process can be realized to meet the requirements of actual engineering.
As shown in fig. 1 and 2, the dry-wet circulation system is used for injecting water or dry air into the soil sample 1 in the shear box 9; preferably, but not limited to, a drainage tube 15 is arranged in the middle of the bottom cover 14, one end of the drainage tube 15 is communicated with the inside of the steel casing 10, the other end of the drainage tube is communicated with the outside, a three-way valve 17 is arranged on the drainage tube 15, and two ports in the three-way valve 17 are respectively communicated with two ends of the drainage tube 15; a soil sample dry-wet pipeline 16 is arranged in the bottom cover 14, one end of the soil sample dry-wet pipeline 16 is communicated with the interior of the shearing box body 9, and the other end of the soil sample dry-wet pipeline is communicated with the interior of the steel casing 10 through a left port of a three-way valve 17; the dry-wet circulation system comprises a humidifying and air-drying device 29 arranged on the workbench and a water injection and air passage 11 communicated with the humidifying and air-drying device 29, wherein the water injection and air passage 11 passes through the top cover 13 and is communicated with the inside of the steel casing 10; the water-filling ventilation pipe 11 is provided with a water-filling ventilation switch 28. The three-way valve 17 has two gears, and when the three-way valve 17 is in first gear, the drainage tube 15 is communicated with the soil sample dry-wet pipeline 16, so that water or dry air sequentially flows through the inside of the steel casing 10, the drainage tube 15, the three-way valve 17 and the soil sample dry-wet pipeline 16 from the water injection ventilation pipeline 11 and enters the soil sample 1 in the shearing box body 9; when the three-way valve 17 is in first gear, water or air in the soil sample 1 sequentially flows through the drainage tube 15 and the three-way valve 17 from the soil sample dry and wet pipeline 16 to be discharged to the outside, and the migration path of injected water or dry air is controlled by controlling the gear of the three-way valve 17; the dry-wet circulation system does not need to arrange pipelines on the inner surface of the bottom cover 14, and the shearing deformation of the soil sample 1 restrained by the external pipelines is avoided in the annular shearing process of the soil sample 1.
The dry-wet circulation system can simulate the change of physical and mechanical parameters of the soil sample 1 after rainfall infiltrates into the soil sample 1 to be tested, and can be further used for researching complex stress path conditions and soil mass shearing large deformation destruction rules under the action of repeated dry-wet processes, so as to provide test support for further theoretical research
The measuring system is used for measuring the vertical pressure of the soil sample 1, the confining pressure of the soil sample 1, the shear stress on the shear surface of the soil sample 1, the shear displacement of the soil sample 1, the volume change of the vertical pressure bag 6 and the volume change of the circumferential pressure bag 5. The preferred measuring system comprises a first flowmeter arranged on the vertical feed pipe 7, a vertical pressure gauge 23 and a vertical pressure transmitter 25, a second flowmeter arranged on the annular feed pipe 8, an annular pressure gauge 22 and an annular pressure transmitter 24, a humidity sensor 3 arranged on the inner wall of the shear box 9, a signal collector 18 arranged on the workbench and used for being electrically connected with the humidity sensor 3, and a rotation angle and torque measuring element arranged in the rotation power driving device 31.
The first flow meter may measure the volume change of the vertical pressure bladder 6 and the second flow meter may measure the volume change of the circumferential pressure bladder 5, which are not shown in the drawings.
The vertical pressure gauge 23 and the annular pressure gauge 22 can measure the vertical pressure and the annular pressure of the soil sample 1; the vertical pressure transmitter 25 and the circumferential pressure transmitter 24 are used for adjusting the hydraulic pressure transmitted to the two pressure bags by the hydraulic power source device 21; the rotation angle and torque measuring element, not shown in the drawings, is used to measure the torque magnitude and the shear displacement of the soil sample 1. In the scheme, the vertical pressurizing system, the annular pressurizing system and the dry-wet circulating system are mutually independent, and in the shearing process, the steel casing 10, the annular pressure bag 5, the upper shearing box 4 and the vertical pressure bag 6 do not rotate, so that the annular shearing process is ensured not to influence the operation of annular, vertical pressurizing and dry-wet circulating control on the workbench.
The invention also provides a test method of the bidirectional flexible loading and unloading ring shear device, wherein the test object is undisturbed expansive soil on a foundation pit engineering site, the initial water content of the undisturbed expansive soil is 25 percent, the initial pore ratio is 0.85, the vertical stress of a soil unit on the inner side of the side wall of the foundation pit before excavation of the foundation pit is 100kPa, the horizontal stress is 50kPa, the horizontal stress of the soil unit caused by excavation of the foundation pit is reduced from 50kPa to 25kPa, and the vertical stress is still 100kPa. The vertical stress of the soil unit at the lower part of the foundation pit is 200kPa, the horizontal stress is 100kPa, the vertical stress after excavation is reduced from 200kPa to 150kPa, and the horizontal stress remains unchanged and is still 100kPa. Rainfall occurs after the foundation pit is excavated, and the water content of the expansive soil in the foundation pit engineering site is increased from 25% to 35%. The expansion deformation and strength change of the expansion soil sample 1 at different positions of the foundation pit caused by the increase of the water content due to rainfall after the excavation unloading of the foundation pit are researched, and the test can be carried out by adopting the following steps;
step 1, obtaining a soil sample 1 to be detected, and placing the soil sample 1 to be detected in a shearing box body 9; specifically, mixing the dried expansive soil sample 1 with water according to the mass ratio of 1:0.25, and tamping in a container until the pore ratio reaches 0.85, and shearing (such as cutting by a ring) to obtain a hollow cylindrical expansive soil sample 1, wherein the height of the hollow cylindrical expansive soil sample 1 is h 0 An inner diameter r 0 An outer diameter r 1 The total weight of the soil sample 1 to be measured is W, and the weight ratio of the dry soil to the water of the soil sample 1 to be measured is 1:0.25;
the hollow cylindrical expansive soil sample 1 is installed and fixed in the shearing box body 9, the shearing box body 9 is fixed on the working platform 20, and corresponding equipment pipelines are connected according to the figure 1, so that the water injection ventilation pipeline 11 is not required to be connected with the humidifying and air-drying device 29;
specifically, the hydraulic power source device 21 applies vertical pressure and circumferential pressure with the same magnitude to the hollow cylindrical expansive soil sample 1 through the circumferential pressure bag 5 and the vertical pressure bag 6 at the same time, and for experiments for researching the foundation pit side wall soil unit, the vertical pressure and the circumferential pressure are loaded to 50kPa; for experiments for researching the soil unit at the bottom of the foundation pit, the vertical and circumferential pressures are loaded to 100kPa; the three-way valve 17 is opened to a gear in loading, gas in the hollow cylindrical expanded soil sample 1 can be discharged, at the moment, the water injection and ventilation pipeline 11 is connected with the atmosphere, the seepage of water in the hollow cylindrical expanded soil sample 1 can be ignored due to the low permeability coefficient of the expanded soil and the short loading time in the step, and the pore ratio of the soil can still be approximately 0.85 under the condition that the pore volume change of the soil is negligible;
for a soil unit at the bottom of a foundation pit, the vertical stress at the upper part is reduced in the process of excavation of the foundation pit, a mode of unloading a vertical pressure bag 6 is adopted for facilitating the subsequent simulation of excavation unloading of the foundation pit, and the pressure of the vertical pressure bag 6 is recommended to be increased so that the vertical pressure on a soil sample 1 is increased from 100kPa to 200kPa, and meanwhile, the hydraulic pressure of a circumferential pressure bag 5 is kept unchanged; the water ventilation valve is kept at a first gear during loading;
outer diameter r of hollow cylinder expansion soil sample 1 1 The inner diameter r of the hollow cylinder expansion soil sample 1 after being pressed is calculated unchanged 0L And height h after compression L The calculation formula is as follows:
step 4, unloading test is carried out on the hollow cylindrical expansive soil sample 1; and physical parameters of the unloading hollow cylinder expansive soil sample 1 are recorded;
specifically, in the test of researching the foundation pit side wall soil unit, the vertical pressure is reduced from 50kPa to 25kPa, and the circumferential pressure is kept unchanged; for the test of researching the soil unit at the bottom of the foundation pit, the vertical pressure is reduced from 200kPa to 150kPa, and the circumferential pressure is kept unchanged;
recording the liquid discharge volume of the vertical pressure bladder 6 as Deltav h1 The liquid discharge volume of the circumferential pressure bag 5 is Δv r1 ；
Outer diameter r of hollow cylinder expansion soil sample 1 1 Unchanged, the inner diameter r of hollow cylinder expansive soil sample 1 in the unloading test is calculated 0u And height h u The calculation formula is as follows:
the three-way valve 17 is opened, water flows through the soil and sample dry and wet pipelines of the steel casing 10 and enters the shearing box body 9, water is added into the hollow cylindrical expanded soil sample 11, the water content of the hollow cylindrical expanded soil sample 1 is increased from 25% to 35%, and the hollow cylindrical expanded soil sample is obtainedThe water added weight of the cylindrical expansive soil sample 1 is
In the process, the pressures of the annular pressure bag 5 and the vertical pressure bag 6 are kept unchanged and are preset pressures;
then recording the humidity value of the hollow cylinder expansive soil sample 1 every 1 hour until the humidity value is kept unchanged, and measuring the liquid discharge volume of the vertical pressure bag 6 to be Deltav h2 The liquid discharge volume of the circumferential pressure bag 5 is Δv r2 ；
Measuring the outer diameter r of the hollow cylindrical expansive soil sample 1 1 The inner diameter r of the hollow cylindrical expansive soil sample 1 is calculated unchanged 0w And height h w The calculation formulas are respectively as follows:
the calculation formula is as follows:
wherein ,r0f The inner diameter value of the soil sample before the start of the ring shear is r 0f R is 0w The method comprises the steps of carrying out a first treatment on the surface of the And drawing a relation curve between the shear stress tau and the shear displacement s, and evaluating the slip deformation of the foundation pit.
Claims (2)
1. The test method of the bidirectional flexible loading and unloading ring shear device is characterized in that the bidirectional flexible loading and unloading ring shear device comprises a working platform, a vertical pressurizing system, a circumferential pressurizing system, a shear loading system, a dry-wet circulating system and a measuring system;
an upper shearing box with an opening at the top and a lower shearing box with an opening at the bottom are arranged on the working platform, a detachable top cover is arranged at the top of the upper shearing box, and a detachable bottom cover is arranged on the lower shearing box; a steel pile casing is arranged in the upper shearing box, the top of the steel pile casing is fixedly connected with the top cover, and the bottom of the steel pile casing is in rotary sealing connection with the bottom cover; the upper shearing box, the lower shearing box, the top cover, the bottom cover and the steel casing are enclosed to form a shearing box body for accommodating the soil sample to be tested;
the vertical pressurizing system comprises a vertical pressure bag which applies vertical pressure to the soil sample in the shearing box body when the vertical pressurizing system is full; the annular pressurizing system comprises an annular pressure bag which applies annular pressure to the soil sample in the shearing box body when filling; the shear loading system is used for applying torque to the soil sample in the shear box body; the dry-wet circulation system is used for injecting water or dry air into the soil sample in the shearing box body;
the test method comprises the following steps:
step 1, obtaining a soil sample to be detected, and placing the soil sample to be detected in a shearing box body;
step 2, consolidating the soil sample to be tested, and entering step 3;
step 3, simulating the pressed state of the soil sample to be tested before excavation of the foundation pit, recording the physical parameters of the soil sample to be tested after pressing, and then entering any one of the steps 4-6;
applying vertical pressure to the soil sample to be tested by adopting a vertical pressure bag until the vertical pressure to be tested in the shearing box body is the same as the vertical pressure to be tested before excavation of the foundation pit, stopping the circumferential pressure bag, and recording the volume of liquid in the vertical pressure bag
；
Applying circumferential pressure to the soil sample to be tested by the circumferential pressure bag until the circumferential pressure applied to the soil sample to be tested in the shearing box body and the soil sample to be tested are in the foundation pitAfter the circumferential pressure applied before excavation is the same, the circumferential pressure bag stops, and the volume of liquid in the circumferential pressure bag is recorded
；
Calculating the inner diameter of the soil sample to be measured after being pressed
And height after compression +.>
：
wherein ,
、/>
respectively the initial height, the inner diameter and the outer diameter of the soil sample to be measured;
step 4, carrying out unloading test on the soil sample to be tested, and recording physical parameters of the soil sample to be tested;
the circumferential pressure of the soil sample to be detected is kept unchanged, and the hydraulic pressure of the vertical pressure bag is reduced until the vertical pressure of the soil sample to be detected is reduced to a preset pressure;
simulating unloading effect of foundation pit excavation and recording liquid discharge volume of vertical pressure bag
Liquid discharge volume of circumferential pressure bladder +.>
；
Calculating the inner diameter of the soil sample to be measured after the soil sample to be measured unloading test
And height->
：
Step 5, adopting a rainfall simulation test of the soil sample to be tested, and recording physical parameters of the soil sample to be tested after water seepage;
opening a three-way valve, enabling water to enter a shearing box body through a steel casing soil and soil sample dry-wet pipeline, adjusting the water content of the soil sample to be detected to a preset water content, and keeping the pressure of the annular pressure bag and the vertical pressure bag equal to the preset pressure in the process;
recording the humidity value of the soil sample to be measured every preset time until the humidity value is unchanged, and recording the liquid discharge volume of the vertical pressure bag
Liquid discharge volume of circumferential pressure bladder +.>
；
Calculating the inner diameter of the soil sample to be measured after water seepage
And height->
：
Step 6, performing a ring shear test on the soil sample to be tested, and recording physical parameters of the soil sample to be tested after the ring shear test;
step 7, obtaining deformation of the soil sample to be measured caused by unloading according to the physical parameters of the step 3 and the step 4;
step 8, obtaining the deformation of the soil sample to be detected caused by the increase of the water content according to the physical parameters of the step 3 and the step 5;
and 9, according to the physical parameters of the step 3, the step 4, the step 5 and the step 6, obtaining the relationship between the shear displacement and the shear stress of the soil sample to be tested after consolidation, after an unloading test or after a rainfall simulation test.
2. The test method according to claim 1, wherein,
the step 6 further comprises: the water content of the soil sample to be measured is kept unchanged, the volumes of the vertical pressure bag and the annular pressure bag are kept unchanged, the rotary power driving device applies annular shearing force to the soil sample to be measured through the torque dowel bar until the soil sample to be measured is damaged, the torque values measured by the rotary power driving device and the measuring device are kept unchanged, and the rotation angle is recorded
And torque->
；
The step 7 further comprises: according to the change amount of the size of the soil sample to be measured in the step 3 and the step 4, calculating unloading to cause circumferential deformation of the soil sample
Vertical deformation->
Deformation of volume>
：
The step 8 further comprises: according to the change amount of the soil sample size to be measured in the step 3 and the step 6, calculating the circumferential deformation to be measured after the water content is increased
Vertical deformation->
Deformation of volume>
：
According to circumferential deformation
Vertical deformation->
Deformation of volume>
Evaluating deformation conditions of the foundation pit in which rainwater infiltrates after the foundation pit is excavated;
said step 9 further comprises: according to the variation of the size of any soil sample to be measured in the steps 3-5 and the rotation angle in the step 6
And torque->
Calculating the average shear displacement of the soil sample>
And average shear stress->
：
wherein ,
the inner diameter value of the soil sample before the start of the ring shear; drawing shear stress->
And shear displacement->
And the relation curve is used for evaluating the slip deformation of the foundation pit.
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