CN212432829U - Automatic control type plane strain test mechanism - Google Patents
Automatic control type plane strain test mechanism Download PDFInfo
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- CN212432829U CN212432829U CN202021760432.XU CN202021760432U CN212432829U CN 212432829 U CN212432829 U CN 212432829U CN 202021760432 U CN202021760432 U CN 202021760432U CN 212432829 U CN212432829 U CN 212432829U
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Abstract
The utility model discloses an automatic control type plane strain test mechanism has solved the well main stress of current strain test device and has adjusted the problem of relying on the manual work, the difficult assurance of precision. The test device comprises: a pressure chamber having an internal cavity; the plane strain pressure chamber is positioned in the inner cavity of the pressure chamber, is internally provided with a cavity and is used for placing a soil sample to be tested, and comprises two hydraulic bags and two baffle plates; the bottom of each jack is fixed on the pressure chamber, and the telescopic end of each jack is connected to the baffle and used for driving the baffle to move in a reciprocating manner, so that the loading or unloading of the main stress in the soil sample to be tested is realized; and the at least two soil pressure cells are respectively embedded on the inner walls of the two baffles and used for acquiring the medium main stress data of the soil sample to be detected.
Description
Technical Field
The utility model belongs to the technical field of geotechnical engineering test equipment, concretely relates to automatic control type plane strain test mechanism.
Background
Many engineering problems (such as deep foundation pits, retaining walls, high fill embankments, dams, tunnels and the like) in actual engineering are in or approximate to a plane strain state, and in the current engineering aiming at the plane strain problem, strength parameters of soil are generally determined according to conventional triaxial or direct shear test results during design, and the constraint of the main stress direction and the contribution of the stress change to the soil strength under the condition of a plane strain stress path are not considered. Therefore, the strength parameters of the soil determined according to the plane strain test can give full play to the strength of the soil, improve the engineering economy and be more consistent with the stress-strain state of the soil in the actual engineering.
Since Kjellman (1936) modified the 3 groups of rigid baffle loading modes which are parallel to each other, the device can apply plane strain stress state to cubic samples by limiting the displacement of a pair of rigid baffles in the main stress direction, and the device is regarded as the earliest plane strain device, but the loading mechanism of the device is complicated, and the loading plates in two adjacent directions interfere with each other. Then Hamfly, Jakobson and Roscoe et al in KjellmanA similar plane strain tester is developed on the basis of the developed plane strain device, but the instrument is still difficult to overcome the stress and strain corner interference effect generated by crossing between the rigid plates. Wood then modifies the pressure cell on the basis that the sample is elongated and the instrument achieves essentially a planar strain condition due to the combination of σ2The length of the action surface is increased, the friction force on the surface is increased, and the central principal stress sigma in the test process is caused2Shear stress exists on the action surface, and the measurement precision is reduced. Green developed a planar strain gauge for small-sized samples that reduced the friction between the load plate and the sample, but also allowed sigma2The large range of movement of the loading device makes the test process difficult to implement. The common disadvantage of these types of plane strain gauges is that the mutual compression of the rigid and flexible interfaces and the friction between the sample and the constraining plate affect the accuracy of the test results. The corresponding plane modification based on the conventional triaxial pressure chamber and the true triaxial apparatus pressure chamber is one of the important trends in the development of the plane strain gauge. Two steel plates are added in a triaxial pressure chamber, rapid development of a shear true triaxial apparatus for realizing a plane strain state drives rapid development of the plane strain apparatus, and most of the plane strain apparatuses are transformed on the pressure chamber and a stress control system of the true triaxial apparatus or a true triaxial apparatus is directly adopted to complete a plane strain test. With separate means for ensuring sigma during loading2Strain in direction epsilon2＝0，σ2Direction is a rigid constraint, σ1Direction of rigid loading, σ3The direction is loaded by adopting a flexible water sac. The two types of modified pressure chambers have the defects that the friction between the rigid plate and the soil sample influences the measurement of the axial force and the test result, and sigma cannot be realized mostly2And measuring the stress in the direction.
The existing plane strain system based on transformation of true triaxial pressure chamber has simple and feasible principle, and realizes sigma2Strain in direction epsilon 20, the plane strain state in the actual engineering corresponds to a definite strain condition epsilon 20 does not correspond to a definite stress condition. The existing transformation only meets the deformation condition, and the rigid baffle is arrangedThe horizontal displacement of the pressure chamber cannot be regulated and controlled, so that the sample is solidified at the consolidation stage sigma2The main stress in the direction can not reach the consolidation confining pressure and can only be passively stressed, so that the sigma of the soil body at the initial shearing stage is increased2The main stress in the direction is actually small, and along with the continuous development of the shear deformation, the lateral soil body extrudes the rigid plate sigma2After the direction is passively stressed, the direction is gradually developed into a central main stress, and at the moment, the soil body really enters a plane strain state. Due to the difference, the existing instrument cannot completely simulate the plane strain state of the soil in the actual engineering. Existing sigma2The direction main stress adjusting mechanism is mainly controlled manually, and the precision is difficult to guarantee.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing an automatic control type plane strain test mechanism to the well main stress of solving current strain test device is adjusted and is relied on artifically, the difficult problem of guaranteeing of precision.
The utility model adopts the following technical scheme: an automatic control type plane strain test mechanism, comprising:
a pressure chamber having an internal cavity;
a plane strain pressure chamber is arranged in an inner cavity of the pressure chamber, a cavity is also arranged in the pressure chamber, the pressure chamber is used for placing a soil sample to be tested, the pressure chamber comprises two hydraulic bags and two baffle plates, and the pressure chamber specifically comprises:
the two hydraulic bags are oppositely arranged in the pressure chamber, the relative distance between the two hydraulic bags is a fixed value, and the two hydraulic bags are used for applying pressure to the surface of the soil sample to be detected in contact with the hydraulic bags in a water-filled expansion state;
the two baffle plates are smooth rigid plates, are oppositely arranged in the pressure chamber and between the two hydraulic bags and are intersected with the two hydraulic bags, and are used for moving in opposite directions so as to apply pressure to the surface of the soil sample to be detected, which is in contact with the baffle plates;
the bottom of each jack is fixed on the pressure chamber, and the telescopic end of each jack is connected to the baffle and used for driving the baffle to move in a reciprocating manner, so that the loading or unloading of the main stress in the soil sample to be tested is realized;
and the at least two soil pressure cells are respectively embedded on the inner walls of the two baffles and used for acquiring the medium main stress data of the soil sample to be detected.
Furthermore, the bottom parts of the two jacks are fixedly connected to the outer wall of the pressure chamber through bolts.
Furthermore, the bottom of the pressure chamber is provided with a pressure chamber base to seal the bottom of the pressure chamber and be used as the bottom support of the soil sample to be measured.
Further, a pressure chamber top cover is detachably provided on the top of the pressure chamber to close the top of the pressure chamber.
The utility model has the advantages that: 1. structural design of a jack and a bolt is added, so that the soil sample to be measured is at sigma2The main stress in the direction can be automatically controlled and adjusted, good operability can be guaranteed, the plane strain state of the soil can be more consistent with the actual engineering situation, the measurement precision and the control precision of the middle main stress are higher, and the method has good application value.
2. By controlling the distance between the two baffles and controlling the pressure change of the hydraulic bag, the switching of the main stress direction in the soil sample to be tested can be conveniently realized according to the requirement, the change of the stress state when the soil body is piled or unloaded in the actual engineering can be adapted, and the real stress state of the soil can be closely reflected.
Drawings
Fig. 1 is a top view of an automatic control type plane strain test mechanism of the present invention;
fig. 2 is a longitudinal sectional view of an automatic control type plane strain test mechanism of the present invention;
fig. 3 shows the loading state of the sample of the automatic control type plane strain testing mechanism under the plane strain stress path.
The device comprises a pressure chamber base 1, a pressure chamber top cover 2, a pressure chamber 3, a pressure chamber 4, a baffle plate 5, a jack 6, a soil pressure box 7, a bolt 8 and a hydraulic bag.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
The utility model provides an automatic control type plane strain test mechanism, as shown in figure 1-2, including plane strain pressure chamber and well principal stress add, uninstallation mechanism. Comprises a pressure chamber 3 having a cavity therein. The device also comprises a plane strain pressure change chamber which is positioned in the inner cavity of the pressure chamber 3, a cavity is also arranged in the plane strain pressure change chamber and is used for placing a soil sample to be tested, and the plane strain pressure change chamber specifically comprises two baffle plates 4 and two hydraulic bags 8 which jointly enclose a space for placing the soil sample to be tested.
The two hydraulic bags 8 are oppositely arranged in the pressure chamber 3, and the relative distance between the two hydraulic bags 8 is a fixed value, so that the two hydraulic bags are used for applying small main stress pressure to the surface of the soil sample to be detected in contact with the two hydraulic bags under the water-filled expansion state. The two baffle plates 4 are smooth rigid plates, are oppositely arranged in the pressure chamber 3 and between the two hydraulic bags 8, are intersected with the two hydraulic bags 8, and are preferably perpendicular to the two hydraulic bags 8. The two baffle plates 4 are movably arranged in the pressure chamber 3, and under the thrust action of the hydraulic ultrathin jack 5, the two baffle plates 4 can move in opposite directions to apply medium main stress pressure to the soil sample to be tested and can also move away from each other to unload the pressure applied to the soil sample to be tested. At least two soil pressure boxes 6 are respectively embedded on the inner walls of the two baffles 4 and used for collecting the medium main stress of the soil sample to be measured. The steel string type soil pressure cell with larger size can be selected to ensure that the soil pressure cell 6 can be fully contacted with the surface of a soil sample so as to solve the problem that the plane strain direction main stress measurement of the existing plane strain gauge is inaccurate due to the unevenness of the side surface of the soil sample in the test process.
The technical scheme of the utility model can also include two jack 5, and the bottom of every jack 5 is fixed in on the pressure chamber 3, the flexible end of every jack 5 is connected to baffle 4 is used for driving 4 reciprocating motion of baffle to the realization is to the loading or the uninstallation of the main stress in the soil sample that awaits measuring. Wherein, the jack 5 can be a computer-controlled hydraulic ultrathin jack. The bottoms of the two jacks 5 are fixedly connected to the outer wall of the pressure chamber 3 through bolts 7.
The technical scheme of the utility model can also arrange a pressure chamber base 1 at the bottom of the pressure chamber 3 to seal the bottom of the pressure chamber 3 for being used as the bottom support of the soil sample to be measured; a pressure chamber top cover 2 is detachably provided on the top of the pressure chamber 3 to close the top of the pressure chamber 3.
1. Peripheral structure of plane strain pressure chamber
The pressure chamber comprises a pressure chamber top cover 2, a pressure chamber 3 body and a pressure chamber base 1, and the materials of the pressure chamber top cover, the pressure chamber 3 body and the pressure chamber base are all smooth stainless steel materials. The outer wall of the pressure chamber 3 is reformed in that an M10 screw hole is formed in the center of the outer cylinder, a hydraulic ultrathin jack 5 can be fixed on the outer wall of the pressure chamber 3 through an M10 bolt with the length of 40mm, the jack 5 can push and pull back the smooth rigid baffle 4, and loading and unloading of the smooth rigid baffle 4 in the direction of the central principal stress can be realized; and the lower part of the outer cylinder of the pressure chamber 3 is provided with a square hole of 20mm, so that the external pipelines of the hydraulic ultrathin jack 5 and the soil pressure box 6 extend out; the rest of the device is consistent with the existing true triaxial.
2. Internal structure of plane strain pressure chamber
The transformation is that a pair of concave smooth rigid baffle mechanisms are additionally arranged in the plane strain symmetric direction to limit strain development in the direction so as to simulate the plane strain state, the width of each lengthened rigid baffle is used for sealing a gap left after a partition is removed, the hydraulic bag 8 after water injection and pressurization is prevented from being damaged when being drilled into the gap, the concave smooth rigid baffle and the hydraulic bag 8 can be ensured to be directly contacted with a soil body sample, and therefore lateral confining pressure can be normally transmitted to the soil body sample.
3. Middle main stress loading and unloading mechanism
As shown in FIG. 3, when the soil sample begins to be consolidated, the principal stress σ in the middle2The pressure is provided by the pressure generated by pushing the soil test block by the two concave smooth rigid baffles 4 to move horizontally inwards under the control of the hydraulic ultrathin jack 5 controlled by a computer. The horizontal moving mode of the concave smooth rigid baffle 4 is that the horizontal distance between the rigid baffle 4 and the outer cylinder of the pressure chamber 3 is changed by the extension and propulsion of an automatic loading hydraulic ultrathin jack 5. ByThe outer cylinder of the pressure chamber 3 outside the jack 5 limits the outward horizontal displacement generated by the extension of the jack 5, so that the horizontal displacement only develops into the pressure chamber 3, and the rigid baffle 4 is pushed to extrude the soil mass test block inwards to apply confining pressure. When a shear test is carried out, the pressure generated by extrusion of the soil body deformation on the rigid baffle generates counter force on the jack 5, the rigid baffle 4 can be moved, but the jack 5 is a one-way valve to prevent the smooth baffle from moving, so that the strain of the soil body in the direction is always limited to simulate epsilon in the test process2A planar strain state of 0. In addition, if the consolidation stress in the plane strain direction is larger, the jack 5 can be controlled to retract through a computer, so that the concave rigid baffle 4 generates reverse movement to unload confining pressure, and the test reasonability is ensured.
Small principal stress sigma3The directional consolidation pressurizing system is consistent with the original true triaxial apparatus. The consolidation pressure is controlled by a microcomputer, a servo stepping motor pushes a hydraulic cylinder piston to generate hydraulic pressure, and the hydraulic pressure is transmitted to the flexible hydraulic bag 8 through a pipeline and then applied to a soil sample. In order to prevent the hydraulic bag from being squeezed into the gap between the rigid plate in the middle main stress direction and the pressure chamber to be damaged in the test process, a layer of thin rubber film is arranged between the hydraulic bag and the soil sample, and the hydraulic bag is wrapped to seal the gap.
4. Main stress measuring device
And the at least two soil pressure boxes 6 are embedded on the inner walls of the two baffles 4 and are used for acquiring the medium main stress data of the soil sample to be measured. In practice there may be four earth pressure cells 6, for example one for each baffle 4 at 1/3 and 2/3.
The centers of the two symmetrical baffles 4 are provided with holes and respectively embedded with a steel string type soil pressure cell 6. The jack 5 contacted with the baffle 4 is used for pushing the baffle 4 to generate pressure on a soil body to be measured, the stress generated when the soil body is contacted with the baffle 6 is measured through the soil pressure box 6 to record the change of the main stress value in the direction, and the steel string type soil pressure box with larger size is selected to ensure that the pressure box can be fully contacted with the surface of a soil body sample, so that the problem that the measurement of the main stress in the plane strain direction is inaccurate due to the unevenness of the side surface of the soil body in the test process of the existing plane strain gauge is solved.
The utility model relates to a plane strain direction main stress test method of an automatic control type plane strain test mechanism, which comprises the following steps that S1, a soil body to be tested is placed into a plane strain pressure variable chamber formed by enclosing a baffle 4 and a hydraulic bag 8, pressure P is applied to the surface of a soil sample to be tested and is kept through the water pressure of the hydraulic bag 8, and the pressure in the direction is small main stress; applying pressure P to the surface of the soil sample to be tested through the opposite movement of the two baffle plates 4, continuously moving the two baffle plates in opposite directions, and continuously and actively applying pressure to the surface of the soil sample to be tested to ensure that the pressure in the direction is the central main stress; and S2, measuring the stress generated when the soil body contacts the soil pressure cell 6 through the soil pressure cell to record the numerical change of the main stress in the direction. When the direction of the central main stress of the soil body to be tested is switched, the relative positions of the two baffle plates 4 are kept unchanged, the pressure of the hydraulic bag 8 is increased by controlling the hydraulic bag 8, and the stress in the direction of the hydraulic bag 8 is always controlled to be greater than the pressure on the rigid baffle plate 4 in the test process, so that the direction of the central main stress is switched from the direction of the connecting line of the two baffle plates 4 to the direction of the connecting line of the two hydraulic bags 8.
And in the soil sample consolidation stage, controlling the stress of the hydraulic bag 8 in the direction and keeping a constant numerical value, and pushing the two rigid baffles 4 by a hydraulic automatic control jack to enable the pressure on the two rigid baffles 4 to be equal to the pressure of the hydraulic bag 8. In the process of the plane strain test, the small principal stress on the hydraulic bag 8 is kept unchanged, and the rigid baffle 4 is extruded after the soil body deforms under the vertical load, so that the pressure on the rigid baffle 4 is increased and is always the middle principal stress; or the pressure value on the hydraulic bag 8 is controlled to be always greater than the main stress on the two rigid baffles 4 in the shearing process, so that the main stress in the direction of the hydraulic bag 8 is always kept as the middle main stress in the shearing process, the main stress on the two rigid baffles 4 is kept as the small main stress, and the rotation of the middle main stress main shaft can be realized. The rotation of the main stress in the soil shearing engineering can adapt to the change of the stress state when the soil is piled or unloaded in the actual engineering and can closely reflect the real stress state of the soil.
Example (b):
the soil body to be measured is placed in a plane strain pressure variable chamber enclosed by the baffles 4 and the hydraulic bag 8, holes are formed in the centers of the two symmetrical baffles 4, and one steel string type soil pressure box 6 is embedded into each of the holes. After a sample is assembled, a hydraulic ultrathin jack 5 is rotationally fixed on an outer cylinder of a pressure chamber in the plane strain direction of the pressure chamber 3 through an M10 loading bolt 7 with the length of 40mm, two pairs of concave smooth rigid baffles 4 are vertically placed, two wings of the jack 5 are embedded into grooves in the back of the smooth rigid baffles 4, so that the hydraulic ultrathin jack 5 is fixed, and the small principal stress direction confining pressure application mode is consistent with the operation of the existing true triaxial apparatus; the pressure chamber top cover 2 is covered, the hydraulic ultrathin jack 5 is pushed to extend through the operation of a computer, the smooth rigid baffle 4 is enabled to move towards the inside of the pressure chamber 3, and therefore the smooth rigid baffle 4 is pushed to be in close contact with a sample, and confining pressure is applied to the sample. The main stress in the soil sample to be measured can be collected through the soil pressure cell 6.
Because the outer cylinder of the pressure chamber 3 outside the hydraulic ultrathin jack 5 and the check valve of the hydraulic ultrathin jack 5 limit the horizontal displacement of the smooth rigid baffle 4 outside caused by the reaction force, the displacement can only develop into the pressure chamber in the soil consolidation and shearing process, so that the smooth rigid baffle 4 is pushed to contact with the sample tightly and the confining pressure is applied to the sample. When confining pressure is applied by the hydraulic ultrathin jack 5 and is slightly larger than the set confining pressure, the hydraulic ultrathin jack 5 is automatically retracted to a certain degree under the control of a computer, pressure generated by the concave smooth rigid baffle 4 on a soil sample is released, a fixed confining pressure set value is reached, and due to the dual displacement limiting characteristics of the system, horizontal movement of the concave smooth rigid baffle 4 is prevented, and a plane strain state in the direction is kept.
During the test, along with the increase of the axial pressure, due to the characteristic of the one-way valve of the jack 5, the jack 5 can not be moved due to the pressure stress generated by the deformation of the soil body to the optical surface rigid baffle 4, thereby ensuring that the sigma is ensured to be moved in the test process2Strain in direction epsilon2Is always zero. To ensure the normal use of the latex mold in the small principal stress direction during the test, the width of the concave smooth rigid baffle 4 is generally increased and the gap is reduced.
The utility model discloses a realize that can regulate and control the reciprocal loading mechanism of plane strain direction principal stress size automatically and design, but the plane strain mechanism of principal stress size on the plane strain direction of direct regulation in soil sample consolidation stage. The plane strain mechanism has the advantages that through reasonable design, the plane strain mechanism is simple and convenient to use and operate, has the function of effectively and automatically adjusting and measuring the magnitude of main stress in the plane strain direction, and effectively overcomes the defect and the defect that the existing rigid baffle plate simulates the stress state of a soil body in the plane strain state. The method is characterized in that the method comprises the following steps of automatically adjusting the magnitude of main stress in the plane strain direction, ensuring that the main stress in the plane strain direction is the middle main stress when a shear test is started, and ensuring that a soil body is in a plane strain state, so that the method is more in line with the actual engineering situation, and further obtaining the strength and deformation characteristics of the geotechnical material under the condition of the plane strain state.
Claims (4)
1. An automatic control type plane strain test mechanism, characterized by comprising:
a pressure chamber (3) having an internal cavity;
a plane strain pressure chamber, which is arranged in the inner cavity of the pressure chamber (3), the inner part of the pressure chamber is also provided with a cavity for placing a soil sample to be tested, the pressure chamber comprises two hydraulic bags (8) and two baffle plates (4), and the plane strain pressure chamber specifically comprises:
the two hydraulic bags (8) are oppositely arranged in the pressure chamber (3), and the relative distance between the two hydraulic bags (8) is a fixed value and is used for applying pressure to the surface of the soil sample to be detected in contact with the hydraulic bags under the water-filled expansion state;
the two baffle plates (4) are smooth rigid plates, are oppositely arranged in the pressure chamber (3) and between the two hydraulic bags (8), and are intersected with the two hydraulic bags (8), and the two baffle plates (4) are used for moving in opposite directions so as to apply pressure to the surface of the soil sample to be detected, which is in contact with the baffle plates;
the bottom of each jack (5) is fixed on the pressure chamber (3), and the telescopic end of each jack (5) is connected to the baffle (4) and used for driving the baffle (4) to move in a reciprocating manner, so that loading or unloading of main stress in the soil sample to be tested is realized;
and the at least two soil pressure boxes (6) are respectively embedded on the inner walls of the two baffles (4) and are used for acquiring the medium main stress data of the soil sample to be measured.
2. An automatic control type plane strain test mechanism as claimed in claim 1, further comprising two jacks (5) whose bottoms are fixedly connected to the outer wall of the pressure chamber (3) through bolts (7).
3. An automatic control type plane strain test mechanism as claimed in claim 1 or 2, characterized in that the bottom of the pressure chamber (3) is provided with a pressure chamber base (1) to seal the bottom of the pressure chamber (3) for being used as a bottom support of a soil sample to be tested.
4. An automatic control type plane strain test mechanism as claimed in claim 1 or 2, wherein a pressure chamber top cover (2) is detachably provided on the top of said pressure chamber (3) to close the top of said pressure chamber (3).
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| Application Number | Priority Date | Filing Date | Title |
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| CN2020209504071 | 2020-05-29 | ||
| CN202020950407 | 2020-05-29 |
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| CN212432829U true CN212432829U (en) | 2021-01-29 |
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