Test device for simulating freeze-thaw mechanical behavior of surrounding rock of tunnel in cold region

Abstract

The application discloses a test device for simulating the freeze-thaw mechanical behavior of the freeze-thaw circle surrounding rock of a tunnel in a cold region. The device comprises a frame, an upper cover plate, a hydraulic system, springs and rigid pads. The hydraulic system can apply stress to the rock sample in three directions to simulate the stress state of the tunnel surrounding rock. The springs can provide constant stiffness constraint action to the sample to simulate the constant stiffness constraint boundary condition of the tunnel surrounding rock. Through the device and method, the freeze-thaw cycle test of the rock under the constant stiffness constraint condition can be carried out in the freeze-thaw cycle environment, the mechanical state of the tunnel freeze-thaw circle surrounding rock can be effectively simulated, and the research on the freeze-thaw physical and mechanical behavior of the rock under the constant stiffness constraint condition can be carried out.

Description

Technical Field

[0001] The present invention relates to the field of rock mechanics, and in particular to a test device and a test method for simulating the freeze-thaw mechanical behavior of surrounding rock in a freeze-thaw zone of a tunnel in cold regions. Background Art

[0002] Traffic accidents caused by tunnel frost damage often occur, and there have even been cases where tunnels have been abandoned and rebuilt due to severe frost damage.

[0003] As can be seen from this, tunnel frost damage poses a serious threat to the service life and operational safety of tunnels in my country. Based on the temperature field of tunnel surrounding rock, surrounding rock can be divided into freeze-thaw zone surrounding rock and non-freeze-thaw zone surrounding rock. Frost heaving and deformation of tunnel freeze-thaw zone surrounding rock under low temperature is a major cause of tunnel frost damage. Therefore, it is crucial to conduct freeze-thaw cycle tests on rock to study its physical and mechanical behavior. Current experimental research on the physical and mechanical behavior of rock freeze-thaw mainly involves collecting rock samples and conducting unconstrained freeze-thaw cycle tests, followed by physical and mechanical tests to study the physical and mechanical behavior of rock during and after freeze-thaw cycles. However, in addition to enduring long-term freeze-thaw cycles, tunnel freeze-thaw zone surrounding rock is also subject to the constraints of non-freeze-thaw zone surrounding rock and lining. According to the "Code for Design of Railway Tunnels" and the "Code for Design of Highway Tunnels," tunnel freeze-thaw zone surrounding rock is subject to constant stiffness constraints from both non-freeze-thaw zone surrounding rock and lining. Freeze-thaw cycle tests under unconstrained conditions cannot truly reflect the stress state of tunnel surrounding rock. Therefore, it is necessary to develop a test apparatus and method that can simulate the freeze-thaw mechanical behavior of tunnel freeze-thaw zone surrounding rock in cold regions. Summary of the Invention

[0004] The present invention provides a simple-to-operate, reliable-result test device and method for simulating the freeze-thaw mechanical behavior of surrounding rock in tunnel freeze-thaw cycles in cold regions. The device enables rock samples in freeze-thaw cycle experiments to meet realistic constraints and stress conditions.

[0005] The technical solution adopted to achieve the purpose of the present invention is as follows:

[0006] A test device for simulating the freeze-thaw mechanical behavior of surrounding rock in a freeze-thaw zone of a cold region tunnel, characterized by comprising a frame, an upper cover plate, a hydraulic system, springs, and rigid pads;

[0007] The frame includes a first column, a second column, a third column, and a fourth column.

[0008] The hydraulic system includes a first hydraulic system, a second hydraulic system, and a third hydraulic system. The hydraulic system has an automatic force measurement function and can read the forces on the sample in three directions in real time.

[0009] The bottom of the frame is connected to the first hydraulic system, and the two columns on the frame that are not in the same straight line are respectively equipped with the second hydraulic system and the third hydraulic system;

[0010] The upper parts of the first column, the second column, the third column and the fourth column are fixedly connected to the upper cover plate;

[0011] The spring includes a first spring and a second spring, and the spring provides a constant stiffness constraint for the rock sample to be tested in the vertical direction; the stiffness of the second spring is equal to the stiffness of the surrounding rock in the non-freeze-thaw zone, and the stiffness of the first spring is equal to the stiffness of the lining;

[0012] Rigid pads are attached to the six sides of the rock sample to be tested, and the cross-sectional dimensions of the rigid pads are smaller than the surface dimensions of the corresponding rock sample.

[0013] The upper cover plate is a "cross"-shaped plate, and each edge end of the "cross"-shaped plate is vertically fixed to a column; the cross-section of the rigid pad is square, and the cross-sectional width and length of the rigid pad are 1mm smaller than the width and length of the corresponding side of the specimen.

[0014] The rigid pad is in the shape of a cuboid.

[0015] The present invention also protects a test method for simulating the freeze-thaw mechanical behavior of surrounding rock in a tunnel freeze-thaw zone in cold regions. The test method uses the above-mentioned test device and includes the following steps:

[0016] (1) Obtain the stiffness of the non-freeze-thaw zone surrounding rock and the stiffness of the lining where the rock sample to be tested is located, determine the stiffness of the second spring 402 according to the stiffness of the non-freeze-thaw zone surrounding rock, and determine the stiffness of the first spring 401 according to the stiffness of the lining. The stiffness of the springs is equal to the stiffness of the corresponding non-freeze-thaw zone surrounding rock and lining;

[0017] (2) Prepare rock samples collected from the surrounding rock of the freeze-thaw zone;

[0018] (3) Install the three hydraulic systems on the bottom support and two columns of the frame respectively. The two columns are not in the same straight line. Install the first spring 401 on the hydraulic system connected to the bottom support.

[0019] (4) A rigid pad is installed on the first spring, and rigid pads are also installed on the output surfaces of the other two hydraulic systems. Rigid pads are directly fixed on the other two columns, and all rigid pads form a semi-enclosed space; the rock sample to be tested is placed in the semi-enclosed space, and the corresponding hydraulic system is adjusted so that each side of the rock sample to be tested can fit with the corresponding rigid pad; then a rigid pad is also installed on the top of the rock sample to be tested, and the second spring is installed at the same time, and an upper cover plate is fixed above the second spring, and the upper cover plate is fixed to the top surfaces of the four columns; one end of the second spring is fixed on the rigid pad, and the other end is fixed in contact with the upper cover plate. At this time, the second spring and the first spring are in a natural extension state or a slightly compressed state;

[0020] (5) The initial stress and boundary conditions are applied to the rock sample through three hydraulic systems to meet the state of the rock before mining. At this time, the two springs give initial stress in the axial direction, and the other two directions are self-constrained. The initial stress is applied to restore the rock sample to the state before mining. At this time, all rigid pads are tightly fitted with the rock sample and the column to be tested, generating a constraint effect; the frame and the upper cover are connected by bolts to form a reaction frame. The rock sample to be tested is constrained by the constant stiffness of the two springs in the vertical direction, and by the constant stiffness of the rigid pads and the hydraulic system in other directions;

[0021] (6) Place the device with the rock sample to be tested installed in step (7) into a freeze-thaw environment to conduct a freeze-thaw cycle test under constant stiffness constraints.

[0022] Compared with the prior art, the technical effects of the present invention are undoubted:

[0023] (a) The device of the present invention is easy to operate and can be assembled by bolt connection.

[0024] (b) The device of the present invention can apply stress to the rock sample in three directions through the hydraulic system to simulate the stress state of the tunnel surrounding rock.

[0025] (c) The first spring and the second spring can provide the specimen with a constant stiffness constraint boundary condition, simulating the constant stiffness constraint of the lining and the non-freeze-thaw zone surrounding rock on the freeze-thaw zone surrounding rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of the three-dimensional structure of an embodiment of a test device for simulating the freeze-thaw mechanical behavior of surrounding rock in the freeze-thaw zone of a tunnel in cold regions.

[0027] Figure 2 The present invention is a schematic diagram of the three-dimensional structure of the framework of an embodiment of the test device for simulating the freeze-thaw mechanical behavior of the surrounding rock of the freeze-thaw zone of a tunnel in cold regions.

[0028] Figure 3 The figure is a schematic diagram of the top cover structure of an embodiment of the test device for simulating the freeze-thaw mechanical behavior of surrounding rock in the freeze-thaw zone of a tunnel in cold regions according to the present invention.

[0029] Figure 4 This is a schematic diagram of the installation structure of the rigid pad, spring, and hydraulic system assembly.

[0030] In the figure: frame 1; first column 101; second column 102; third column 103; fourth column 104; countersunk hole 105; upper cover plate 2; upper cover plate countersunk hole 201; hydraulic system 3; first hydraulic system 301; second hydraulic system 302; third hydraulic system 303; spring 4; first spring 401; second spring 402; rigid pad 5; first rigid pad 501; second rigid pad 502; third rigid pad 503; fourth rigid pad 504; fifth rigid pad 505; sixth rigid pad 506. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the following examples, but it should not be understood that the scope of the present invention is limited to the following examples. Without departing from the above technical ideas of the present invention, various substitutions and modifications can be made according to common technical knowledge and customary means in the art, and all should be included in the scope of protection of the present invention.

[0032] Example 1:

[0033] This embodiment discloses a test device for simulating the freeze-thaw mechanical behavior of the surrounding rock of the freeze-thaw zone of a tunnel in a cold region. Figure 1 , including: frame 1, upper cover 2, hydraulic system 3, spring 4, rigid pad 5. The frame 1 has a bottom support and four columns perpendicular to the bottom support. The upper part is open and connected to the upper cover 2 by bolts to form a whole. The upper cover is a "cross" plate, and each edge end of the "cross" plate is vertically fixed to a column.

[0034] A first hydraulic system is fixed on the upper surface of the bottom support, and a fourth rigid pad 504 is installed in the first hydraulic system through a first spring 401, and a sample to be tested is placed on the fourth rigid pad. The rock sample to be tested is a rectangular structure, and a third rigid pad 503 is arranged on the top surface of the rectangular block. A second spring 402 is installed in the center of the third rigid pad 503, and the upper end of the second spring 402 contacts the upper cover plate 2; one of the two opposite sides of the rectangular block is connected to a hydraulic system through a rigid pad, and the two hydraulic systems are fixed together with the columns on the corresponding frame by bolts, and the other two sides of the two opposite sides of the rectangular block are directly attached with rigid pads; all the sides of the rectangular block are fixed to the frame columns through the corresponding rigid pads and the hydraulic system or directly through the corresponding rigid pads; the axes of the first spring and the second spring are in the same straight line with the vertical axis of the rock sample.

[0035] See also Figure 1 and Figure 2 The frame includes a first column 101, a second column 102, a third column 103, and a fourth column 104. The first column 101, the second column 102, the third column 103, and the fourth column 104 each have a countersunk hole 105 on the side, and each column has two threaded holes 106 on the top.

[0036] See also Figure 4 The hydraulic system includes a first hydraulic system 301, a second hydraulic system 302, and a third hydraulic system 303. The hydraulic system has an automatic force measurement function and can read the forces on the sample in three directions in real time.

[0037] See also Figure 1 The bottom of the frame 1 is connected to the first hydraulic system 301 by bolts. The first column 101 and the second column 102 are connected to the second hydraulic system 302 and the third hydraulic system 303 by bolts respectively.

[0038] See also Figure 1 The first column 101, the second column 102, the third column 103, and the fourth column 104 are connected to the upper cover plate 2 by bolts through corresponding threaded holes.

[0039] See also Figure 3 The upper cover plate 2 is in a "cross" shape, and has a countersunk hole 201 on the upper cover plate, which is connected to the frame column by bolts.

[0040] See also Figure 1 The spring 4 includes a first spring 401 and a second spring 402 , and the spring 4 provides a constant stiffness constraint for the sample in the vertical direction.

[0041] See also Figure 4The rigid pads 5 include a first rigid pad 501, a second rigid pad 502, a third rigid pad 503, a fourth rigid pad 504, a fifth rigid pad 505, and a sixth rigid pad 506. The rigid pads 5 are tightly attached to the surface of the sample, and the cross-sectional area of the rigid pads 5 is slightly smaller than the size of the corresponding sample surface, so that the sample can deform freely. In this embodiment, there are two thicknesses of rigid pads, the first rigid pad 501 and the fifth rigid pad 505 have a thickness of about 50 mm, and the other rigid pads have a thickness of about 10 mm.

[0042] The cross section of the rigid pad is a square, which is slightly smaller than the sample 1 mm, and the thickness of different rigid pads can be different, so as to ensure that the rigid pad can be tightly attached to the sample in the presence of the rigid pad. The rock sample is a cube sample with a size of 100 mm*100 mm*100 mm. The second spring is used to simulate the constant stiffness constraint of the non-frozen circle surrounding rock on the frozen circle surrounding rock, and the first spring is used to simulate the constant stiffness constraint of the lining on the frozen circle surrounding rock.

[0043] Embodiment 2:

[0044] The embodiment discloses a test method for the test device for simulating the freezing and thawing mechanical behavior of the frozen and thawing circle surrounding rock of a tunnel in a cold region according to embodiment 1, and the test method comprises the following steps:

[0045] (1) Obtain the stiffness of the non-frozen circle surrounding rock where the rock sample to be tested is located and the stiffness of the lining. The stiffness can be obtained according to actual measurement or experience. The stiffness of the second spring 402 is determined according to the stiffness of the non-frozen circle surrounding rock, and the stiffness of the first spring 401 is determined according to the stiffness of the lining. The stiffness of the spring is equal to the stiffness of the corresponding non-frozen circle surrounding rock and lining.

[0046] (2) Prepare the rock sample collected from the frozen and thawing circle surrounding rock.

[0047] (3) Install three hydraulic systems on the bottom support of the frame and the two columns, respectively. The two columns are not on the same straight line. The first spring 401 is installed on the hydraulic system connected to the bottom support.

[0048] (4) A pad is installed on the first spring, and rigid pads are also installed on the output surfaces of the other two hydraulic systems. Rigid pads are directly fixed on the other two columns, and all rigid pads form a semi-enclosed space; the rock sample to be tested is placed in the semi-enclosed space, and the corresponding hydraulic system is adjusted so that each side of the rock sample to be tested can fit with the corresponding rigid pad. At this time, each side of the rock sample to be tested can fit with the corresponding rigid pad, and the pad just fits with the sample but does not exert any force; then a rigid pad is also installed on the top of the rock sample to be tested, and the second spring is installed at the same time, and an upper cover is fixed above the second spring, and the upper cover is fixed to the top surfaces of the four columns; one end of the second spring is fixed on the rigid pad, and the other end is fixed in contact with the upper cover. At this time, the second spring and the first spring are in a natural extension state or a slightly compressed state;

[0049] (5) Initial stress and boundary conditions are applied to the rock sample through three hydraulic systems to meet the state of the rock before mining. At this time, the two springs give initial stress in the axial direction, and the other two directions are self-constrained. The initial stress is applied to restore the rock sample to its unmined state. At this time, all rigid pads are tightly fitted with the rock sample and the column to be tested, generating a constraint effect. The frame is connected by bolts to form a reaction frame. The rock sample to be tested is constrained by the constant stiffness of the two springs in the vertical direction, and by the constant stiffness of the rigid pads and the hydraulic system in other directions.

[0050] (6) Place the device with the rock sample to be tested installed in step (7) into a freeze-thaw environment to conduct a freeze-thaw cycle test under constant stiffness constraints.

[0051] Once the spring stiffness is determined, freeze-thaw cycles will cause the rock specimen to expand in volume, compressing the rigid spacers. During experimental use, neither spring nor hydraulic system adjustment is required. However, if the specimen's restraint and stress state need to be altered before testing, the stress applied by the hydraulic system can be adjusted or springs of different stiffness can be replaced to simulate the unmined surrounding rock of a tunnel in a cold region with different geographical environments. The hydraulic system in three directions is adjusted based on the stress state of the surrounding rock in the freeze-thaw zone.

[0052] The present invention can regard the second spring and the third rigid pad at the top as the surrounding rock as a whole, and the first spring and the fourth rigid pad at the bottom as the lining, which can simulate the constant stiffness effect of the non-freeze-thaw zone surrounding rock and the lining on the freeze-thaw zone surrounding rock, and at the same time can simulate the initial stress state of the freeze-thaw zone surrounding rock to realize three-dimensional force.

[0053] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A test method for simulating the freeze-thaw mechanical behavior of surrounding rock in a tunnel freeze-thaw zone in cold regions, characterized in that: The method uses a test device that simulates the freeze-thaw mechanical behavior of surrounding rock in the freeze-thaw zone of a cold region tunnel. The test device includes a frame, an upper cover plate, a hydraulic system, springs, and rigid pads. The frame includes a first column, a second column, a third column, and a fourth column. The hydraulic system includes a first hydraulic system, a second hydraulic system, and a third hydraulic system. The hydraulic system has an automatic force measurement function and reads the force in three directions of the sample in real time. The first hydraulic system is installed at the bottom of the frame, and the second hydraulic system and the third hydraulic system are installed on two columns on the frame that are not in the same straight line respectively; The upper parts of the first column, the second column, the third column and the fourth column are fixedly connected to the upper cover plate; The spring includes a first spring and a second spring, and the spring provides a constant stiffness constraint for the rock sample to be tested in the vertical direction; the stiffness of the second spring is equal to the stiffness of the surrounding rock in the non-freeze-thaw zone, and the stiffness of the first spring is equal to the stiffness of the lining; Rigid pads are attached to the six sides of the rock sample to be tested, and the cross-sectional dimensions of the rigid pads are smaller than the surface dimensions of the corresponding rock sample; The test method comprises the following steps: (1) Obtain the stiffness of the non-freeze-thaw zone surrounding rock and the stiffness of the lining where the rock sample to be tested is located. Determine the stiffness of the second spring based on the stiffness of the non-freeze-thaw zone surrounding rock, and determine the stiffness of the first spring based on the stiffness of the lining. The stiffness of the spring is equal to the stiffness of the corresponding non-freeze-thaw zone surrounding rock and lining. (2) Prepare rock samples collected from the surrounding rock of the freeze-thaw zone; (3) Install the three hydraulic systems on the bottom support and two columns of the frame respectively. The two columns are not in the same straight line. Install the first spring on the hydraulic system connected to the bottom support. (4) A rigid pad is installed on the first spring, and rigid pads are also installed on the output surfaces of the other two hydraulic systems. Rigid pads are directly fixed on the other two columns, and all rigid pads form a semi-enclosed space; the rock sample to be tested is placed in the semi-enclosed space, and the corresponding hydraulic system is adjusted so that each side of the rock sample to be tested can fit with the corresponding rigid pad; then a rigid pad is also installed on the top of the rock sample to be tested, and the second spring is installed at the same time, and an upper cover plate is fixed above the second spring, and the upper cover plate is fixed to the top surfaces of the four columns; one end of the second spring is fixed on the rigid pad, and the other end is fixed in contact with the upper cover plate; at this time, the second spring and the first spring are in a natural extension state or a slightly compressed state; (5) The initial stress and boundary conditions are applied to the rock sample through three hydraulic systems to meet the state of the rock before mining. At this time, the two springs give initial stress in the axial direction, and the other two directions are self-constrained. The initial stress is applied to restore the rock sample to the state before mining. At this time, all rigid pads are tightly fitted with the rock sample and the column to be tested, generating a constraint effect; the frame and the upper cover are connected by bolts to form a reaction frame. The rock sample to be tested is constrained by the constant stiffness of the two springs in the vertical direction, and by the constant stiffness of the rigid pads and the hydraulic system in other directions; (6) Place the device with the rock sample to be tested in a freeze-thaw environment to conduct a freeze-thaw cycle test under constant stiffness constraints; The hydraulic system applies stress to the rock sample in three directions to simulate the stress state of the tunnel surrounding rock, and at the same time simulates the initial stress state of the freeze-thaw zone surrounding rock to achieve three-dimensional stress.

2. The test method for simulating the freeze-thaw mechanical behavior of surrounding rock in a tunnel freeze-thaw zone in cold regions according to claim 1, characterized in that: The upper cover plate is a "cross"-shaped plate, and each edge end of the "cross"-shaped plate is vertically fixed to a column; the cross-section of the rigid pad is square, and the cross-sectional width and length of the rigid pad are 1mm smaller than the width and length of the corresponding side of the specimen.

3. The test method for simulating the freeze-thaw mechanical behavior of surrounding rock in a tunnel freeze-thaw zone in cold regions according to claim 1, characterized in that: The rigid pad is in the shape of a cuboid.

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