Method for testing triaxial shear strength of drainage tunnel circular seam plugging ice plug body

Abstract

The invention discloses a triaxial shear strength testing method for a sewage discharge tunnel circular seam plugging ice plug body. The method comprises the following steps: S1, cutting a cylindrical sponge sample from medium-density sponge; s2, sleeving the side surface of the cylindrical sponge sample with a rubber membrane, and mounting a bottom steel support at the bottom; s3, injecting water into the cylindrical sponge sample in the rubber membrane to obtain a cylindrical sponge sample after water injection; s4, the cylindrical sponge sample after water injection is placed in a test block curing box and frozen at different set temperatures to form cylindrical sponge ice samples, and the set temperatures are the same as the average temperature of an ice plug body planned to be formed through liquid nitrogen freezing construction; s5, placing the cylindrical sponge ice sample in a triaxial testing machine, and performing a triaxial shear strength test under a set confining pressure to determine the shear strength of the cylindrical sponge ice sample under a simulated working condition; and S6, according to the test data in the S5, obtaining the triaxial shear characteristics of the cylindrical sponge ice at different set temperatures. The technical difficulty that an in-situ shear test cannot be performed on the ice plug body on site is solved.

Description

Technical Field

[0001] This invention relates to the technical field of testing triaxial shear strength. Specifically, it relates to a method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels. Background Technology

[0002] In a certain area, a sewage tunnel is planned to be sealed using liquid nitrogen freezing to form an ice plug. The liquid nitrogen freezer coil is fixed to a semi-circular steel plate, which serves to fix the tunnel, conduct heat, and block water flow. The circumferential joint between the outer edge of the steel plate and the inner wall of the tunnel is 80mm wide. The circumferential joint is sealed by wrapping the outer edge of the steel plate with sponge to reduce heat convection between the water in the area to be frozen and the surrounding water, thus accelerating the formation of the frozen body.

[0003] To understand the mechanical properties of ice plugs formed after sponge freezing, and to provide necessary parameters and basis for the liquid nitrogen freezing construction of the tunnel, it is necessary to obtain the triaxial shear strength of the ice plugs. However, since the sewage tunnel is filled with sewage, in-situ shear tests on the ice plugs cannot be conducted on-site. Therefore, this invention proposes a method for testing the triaxial shear strength of ice plugs used for sealing circumferential joints in sewage tunnels. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a triaxial shear strength test method for ice plugs used to seal circumferential joints in sewage tunnels. The data obtained can be used to guide the construction of circumferential joint sealing in sewage tunnels, reducing the major risks of liquid nitrogen freezing and sealing sewage pipelines, and ensuring the safety of liquid nitrogen freezing and sealing sewage construction.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels includes the following steps:

[0007] S1, Sample Preparation

[0008] Cylindrical sponge samples were cut from medium-density sponge for later use;

[0009] S2, Packaging

[0010] A rubber membrane is fitted onto the side of a cylindrical sponge sample, with the top and bottom surfaces exposed. The bottom of the rubber membrane is installed inside a bottom steel support, with the bottom end of the bottom steel support closed and the top end open, so that the bottom of the rubber membrane can extend into it.

[0011] S3, Water Injection

[0012] Water is injected into the cylindrical sponge sample inside the rubber membrane from the top bottom of the cylindrical sponge sample, so that the cylindrical sponge sample fully absorbs water to obtain the cylindrical sponge sample after water injection.

[0013] S4, Freezing Maintenance

[0014] The cylindrical sponge samples after being injected with water were placed in the test block curing box and frozen at different set temperatures to form cylindrical sponge ice samples. The set temperatures were the same as the average temperature of the ice plug body to be formed by liquid nitrogen freezing in the sewage tunnel annular joint sealing freezing condition. The cylindrical sponge ice samples were used to simulate the ice plug body to be formed by the sponge in the sewage tunnel annular joint sealing freezing condition.

[0015] S5, Triaxial Shear Test

[0016] After the top of the rubber membrane is installed in the top steel support, the cylindrical sponge ice sample is placed in the triaxial testing machine. The upper end of the top steel support is closed and the lower end is open so that the top of the rubber membrane can be inserted into it. Under the set confining pressure, the cylindrical sponge ice sample is kept in an unconsolidated and undrained state, and axial loading is applied until the cylindrical sponge ice sample is destroyed. The axial load and deformation data are recorded in real time.

[0017] S6. Results Analysis

[0018] Based on the experimental data from S5, the triaxial shear characteristics of cylindrical sponge ice samples at different set temperatures were obtained.

[0019] This application uses medium-density sponge, whose water absorption efficiency, freezing expansion force, and mechanical strength are more suitable for the on-site working conditions of freezing and sealing sewage tunnels. Furthermore, as a soft sponge, it provides better adhesion to the circumferential joint between the sealing steel plate and the sewage tunnel wall, facilitating on-site wrapping construction. A rubber membrane is fitted over the sides of a cylindrical sponge sample, with the top and bottom surfaces exposed. A bottom steel support is placed at the bottom of the rubber membrane, and a rubber band is installed at the connection between the bottom steel support and the rubber membrane. Water is injected into the cylindrical sponge sample, and it is frozen at a set temperature to form a cylindrical sponge ice sample, which is used for... This invention simulates the ice plug formed by a sponge during liquid nitrogen freezing. It transforms the challenging on-site condition of sponge filling annular joints and then freezing into a model that can be precisely replicated and measured in a laboratory. During triaxial shear testing, a top steel support is installed on top of a rubber membrane, with a rubber band at the connection between the support and the membrane, and the membrane is placed in a triaxial testing machine. This testing method yields accurate and reliable shear strength parameters for the ice plug formed by the frozen sponge within the annular space between the sealing steel plate and the sewage tunnel wall. The parameters obtained from this method can then be used to guide the liquid nitrogen freezing construction for sealing annular joints in sewage tunnels. Each step in this application is interconnected and indispensable, precisely solving complex practical engineering problems. It overcomes the technical difficulty of conducting in-situ shear tests on the ice plug formed between the sealing steel plate and the sewage tunnel wall at the sewage tunnel freezing and sealing site, reducing the significant risks of liquid nitrogen freezing for sewage pipeline construction and ensuring the safety of this construction.

[0020] In the above-mentioned triaxial shear strength test method for ice plugs used to seal the circumferential joint of the sewage tunnel, in S1, the cylindrical sponge sample has a size of Φ61.8mm×100mm.

[0021] In the above-mentioned triaxial shear strength test method for ice plugs used to seal circumferential joints in sewage tunnels, in step S1, the density of the medium-density sponge is 20 kg / m³. 3 Medium-density sponge samples were taken using an electrothermal cutting knife and a ring cutter to ensure that the cylindrical sponge samples were uniform in size and shape, thus improving the reliability of the test.

[0022] In the above-mentioned triaxial shear strength test method for ice plugs used to seal the circumferential joints of sewage tunnels, a fastening mechanism is installed at the connection between the bottom steel support and the rubber diaphragm in S2; and at the connection between the top steel support and the rubber diaphragm in S5. By installing bottom and top steel supports, necessary support and stability are provided during the triaxial shear strength test under loading conditions.

[0023] The above-mentioned triaxial shear strength test method for the ice plug body of the circumferential joint sealing of the sewage tunnel uses a rubber band as the fastening mechanism, so that water will not flow out after the cylindrical sponge sample is injected, thus ensuring the formation of the subsequent cylindrical sponge ice sample.

[0024] In the above-mentioned triaxial shear strength test method for ice plugs used to seal the circumferential joints of sewage tunnels, in S4, the set temperatures are -15℃, -20℃ and -25℃, which are the same as the temperatures of the ice plugs to be formed during liquid nitrogen freezing.

[0025] The above-mentioned method for testing the triaxial shear strength of ice plugs used to seal the circumferential joints of sewage tunnels involves preparing multiple cylindrical sponge ice samples at each temperature for parallel testing.

[0026] In the above-mentioned triaxial shear strength test method for ice plugs used to seal the circumferential joints of sewage tunnels, S5 employs a constant axial strain rate control method for axial loading, with the confining pressure determined based on the water level height within the sewage tunnel to be treated. For viscoplastic materials like sponge ice, constant axial strain rate loading can avoid creep effects, facilitating the acquisition of accurate stress-strain curves and thus accurately determining shear strength.

[0027] The above-mentioned method for testing the triaxial shear strength of ice plugs used to seal the circumferential joints of sewage tunnels has an axial strain rate of 0.5~1% / min.

[0028] The above-mentioned method for testing the triaxial shear strength of ice plugs used to seal the circumferential joints of sewage tunnels uses an axial strain rate of 1% / min.

[0029] The technical solution of the present invention achieves the following beneficial technical effects:

[0030] Because the sewage tunnel is filled with sewage, it is impossible to conduct in-situ shear tests on the ice block between the sealing steel plate and the sewage tunnel wall on site. This application uses a cylindrical sponge sample with a rubber membrane fitted on the side and the top and bottom surfaces exposed. A bottom steel support is placed at the bottom of the rubber membrane, and a rubber band is placed at the connection between the bottom steel support and the rubber membrane. Water is injected into the cylindrical sponge sample and it freezes at a set temperature to form a cylindrical sponge ice sample, which is used to simulate the ice block to be formed by the sponge during liquid nitrogen freezing construction. This simulates the difficult-to-test on-site working condition of sponge filling the circumferential joint and freezing after absorbing water in the project into a model that can be accurately replicated and measured in the laboratory. When conducting triaxial shear tests, a top steel support is installed on top of the rubber membrane, and a rubber band is placed at the connection between the top steel support and the rubber membrane. The sample is then placed in a triaxial testing machine for testing. This testing method can obtain accurate and reliable shear strength parameters of the ice block suitable for sponge freezing in the annular space between the sealing steel plate and the sewage tunnel wall.

[0031] The testing method of this invention is simple, requires few equipment, and has the technical advantages of short testing time, low cost, and accurate test results. Ultimately, the parameters obtained from this testing method can be applied to guide the liquid nitrogen freezing and sealing construction of sewage tunnel circumferential joints. Each step of this application is interconnected and indispensable, accurately restoring and testing the triaxial shear strength of sponge ice. This solves the technical difficulty of not being able to conduct in-situ shear tests on the ice plug between the sealing steel plate and the sewage tunnel wall at the sewage tunnel freezing and sealing site, reducing the significant risks of liquid nitrogen freezing and sealing sewage pipeline construction, and ensuring the safety of liquid nitrogen freezing and sealing sewage construction. Attached Figure Description

[0032] Figure 1 This describes the density sponge sampling process in this invention;

[0033] Figure 2 Image of the cylindrical sponge sample of the present invention;

[0034] Figure 3 This is a picture of the cylindrical sponge sample of the present invention after the rubber membrane, bottom steel support, and rubber band have been installed. Detailed Implementation

[0035] A method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels includes the following steps:

[0036] Step A: Use an electrothermal cutting blade and a ring cutter to sample the medium-density sponge, obtaining cylindrical sponge samples, see attached. Figure 1 The cylindrical sponge sample measures Φ61.8mm × 100mm (diameter × height), see attached. Figure 2 ;

[0037] Specifically, the ring cutter is pressed onto the surface of the medium-density sponge, and an electrothermal cutting blade is used to cut the medium-density sponge around the outer surface of the ring cutter while cutting, until a complete cylindrical sponge sample is removed.

[0038] Step B: Place the cut cylindrical sponge sample side-mounted with a rubber membrane, leaving the top and bottom surfaces exposed. Install the bottom of the rubber membrane inside the bottom steel support. The bottom end of the bottom steel support is closed, while the top end is open, allowing the bottom of the rubber membrane to extend into it. A rubber band is installed at the connection point between the bottom steel support and the rubber membrane. (See attached document) Figure 3 ;

[0039] Step C: Inject tap water into the cylindrical sponge sample inside the rubber membrane from the bottom of the cylindrical sponge sample, so that the cylindrical sponge sample can fully absorb water to obtain the cylindrical sponge sample after water injection.

[0040] Step D: Place the water-filled cylindrical sponge samples into a curing chamber. The curing chamber temperatures are set to -15℃, -20℃, and -25℃, respectively. These temperatures are the same as the average temperature of the ice plugs to be formed during liquid nitrogen freezing in the sewage tunnel annular joint sealing freezing condition. Three temperature test groups are used, with three cylindrical sponge samples prepared in each group, for a total of nine cylindrical sponge samples. After freezing for at least 24 hours, cylindrical sponge ice samples are prepared. These cylindrical sponge ice samples are used to simulate the ice plugs to be formed during liquid nitrogen freezing in the sewage tunnel annular joint sealing freezing condition.

[0041] Step E: Install the top of the rubber membrane inside the top steel support. The top end of the top steel support is closed and the bottom end is open so that the top of the rubber membrane can extend into it. (A rubber band is also provided at the connection between the top steel support and the rubber membrane.) Then, place the cylindrical sponge ice sample into the frozen soil triaxial testing machine controlled by the WDTS-200 microcomputer. Under the set confining pressure (0.5MPa), keep the sample in an unconsolidated and undrained state (drainage and volume deformation of the cylindrical sponge ice sample are not allowed when the confining pressure is applied). Perform axial loading until the cylindrical sponge ice sample fails, and record the axial load and deformation data in real time. A constant axial strain rate control method is used for axial loading, and the axial strain rate is 1% / min.

[0042] Step F: Analyze the triaxial shear test results of cylindrical sponge ice at different temperatures, and analyze the triaxial shear characteristics of cylindrical sponge ice. This provides mechanical parameters for liquid nitrogen freezing and sealing of sewage pipelines, reduces the significant risks of liquid nitrogen freezing and sealing of sewage pipelines, and ensures the safety of liquid nitrogen freezing and sealing of sewage pipelines. Partial results of the triaxial shear strength test of the ice plug are shown in Table 1 below; where... This represents the maximum axial stress of the specimen at shear failure. For confining pressure.

[0043] Table 1

[0044]

[0045] Ultimately, based on the parameters obtained in the simulation environment, it can be applied to guide the liquid nitrogen freezing and sealing construction of the circumferential joint of sewage tunnels. This solves the technical dilemma of not being able to conduct in-situ shear tests on the ice plug between the sealing steel plate and the sewage tunnel wall at the sewage tunnel freezing and sealing site, reduces the major risks of liquid nitrogen freezing and sealing sewage pipeline construction, and ensures the safety of liquid nitrogen freezing and sealing sewage construction.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels, characterized in that... Includes the following steps: S1, Sample Preparation Cylindrical sponge samples were cut from medium-density sponge for later use; S2, Packaging A rubber membrane is fitted onto the side of a cylindrical sponge sample, with the top and bottom surfaces exposed. The bottom of the rubber membrane is installed inside a bottom steel support, with the bottom end of the bottom steel support closed and the top end open, so that the bottom of the rubber membrane can extend into it. S3, Water Injection Water is injected into the cylindrical sponge sample from the top bottom onto the inner side of the rubber membrane, allowing the sample to fully absorb water, resulting in a water-filled cylindrical sponge sample; S4, Freeze curing. The cylindrical sponge samples after being injected with water were placed in the test block curing box and frozen at different set temperatures to form cylindrical sponge ice samples. The set temperatures were the same as the average temperature of the ice plug body to be formed by liquid nitrogen freezing in the sewage tunnel annular joint sealing freezing condition. The cylindrical sponge ice samples were used to simulate the ice plug body to be formed by the sponge in the sewage tunnel annular joint sealing freezing condition. S5. Triaxial Shear Test: After the top of the rubber membrane is installed in the top steel support, the cylindrical sponge ice sample is placed in the triaxial testing machine. The upper end of the top steel support is closed and the lower end is open so that the top of the rubber membrane can extend into it. Under the set confining pressure, the cylindrical sponge ice sample is kept in an unconsolidated and undrained state, and axial loading is applied until the cylindrical sponge ice sample is destroyed. The axial load and deformation data are recorded in real time. S6. Results Analysis Based on the data from S5, the triaxial shear characteristics of the cylindrical sponge ice sample at different set temperatures were obtained.

2. The method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels according to claim 1, characterized in that, In S1, the cylindrical sponge sample has dimensions of Φ61.8mm×100mm.

3. The method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels according to claim 1, characterized in that, In S1, the density of the medium-density sponge is 20 kg / m³. 3 Medium-density sponge was sampled using an electrothermal cutting blade and a ring cutter.

4. The method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels according to claim 1, characterized in that, In S2, a fastening mechanism is provided at the connection between the bottom steel support and the rubber membrane; in S5, a fastening mechanism is provided at the connection between the top steel support and the rubber membrane.

5. The method for testing the triaxial shear strength of the ice plug body used to seal the circumferential joint of a sewage tunnel according to claim 4, characterized in that, The fastening mechanism is a rubber band.

6. The method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels according to claim 1, characterized in that, In S4, the set temperatures are -15℃, -20℃, and -25℃.

7. The method for testing the triaxial shear strength of an ice plug in a sewage tunnel circumferential joint as described in claim 6, characterized in that, Multiple cylindrical sponge ice samples were prepared at each temperature for parallel testing.

8. The method for testing the triaxial shear strength of ice plugs used to seal circumferential joints in sewage tunnels according to claim 1, characterized in that, In S5, a constant axial strain rate control method is used for axial loading; the confining pressure is determined based on the water level in the sewage tunnel to be treated.

9. The method for testing the triaxial shear strength of an ice plug in a sewage tunnel annular joint seal according to claim 8, characterized in that, The axial strain rate is 0.5~1% / min.

10. The method for testing the triaxial shear strength of an ice plug in a sewage tunnel annular joint seal according to claim 9, characterized in that, The axial strain rate is 1% / min.

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