Test device and method for long-term mechanical properties of tunnel concrete considering stress history

Abstract

A test device and method for the long-term mechanical properties of tunnel concrete considering the stress history. The 90° bending plate is composed of a horizontal bottom plate and a vertical plate. The left and right vertical plates are clamped on the left and right side surfaces of the concrete specimen placed on the bottom plate by four transverse bolts. The top surface of the specimen overlaps with the pressure plate, and the top plate is placed on the pressure plate. The top plate and the horizontal bottom plate are clamped on the top and bottom surfaces of the specimen by four vertical bolts. A plurality of springs are arranged between the rear vertical plate attached to the back surface of the specimen and the vertical plate. Elastic gaskets and sheet-type pressure sensors are pressed under the nuts of the above-mentioned bolts. The present invention aims to simulate the 2.5D stress characteristics of the tunnel lining structure under the restraint of the primary lining or surrounding rock behind, and to study and test the mechanical properties of the tunnel under groundwater and erosion conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete mechanical property tests for tunnel engineering, and particularly to a concrete mechanical test device and method considering the stress history. Background Art

[0002] Tunnel engineering is a complex systematic project. During its life cycle, under the action of factors such as the variation of the service environment of the support structure, especially under the action of groundwater and corrosive ions, the concrete material will corrode and deteriorate, resulting in the continuous degradation of the bearing capacity and stiffness of the support structure, and the stress state of the entire tunnel structure system will continuously adjust and evolve dynamically. Therefore, studying the long-term mechanical properties of concrete materials has important engineering value and academic significance.

[0003] Currently, when studying the strength and long-term mechanical properties of tunnel lining concrete, the stress history is usually not considered. In particular, as an underground structure excavated in rock and soil, there is a strong interaction between the support structure and the surrounding rock in tunnel engineering. Due to the resistance generated by the restraint of the surrounding rock or the primary lining behind the tunnel lining, the stress of the tunnel lining usually shows a 2.5D stress characteristic with a free surface (the tunnel clearance side).

[0004] The Chinese patent literature discloses the following: Document 1, a mechanical property detection device for concrete (CN216816271): The concrete specimen is placed between the upper pressure plate and the lower pressure plate, and a vertical pressure is applied through a hydraulic cylinder. Two clamping plates clamp the specimen horizontally through a pair of screws to perform tests such as pressure and tension on the specimen.

[0005] Document 2, a mechanical property detection device for reinforced concrete (CN201893936): There is an upper pressure plate at the top of the concrete specimen and a lower pressure plate at the bottom. Positioning components are arranged on both sides of the specimen. During the process of the testing machine pressing the specimen, the movable plate of the positioning component is pushed down by a push rod, so as to release the support of the movable plate on the strut, ensuring that the specimen is completely separated on both side brackets during the detection process and improving the accuracy of the detection data.

[0006] The tests of the concrete specimens in the above two documents cannot accurately simulate the 2.5D stress characteristics of tunnel lining concrete, and it is difficult to reflect the strength characteristics of the long-term stress of tunnel lining concrete under corrosive groundwater conditions. Currently, there is still a blank in the experimental devices and methods for studying the long-term mechanical properties that can adapt to the stress characteristics of tunnel lining concrete. Summary of the Invention

[0007] To solve the existing technical problems, the present invention proposes a test device for the long-term mechanical properties of concrete considering the stress history, aiming to simulate the 2.5D stress characteristics of a tunnel lining structure under the constraint of the primary lining or surrounding rock behind it, and to study and test the mechanical properties of the tunnel lining structure under groundwater and erosion conditions.

[0008] The object of the present invention is achieved as follows:

[0009] A test device for the long-term mechanical properties of concrete considering the stress history. The 90° bending plate is integrally composed of a horizontal bottom plate and a vertical plate. A cube-shaped concrete specimen is placed on the bottom plate. The left and right side plates are clamped on the left and right side surfaces of the concrete specimen by four transverse bolts. A loading plate with the same length and width as the top surface of the specimen overlaps on the top surface of the concrete specimen. The thickness of the loading plate is greater than the downward distance of the loading plate when the concrete specimen fails in the top-down compression test on a universal testing machine. The top plate is placed on the loading plate, and the top plate and the horizontal bottom plate are clamped on the top and bottom surfaces of the concrete specimen by four vertical bolts. The four vertical bolts are respectively located outside the left and right side plates in pairs (two bolts are located outside the left side plate, and the other two bolts are located outside the right side plate). A plurality of springs for simulating different resistances on the back of the tunnel lining concrete are evenly arranged between the rear side plate that fits the back surface of the concrete specimen and the vertical plate; elastic gaskets and sheet pressure sensors are pressed under the nuts of the four transverse bolts used to apply transverse prestress to the left and right side surfaces of the specimen and the four vertical bolts used to apply longitudinal prestress to the top and bottom surfaces of the specimen.

[0010] The 90° bending plate, the left and right side plates, the loading plate, and the top plate are all corrosion-resistant high-strength steel plates. The four transverse bolts and the four vertical bolts are all corrosion-resistant high-strength bolts; the length and width dimensions of the rear side plate are the same as those of the concrete specimen. [[ID=!0]]

[0011] The thickness of the loading plate is 3 cm, the side length of the concrete specimen is 100 mm, the top surfaces of the left and right side plates are flush with the top surface of the concrete specimen, and the height of the vertical plate is not less than the height of the concrete specimen.

[0012] Another object of the present invention is to provide a test method using the above device.

[0013] Another object of the present invention is achieved as follows:

[0014] A test method for the long-term mechanical properties of concrete considering the stress history, including the following steps:

[0015] Step 1: Fabricate and cure concrete specimens with a side length of 100 mm according to the test requirements. Apply corrosion-resistant high-strength steel plates to the five set stress-bearing surfaces of the concrete specimens. Among them, the steel plate on the top surface (along the loading direction of the press) consists of the top plate and a pressing plate with the same length and width as the concrete specimen and a height of not less than 3 cm. A plurality of springs are evenly arranged directly between the rear vertical plate behind the free surface of the specimen and the vertical plate of the 90° bent plate.

[0016] Step 2: Place the concrete specimens into the device.

[0017] Step 3: Connect the two corrosion-resistant high-strength steel plates on the left and right sides of the specimen with four corrosion-resistant high-strength bolts to prevent the steel plates on the sides from opening during the test. The top plate and the bottom plate are connected by four corrosion-resistant high-strength vertical bolts.

[0018] Step 4: Adjust the prestress applied by the above eight bolts to simulate the stress history under different environments.

[0019] Step 5: Immerse the entire device with the concrete specimens into water or a liquid containing corrosive ions (for the corrosive solution, the concentration of its corrosive ions can be determined and changed according to the test requirements), and soak it to the set conditions according to the test plan: soaking time, number of wet-dry cycles.

[0020] Step 6: Before placing the specimen on the testing machine, the surfaces of the specimen and the upper and lower bearing plates should be wiped clean. The center of the specimen should be aligned with the center of the lower platen of the universal testing machine. Start the universal testing machine for the compression test. The surface of the specimen is in uniform contact with the pressing plate and the bottom plate. The stress-strain curve, failure mode, and its key mechanical parameters (compressive strength, elastic modulus, Poisson's ratio) of the entire process of material failure are obtained through the measurement system of the universal material testing machine output to the control system and the computer.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1) For a concrete mechanical test device and method considering stress history according to the present invention, a combined structure is formed by corrosion-resistant high-strength bolts and surrounding corrosion-resistant high-strength steel plates, and the 2.5D stress characteristics of the tunnel lining structure under the restraint of the primary lining or surrounding rock behind are simulated through the combined structure, so as to provide a new idea and method for a test device and method for studying the long-term mechanical properties of tunnel lining concrete under 2.5D stress characteristics.

[0023] 2) The concrete mechanical test device and method considering the stress history according to the present invention immerse the entire device with the concrete specimen into water or corrosive liquid and soak it to the set conditions (such as time, number of wet-dry cycles) according to the test plan, so as to simulate and study the long-term mechanical properties of tunnel lining concrete under different stress histories and the coupling action of groundwater or groundwater with corrosive ions, and has the advantage of simple operation.

[0024] 3) The concrete mechanical test device and method considering the stress history according to the present invention equivalently simulate different resistances behind the tunnel lining concrete by using springs with different elastic coefficients. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of the test device of the present invention (the height of the vertical plate is flush with the heights of the left and right side plates).

[0026] Figure 2 It is a schematic internal sectional view of the test device of the present invention (the height of the vertical plate is flush with the heights of the left and right side plates).

[0027] Figure 3 It is a front view of the test device of the present invention. (The height of the vertical plate is flush with the heights of the left and right side plates).

[0028] Figure 4 It is a side view of the test device of the present invention. (The height of the vertical plate is greater than the heights of the left and right side plates)

[0029] Figure 5 It is a top view of the test device of the present invention. (The height of the vertical plate is greater than the heights of the left and right side plates)

[0030] Figure 6 It is a schematic diagram of the anti-loosening specimen in the test device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, where: Figure 1It is shown that: The 90° bending plate 9 is integrally composed of a horizontal bottom plate and a vertical plate. The cube-shaped concrete specimen 3 is placed on the bottom plate. The left and right side plates 5 are clamped on the left and right side surfaces of the concrete specimen by four transverse bolts 6. A pressure plate 7 with the same length and width as the top surface of the specimen is overlapped on the top surface of the left concrete specimen. The thickness of the pressure plate is greater than the downward distance of the pressure plate when the concrete specimen is damaged during the compression test from top to bottom on the universal testing machine. The top plate 1 is placed on the pressure plate, and the top plate and the horizontal bottom plate are clamped on the top and bottom surfaces of the concrete specimen by four vertical bolts 2. The four vertical bolts 2 are located outside the left and right side plates 5 and are in contact with the back surface of the concrete specimen. A plurality of springs 8 for simulating different resistances on the back surface of the tunnel lining concrete are evenly arranged between the rear side plate 11 in contact with the back surface of the concrete specimen and the vertical plate; below the nuts of the four transverse bolts used to apply transverse prestress to the left and right side surfaces of the specimen and the four vertical bolts used to apply longitudinal prestress to the top and bottom surfaces of the specimen, elastic gaskets 4 and chip pressure sensors 10 are press-connected (see Figure 2 Figure 3 Figure 4 Figure 5 ).

[0032] See Figure 4 , the lengths of the left and right side plates are greater than the length of the specimen, and the four transverse bolts are respectively located outside the front and back of the specimen. The 90° bending plate 9, the left and right side plates 5, the pressure plate 7, the rear side plate 11, and the top plate 1 are all corrosion-resistant high-strength steel plates, and the four transverse bolts 6 and the four vertical bolts 2 are all corrosion-resistant high-strength bolts; the width of the rear side plate 10 is equal to the width of the concrete specimen, and the height is the same as the height of the left and right side plates 5.

[0033] The thickness of the pressure plate 7 is 3 cm, the side length of the concrete specimen 3 is 100 mm, the top surfaces of the left and right side plates 5 are flush with the top surface of the concrete specimen, and the height of the vertical plate is not less than the height of the concrete specimen.

[0034] First, drill holes at the four corners of the top plate 1 and the horizontal bottom plate to place four vertical bolts 2. Also, drill holes at the four corners of the left and right side vertical plates 5 to place four horizontal bolts 6. Apply prestress through anti-corrosion high-strength bolts to simulate the stress history of the lining concrete in the tunnel lining structure. Among them, the pressure plate 7 also needs to be combined with a steel plate that has the same length and width as the concrete specimen 3 and a height of not less than 3 cm. Its function is to prevent the concrete specimen from being unable to displace during loading due to contact with the three steel plates on the left, right, and each side. The pressure plate 11 is a steel plate that has the same length and width as the concrete specimen 3 and a height of not less than 3 cm. Then, connect and fix the concrete specimen 3 from all four sides by tightening the anti-corrosion high-strength bolts. The anti-corrosion high-strength steel plate simulates the 2.5D stress characteristics of the concrete specimen. The anti-loosening elastic gasket 4 is located between the nut applying prestress and the steel plate to prevent prestress loss during the test. A plurality of springs 8 are arranged between the rear side vertical plate 11 that fits the back surface of the specimen, i.e., the free surface of the specimen, and the vertical plate. By using springs 8 with different elastic coefficients, different resistances behind the tunnel lining concrete are equivalently simulated. Then, immerse the entire fixed device in water or a corrosive liquid and soak it to the set conditions (such as time, number of wet-dry cycles) according to the test plan to simulate the environment of the concrete specimen in the tunnel project. Finally, start the universal testing machine to conduct a compression test to obtain the stress-strain curve of the entire process of material failure.

[0035] The anti-corrosion high-strength steel plates 1 and 5 are fixed from five sides to simulate the stress history and 2.5D stress characteristics of the tunnel lining concrete specimen 3.

[0036] The anti-corrosion high-strength steel plates in contact with the concrete specimen on the upper and lower sides of the loading direction are square steel plates with the same length and width as the concrete specimen 3, and a certain thickness is ensured to prevent the concrete specimen from being unable to displace during loading and being damaged due to contact with the three steel plates on the left, right, and rear sides. For the spring, by using springs 8 with different elastic coefficients and observing the force or deformation of the spring, different resistances behind the tunnel lining concrete are simulated.

[0037] Before loading, the concrete specimen 3 should be immersed in water or a corrosive liquid together with the mechanical device until the set conditions (such as time, number of wet-dry cycles) are reached to simulate the environment of the concrete specimen in the tunnel project.

[0038] The corrosive liquid is a common corrosive factor for tunnel lining concrete, such as containing sulfates, magnesium salts, carbonates, chlorides, etc.

[0039] For the anti-corrosion high-strength bolt 2, apply torque according to the set prestress value during the process of screwing the bolt to generate a pre-tightening force along the axis of the bolt between the bolt and the connected part.

[0040] The high-strength bolts in the longitudinal direction (non-free surface direction) can adjust the prestress according to specific conditions.

[0041] The anti-loosening elastic gasket 4 is located between the nut applying prestress and the steel plate to prevent prestress loss during the test.

[0042] The pressure sensing sheet 10 is located under the anti-loosening elastic gasket 4 to measure the magnitude of the applied prestress.

[0043] The two bolts on the free surface of the concrete specimen are for structural purposes, preventing the two side steel plates 5 from opening during the loading process and ensuring an effective simulation of the mechanical characteristics of the 2.5D tunnel lining.

[0044] A test method for the mechanical properties of concrete considering the stress history includes the following steps:

[0045] Step 1: Fabricate and cure concrete specimens with a side length of 100 mm according to the standard method, and apply anti-corrosion high-strength steel plates to the five set stress surfaces of the concrete specimens. The steel plate on the top surface (along the loading direction of the press) consists of the top plate 1 and a pressing steel plate 7 with the same length and width as the concrete specimen and a height of not less than 3 cm. A plurality of springs are evenly arranged between the rear vertical plate 11 behind the free surface of the specimen and the vertical plate of the 90° bending plate 9.

[0046] Step 2: Place the concrete specimens into the device.

[0047] Step 3: Connect the two anti-corrosion high-strength steel plates on the left and right sides of the specimen with four anti-corrosion high-strength bolts to prevent the steel plates on the sides from opening during the test; connect the top plate and the bottom plate with four anti-corrosion high-strength vertical bolts.

[0048] Step 4: Adjust the prestress applied by the above eight bolts to simulate the stress history under different environments.

[0049] Step 5: Immerse the entire device with the concrete specimens in water or corrosive liquid and soak it to the set conditions according to the test plan: soaking time, number of wet-dry cycles. [[ID=2,9]]

[0050] Before placing the specimen on the testing machine, the surface of the specimen and the upper and lower bearing plate surfaces should be wiped clean. The center of the specimen should be aligned with the center of the lower platen of the universal testing machine. Start the universal testing machine to conduct a compression test. The surface of the specimen is in uniform contact with the pressing plate and the bottom plate. Obtain the stress-strain curve, failure mode, and its key mechanical parameters of the entire process of material failure through the measurement system of the universal material testing machine output to the control system and the computer.

Claims

1. A test device for the long-term mechanical properties of tunnel concrete considering the stress history, characterized in that The 90° bending plate (9) is integrally composed of a horizontal bottom plate and a vertical plate. The cube-shaped concrete specimen (3) is placed on the horizontal bottom plate. The left and right side plates (5) are clamped on the left and right side surfaces of the concrete specimen by four transverse bolts (6). A pressure plate (7) with the same length and width as the top surface of the specimen is overlapped on the top surface of the concrete specimen. The thickness of the pressure plate is greater than the downward distance of the pressure plate when the concrete specimen fails in the compression test from top to bottom on the universal testing machine. The top plate (1) is placed on the pressure plate, and the top plate and the horizontal bottom plate are clamped on the top and bottom surfaces of the concrete specimen by four vertical bolts (2). The four vertical bolts (2) are respectively located outside the left and right side plates (5) in pairs and are in contact with the back surface of the concrete specimen. A plurality of springs (8) for simulating different resistances on the back surface of the tunnel lining concrete are evenly arranged between the rear side plate (11) in contact with the back surface of the concrete specimen and the vertical plate. Elastic gaskets (4) and chip pressure sensors (10) are pressed under the nuts of the four transverse bolts used to apply transverse prestress to the left and right side surfaces of the specimen and the four vertical bolts used to apply longitudinal prestress to the top and bottom surfaces of the specimen.

2. The long-term mechanical property test device for tunnel concrete considering stress history according to claim 1, characterized in that The 90° bending plate (9), the left and right side plates (s), the rear side plate (11), the pressure plate (7) and the top plate (1) are all corrosion-resistant high-strength steel plates. The four transverse bolts (6) and the four vertical bolts (2) are all corrosion-resistant high-strength bolts. The length and width dimensions of the rear side plate (11) are the same as those of the concrete specimen.

3. The long-term mechanical property test device for tunnel concrete considering stress history according to claim 1, characterized in that The thickness of the pressure plate (7) is 3 cm, the side length of the concrete specimen (3) is 100 mm, the top surfaces of the left and right side plates (5) are flush with the top surface of the concrete specimen, and the height of the vertical plate is not less than the height of the concrete specimen.

4. A test method for the long-term mechanical properties test device of tunnel concrete considering the stress history described in claim 2, characterized in that, It includes the following steps: Step 1: Fabricate and cure a concrete specimen with a side length of 100 mm according to the test requirements, and apply corrosion-resistant high-strength steel plates to the five set stress surfaces of the concrete specimen. Among them, on the top surface along the loading direction of the press, the steel plate is composed of the top plate (1) and a pressure plate with the same length and width as the concrete specimen and a height of not less than 3 cm, that is, the pressure plate (7). A plurality of springs (8) are evenly arranged between the rear side plate (11) behind the free surface of the specimen and the vertical plate of the 90° bending plate (9). Chip pressure sensors are arranged on the front side surface of the rear side plate (11). Step 2: Place the concrete specimen (3) into the device. Step 3: Connect the two left and right side plates (5) on the left and right side surfaces of the concrete specimen (3) with four transverse bolts (6) to prevent the left and right side plates (5) from opening during the test. The top plate (1) and the horizontal bottom plate are connected by four vertical bolts (2). Step h: Apply prestress through the above eight bolts to simulate the stress history. Step 5: Immerse the entire device with the concrete specimen (3) in water or corrosive ionic liquid, and immerse it to the set conditions according to the test plan: immersion time, number of wet-dry cycles. For the corrosive solution, its corrosive ion concentration is determined and changed according to the test requirements. Step 6: Before placing the test piece on the testing machine, the center of the test piece should be aligned with the center of the lower platen of the universal testing machine. Start the universal testing machine to conduct the compression test. The surface of the test piece is evenly contacted with the loading platen and the bottom plate. The stress-strain curve, failure mode, and its key mechanical parameters of the entire process of the concrete test piece failure are obtained through the measurement system of the universal testing machine output to the control system and the computer. The key mechanical parameters include compressive strength, elastic modulus, and Poisson's ratio.

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