Dynamic bond test model between shotcrete and rock and method for determining safe blasting point

Abstract

The present invention relates to a dynamic bonding test model for shotcrete and rock, comprising: a base with a compression rod movably inserted thereon; an explosive charge arranged at one end of the compression rod; a rock beam coaxially arranged at the other end of the compression rod and suspended on a hanger, with concrete sprayed on the end face thereof away from the compression rod; and a plurality of accelerometers, some of which are arranged on the rock beam and one is arranged on the free interface of the concrete. The beneficial effects are: in-depth research can be conducted on the cumulative damage mechanism of rock-shotcrete structures under cyclic blasting. The expected research results will contribute to a profound understanding of the dynamic response characteristics, influencing factors, and cumulative damage mechanism of rock-shotcrete support structures under cyclic blasting, further enrich the basic theory of tunnel mechanics, and lay an important foundation for intelligent tunnel blasting design. At the same time, the research has important theoretical guidance significance and engineering application value for the safety assessment and strength verification of tunnel structures under the cumulative damage of cyclic blasting loads.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a dynamic bonding test model of shotcrete and rock and a method for determining a safe blasting point. Background Art

[0002] With the rapid growth of the national economy in recent years, a modern, high-quality, integrated national transportation network is being built in an orderly manner. With systematic national planning and construction goals and a vigorous development of infrastructure, China has entered an era of rapid development in transportation engineering. According to statistics, by the end of 2020, China's railway operating mileage reached 145,000 km, of which 16,798 railway tunnels were in operation, totaling approximately 19,630 km. Railway construction in western my country has also gradually increased, with an increasing number of deep and ultra-long railway tunnels. For example, in 2020, my country added 15 new extra-long tunnels with a total length of 176 km to its operation, 50 extra-long tunnels with a total length of approximately 645 km were under construction, and 136 extra-long tunnels with a total length of approximately 1,891 km were planned.

[0003] The drill-and-blast method, a proven and effective construction method for mountain tunnel excavation, forms a cyclical construction process of "blasting-loading-transporting-supporting." Shotcrete, as the component of the tunnel support system that adheres firmly to the surrounding rock over a large area, bears the entire surrounding rock load during tunnel construction and, together with the secondary lining, shares this load during the tunnel's operation.

[0004] During tunnel blasting construction, in order to prevent weathering, deformation and damage of the surrounding rock near the face, the initial shotcrete must be supported as early as possible. However, considering factors such as the tunnel construction progress, tunnel excavation blasting and shotcrete support are often carried out simultaneously or interspersed. The next cycle of blasting construction must be carried out before the shotcrete has finally set. Within a few hours, the shotcrete is inevitably affected by the cyclic blasting shock wave and blasting stress wave, which will inevitably affect the early strength growth of the shotcrete and directly affect the later strength growth, making its final setting strength unable to meet the design requirements, causing deformation, cracking, and even spalling damage of the shotcrete layer, and reducing the bearing capacity of the support structure. How to balance the relationship between construction progress requirements and concrete strength quality and resolve the contradiction between the two is an urgent problem to be solved in the geotechnical engineering and tunnel engineering fields. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a dynamic bonding test model of shotcrete and rock and a method for determining a safe blasting point, so as to overcome the deficiencies in the above-mentioned prior art.

[0006] The present invention solves the above-mentioned technical problem with the following technical solution: A dynamic bonding test model for shotcrete and rock, comprising:

[0007] A base, on which pressure rods are movably inserted;

[0008] an explosive charge arranged at one end of the compression rod;

[0009] a rock beam, which is coaxially arranged at the other end of the compression rod and suspended on a hanger, and whose end face away from the compression rod is sprayed with concrete;

[0010] Several accelerometers are installed, some on the rock beam and one on the free interface of the concrete.

[0011] The beneficial effects of the present invention are:

[0012] The explosive pack is detonated. The shock wave generated by the explosion causes the compression rod to impact the rock beam and transmits stress waves in the rock beam. The stress waves generate disturbance loads on the concrete sprayed at the end of the rock beam. The stress wave information can be collected by the accelerometer.

[0013] Through this indoor test model, we can conduct in-depth research on the cumulative damage mechanism of rock-shotcrete structures under cyclic blasting. The expected research results will help us to deeply understand the dynamic response characteristics, influencing factors and cumulative damage mechanism of rock-shotcrete support structures under cyclic blasting. It can further enrich the basic theory of tunnel mechanics and lay an important foundation for intelligent tunnel blasting design. At the same time, it has important theoretical guidance significance and engineering promotion and application value for the safety assessment and strength verification of tunnel structures under the cumulative damage of cyclic blasting loads.

[0014] On the basis of the above technical solution, the present invention can also be improved as follows.

[0015] Furthermore, there are three accelerometers arranged on the rock beam, and the three accelerometers are distributed at equal intervals.

[0016] Furthermore, the rock beam is made of granite, has a length of 2.5 m, and a cross-sectional size of 0.3 m×0.3 m; the compression rod has a length of 1 m and a diameter of 100 mm.

[0017] Furthermore, the amount of the explosive pack is 20g to 500g, and the speed of the compression rod incident on the rock beam by the shock wave of the explosive pack explosion is 0 to 10m / s.

[0018] Based on the above solution, the present invention also provides a method for determining a safe blasting point, using the above dynamic bonding test model of shotcrete and rock:

[0019] S100. Conduct rock-shotcrete dynamic bond tests based on a dynamic bond test model to explore the interfacial bond stress between rock and shotcrete under different factors.

[0020] S200. Based on elastic stress wave theory and elastoplastic damage theory, a dynamic damage model describing the dynamic damage and evolution process of the rock-shotcrete and bond interface was established. A three-dimensional finite element model of the rock-shotcrete test beam was also established. The dynamic damage model was embedded in the three-dimensional finite element model. Through numerical simulation of the rock-shotcrete dynamic bond test experiment and comparison with the test results, an applicable dynamic damage model and parameters were obtained.

[0021] S300. Based on the obtained dynamic damage model, analyze the blasting vibration response and damage degree of shotcrete in actual tunnel blasting excavation under different working conditions to determine the safe blasting point and charge amount during blasting excavation.

[0022] The further beneficial effect of adopting the above is that through the research method combining theoretical analysis, numerical simulation, indoor experiments and field tests, the cumulative damage mechanism of the surrounding rock-shotcrete structure of high geothermal tunnels under cyclic blasting can be studied more deeply with higher accuracy.

[0023] Further factors include: the amount of explosives, the location of the explosive explosion point, the type, thickness and age of the sprayed concrete.

[0024] A further beneficial effect of adopting the above method is that test data under different factors can be obtained, thereby improving the accuracy.

[0025] Furthermore, the specific operation of the dynamic bonding test model is as follows:

[0026] Determine the type, thickness and age of the shotcrete to be sprayed;

[0027] The explosive pack is detonated. The shock wave generated by the explosion of the explosive prompts the compression rod to impact the rock beam and transmits stress waves in the rock beam. The stress waves generate disturbance loads on the concrete sprayed at the end of the rock beam.

[0028] By adjusting the explosion point and / or charge of the explosive charge, the relationship between the impact velocity and the maximum mass vibration velocity that the rock-shotcrete can withstand is explored;

[0029] By analyzing the attenuation law of the acceleration peak value of the signal measured by each accelerometer, the propagation and attenuation process of the stress wave in the rock-shotcrete is obtained.

[0030] Furthermore, the accelerometer is used to obtain the acceleration time history and acceleration spectrum under different working conditions; the three-dimensional finite element model obtains the simulated acceleration time history and acceleration spectrum.

[0031] Furthermore, the three-dimensional finite element model was modeled using ABAQUS finite element software.

[0032] Furthermore, the parameters of each unit in the model include: size and calculation time step, hourglass, and damping coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the dynamic bonding test model between shotcrete and rock according to the present invention;

[0034] Figure 2 Schematic diagram of the dynamic damage model of rock-shotcrete according to the present invention;

[0035] Figure 3 This is the blasting construction drawing for the front of the tunnel;

[0036] Figure 4 Exploding construction drawings for nearby tunnels. DETAILED DESCRIPTION

[0037] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0038] Example 1

[0039] like Figure 1 As shown, a dynamic bonding test model of shotcrete and rock includes:

[0040] Base 1, compression rod 2, explosive pack 3, rock beam 4, hanger 5, concrete 6 and accelerometer 7;

[0041] A pressure rod 2 is movably inserted into the base 1, an explosive pack 3 is arranged at one end of the pressure rod 2, and a rock beam 4 is coaxially arranged at the other end of the pressure rod 2. The rock beam 4 is suspended on a hanger 5. The explosive pack 3 is preferably an emulsion explosive.

[0042] In addition, concrete 6 is sprayed on the end surface of the rock beam 4 away from the compression rod 2, and the thickness of the sprayed concrete 6 is determined according to actual needs;

[0043] A plurality of accelerometers 7 are arranged on the rock beam 4, and one accelerometer 7 is arranged on the free interface of the concrete 6;

[0044] The shock wave of the explosive package 3 acts on the compression rod 2, and the explosion transmits stress waves in the compression rod 2. The stress waves act on the rock beam-shotcrete to simulate the disturbance load of the explosion stress wave generated by tunnel drilling and blasting on the rock-shotcrete.

[0045] The accelerometer 7 is used to collect stress wave information.

[0046] Example 2

[0047] like Figure 1As shown, this embodiment is a further improvement on the basis of embodiment 1, specifically as follows:

[0048] There are three accelerometers 7 arranged on the rock beam 4 , and the three accelerometers 7 are distributed at equal intervals.

[0049] Going further:

[0050] The rock beam 4 used in the present invention is made of granite, has a length of 2.5 m and a cross-sectional size of 0.3 m×0.3 m; the compression rod 2 is 1 m long and 100 mm in diameter, and is made of metal.

[0051] Example 3

[0052] like Figure 1 As shown, this embodiment is a further improvement on the basis of embodiment 1 or 2, specifically as follows:

[0053] The speed of the compression rod 2 incident on the rock beam 4 by the explosion shock wave of the explosive package 3 is 0 to 10 m / s. This speed range meets the dynamic bonding test requirements of the blasting stress wave and the blasting seismic wave on the disturbance of early-age shotcrete and rock. The amount of the explosive package 3 can be adjusted from 20g to 500g, so that the speed of the compression rod 2 can be adjusted. At the same time, the speed of the compression rod 2 can also be adjusted by changing the explosion position of the explosive package 3.

[0054] Example 4

[0055] A method for determining a safe blasting point uses the above-mentioned dynamic bond test model of shotcrete and rock:

[0056] S100. Conduct rock-shotcrete dynamic bond tests based on a dynamic bond test model to explore the interfacial bond stress between rock and shotcrete under different factors.

[0057] S200. Based on elastic stress wave theory and elastoplastic damage theory, a dynamic damage model describing the dynamic damage and evolution process of the rock-shotcrete and bond interface was established. A three-dimensional finite element model of the rock-shotcrete test beam was also established. The dynamic damage model was embedded in the three-dimensional finite element model. Through numerical simulation of the rock-shotcrete dynamic bond test experiment and comparison with the test results, an applicable dynamic damage model and parameters were obtained.

[0058] S300. Based on the obtained dynamic damage model, analyze the blasting vibration response and damage degree of shotcrete in actual tunnel blasting excavation under different working conditions to determine the safe blasting point and charge amount during blasting excavation.

[0059] Example 5

[0060] This embodiment is a further improvement on the basis of embodiment 4, specifically as follows:

[0061] The bonding properties between rock and shotcrete are related to a variety of factors. In this example, the thickness, age, and type of shotcrete are taken into consideration. Different impact velocities are applied by the compression rod 2 to conduct dynamic bonding tests between early-stage shotcrete and rock.

[0062] During the test, the density, elastic modulus, and Poisson's ratio of the rock beam 4 are also measured;

[0063] In this embodiment, three different types of concrete are selected, namely C20, C25 and C30. Different types of concrete have different densities, elastic moduli, Poisson's ratios, compressive strengths, tensile strengths and bonding strengths with rocks.

[0064] The thickness of shotcrete was set at 50 mm, 100 mm and 150 mm;

[0065] The ages of shotcrete are 8h, 16h and 24h after pouring;

[0066] A total of 27 experiments were conducted;

[0067] The experimental design is as follows

[0068]

[0069] The specific operation of the dynamic bonding test model is as follows:

[0070] Determine the type, thickness and age of the shotcrete to be sprayed;

[0071] The explosive pack is detonated. The shock wave generated by the explosion of the explosive prompts the compression rod to impact the rock beam and transmits stress waves in the rock beam. The stress waves generate disturbance loads on the concrete sprayed at the end of the rock beam.

[0072] By adjusting the explosion point and / or charge of the explosive charge, the relationship between the impact velocity and the maximum particle vibration velocity that the rock-shotcrete can withstand is explored, and the influence of different factors on the bond stress at the rock-shotcrete interface is analyzed.

[0073] By analyzing the attenuation law of the acceleration peak value of the signal measured by each accelerometer, the propagation and attenuation process of the stress wave in the rock-shotcrete is obtained.

[0074] When acquiring the acceleration time history and acceleration spectrum through multiple accelerometers 7 , the sampling time and sampling frequency may be adjusted to obtain optimal signal acquisition parameters.

[0075] Example 6

[0076] This embodiment is a further improvement on the basis of embodiment 4, specifically as follows:

[0077] Based on the elastic stress wave theory and concrete elastoplastic damage theory, a dynamic damage model of rock-shotcrete is established;

[0078] The schematic diagram is as follows Figure 2 As shown in Figure 1, the stress wave generated at the blast source Q is transmitted to the shotcrete through the rock. Assuming that the propagation direction of the wave is orthogonal to the bonding surface under study, when the compression wave passes through the rock and reaches the free interface of the shotcrete, it will be emitted backward in the form of a tensile wave. The incident compression stress wave and the reflected tensile wave are superimposed. When the tensile stress exceeds the bonding stress at the interface, the shotcrete will fall off. The stress σ generated by the stress wave can be calculated by formula (1):

[0079] σ=ρ·ν·c (1)

[0080] Where: ρ is the density of rock / shotcrete, c is the wave propagation velocity, ν is the particle vibration velocity;

[0081] Since stress waves include shear waves (S), longitudinal waves (P waves), and Rayleigh waves, the fastest propagating wave type is the P wave. Therefore, the propagation of the P wave is considered in detail, and its propagation velocity is calculated using formula (2):

[0082]

[0083] Where, E is the elastic modulus of rock / shotcrete;

[0084] The damage relationship of shotcrete is constructed based on the elastic-plastic model, and the strain ε of shotcrete is derived from the elastic strain ε e and plastic strain ε p Composition, material strain can be expressed as:

[0085] ε=ε e +ε p (3)

[0086] By introducing the damage variable D and using the irreversible thermodynamics theory, we can deduce:

[0087] σ=(1-D)·E·(ε-ε p ) (4)

[0088] Based on the constructed rock-shotcrete dynamic damage model, the dynamic damage and evolution process of the rock-shotcrete composite and the bonding interface are described.

[0089] Finite element software was used to establish a three-dimensional finite element model of rock-shotcrete, and finite element numerical simulation calculations were carried out. The acceleration time history and acceleration spectrum obtained from the three-dimensional finite element model were analyzed and compared with the data measured in the dynamic bond test model to obtain a suitable dynamic damage model and parameters, and to determine the size of each unit in the appropriate model and the calculation time step, hourglass, and damping coefficient.

[0090] Dynamic response of shotcrete and rock under tunnel blasting vibration Consider the situation when early-stage shotcrete is disturbed by blasting in actual tunnel construction;

[0091] like Figure 3 Shown: One is blasting construction in front of the tunnel;

[0092] like Figure 4 As shown: Another method is blasting construction near the tunnel:

[0093] Based on the constructed dynamic damage model, by considering different explosive quantities (1kg, 2kg, and 3kg) and different transmission distances R (2m, 3m, and 4m), the blasting vibration response and damage degree of shotcrete in actual tunnel blasting excavation under different working conditions are analyzed. The safe blasting point and explosive quantity during blasting excavation are determined, providing a safe construction plan for engineering construction.

[0094] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A dynamic bonding test model for shotcrete and rock, characterized in that: include: A base (1) having a pressure rod (2) movably interlaced thereon; An explosive pack (3) is arranged at one end of the pressure rod (2); A rock beam (4) is coaxially arranged at the other end of the compression rod (2) and suspended on a hanger (5), and concrete (6) is sprayed on the end surface of the rock beam away from the compression rod (2); A plurality of accelerometers (7), some of which are arranged on the rock beam (4) and one of which is arranged on the free interface of the concrete (6), the accelerometer (7) being used to collect stress wave information; The explosion shock wave of the explosive package (3) acts on the compression rod (2), and the explosion is incident on the compression rod (2) to transmit stress waves. The stress waves act on the rock beam-shotcrete to simulate the disturbance load of the explosion stress wave generated by tunnel drilling blasting on the rock-shotcrete. The speed of the compression rod (2) incident on the rock beam (4) by the explosion shock wave of the explosive package (3) is 0 to 10 m / s. This speed range meets the dynamic bonding test requirements of the blasting stress wave and the blasting seismic wave on the early-age shotcrete and rock disturbance.

2. The dynamic bonding test model of shotcrete and rock according to claim 1, characterized in that: The number of accelerometers (7) arranged on the rock beam (4) is three, and the three accelerometers (7) are distributed at equal intervals.

3. A dynamic bonding test model for shotcrete and rock according to claim 1 or 2, characterized in that: The rock beam (4) is made of granite, has a length of 2.5 m and a cross-sectional size of 0.3 m×0.3 m; the compression rod (2) has a length of 1 m and a diameter of 100 mm.

4. The dynamic bonding test model of shotcrete and rock according to claim 3, characterized in that: The explosive pack (3) has a charge amount of 20 g to 500 g.

5. A method for determining a safe blasting point, characterized in that: The dynamic bonding test model between shotcrete and rock as claimed in any one of claims 1 to 4 is used: S100. Conduct rock-shotcrete dynamic bond tests based on a dynamic bond test model to explore the interfacial bond stress between rock and shotcrete under different factors. S200. Based on elastic stress wave theory and elastoplastic damage theory, a dynamic damage model describing the dynamic damage and evolution process of the rock-shotcrete and bond interface is established. A three-dimensional finite element model of the rock-shotcrete test beam is also established. The dynamic damage model is embedded in the three-dimensional finite element model. Through numerical simulation of the rock-shotcrete dynamic bond test experiment and comparison with the test results, an applicable dynamic damage model and parameters are obtained. S300. Based on the obtained dynamic damage model, analyze the blasting vibration response and damage degree of shotcrete in actual tunnel blasting excavation under different working conditions to determine the safe blasting point and charge amount during blasting excavation.

6. A method for determining a safe blasting point according to claim 5, characterized in that: Factors include: the amount of explosives, the location of the explosive blast point, and the type, thickness and age of the shotcrete.

7. A method for determining a safe blasting point according to claim 5, characterized in that: The specific operation of the dynamic bonding test model is as follows: Determine the type, thickness and age of the shotcrete to be sprayed; The explosive pack is detonated. The shock wave generated by the explosion of the explosive prompts the compression rod to impact the rock beam and transmits stress waves in the rock beam. The stress waves generate disturbance loads on the concrete sprayed at the end of the rock beam. By adjusting the explosion point and / or charge of the explosive charge, the relationship between the impact velocity and the maximum mass vibration velocity that the rock-shotcrete can withstand is explored; By analyzing the attenuation law of the acceleration peak value of the signal measured by each accelerometer, the propagation and attenuation process of the stress wave in the rock-shotcrete is obtained.

8. A method for determining a safe blasting point according to claim 7, characterized in that: The accelerometer is used to obtain the acceleration time history and acceleration spectrum under different working conditions; the three-dimensional finite element model obtains the simulated acceleration time history and acceleration spectrum.

9. The method for determining a safe blasting point according to claim 5, wherein: The three-dimensional finite element model was built using ABAQUS finite element software.

10. The method for determining a safe blasting point according to claim 5, wherein: The parameters of each unit in the model include: size and calculation time step, hourglass, and damping coefficient.

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