Quantitative design method for rockburst energy absorption prevention and control

Abstract

The present invention relates to the technical field of underground engineering rockburst prevention and control safety. Provided is a quantitative design method for rockburst energy absorption prevention and control. The method comprises: firstly, establishing an underground-engineering finite-element numerical calculation model, and performing underground-engineering excavation simulation calculation; delineating the location and range of rockburst damage and a rockburst pit depth according to an LERR value, and providing the amount of released energy at different positions during a rockburst; then, determining the location, trend and inclination angle of a structural plane; and then, determining the design length of a free section of each energy absorption anchor bolt, and determining an optimal length of each single energy absorption anchor bolt in combination with a design anchoring force of the anchor bolt; then, calculating ejection kinetic energy of rockburst rocks; and finally, determining the length of an anchoring section of each energy absorption anchor bolt, the total length of each anchor bolt, and the number of anchor bolts, such that the total energy absorption capacity of all the energy absorption anchor bolts is greater than the ejection kinetic energy when a rockburst occurs. The method provides a quantitative design method and process for energy absorption anchor bolts, and provides a design basis for scientific design of rockburst energy absorption prevention and control.

Description

A quantitative prevention and control design method for rockburst energy absorption Technical Field

[0001] The present invention relates to the field of underground engineering rockburst prevention and control safety technology, and in particular to a rockburst energy absorption quantitative prevention and control design method. Background Art

[0002] Rockburst is a geological disaster caused by the rapid release of elastic strain energy stored in the surrounding rock during excavation, resulting in a kinetic impact. Due to the sudden nature of its occurrence and the severity of its consequences, rockburst has become a widespread concern for deep underground projects both domestically and internationally. With the development of underground projects such as railways, highways, and hydropower stations deep within the Earth, the construction of numerous tunnels with high ground stress and hard surrounding rock has made rockburst a more prominent problem. To reduce the risk of rockburst disasters during underground construction and ensure construction safety, a quantitative rockburst energy absorption prevention and control principle and design method are urgently needed.

[0003] Currently, in the design of deep-buried hard rock and high-in-situ stress tunnels, the energy failure criterion based on strain energy theory has obvious advantages in dealing with rock masses under complex in-situ stress states. Therefore, it is widely used in rockburst assessment in tunnel design. The rockburst failure process is a dynamic instability failure process, which releases a large amount of accumulated elastic strain energy, accompanied by the conversion of elastic strain energy into residual strain energy, ejection kinetic energy, and shear sliding dissipation energy. Among them, ejection kinetic energy is one of the important indicators for evaluating the severity of rockburst disasters. The quantification of various impact energies, especially the quantification of ejection kinetic energy, can provide an important basis for the quantitative design of support structures for rockburst prevention and control. In terms of rockburst energy control, technical personnel in this field have designed and developed a wide variety of energy-absorbing anchor rods. When the reinforced surrounding rock is subjected to impact loads, the energy-absorbing anchor rods can produce large deformations while maintaining a certain bearing capacity, without causing the energy-absorbing anchor rods to be destroyed, thereby continuing to support the loosened and cracked rock mass. However, in the specific design, the length (anchor section, free section) and the number of energy-absorbing anchor rods still lack reliable design basis and methods. Therefore, it is urgent to develop a scientific rockburst active energy absorption control technology.

[0004] Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a rockburst energy absorption quantitative prevention and control design method and design an energy-absorbing anchor support scheme in response to the above-mentioned deficiencies in the existing technology.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a rockburst energy absorption quantitative prevention and control design method, comprising the following steps:

[0007] Step 1: Based on the underground engineering excavation and support design plan, establish the underground engineering finite element numerical calculation model and perform underground engineering excavation simulation calculation;

[0008] Step 1-1: In the numerical calculation analysis, the initial in-situ stress field is set according to the actual in-situ stress data, and the elastic-brittle-plastic constitutive model is selected;

[0009] Step 1-2: Determine the rock mass constitutive parameters required for numerical calculations based on indoor rock mechanics tests or using the inverse analysis method;

[0010] Step 2: Consider the local energy release rate (LERR) during the simulation calculation of underground engineering excavation. After the simulation calculation is completed, extract the local energy release rate (LERR) results. Based on the LERR value, delineate the location and range of rock burst damage, as well as the depth of the rock burst crater, and quantify the energy release during rock burst at different locations.

[0011] Step 2-1: Determine the local energy release rate LERR index, as shown in the following formula: LERR i =U imax -U imin

[0012] Where, LERR i is the local energy release rate of the i-th unit; U imax is the peak value of elastic strain energy density before brittle failure of the i-th unit; U imin is the elastic strain energy density valley value after brittle failure of the i-th unit; σ1, σ2, σ3 are the maximum stress, intermediate stress and maximum principal stress tensors corresponding to the unit strain energy peak value; σ′1, σ′2, σ′3 are the maximum stress, intermediate stress and maximum principal stress tensors corresponding to the unit strain energy valley value; v is the Poisson's ratio of the surrounding rock; E is the elastic modulus of the surrounding rock;

[0013] Step 2-2: Calculate the LERR values ​​at different locations and depths of the tunnel surrounding rock. Based on the LERR values, determine the location of the rockburst, the damaged area, and the depth of the blast crater. The intensity of energy release is given, and the energy release area is the potential rockburst area.

[0014] Step 3: Determine the location, direction, and inclination of the structural surface based on advance geological exploration at the underground engineering site;

[0015] Step 4: Determine the design length of the free section of the energy-absorbing anchor based on the rockburst location, blast pit depth, and structural surface location. Combined with the anchoring force design of the anchor, and taking into account the size of the underground excavation space, determine the optimal length of a single energy-absorbing anchor.

[0016] Step 4-1: The free section of the energy-absorbing anchor should be designed to pass through the blast crater. The length of the free section should be greater than the estimated blast crater depth, so that the energy-absorbing anchor can freely extend and absorb energy when a rockburst occurs.

[0017] Step 4-2: The free section of the energy-absorbing anchor should pass through the structural surface that controls rockbursts, acting as a pin to prevent relative sliding of rock blocks on both sides of the structural surface. The length of the free section should be greater than the distance from the structural surface to the tunnel wall.

[0018] Step 4-3: The free section length of the energy-absorbing anchor rod is the larger value obtained from steps 4-1 and 4-2.

[0019] Step 4-4: With the free section length of the energy-absorbing anchor determined, conduct indoor static tensile and impact tensile tests on anchors with different anchor lengths, different anchor materials, different rod sizes, and different rod materials to determine the elongation, yield strength, breaking strength, and energy absorption capacity of the anchor, and determine the optimal length of the energy-absorbing anchor;

[0020] Step 5: Use discontinuous deformation software to calculate the kinetic energy of rock burst ejection;

[0021] Step 5-1: Determine the energy conversion of the rockburst process;

[0022] The rockburst process involves complex energy transformation of the surrounding rock. The total elastic strain energy before excavation is converted into residual strain energy, dissipated energy, and ejection kinetic energy after the rockburst occurs, as shown in the following formula:

[0023] Where U o is the total elastic strain energy before excavation; is the residual strain energy after excavation; is the energy dissipated during the excavation process; is the ejection kinetic energy after excavation;

[0024] Step 5-2: Calculate the ejection kinetic energy generated by the rockburst;

[0025] The ejection kinetic energy generated by rock burst is expressed as follows:

[0026] in, is the total ejection kinetic energy of the area affected by rock burst after excavation; n is the number of blocks in the area affected by rock burst after excavation; m i is the mass of the i-th block; v i is the rockburst ejection velocity of the i-th block;

[0027] Step 6: Based on the optimal energy-absorbing anchor parameters selected in step 4 and the rockburst ejection kinetic energy obtained in step 5, determine the anchoring section length, total anchor length, and number of anchors so that the total energy-absorbing capacity of all energy-absorbing anchors is greater than the ejection kinetic energy when the rockburst occurs, as shown in the following formula:

[0028] Where W is the energy absorption capacity of a single energy-absorbing anchor, kJ; S is the minimum number of anchors required within the rockburst range, roots; is the total ejection kinetic energy of the area affected by rockburst after excavation, kJ.

[0029] The beneficial effects of adopting the above technical solution are: the present invention provides a quantitative rock burst energy absorption prevention and control design method, provides a quantitative design method and process of energy-absorbing anchor rods, provides a design basis for the scientific design of rock burst energy absorption prevention and control, and solves the current problem of blindness in the energy absorption prevention and control design of rock burst problems in underground engineering; the present invention proposes a method for quantitatively calculating the kinetic energy of rock burst ejection, and proposes a design method for energy-absorbing anchor rods from an energy perspective. By circling the location of the rock burst, the destruction area, and the depth of the blast pit, combined with the structural surface position, the design length of the free section of the energy-absorbing anchor rod can be determined, which can avoid the problems of low elongation and insufficient energy absorption capacity of traditional anchor rod designs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a flow chart of a method for designing a quantitative prevention and control system for rockburst energy absorption according to an embodiment of the present invention;

[0031] FIG2 is a schematic diagram of a gradually decoupling energy-absorbing anchor provided by an embodiment of the present invention;

[0032] FIG3 is a schematic diagram of a tunnel numerical calculation model provided by an embodiment of the present invention;

[0033] FIG4 is a schematic diagram of a rockburst area estimated by a local energy release rate indicator according to an embodiment of the present invention, wherein (a) is a diagram of a local energy release rate indicator result, and (b) is a schematic diagram of a rockburst crater depth;

[0034] FIG5 is a performance test diagram of a gradually decoupling energy-absorbing anchor provided by an embodiment of the present invention;

[0035] FIG6 is a schematic diagram of calculating rockburst ejection kinetic energy using discontinuous deformation software according to an embodiment of the present invention.

[0036] In the figure: 1. Nut; 2. Washer; 3. Plate; 4. Anchor rod; 5. Gradual decoupling material; 6. Anchor head; 7. LERR index to determine potential rockburst area; 8. Actual rockburst area; 9. Rockburst ejection block. DETAILED DESCRIPTION

[0037] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0038] This example uses a circular tunnel as an example, employing the rockburst energy absorption quantitative prevention and control design method of the present invention to design an energy-absorbing anchor support solution for the tunnel. In this example, the energy-absorbing anchor adopts a progressive decoupling anchor, which includes a nut 1, a washer 2, a backing plate 3, an anchor body 4, a progressive decoupling material 5, and an anchor head 6.

[0039] In this embodiment, a rockburst energy absorption quantitative prevention and control design method, as shown in FIG1 , includes the following steps:

[0040] Step 1: Based on the underground engineering excavation and support design plan, establish the underground engineering finite element numerical calculation model and perform underground engineering excavation simulation calculation;

[0041] Step 1-1: In the numerical calculation analysis, the initial in-situ stress field is set according to the actual in-situ stress data, and the elastic-brittle-plastic constitutive model is selected;

[0042] Step 1-2: Determine the rock mass constitutive parameters required for numerical calculations based on indoor rock mechanics tests or using the inverse analysis method;

[0043] In this embodiment, the numerical calculation model of the tunnel is established as shown in FIG3 , the elastic-brittle-plastic constitutive strain hardening (CWFS) model is selected for the rock mass, and the surrounding rock parameters are shown in Table 1;

[0044] Table 1 Surrounding rock mechanical parameters

[0045] In the table, E is the elastic modulus of the surrounding rock; v is the Poisson's ratio of the surrounding rock; c0 and φ0 are the initial cohesion and internal friction angle respectively; c d and φ d are the residual cohesion and internal friction angle respectively; ψ is the dilatancy angle; σ t is the tensile strength; and are the equivalent plastic strain thresholds for cohesion and internal friction angle to enter the residual segment, respectively.

[0046] Step 2: Consider the local energy release rate (LERR) during the simulation calculation of underground engineering excavation. After the simulation calculation is completed, extract the local energy release rate (LERR) results. Based on the LERR value, delineate the location and range of rock burst damage, as well as the depth of the rock burst crater, and quantify the energy release during rock burst at different locations.

[0047] Step 2-1: Determine the local energy release rate LERR index, as shown in the following formula: LERR i =U imax -U imin

[0048] Where, LERRi is the local energy release rate of the i-th unit; U imax is the peak value of elastic strain energy density before brittle failure of the i-th unit; U imin is the elastic strain energy density valley value after brittle failure of the i-th unit; σ1, σ2, σ3 are the maximum stress, intermediate stress and maximum principal stress tensors corresponding to the unit strain energy peak value; σ′1, σ′2, σ′3 are the maximum stress, intermediate stress and maximum principal stress tensors corresponding to the unit strain energy valley value; v is the Poisson's ratio of the surrounding rock; E is the elastic modulus of the surrounding rock;

[0049] Step 2-2: Calculate the LERR values ​​at different locations and depths of the tunnel surrounding rock. Based on the LERR values, determine the location of the rockburst, the damaged area, and the depth of the blast crater. The intensity of energy release is given, and the energy release area is the potential rockburst area.

[0050] In this example, the local energy release rate (LERR) index was used to delineate the location of rockburst damage. It was estimated that rockbursts primarily occurred on the left and right sides of the tunnel, with a maximum crater depth of approximately 1 m. The specific rockburst location and range are shown in Figure 4, where a represents the tunnel radius and r represents the distance from the depth of the tunnel after damage to the tunnel center.

[0051] Step 3: Determine the location, direction, and inclination of the structural surface based on advance geological exploration at the underground engineering site;

[0052] Step 4: Determine the design length of the free section of the energy-absorbing anchor based on the rockburst location, blast pit depth, and structural surface location. Combined with the anchoring force design of the anchor, and taking into account the size of the underground excavation space, determine the optimal length of a single energy-absorbing anchor.

[0053] Step 4-1: The free section of the energy-absorbing anchor should be designed to pass through the blast crater. The length of the free section should be greater than the estimated blast crater depth, so that the energy-absorbing anchor can freely extend and absorb energy when a rockburst occurs.

[0054] Step 4-2: The free section of the energy-absorbing anchor should pass through the structural surface that controls rockbursts, acting as a pin to prevent relative sliding of rock blocks on both sides of the structural surface. The length of the free section should be greater than the distance from the structural surface to the tunnel wall.

[0055] Step 4-3: The free section length of the energy-absorbing anchor rod is the larger value obtained from steps 4-1 and 4-2.

[0056] Step 4-4: With the free section length of the energy-absorbing anchor determined, conduct indoor static tensile and impact tensile tests on anchors with different anchor lengths, different anchor materials, different rod sizes, and different rod materials to determine the elongation, yield strength, breaking strength, and energy absorption capacity of the anchor, and determine the optimal length of the energy-absorbing anchor;

[0057] In this embodiment, based on the results of steps 2 and 3, the anchoring length of the gradually decoupling energy-absorbing anchor bolt is designed to be 1700 mm, the decoupling section length is 1300 mm, and the total length of the anchor bolt is 3 m. The designed decoupling section length is greater than the estimated maximum crater depth of the rockburst. Indoor anchor bolt testing was conducted. The rod body 4 was made of HRB300 threaded steel anchor bolt with a diameter of 22 mm. Two nuts were directly used as the anchor head 6. The anchoring agent was mortar. The gradually decoupling material 5 was a thermoplastic tube. The contact surface between the inner surface of the gradually decoupling material 5 and the rod body 4 was lubricated with dry oil. The peak load of the anchor bolt was measured to reach 233 kN. The maximum deformation of the rod body 4 in the non-anchoring section reached 240 mm, and the energy it absorbed reached approximately 48 kJ. The test results are shown in Figure 5.

[0058] Step 5: Use discontinuous deformation software to calculate the kinetic energy of rock burst ejection;

[0059] Step 5-1: Determine the energy conversion of the rockburst process;

[0060] The rockburst process involves complex energy transformation of the surrounding rock. The total elastic strain energy before excavation is converted into residual strain energy, dissipated energy, and ejection kinetic energy after the rockburst occurs, as shown in the following formula:

[0061] Where U o is the total elastic strain energy before excavation; is the residual strain energy after excavation; is the energy dissipated during the excavation process; is the ejection kinetic energy after excavation;

[0062] Step 5-2: Calculate the ejection kinetic energy generated by the rockburst;

[0063] The ejection kinetic energy generated by rock burst is expressed as follows:

[0064] in, is the total ejection kinetic energy of the area affected by rock burst after excavation; n is the number of blocks in the area affected by rock burst after excavation; m i For the i The mass of the block; v i is the rockburst ejection velocity of the i-th block;

[0065] In this example, the discontinuous deformation software DDA was used to calculate the kinetic energy of rock burst block ejection. The block kinetic energy in the affected area can be calculated by summing the kinetic energy of all individual blocks in the affected area. The velocity is measured at the point located at the center of mass of each block in the discontinuous deformation software grid. The ejection kinetic energy calculation is shown in Figure 6, which includes the rock burst ejection block 9. The calculation found that the total kinetic energy of the ejection in the tunnel excavation affected area was 414 kJ.

[0066] Step 6: Based on the optimal energy-absorbing anchor parameters selected in step 4 and the rockburst ejection kinetic energy obtained in step 5, determine the anchoring section length, total anchor length, and number of anchors so that the total energy-absorbing capacity of all energy-absorbing anchors is greater than the ejection kinetic energy when the rockburst occurs, as shown in the following formula:

[0067] Where W is the energy absorption capacity of a single energy-absorbing anchor, kJ; S is the minimum number of anchors required within the rockburst range, roots; is the total ejection kinetic energy of the area affected by rockburst after excavation, kJ.

[0068] In this embodiment, according to the test and calculation results of steps 4 and 5, when the energy absorption capacity of the energy-absorbing anchor rods is 48 kJ × 9, it is greater than the total kinetic energy of ejection in the tunnel excavation impact area of ​​414 kJ. Therefore, the number of gradually decoupling energy-absorbing anchor rods required within the rock burst area per meter of tunnel excavation section is greater than 9.

[0069] This embodiment can provide a complete design method and process for the quantitative design of gradually decoupling energy-absorbing anchor rods from the perspective of rockburst energy absorption and prevention, and provide important design basis and support for the energy absorption and prevention design of rockburst tunnels.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for designing quantitative prevention and control of rockburst energy absorption, characterized by: The following steps are involved: Step 1: According to the underground engineering excavation support design plan, establish the underground engineering finite element numerical calculation model and perform underground engineering excavation simulation calculation; Step 2: Consider the local energy release rate LERR during the simulation calculation of underground engineering excavation, and extract the local energy release rate LERR results after the simulation calculation is completed. According to the LERR value, the location and range of rock burst damage and the depth of rock burst pit are delineated, and the energy release amount of rock burst in different parts is quantitatively given; Step 3: Determine the location, direction and inclination of the structural surface based on the advanced geological survey of the underground engineering site; Step 4: Determine the design length of the free section of the energy-absorbing anchor according to the rockburst location, blast pit depth and structural surface location, combine the anchor design force with the size of the underground engineering excavation space, and determine the optimal length of a single energy-absorbing anchor; Step 5: Use discontinuous deformation software to calculate the kinetic energy of rock burst rock blocks; Step 5-1: Determine the energy conversion of the rockburst process; Step 5-2: Calculate the ejection kinetic energy generated by the rockburst; Step 6: According to the optimal energy-absorbing anchor parameters selected in step 4 and the rockburst ejection kinetic energy obtained in step 5, determine the anchoring section length, total anchor length and number of anchors so that the total energy-absorbing capacity of all energy-absorbing anchors is greater than the ejection kinetic energy when the rockburst occurs.

2. A rockburst energy absorption quantitative prevention and control design method according to claim 1, characterized in that: In the step 1, in the numerical calculation, the initial in-situ stress field of the numerical calculation is set according to the actual in-situ stress data, and the elastic-brittle-plastic constitutive model is selected; and the rock mass constitutive parameters required for the numerical calculation are determined according to the indoor rock mechanics test or by the inverse analysis method.

3. A rockburst energy absorption quantitative prevention and control design method according to claim 2, characterized in that: The specific method of step 2 is: Step 2-1: Determine the local energy release rate LERR index, as shown in the following formula: LERR i =U imax -HE imin Where, LERR i is the local energy release rate of the i-th unit; U imax is the peak value of elastic strain energy density before brittle failure of the i-th unit; U imin is the valley value of elastic strain energy density after brittle failure of the i-th unit; σ1, σ2, σ3 are the maximum stress, intermediate stress and maximum principal stress tensor corresponding to the unit strain energy peak value; σ′1, σ′2, σ′3 are the maximum stress, intermediate stress and maximum principal stress tensor corresponding to the unit strain energy valley value; v is the Poisson's ratio of the surrounding rock; E is the elastic modulus of the surrounding rock; Step 2-2: Count the LERR values ​​at different locations and depths of the tunnel wall in the surrounding rock of the tunnel. According to the LERR values, the location of the rockburst, the damaged area, and the depth of the blast pit are delineated, and the intensity of the energy release is given. The energy release area is the potential rockburst area.

4. A rockburst energy absorption quantitative prevention and control design method according to claim 3, characterized in that: The specific method of step 4 is: Step 4-1: The free section of the energy-absorbing anchor should be designed to pass through the blast pit, and the length of the free section of the anchor should be greater than the estimated depth of the blast pit, so that the energy-absorbing anchor can freely extend and absorb energy when a rockburst occurs; Step 4-2: The free section of the energy-absorbing anchor should pass through the structural surface that controls rock bursts, play the role of a pin, and prevent the rocks on both sides of the structural surface from sliding relative to each other. The length of the free section should be greater than the distance from the structural surface to the tunnel wall; Step 4-3: The free section length of the energy-absorbing anchor rod is the larger value obtained from steps 4-1 and 4-2; Step 4-4: After the free section length of the energy-absorbing anchor is determined, carry out indoor static tensile and impact tensile tests on anchors with different anchoring lengths, different anchoring materials, different rod sizes, and different rod materials to determine the elongation, yield strength, breaking strength, and energy absorption capacity of the anchor, and determine the optimal length of the energy-absorbing anchor.

5. A rockburst energy absorption quantitative prevention and control design method according to claim 4, characterized in that: In the rockburst process described in step 5-1, the total elastic strain energy before excavation will be converted into residual strain energy, dissipated energy and ejection kinetic energy after the rockburst occurs, as shown in the following formula: Where U o is the total elastic strain energy before excavation; is the residual strain energy after excavation; is the energy dissipated during the excavation process; It is the kinetic energy of ejection after excavation.

6. A rockburst energy absorption quantitative prevention and control design method according to claim 5, characterized in that: The ejection kinetic energy generated by the rock burst is shown in the following formula: in, is the total ejection kinetic energy of the area affected by rockburst after excavation; n is the number of blocks in the area affected by rockburst after excavation; m i is the mass of the ith block; v i is the rockburst ejection velocity of the ith block.

7. A rockburst energy absorption quantitative prevention and control design method according to claim 6, characterized in that: The total energy absorption capacity of all energy-absorbing anchor rods in step 6 is made greater than the ejection kinetic energy when the rock burst occurs, as shown in the following formula: Where W is the energy absorption capacity of a single energy-absorbing anchor rod; S is the minimum number of anchor rods required within the rockburst range; It is the total ejection kinetic energy of the area affected by rockburst after excavation.

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