A method for predicting surrounding rock spalling during tunnel excavation

Abstract

The present invention provides a method for predicting spalling of surrounding rock in the process of tunnel excavation, and relates to the technical field of prediction of spalling disasters in tunnels. The method for predicting spalling of surrounding rock in the process of tunnel excavation of the present invention can accurately predict the possibility and depth of spalling by taking samples on site during the excavation process, and can predict various parts of the surrounding rock of the tunnel through indoor tests, theoretical calculations, and stress and energy criteria, with a wide prediction range; the prediction method process is simple to implement, and the prediction analysis efficiency is high, and it can basically realize real-time prediction of spalling of the tunnel, and factors such as changes in geological conditions do not affect the accuracy and efficiency of the prediction; through the prediction method of the present invention, the spalling area can be preventively treated, effectively ensuring the safety and continuity of equipment such as the anchoring and boring machine in the tunnel excavation support operation of coal mines.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel spalling disaster prediction, and in particular to a method for predicting surrounding rock spalling during tunnel excavation. Background Art

[0002] The excavation and support operations of coal mine tunnels are the basic projects for coalfield development. The excavation and support efficiency directly affects the continuation and efficient production of coal mine working faces. For this reason, some coal mines use integrated excavation and anchoring machines to carry out tunnel excavation and support operations, which greatly improves the efficiency of tunnel excavation and support. However, since coal mine tunnels often pass through complex geological structures, the stability of rock formations is poor, and the surrounding rock of the side is prone to spalling, which not only affects the cross-sectional dimensions of the tunnel, but also threatens the safety of construction personnel and equipment. Therefore, it is particularly important to predict spalling in a timely and accurate manner.

[0003] At present, the prediction of rock spalling in the surrounding rock mainly includes technical means such as geological exploration, numerical simulation and machine learning, but each has different defects. Geological exploration, such as geological radar and ultrasonic detection, is limited by detection accuracy and environmental interference, and the detection range is limited, so it is impossible to comprehensively and accurately predict rock spalling. Numerical simulation, including finite element analysis and discrete element analysis, can provide more detailed analysis of rock stress and fracture behavior, but the model establishment is complex and the calculation time is long, making it difficult to achieve real-time prediction. Machine learning makes predictions through data-driven models, but requires a large amount of historical data for training, and the model has poor explanatory power and is not adaptable enough to changes in geological conditions. Summary of the invention

[0004] The present invention provides a method for predicting spalling of surrounding rocks during tunnel excavation, thereby improving the accuracy and efficiency of spalling prediction.

[0005] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] A method for predicting surrounding rock spalling during tunnel excavation, the method comprising the following steps:

[0007] Step 1: During tunnel excavation, samples are taken from the set locations of the surrounding rock on the side of the tunnel and standard specimens are prepared;

[0008] Step 2: Perform uniaxial compression test on standard specimens to measure the stress-strain relationship of the surrounding rock of the sidewall, and then determine the crack initiation stress of the set position of the surrounding rock of the sidewall of the tunnel;

[0009] Step 3, obtaining the energy that the surrounding rock can absorb according to the crack initiation stress;

[0010] Step 4: Calculate the energy of the surrounding rock of the sidewall;

[0011] Step 5: Predict the possibility of film gang;

[0012] Step 6: Predict the depth of the blade.

[0013] Furthermore, the specific implementation process of step 1 is as follows:

[0014] Use a geological coring drill to drill and coring at set locations in the surrounding rock of the tunnel side to obtain complete and undamaged cores, which are then processed in the laboratory to form standard specimens.

[0015] Furthermore, the specific implementation process of step 2 is as follows:

[0016] The standard specimen was subjected to uniaxial compression test to obtain the stress-strain curve, which sequentially presents the crack compression stage, elastic stage, plastic stage and failure stage;

[0017] The stress value corresponding to the inflection point from the elastic stage to the plastic stage on the stress-strain curve is the crack initiation stress of the surrounding rock of the side.

[0018] Furthermore, the specific implementation process of step 3 is as follows:

[0019] The energy value Ea that the rock mass can absorb is obtained by integrating the uniaxial compression specimen from the beginning of compression to the point where the crack initiation stress is reached.

[0020] ; Formula (1)

[0021] in,

[0022] Ea is the energy that the rock mass can absorb, J;

[0023] is the crack initiation strain.

[0024] Furthermore, the specific implementation process of step 4 is as follows:

[0025] For circular tunnels, according to the equilibrium equation, geometric equation and physical equation, we get:

[0026] ; Formula (2)

[0027] in,

[0028] r is the distance from the center of the lane, m;

[0029] u is the displacement of surrounding rock, mm;

[0030] According to the following boundary conditions:

[0031] Under unsupported conditions, when r=R 0 hour, =0; when r→∞, =p0 ;

[0032] Solving equation (2) yields the surrounding rock stress of the circular tunnel:

[0033] The radial stress and tangential stress of the circular tunnel are:

[0034] ; Formula (3)

[0035] ; Formula (4)

[0036] in,

[0037] R 0 is the radius of the roadway, m;

[0038] is the radial stress of the circular tunnel, Pa;

[0039] is the tangential stress of the circular tunnel, Pa;

[0040] is the original rock stress, Pa;

[0041] For non-circular tunnels, the surrounding rock stress of circular tunnels is known, and the surrounding rock stress of non-circular tunnels can be solved by equivalent radius:

[0042] ; Formula (5)

[0043] in,

[0044] —Equivalent radius of the roadway, m;

[0045] S—actual cross-sectional area of ​​the tunnel, m 2 ;

[0046] — Tunnel section correction coefficient;

[0047] According to equations (3) to (5), the surrounding rock stress of non-circular tunnel is obtained:

[0048] The radial stress and tangential stress of non-circular tunnel are:

[0049] ; Formula (6)

[0050] ; Formula (7)

[0051] in,

[0052] is the radial stress of the non-circular tunnel, Pa;

[0053] is the tangential stress of the non-circular tunnel, Pa;

[0054] Calculate the elastic potential energy Es stored in the surrounding rock during tunnel excavation:

[0055] For circular lanes:

[0056] ; Formula (8)

[0057] For non-circular lanes:

[0058] ; Formula (9)

[0059] in,

[0060] Es is the elastic potential energy stored during tunnel excavation, J;

[0061] is Poisson’s ratio;

[0062] G is the shear modulus of rock, Pa.

[0063] Furthermore, the specific implementation process of step 5 is as follows:

[0064] Compare the energy value Ea that the rock mass can absorb with the elastic potential energy Es stored in the surrounding rock during tunnel excavation;

[0065] Es≤ When Ea is reached, the possibility of spalling of the surrounding rock at the set position of the tunnel side is low;

[0066] Es> When Ea, the possibility of the surrounding rock spalling at the set position of the tunnel side is high;

[0067] in,

[0068] is the safety factor.

[0069] Furthermore, the specific implementation process of step 6 is as follows:

[0070] Ea is obtained according to the uniaxial compression test, when Es= When Ea is the maximum depth of the sheet, Es= Substituting Ea into equation (8) and equation (9) to obtain the maximum sidewall depth:

[0071] For circular tunnels, the maximum depth of the slab is :

[0072] ;

[0073] For non-circular tunnels, the maximum depth of the slab is :

[0074] .

[0075] The beneficial technical effects of the present invention are:

[0076] The method for predicting spalling of surrounding rock during tunnel excavation of the present invention can accurately predict the possibility and depth of spalling by taking samples on site during the excavation process through indoor tests, theoretical calculations, and stress and energy criteria, and can predict various parts of the surrounding rock of the tunnel side with a wide prediction range; the prediction method process is simple to implement and the prediction analysis efficiency is high, and it can basically realize real-time prediction of spalling of the tunnel side, and factors such as changes in geological conditions do not affect the accuracy and efficiency of the prediction; through the prediction method of the present invention, the spalling area can be preventively treated, effectively ensuring the safety and continuity of equipment such as the anchoring and boring machine in coal mine tunnel excavation support operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 It is a schematic flow chart of a method for predicting surrounding rock spalling during tunnel excavation according to an embodiment of the present invention;

[0078] Figure 2 The stress-strain diagram obtained from the uniaxial compression test of the embodiment of the present invention;

[0079] Figure 3 This is the surrounding rock stress diagram of the tunnel side according to an embodiment of the present invention. DETAILED DESCRIPTION

[0080] In order to make the purpose, technical scheme and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Certain embodiments of the present invention will be described more comprehensively with reference to the accompanying drawings, in which some but not all embodiments will be shown. In fact, the various embodiments of the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments described herein; rather, these embodiments are provided so that the present invention meets applicable legal requirements.

[0081] In the description of the present invention, it should be noted that the terms "inside", "outside", "upper", "lower", "front", "back" and the like indicate directions or positional relationships based on directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0082] This embodiment is combined with the actual situation of a coal mine. Figures 1 to 3 As shown, a method for predicting rock spalling of the surrounding rock during tunnel excavation is provided, comprising the following steps.

[0083] Step 1: During tunnel excavation, samples are taken from the set locations of the surrounding rock on the side of the tunnel and standard specimens are prepared;

[0084] The specific implementation process of step 1 is as follows:

[0085] Use a geological coring drill to drill and coring at the set location of the surrounding rock of the tunnel. The coring location should avoid abnormal geological structures such as cracks and faults as much as possible to ensure the representativeness and uniformity of the sampling. The coring drill bit is selected according to the hardness and structural characteristics of the rock. The coring process maintains the stability and uniform advancement of the drill to obtain complete and undamaged cores. After the coring is completed, the core is taken out and placed in a special core box. Each section of the core is numbered and marked, and the coring depth, location and lithological characteristics are recorded. The core is transported to the laboratory, where it is processed into a standard specimen. The size and shape of the specimen should comply with relevant standards and specifications. Common specimen shapes are cylinders and cubes, of which the standard size of cylindrical specimens is 50mm×50mm and the standard size of cube specimens is 100mm×100mm×100mm.

[0086] Step 2: Perform uniaxial compression test on standard specimens to measure the stress-strain relationship of the surrounding rock of the sidewall, and then determine the crack initiation stress of the set position of the surrounding rock of the sidewall of the tunnel;

[0087] The specific implementation process of step 2 is as follows:

[0088] Use a high-precision uniaxial compression testing machine to ensure that the range and accuracy of the testing machine meet the experimental requirements. The testing machine should be equipped with a displacement sensor, a strain gauge and a data acquisition system to record the stress and strain data of the specimen in real time. Install the prepared standard specimen in the fixture of the testing machine to ensure that the axis of the specimen is coaxial with the loading axis of the testing machine. The fixture should be tightened reliably to avoid tilting or displacement of the specimen during loading. Set experimental parameters such as loading rate and termination conditions. The loading rate should be reasonably selected according to the rock type and specimen size, generally controlled at 0.5-1 mm / min, to avoid brittle failure of the specimen due to excessive loading rate. Start the experimental equipment and perform uniaxial compression loading on the standard specimen at the set loading rate. During the loading process, the data acquisition system records the stress and strain data of the specimen in real time and generates a stress-strain curve, which sequentially presents the crack compression stage, elastic stage, plastic stage and failure stage. The crack compression stage is characterized by the closure of cracks inside the rock and slow stress growth; the elastic stage is characterized by a linear stress-strain relationship, with stress being proportional to strain; the plastic stage is characterized by a slowdown in stress growth and a gradual increase in strain; the destruction stage is characterized by a rapid drop in stress after reaching a peak value, and rock destruction.

[0089] The stress value corresponding to the inflection point of the transition from the elastic stage to the plastic stage on the stress-strain curve is the crack initiation stress of the surrounding rock. The test results of multiple specimens are statistically analyzed, and the average and standard deviation of the crack initiation stress are calculated to evaluate the uniformity of the rock mass and the reliability of the experimental results. Figure 2 As shown, the crack initiation stress of the rock mass on the side of the tunnel is 54.1 MPa and the damage stress is 57.8 MPa.

[0090] Step 3, obtaining the energy that the surrounding rock can absorb according to the crack initiation stress;

[0091] The specific implementation process of step 3 is as follows:

[0092] The energy value Ea that the rock mass can absorb is obtained by integrating the uniaxial compression specimen from the beginning of compression to the point where the crack initiation stress is reached.

[0093] ; Formula (1)

[0094] in,

[0095] Ea is the energy that the rock mass can absorb, J;

[0096] is the crack initiation strain.

[0097] right Figure 2 By integrating the stress-strain curve, we can obtain that the energy that the rock mass can absorb is 33680J.

[0098] Step 4: Calculate the energy of the surrounding rock of the sidewall;

[0099] The specific implementation process of step 4 is as follows:

[0100] For circular tunnels, according to the equilibrium equation, geometric equation and physical equation, we get:

[0101] ; Formula (2)

[0102] in,

[0103] r is the distance from the center of the lane, m;

[0104] u is the displacement of surrounding rock, mm;

[0105] According to the following boundary conditions:

[0106] Under unsupported conditions, when r=R 0 hour, =0; when r→∞, =p 0 ;

[0107] Solving equation (2) yields the surrounding rock stress of the circular tunnel:

[0108] The radial stress and tangential stress of the circular tunnel are:

[0109] ; Formula (3)

[0110] ; Formula (4)

[0111] in,

[0112] R 0 is the radius of the roadway, m;

[0113] is the radial stress of the circular tunnel, Pa;

[0114] is the tangential stress of the circular tunnel, Pa;

[0115] is the original rock stress, Pa, which is 17.5MPa here;

[0116] For non-circular tunnels, the surrounding rock stress of circular tunnels is known, and the surrounding rock stress of non-circular tunnels can be solved by equivalent radius:

[0117] ; Formula (5)

[0118] in,

[0119] —Equivalent radius of the roadway, m;

[0120] S—actual cross-sectional area of ​​the tunnel, m 2 The cross-sectional area of ​​this tunnel is 20.8m 2 ;

[0121] —Tunnel section correction coefficient, take the value according to Table 1, this tunnel is a rectangular tunnel and should be 1.2;

[0122] Table 1 Tunnel section correction coefficient

[0123]

[0124] The calculated equivalent radius of the tunnel is 3.08m.

[0125] According to equations (3) to (5), the surrounding rock stress of non-circular tunnel is obtained:

[0126] The radial stress and tangential stress of non-circular tunnel are:

[0127] ; Formula (6)

[0128] ; Formula (7)

[0129] in,

[0130] is the radial stress of the non-circular tunnel, Pa;

[0131] is the tangential stress of the non-circular tunnel, Pa;

[0132] Calculate the elastic potential energy Es stored in the surrounding rock during tunnel excavation:

[0133] For circular lanes:

[0134] ; Formula (8)

[0135] For non-circular lanes:

[0136] ; Formula (9)

[0137] in,

[0138] Es is the elastic potential energy stored during tunnel excavation, J;

[0139] is Poisson’s ratio, which is taken as 0.25 here;

[0140] G is the rock shear modulus, Pa, which is taken as 2.12×10 9 Pa.

[0141] Step 5: Predict the possibility of film gang;

[0142] The specific implementation process of step 5 is as follows:

[0143] Compare the energy value Ea that the rock mass can absorb with the elastic potential energy Es stored in the surrounding rock during tunnel excavation;

[0144] Es≤ When Ea is reached, the possibility of spalling of the surrounding rock at the set position of the tunnel side is low;

[0145] Es> When Ea, the possibility of the surrounding rock spalling at the set position of the tunnel side is high;

[0146] in,

[0147] is the safety factor, which is taken as 1.2 here.

[0148] Step 6: predict the depth of the sheet;

[0149] The specific implementation process of step 6 is as follows:

[0150] Ea is obtained according to the uniaxial compression test. When Es=1.2Ea, it is the maximum depth of the spalling. Substituting Es=1.2Ea into equations (8) and (9) to obtain the maximum spalling depth:

[0151] For circular tunnels, the maximum depth of the slab is :

[0152] ; Formula (10)

[0153] For non-circular tunnels, the maximum depth of the slab is :

[0154] Formula (11)

[0155] Substituting the above parameters into equation (11), the solution yields the maximum slab depth of 0.077 m.

[0156] So far, the present embodiment has been described in detail in conjunction with the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the method for predicting spalling of the surrounding rock of the sidewall during tunnel excavation of the present invention. The method for predicting spalling of the surrounding rock of the sidewall during tunnel excavation of the present invention takes samples on-site during the excavation process, and through indoor experiments, theoretical calculations, combined with stress and energy criteria, can accurately predict the possibility and depth of spalling, and predict various parts of the sidewall of the tunnel surrounding rock, with a wide prediction range; the prediction method process is simple to implement, and the prediction analysis efficiency is high, and it can basically realize real-time prediction of spalling of the sidewall of the tunnel, and factors such as changes in geological conditions do not affect the accuracy and efficiency of the prediction; through the prediction method of the present invention, the spalling area can be preventively treated, effectively ensuring the safety and continuity of equipment such as the anchoring and boring machine in coal mine tunnel excavation support operations.

[0157] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting surrounding rock spalling during tunnel excavation, characterized in that: The method comprises the following steps: Step 1: During tunnel excavation, samples are taken from the set locations of the surrounding rock on the side of the tunnel and standard specimens are prepared; Step 2: Perform uniaxial compression test on standard specimens to measure the stress-strain relationship of the surrounding rock of the sidewall, and then determine the crack initiation stress of the set position of the surrounding rock of the sidewall of the tunnel; Step 3, obtaining the energy that the surrounding rock can absorb according to the crack initiation stress; Step 4: Calculate the energy of the surrounding rock of the sidewall; Step 5: Predict the possibility of film gang; The specific implementation process of step 5 is as follows: Compare the energy value Ea that the rock mass can absorb with the elastic potential energy Es stored in the surrounding rock during tunnel excavation; When Es≤δEa, the possibility of spalling of the surrounding rock at the set position of the tunnel side is low; When Es>δEa, the possibility of spalling of the surrounding rock at the set position of the tunnel wall is high; in, δ is the safety factor; Step 6: predict the depth of the sheet; The specific implementation process of step 6 is as follows: Ea is obtained from the uniaxial compression test. When Es = δEa, it is the maximum depth of the slab. Substituting Es = δEa into and Find the maximum depth of the patch: in, Es is the elastic potential energy stored during tunnel excavation, J; μ is Poisson’s ratio; G is the rock shear modulus, Pa; σ r is the radial stress of the circular tunnel, Pa; σ θ is the tangential stress of the circular tunnel, Pa; σ r ′ is the radial stress of the non-circular tunnel, Pa; σ θ ′ is the tangential stress of the non-circular tunnel, Pa; For circular tunnels, the maximum depth of the spalling is D: in, R0 is the radius of the roadway, m; p0 is the original rock stress, Pa; For non-circular tunnels, the maximum spalling depth D′ is: in, r s —Equivalent radius of the tunnel, m.

2. The method for predicting surrounding rock spalling during tunnel excavation according to claim 1, characterized in that: The specific implementation process of step 1 is as follows: Use a geological coring drill to drill and coring at set locations in the surrounding rock of the tunnel side to obtain complete and undamaged cores, which are then processed in the laboratory to form standard specimens.

3. The method for predicting rock spalling during tunnel excavation according to claim 2, characterized in that: The specific implementation process of step 2 is as follows: The standard specimen was subjected to uniaxial compression test to obtain the stress-strain curve, which sequentially presents the crack compression stage, elastic stage, plastic stage and failure stage; The stress value corresponding to the inflection point from the elastic stage to the plastic stage on the stress-strain curve is the crack initiation stress of the surrounding rock of the side.

4. The method for predicting surrounding rock spalling during tunnel excavation according to claim 3 is characterized in that: The specific implementation process of step 3 is as follows: The energy value Ea that the rock mass can absorb is obtained by integrating the uniaxial compression specimen from the beginning of compression to the point where the crack initiation stress is reached. in, Ea is the energy that the rock mass can absorb, J; ε a is the crack initiation strain.

5. The method for predicting surrounding rock spalling during tunnel excavation according to claim 4, characterized in that: The specific implementation process of step 4 is as follows: For circular tunnels, according to the equilibrium equation, geometric equation and physical equation, we get: in, r is the distance from the center of the lane, m; u is the displacement of surrounding rock, mm; According to the following boundary conditions: Under unsupported conditions, when r=R0, σ r =0; when r→∞, σ r =p0; Solving equation (2) yields the surrounding rock stress of the circular tunnel: The radial stress and tangential stress of the circular tunnel are: in, R0 is the radius of the roadway, m; σ r is the radial stress of the circular tunnel, Pa; σ θ is the tangential stress of the circular tunnel, Pa; p0 is the original rock stress, Pa; For non-circular tunnels, the surrounding rock stress of circular tunnels is known, and the surrounding rock stress of non-circular tunnels can be solved by equivalent radius: r s =k x (S / π) 0.5 ; Formula (5) in, r s —Equivalent radius of the tunnel, m; S—actual cross-sectional area of ​​the tunnel, m 2 ; k x — Tunnel section correction coefficient; According to equations (3) to (5), the surrounding rock stress of non-circular tunnel is obtained: The radial stress and tangential stress of non-circular tunnel are: in, σ r ′ is the radial stress of the non-circular tunnel, Pa; σ θ ′ is the tangential stress of the non-circular tunnel, Pa; Calculate the elastic potential energy Es stored in the surrounding rock during tunnel excavation: For circular tunnels: For non-circular lanes: in, Es is the elastic potential energy stored during tunnel excavation, J; μ is Poisson’s ratio; G is the shear modulus of rock, Pa.

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