Method for determining safe distance between broken surrounding rock and water-rich high-pressure karst cave

Abstract

The invention discloses a method for determining the safe distance between broken surrounding rock and a water-rich high-pressure karst cave, and belongs to the field of underground structure engineering. The method aims at solving the problems that in the prior art, errors are large due to dependence on empirical formulas, numerical simulation is complex and time-consuming, and safe distance calculation is inaccurate due to the fact that the coupling effect of multiple factors such as blasting disturbance and water pressure is not fully considered. According to the technical scheme, the method is characterized in that the safety distance is decomposed into the tunnel excavation side damage zone thickness, the protection layer thickness and the karst cave side influence zone thickness; respectively determining the thickness of each part by fusing a multi-field coupling analytical calculation method of blasting stress wave, blasting gas, karst cave water pressure permeation, stress wave reflection and the like; and finally, superposing the thicknesses of the three parts to obtain an accurate safety distance. The method improves the calculation precision and efficiency of the safety distance, and is suitable for risk control of projects such as tunnels, mines and underground caverns.

Description

Technical Field

[0001] This invention belongs to the field of underground structure engineering technology, and in particular relates to a method for determining the safe distance between fractured surrounding rock and water-rich, high-pressure karst caves. Background Technology

[0002] In the field of underground structural engineering, especially in tunnel excavation, mining, and underground cavern construction, geological conditions often arise where fractured surrounding rock coexists with water-rich, high-pressure karst caves. Construction in such adverse geological areas can easily induce disasters such as surrounding rock instability, karst cave collapse, and mudslides or water inrushes, seriously threatening project safety and the lives of construction workers. Therefore, accurately calculating the reasonable safe thickness between the tunnel wall or excavation outline and the concealed karst cave is a key technical step in effectively controlling project risks.

[0003] Currently, the methods for determining safe distances in engineering practice mainly rely on empirical formulas and numerical simulations. Empirical formula methods are typically based on simplifying assumptions and historical statistical data, failing to fully consider the heterogeneity of fractured surrounding rock, the discreteness of mechanical parameters, and the dynamic changes in karst water pressure. This often results in large errors in the calculations, making it difficult to accurately guide construction decisions in high-risk areas. Numerical simulation methods, such as using software like FLAC3D to build three-dimensional fluid-structure interaction models, can simulate the stress and seepage field distribution of the surrounding rock after tunnel excavation and find safe distances through iterative calculations. However, this method has significant limitations. First, the modeling process is complex, requiring the input of a large number of geotechnical parameters that are difficult to obtain accurately, making preparation time-consuming and labor-intensive. Second, numerical calculations themselves are time-consuming, failing to meet the urgent needs of construction sites for rapid assessment and real-time decision-making. More importantly, existing numerical methods primarily focus on the coupled analysis of the seepage field and stress field, failing to systematically incorporate key factors such as blasting disturbance loads during tunnel excavation, damage and deterioration of the rock mass caused by blasting and geological structures, and dynamic fluctuations in karst water pressure caused by seasonal changes and construction disturbances into a unified analytical framework. Furthermore, the selection of safety factors in existing technologies largely relies on the subjective judgment of engineers, lacking objective and quantitative criteria directly related to the degree of surrounding rock fracturing, the specific size of the karst cave, and the magnitude of water pressure. This makes it difficult to achieve a scientific balance between safety reserves and economic costs in engineering projects.

[0004] To address the aforementioned issues, the industry has been seeking a method for determining safe distances that can ensure both computational accuracy and efficiency, while comprehensively reflecting the coupled effects of multiple factors such as blasting, water pressure, and surrounding rock damage. However, due to the complexity of the interaction between fractured surrounding rock and the karst cave system, establishing an analytical or semi-analytical computational model that accurately describes each physical process and is easy to apply in engineering faces numerous difficulties. This constitutes a pressing technical bottleneck in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for determining the safe distance between fractured surrounding rock and water-rich, high-pressure karst caves, thereby resolving the issues present in the prior art.

[0006] In a first aspect, to achieve the above objective, the present invention provides a method for determining a safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave, comprising the following steps:

[0007] Obtain the physical and mechanical parameters of the surrounding rock and the geometric parameters of the karst caves in the engineering area;

[0008] The safety distance is decomposed into the thickness of the damage zone on the tunnel excavation side, the thickness of the intermediate protective layer, and the thickness of the influence zone on the karst cave side.

[0009] Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the blasting parameters, the thickness of the damage zone on the tunnel excavation side is calculated, wherein the calculation process is coupled with the interaction effect of blasting stress wave and explosive gas.

[0010] Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the water pressure in the karst cave, the thickness of the influence zone on the side of the karst cave is calculated. The calculation process is coupled with the effects of seepage water pressure and stress wave reflection.

[0011] Determine the thickness of the intermediate protective layer;

[0012] The calculated thicknesses of the tunnel excavation side damage zone, the intermediate protective layer, and the karst cave side influence zone are added together to determine the final safe distance.

[0013] Optionally, the process of decomposing the safety distance includes: considering the safety distance as a linear superposition of three parts: the thickness of the surrounding rock damage zone caused by tunnel excavation, the thickness of the influence zone caused by the existence of karst caves, and the thickness of the protective layer located between the two.

[0014] Optionally, calculating the thickness of the damage zone on the tunnel excavation side includes: determining the range of the crushing zone formed by the blast shock wave, the range of the damage zone caused by the stress wave disturbance, and the range of the crack propagation zone generated by the action of the explosive gas, and superimposing the range of the damage zone and the range of the crack propagation zone, and then subtracting the overlapping range of the crushing zone to obtain the final thickness.

[0015] Optionally, determining the extent of the damage zone caused by stress wave disturbance includes: establishing the yield condition of the surrounding rock based on the Hawke-Brown strength criterion, and substituting the attenuation law of the stress wave generated by the blasting into the yield condition for solution to obtain the critical radius of the damage zone.

[0016] Optionally, determining the extent of the fracture propagation zone caused by the action of explosive gases includes: establishing a composite stress intensity factor model that includes the original rock stress and the explosive gas pressure based on fracture mechanics theory, and determining the propagation length when the fracture stops based on the fracture toughness of the rock, thereby obtaining the extent of the zone.

[0017] Optionally, calculating the thickness of the influence zone on the side of the karst cave includes: determining the extent of the seepage damage zone caused by the seepage effect of the karst cave water pressure and the extent of the tensile cracking zone caused by the reflection of the blast stress wave on the karst cave wall, and superimposing the extent of the seepage damage zone and the extent of the tensile cracking zone, and then subtracting the radius of the karst cave itself to obtain the final thickness.

[0018] Optionally, determining the extent of the seepage failure zone includes: constructing the equilibrium equation of the surrounding rock micro-unit considering the effect of seepage force, and solving for the location of the elastoplastic state transition boundary using the Mohr-Coulomb strength criterion as the extent of the zone.

[0019] Optionally, the karst cave water pressure is the sum of three parts: undisturbed hydrostatic pressure, additional hydrostatic pressure caused by seasonal rainfall, and dynamic water pressure induced by tunnel construction disturbance.

[0020] Secondly, the present invention also provides a computer terminal device, comprising:

[0021] One or more processors;

[0022] A memory, coupled to the processor, for storing one or more programs;

[0023] When the one or more programs are executed by the one or more processors, the one or more processors implement the steps of the method for determining the safe distance between fractured surrounding rock and water-rich high-pressure karst caves in the first aspect described above.

[0024] Thirdly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for determining a safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave as described in the first aspect.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] This invention provides a method for determining the safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave. It integrates the coupled effects of multiple factors, including blasting stress waves and explosive gases, and the effects of karst cave water pressure infiltration and reflected waves. By establishing a segmented calculation model of the tunnel excavation side damage zone, protective layer, and karst cave side influence zone, it achieves an analytical determination of the safe distance between the fractured surrounding rock and the water-rich, high-pressure karst cave. This method effectively overcomes the calculation errors caused by traditional empirical formulas neglecting parameter discreteness and coupling effects, and avoids the shortcomings of complex numerical simulation methods, such as cumbersome modeling and long processing times. This invention significantly improves the accuracy and efficiency of safe distance calculation, providing a scientific and reliable basis for rapid on-site decision-making and risk control in tunnel, mine, and underground cavern engineering projects. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a schematic diagram of the tunnel safety thickness composition according to an embodiment of the present invention;

[0029] Figure 2 This is a model diagram of the seepage effect in a karst cave according to an embodiment of the present invention;

[0030] Figure 3 This is a flowchart illustrating the safe thickness calculation process according to an embodiment of the present invention. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0033] Example 1

[0034] This embodiment provides a method for determining the safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave, including:

[0035] Obtain the physical and mechanical parameters of the surrounding rock and the geometric parameters of the karst caves in the engineering area;

[0036] The safety distance is decomposed into the thickness of the damage zone on the tunnel excavation side, the thickness of the intermediate protective layer, and the thickness of the influence zone on the karst cave side.

[0037] Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the blasting parameters, the thickness of the damage zone on the tunnel excavation side is calculated, wherein the calculation process is coupled with the interaction effect of blasting stress wave and explosive gas.

[0038] Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the water pressure in the karst cave, the thickness of the influence zone on the side of the karst cave is calculated. The calculation process is coupled with the effects of seepage water pressure and stress wave reflection.

[0039] Determine the thickness of the intermediate protective layer;

[0040] The calculated thicknesses of the tunnel excavation side damage zone, the intermediate protective layer, and the karst cave side influence zone are added together to determine the final safe distance.

[0041] Furthermore, the process of decomposing the safety distance includes: considering the safety distance as a linear superposition of three parts: the thickness of the surrounding rock damage zone caused by tunnel excavation, the thickness of the influence zone caused by the existence of karst caves, and the thickness of the protective layer located between the two.

[0042] Specifically, the implementation process of this embodiment includes:

[0043] Step 1: Clarify the process of calculating the safe thickness, as follows: Figure 3 As shown. The impact of tunnel blasting on rock wall stability is analyzed, such as... Figure 1 As shown, the safety thickness is divided into the thickness of the tunnel surrounding rock damage zone H1, the thickness of the influence zone on one side of the karst cave H3, and the thickness of the protective layer H2.

[0044] ;

[0045] In the formula: Thickness of the damaged zone in the surrounding rock of the tunnel (m); The thickness of the protective layer (m); The thickness (m) of the influence zone on one side of the cave.

[0046] Furthermore, calculating the thickness of the damage zone on the tunnel excavation side includes: determining the range of the crushing zone formed by the blast shock wave, the range of the damage zone caused by the stress wave disturbance, and the range of the crack propagation zone generated by the action of the blast gas, and superimposing the range of the damage zone and the range of the crack propagation zone, and then subtracting the overlapping range of the crushing zone to obtain the final thickness.

[0047] Specifically, the implementation process of this embodiment includes:

[0048] Step 2: Calculate the thickness H1 of the damage zone on one side of the tunnel:

[0049] The thickness H1 of the damage zone on one side of the tunnel surrounding rock includes the blasting crushing zone R1, the blasting stress wave disturbance damage zone R2, and the quasi-static crack propagation zone of the blasting gas R3. Based on the superposition effect and the most unfavorable principle, the calculation formula is as follows:

[0050] ;

[0051] In the formula: R1 is the radius of the blasting crushing zone (m); R2 is the radius of the stress wave disturbance damage zone (m); R3 is the radius of the blast gas fissure propagation zone (m).

[0052] Crushing zone R1 generated by the shock wave from tunnel blasting:

[0053] The crushing zone is the area where the rock around the blast hole is extremely compressed and destroyed by the blast shock wave, and its extent mainly depends on engineering experience.

[0054] Combining the drilling and blasting parameters of Xiemashi Tunnel (borehole radius R) c 21mm = 0.021m), crushing zone radius R1:

[0055] Take it as 2 to 3 times the radius of the borehole, that is: ;

[0056] Among them, R c This is the borehole radius. It's generally taken as twice that radius, R1 = 2R. c =2×0.021=0.042m.

[0057] Furthermore, determining the extent of the damage zone caused by stress wave disturbance includes: establishing the yield condition of the surrounding rock based on the Hawke-Brown strength criterion, and substituting the attenuation law of the stress wave generated by the blasting into the yield condition for solution, so as to obtain the critical radius of the damage zone.

[0058] Specifically, the implementation process of this embodiment includes:

[0059] Step 3: Calculate the radius R2 of the stress wave disturbance failure zone based on the HB criterion:

[0060] After the shock wave attenuates into a stress wave, the axial pressure weakens. The rock within the stress wave's range is subjected to complex stresses such as compression, tension, and shear. Within a certain range, the rock mass reaches the yield condition, resulting in a disturbed failure zone. This step uses the HB criterion instead of the traditional DP criterion to accurately describe the yielding characteristics of the fractured surrounding rock.

[0061] (1) Calculate the detonation pressure The formula is:

[0062] ;

[0063] in, Let D be the explosive density, D be the detonation velocity, and K be the isentropic exponent.

[0064] (2) Establishing stress distribution relationship: During the propagation of stress wave, the radial stress σ of the surrounding rock r Attenuation with distance, satisfying

[0065] ;

[0066] Where α = 1.5 (rock medium attenuation coefficient), and r is the distance (m) between the calculation point and the borehole center. Under plane strain conditions, the circumferential stress... With radial stress satisfy:

[0067] .

[0068] In the formula, It is circumferential stress; This is radial stress.

[0069] (3) Substitute the HB criterion to solve for the critical radius: when the surrounding rock reaches the yielding state,

[0070] The critical value of the elastoplasticity of the intermediate principal stress can be simplified as:

[0071] ;

[0072] The expression for the HB criterion is:

[0073] ;

[0074] In the formula: The maximum principal stress ( ); For the minimum principal stress ( ); Uniaxial compressive strength of rock ( ); mb is the rock mass correction factor; s is the rock mass structure factor; a is the strength index.

[0075] ;

[0076] ;

[0077] Substituting into equation (5), we get:

[0078] ;

[0079] Will Substitute:

[0080] ;

[0081] Summarized as follows:

[0082] ;

[0083] For simplicity, let a = 0.5 (a common value), then:

[0084] ;

[0085] Squaring both sides:

[0086] ;

[0087] ;

[0088] Rearranged into a standard quadratic equation:

[0089] ;

[0090] When the rock mass reaches the yielding state, the critical principal stress intensity is:

[0091] ;

[0092] Substituting into equations (3) and (4), we get:

[0093] ;

[0094] Therefore, the half-R2 of the disturbance destruction region can be obtained:

[0095] .

[0096] In the formula, r c The radius of the borehole is... is the rock medium attenuation coefficient, the rest are the same as above.

[0097] Furthermore, determining the extent of the fracture propagation zone caused by the explosive gas action includes: establishing a composite stress intensity factor model that includes the original rock stress and the explosive gas pressure based on fracture mechanics theory, and determining the propagation length when the fracture stops based on the rock fracture toughness, thereby obtaining the extent of the zone.

[0098] Specifically, the implementation process of this embodiment includes:

[0099] Step 4: Crack propagation zone R3 caused by the quasi-static action of blasted gas in the tunnel:

[0100] The high-temperature, high-pressure gas generated after the explosion produces quasi-static pressure, causing the initial crack to propagate. Calculations are performed according to the fracture mechanics arrest condition:

[0101] (1) Calculate the pressure P of the explosive gas. m According to the isentropic adiabatic expansion theory, the formula is:

[0102] ;

[0103] Where P k =280MPa (critical pressure of TNT explosive). For the charge radius, The radius of the borehole is... The adiabatic index is 1.4 in this embodiment, and k is the isentropic index, which is generally taken as 3. Substituting the parameters, we get:

[0104] P m =280× ≈280×0.082≈22.96MPa.

[0105] (2) Stress intensity factor at the fracture tip: Combining the original rock stress and the effect of explosive gases, the intensity factor

[0106] K1=K1 (1) +K1 (2) K1 (1) =P0 (Contribution of original rock stress);

[0107] K1 (2) =2P m (Gas pressure contribution), where a is the crack propagation length (m).

[0108] (3) Solving for the crack arrest condition: The crack propagation length a is determined by the following formula:

[0109] ;

[0110] Among them, K IC This refers to the fracture toughness of rocks, which is related to lithology.

[0111] When K1=K IC The crack stopped expanding.

[0112] Furthermore, calculating the thickness of the influence zone on the side of the karst cave includes: determining the extent of the seepage damage zone caused by the seepage effect of the karst cave water pressure and the extent of the tensile cracking zone caused by the reflection of the blast stress wave on the karst cave wall, and superimposing the extent of the seepage damage zone and the extent of the tensile cracking zone, and then subtracting the radius of the karst cave itself to obtain the final thickness.

[0113] Specifically, the implementation process of this embodiment includes:

[0114] Step 5: Calculate the thickness of the influence zone on one side of the cave. :

[0115] The affected zone on one side of the cave mainly includes the seepage damage zone caused by the water pressure in the cave. and the tensile crack zone caused by reflection The expression for the thickness H3 of the damaged zone on one side of the cave is as follows:

[0116] ;

[0117] In the formula: The radius of the cave; The depth of the infiltration and damage zone; The thickness of the tensile fracture zone.

[0118] Furthermore, determining the extent of the seepage failure zone involves: constructing the equilibrium equation of the surrounding rock micro-unit considering the effect of seepage force, and using the Mohr-Coulomb strength criterion to solve for the location of the elastoplastic state transition boundary as the extent of the zone.

[0119] Specifically, the implementation process of this embodiment includes:

[0120] (1) Infiltration damage zone:

[0121] The long-term presence of high water pressure in the karst cave causes the rock mass to be in a state of seepage in the underground water-rich layer. Affected by the abundant water, seepage damage zones appear within a certain range of the karst cave.

[0122] Assume there exists a water pressure of [value] within the burial depth region. The cave has a radius of Infinitely far At this location, the water pressure is 0; under normal circumstances, it is taken as... This will meet the accuracy requirements; the radius of the seepage damage zone is... The surrounding rock is an isotropic homogeneous medium, and the internal friction angle of the surrounding rock is... Model such as Figure 2 As shown.

[0123] The equilibrium equation for the micro-element considering permeability is as follows:

[0124] ;

[0125] in, , .

[0126] The expression for the MC criterion is:

[0127] ;

[0128] in,

[0129] ;

[0130] The MC criterion then simplifies to:

[0131] ;

[0132] Substituting the MC criterion into the equilibrium equation, we obtain:

[0133] ;

[0134] Simplifying, we get:

[0135] ;

[0136] make:

[0137] ;

[0138] The equation then becomes:

[0139] ;

[0140] This is a first-order linear differential equation, and its general solution is:

[0141] ;

[0142] Boundary conditions:

[0143] when hour, ;

[0144] Substituting into the solution, we obtain the integral constant C:

[0145] ;

[0146] Therefore, the radial stress solution is:

[0147] ;

[0148] in, For water pressure, r a Let A be the radius of the cave, and A and B have the same meaning as above.

[0149] when When the rock mass changes from a plastic state to an elastic state, the following conditions are met:

[0150] ;

[0151] ;

[0152] in, This refers to the stress in the original rock.

[0153] At the elastic-plastic boundary At that point, the stress is continuous, that is... Substituting the values ​​and solving, we get :

[0154] ;

[0155] Where, r a Where is the radius of the karst cave, c is the cohesion of the surrounding rock, and the other parameters are the same as above.

[0156] Furthermore, the karst cave water pressure is the sum of three parts: undisturbed hydrostatic pressure, additional hydrostatic pressure caused by seasonal rainfall, and dynamic water pressure induced by tunnel construction disturbance.

[0157] Specifically, the implementation process of this embodiment includes:

[0158] (2) Water pressure in the karst cave:

[0159] During tunnel excavation, changes in the surrounding rock conditions generate disturbance loads. Under these loads, the karst cave experiences additional stress, causing changes in fissure volume and resulting in additional water pressure. Furthermore, seasonal variations, particularly rainfall during the rainy season, also increase water pressure within the karst cave. Therefore, determining the water pressure in the karst cave requires considering the effects of tunnel excavation disturbance and seasonal rainfall. The expression for the karst cave water pressure under these conditions is as follows:

[0160] ;

[0161] In the formula, , These are the karst cave water pressure under undisturbed conditions and the water pressure increased by seasonal rainfall. These two water pressure data can be obtained by combining the karst cave water occurrence conditions with local meteorological and hydrological data and advanced horizontal drilling during construction. This refers to the additional dynamic water pressure generated by tunnel construction disturbance. The calculation method for the additional water pressure generated by water hammer is as follows:

[0162] ;

[0163] In the formula: R4 represents the maximum charge per segment (kg); R4 represents the distance (m) between the measuring point and the blast source, obtained through surveying; k is a parameter associated with the blasting site. This is the attenuation coefficient.

[0164] (3) Destruction zone of reflected waves in karst caves:

[0165] According to the Hopkinson effect, when a blasting stress wave encounters a karst cave, it is reflected at the water-rock interface, causing tensile stress in the surrounding rock. Under the combined action of tensile stress and water pressure, this stress exceeds the tensile strength of the rock mass, leading to crack propagation. It is assumed that the reflected stress wave follows the same attenuation law as the incident wave. The radius of the failure zone under the action of the reflected wave is calculated using the empirical formula as follows:

[0166] ;

[0167] In the formula: The reflection coefficient; This refers to the axial pressure (MPa) generated when the stress wave reaches the cave wall. This is the water pressure reduction factor; ; It is the internal friction angle.

[0168] Step Six: Calculate the protective layer thickness. Based on the empirical formula:

[0169] ;

[0170] In the formula, H W The water head height (m) , B is the unit weight of water; F is the tunnel excavation width (m); f is the Protodyakonov coefficient, which is generally taken as 1 / 10 of the rock compressive strength, or 10 can be obtained from a table.

[0171] Step 7: Calculate the safe thickness:

[0172] In summary, the safe thickness is calculated as H = H1 + H2 + H3.

[0173] Example 2

[0174] In this embodiment, a computer terminal device is provided, including:

[0175] One or more processors;

[0176] A memory, coupled to the processor, for storing one or more programs;

[0177] When the one or more programs are executed by the one or more processors, the one or more processors perform the steps of the method described above for determining the safe distance between fractured surrounding rock and water-rich, high-pressure karst caves.

[0178] In this embodiment, a computer-readable storage medium is also provided, on which a computer program is stored. When the computer program is executed by a processor, it implements the steps of the method described above for determining the safe distance between fractured surrounding rock and water-rich, high-pressure karst cave.

[0179] An application example of this invention:

[0180] This embodiment uses the case of the water inrush project in Xiemashi Tunnel and the corresponding mechanical parameters as a calculation reference. The tunnel passes through a water-rich, high-pressure karst area. The surrounding rock in this section is mainly limestone with well-developed joints and fissures, severe dissolution, and a fragmented, loose structure. When construction reached section YK138+123.5, a water-rich, high-pressure karst cave was discovered on the side by ground-penetrating radar. It is necessary to accurately calculate the minimum safe distance between the tunnel surrounding rock and the karst cave. The tunnel in this section has a burial depth of 750m, an excavation width of 7m, and a height of 9.8m. The karst cave has an irregular shape, and the average diameter is taken as 6m for calculation. The measured water pressure in the karst cave is 1.902MPa, the original rock stress is calculated to be 19.875MPa, and the internal friction angle of the limestone sample taken at the water inrush point is 35°, and the cohesion is 32.55MPa. Combined with the basic parameters of Xiemashi Tunnel: explosive density ρ (1.4g / cm³), explosive detonation velocity D (4200m / s), and explosive cartridge radius... (10mm), borehole radius (21mm), maximum charge per segment Q (5-15kg), isentropic index k (1.2g / cm³) is taken as 3), adiabatic index γ (1.4).

[0181] Substituting the values, we obtain the radius of the crack propagation zone: =0.021+1.72=1.741m;

[0182] Excavation of blasting disturbance damage zone on one side The calculated result is 0.096m;

[0183] thereby ;

[0184] Calculate the MC parameters:

[0185] ;

[0186] ;

[0187] ;

[0188] ;

[0189] Therefore, we can calculate:

[0190] ;

[0191] Calculate H3:

[0192] ;

[0193] ;

[0194] In summary, the calculated safe thickness is as follows: .

[0195] The safe thickness calculated using the DP criterion is 4.441 m, which is larger than that in this embodiment. This is mainly because the safe thickness values ​​for both the karst cave side and the blasting side in this embodiment did not deduct the borehole radius and the karst cavity radius, resulting in a certain deviation in the calculation results. During the on-site construction of the Xiemashi Tunnel, the safe thickness for preventing mudslides and water inrushes in the limestone section was controlled at 3.5-4.5 m, effectively ensuring protection against mudslides and water inrushes. This result is close to the calculation results in this embodiment. Therefore, the calculation method used in this embodiment has certain guiding significance for on-site construction.

[0196] This invention provides a method for determining the safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave. It integrates the coupled effects of multiple factors, including blasting stress waves and explosive gases, and the effects of karst cave water pressure infiltration and reflected waves. By establishing a segmented calculation model of the tunnel excavation side damage zone, protective layer, and karst cave side influence zone, it achieves an analytical determination of the safe distance between the fractured surrounding rock and the water-rich, high-pressure karst cave. This method effectively overcomes the calculation errors caused by traditional empirical formulas neglecting parameter discreteness and coupling effects, and avoids the shortcomings of complex numerical simulation methods, such as cumbersome modeling and long processing times. This invention significantly improves the accuracy and efficiency of safe distance calculation, providing a scientific and reliable basis for rapid on-site decision-making and risk control in tunnel, mine, and underground cavern engineering projects.

[0197] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the safe distance between fractured surrounding rock and a water-rich, high-pressure karst cave, characterized in that, Includes the following steps: Obtain the physical and mechanical parameters of the surrounding rock and the geometric parameters of the karst caves in the engineering area; The safety distance is decomposed into the thickness of the damage zone on the tunnel excavation side, the thickness of the intermediate protective layer, and the thickness of the influence zone on the karst cave side. Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the blasting parameters, the thickness of the damage zone on the excavation side of the tunnel is calculated. The calculation process is coupled with the interaction effect of the blasting stress wave and the explosive gas. Based on the physical and mechanical parameters of the surrounding rock, the geometric parameters of the karst cave, and the water pressure in the karst cave, the thickness of the influence zone on the side of the karst cave is calculated. The calculation process couples the effects of seepage water pressure and stress wave reflection. Determine the thickness of the intermediate protective layer; The calculated thicknesses of the tunnel excavation side damage zone, the intermediate protective layer, and the karst cave side influence zone are added together to determine the final safe distance.

2. The method according to claim 1, characterized in that, The process of decomposing the safety distance includes: considering the safety distance as a linear superposition of three parts: the thickness of the surrounding rock damage zone caused by tunnel excavation, the thickness of the influence zone caused by the existence of karst caves, and the thickness of the protective layer located between the two.

3. The method according to claim 1, characterized in that, Calculating the thickness of the damage zone on the tunnel excavation side includes: determining the range of the crushing zone formed by the blast shock wave, the range of the damage zone caused by the stress wave disturbance, and the range of the crack propagation zone generated by the action of the blast gas, and superimposing the range of the damage zone and the range of the crack propagation zone, and then subtracting the overlapping range of the crushing zone to obtain the final thickness.

4. The method according to claim 3, characterized in that, Determining the extent of the damage zone caused by stress wave disturbance includes: establishing the yield condition of the surrounding rock based on the Hawke-Brown strength criterion, and substituting the attenuation law of the stress wave generated by the blasting into the yield condition for solution to obtain the critical radius of the damage zone.

5. The method according to claim 3, characterized in that, Determining the extent of the fracture propagation zone caused by explosive gas involves: establishing a composite stress intensity factor model that includes the original rock stress and explosive gas pressure based on fracture mechanics theory, and determining the propagation length at which the fracture stops based on the rock fracture toughness, thereby obtaining the extent of the zone.

6. The method according to claim 1, characterized in that, Calculating the thickness of the side influence zone of the karst cave includes: determining the extent of the seepage damage zone caused by the seepage effect of the karst cave water pressure and the extent of the tensile cracking zone caused by the reflection of the blast stress wave on the karst cave wall, and superimposing the extent of the seepage damage zone and the extent of the tensile cracking zone, and then subtracting the radius of the karst cave itself to obtain the final thickness.

7. The method according to claim 6, characterized in that, Determining the extent of the seepage failure zone involves: constructing the equilibrium equations of the surrounding rock micro-units that take into account the effect of seepage force, and using the Mohr-Coulomb strength criterion to solve for the location of the elastoplastic state transition boundary as the extent of the zone.

8. The method according to claim 1, characterized in that, The karst cave water pressure is the sum of three parts: undisturbed hydrostatic pressure, additional hydrostatic pressure caused by seasonal rainfall, and dynamic water pressure induced by tunnel construction disturbance.

9. A computer terminal device, characterized in that, include: One or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors perform the steps of the method as described in any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1-8.

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