Hydraulic rock mass presplitting method for improving rock breaking efficiency of roadheader

Abstract

The hydraulic rock mass presplitting method for improving the rock breaking efficiency of the roadheader comprises the steps that S1, the initial position of a fracturing hole in a hard rock roadway is determined, and stress distribution and related physical and mechanical parameters of any point around the fracturing hole are actually measured on site; s2, crack initiation pressure is obtained through calculation, and the type and performance parameters of equipment are selected; calculating to obtain a theoretical fracturing radius R1; s3, observation holes are formed in the periphery of the fracturing hole, the actual expansion radius of the hydraulic fracturing fracture of the hard rock roadway is analyzed, and the minimum value is taken; s4, the sufficient hydraulic fracturing area is calculated, and the number of drill holes, the distance between the drill holes and the arrangement scheme of observation holes are determined; s5, the depth of a fracturing hole and the position of a hydraulic fracturing initiation point in the drill hole are determined; s6, carrying out fracturing treatment by adopting a retreating type high-pressure water injection fracturing technology; by drilling the observation hole and the fracturing hole and selecting equipment with performance parameters matched with actual working condition requirements, the cutting performance of the hard rock mass is effectively improved, the rock breaking efficiency of the roadheader is improved, and the cutting pick loss is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, in particular to a hydraulic pre-splitting rock mass method for improving the rock breaking efficiency of a fully-mechanized tunneling machine. Background Art

[0002] Hard rock tunnel excavation creates production conditions for coal mining and serves coal mining. The imbalance of mining and excavation ratio will seriously affect the normal production and development of coal. Nowadays, the common hard rock tunnel excavation mainly adopts the method of explosive blasting, but this method has a large amount of engineering, resulting in low excavation efficiency, high pick loss, and large material waste, which seriously affects the excavation speed, making it difficult to take over the working face excavation, and restricting the production capacity of the mine; at the same time, there are certain safety hazards. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a hydraulic pre-splitting rock method for improving the rock breaking efficiency of a tunnel boring machine to solve the above-mentioned problems.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A hydraulic pre-splitting rock mass method for improving the rock breaking efficiency of a tunnel boring machine comprises the following steps:

[0006] S1: Determine the center position of the hard rock tunnel section as the initial location of the fracturing hole, and measure the stress distribution and related physical and mechanical parameters of any point around the fracturing hole on site;

[0007] S2: Calculate the fracturing pressure according to the stress distribution and related physical and mechanical parameters, and select the model and performance parameters of the hydraulic pre-fracture equipment that match the actual working condition requirements according to the fracturing pressure; and obtain the theoretical fracturing radius R1 using the hydraulic fracturing radius calculation formula based on the performance parameters of the hydraulic pre-fracture equipment;

[0008] S3: setting observation holes around the fracturing holes, analyzing the actual expansion radius of the hydraulic fracturing cracks in the hard rock tunnel according to the theoretical fracturing radius R1 and the on-site fracturing range detection test, and taking the minimum value;

[0009] S4: calculating a sufficient hydraulic fracturing area according to the minimum value of the actual expansion radius of the hydraulic fracturing fissure, and determining the number of drill holes, the drill hole spacing and the arrangement of the observation holes for hydraulic pre-fractured hard rock tunnel to be excavated according to the size of the sufficient hydraulic fracturing area;

[0010] S5: Analyze the range of stress concentration zone of the rock mass to be excavated, determine the depth of the fracturing hole and the location of the hydraulic fracturing starting point in the borehole;

[0011] S6: After the drilling is completed, the backward high-pressure water injection fracturing technology is used to fractur e the hard rock to be excavated.

[0012] In the above invention, further, in step S1, the stress distribution and related physical and mechanical parameters measured on site include plumb stress, lateral stress coefficient, rock mass tensile strength, and height and cross-sectional area of ​​the hard rock tunnel.

[0013] In the above invention, further, step S2 includes:

[0014] S21: The fracture initiation pressure is calculated based on the measured plumb stress, lateral stress coefficient and rock mass tensile strength. The calculation formula for the fracture initiation pressure is as follows:

[0015] P c =min{(3-λ)q0+R t , (3λ-1)q0+R t}

[0016] Where P c is the crack initiation pressure, q0 is the plumb stress, λ is the lateral stress coefficient, R t is the tensile strength of rock mass;

[0017] S22: According to the cracking pressure P c The model and performance parameters of the hydraulic pre-fracture equipment are selected. The hydraulic pre-fracture equipment includes a high-pressure pump and a high-pressure hose. The model and performance parameters of the high-pressure pump and the high-pressure hose include rated flow, pumping time, elastic modulus and fluid pressure in the fracture. The theoretical fracturing radius R1 is calculated in combination with the performance parameters. The calculation formula is as follows:

[0018]

[0019] Where Q is the pumping flow rate, t is the pumping time, E is the elastic modulus, σ is the fluid pressure in the fracture, and h is the fracture height, where the fracture height h is the height of the hard rock tunnel.

[0020] In the above invention, further, in step S3, since the actual hydraulic fracturing fracture space is different from the theoretical hydraulic fracturing fracture space, it is necessary to measure it through a field fracturing range detection test. The specific steps of the field fracturing range detection test are as follows:

[0021] S31: Pre-constructing observation holes in the vertical and horizontal directions with the fracturing hole as the center;

[0022] S32: Observe whether there is water discharge from the observation hole. If there is no water discharge from the observation hole, shorten the distance between the observation hole and the fracturing hole in the radial direction until water discharge occurs in the observation hole. The distance at this time is the fracturing distance.

[0023] S33: Record the vertical fracturing distance R H and horizontal fracturing distance Rh , select the minimum value as the sufficient hydraulic fracturing radius R hy , the sufficient hydraulic fracturing radius R hy The calculation formula is as follows:

[0024] R hy =min(R H , R h )

[0025] In the above invention, further, step S4 specifically includes:

[0026] S41: According to the hydraulic fracturing radius R hy Calculate the sufficient hydraulic fracturing area S hy , the sufficient hydraulic fracturing area S hy The calculation formula is as follows:

[0027]

[0028] S42: The fully hydraulically fractured area S hy and the cross-sectional area S of the hard rock tunnel d For comparison, if the hydraulic fracturing area S hy Proportion of hard rock tunnel cross-sectional area S d If the pressure is more than 80%, single-hole fracturing is used; otherwise, double-hole fracturing is used;

[0029] S43: After the number of fracturing holes is determined according to the above steps, the sufficient hydraulic fracturing area S hy Determine the arrangement of drilling locations, drilling spacing and observation holes.

[0030] In the above invention, further, in step S43, if single-hole fracturing is adopted, the specific steps of arranging the drilling position and the observation hole are as follows:

[0031] The center position of the hard rock tunnel section is used as the drilling position of the fracturing hole, and observation holes G1 and G2 are set at a distance of 0.1 meters from the top plate and bottom plate respectively in the same vertical direction of the fracturing hole; when performing fracturing operations, observe whether water comes out of the observation holes. If water comes out, stop the fracturing operation immediately.

[0032] In the above invention, further, in step S43, if dual-hole fracturing is adopted, the specific steps of arranging the drilling positions, drilling spacing and observation holes are as follows:

[0033] When double-hole fracturing is adopted, the fracturing holes are K1 and K2 respectively. The fracturing holes K1 and K2 are located at the same vertical height as the center position of the hard rock tunnel section. The fracturing holes K1 and K2 are symmetrically arranged about the central axis of the hard rock tunnel section, and the drilling spacing between the fracturing holes K1 and K2 is half of the width of the hard rock tunnel section; and observation holes G1 and G2 are arranged on the central axis line of the hard rock tunnel section at a distance of 0.1 meter from the top plate and the bottom plate respectively; when performing fracturing operations, observe whether water comes out of the observation holes. If water comes out, the fracturing operation is stopped immediately.

[0034] In the above invention, further, in step S5, after the excavation working face is disturbed by mining activities, three regions, namely, a pressure relief zone, a concentrated stress zone and an original rock stress zone, are formed in front, wherein the concentrated stress zone is selected as the hydraulic fracturing range, and the drilling depths of the fracturing holes and the observation holes and the hydraulic fracturing initiation point position in the borehole are determined according to the length of the concentrated stress zone. The specific steps are as follows:

[0035] S51: Parameters related to the friction coefficient of the soft layer, the thickness of the soft layer, the stress concentration factor, the average density of the overlying rock layer, the burial depth and the tensile strength of the rock are obtained based on field measurements;

[0036] S52: The calculation formula of the limit equilibrium zone depth of the limit equilibrium theory is used to calculate the pressure relief zone width L1 and the limit equilibrium zone width L2. The calculation formula of the limit equilibrium zone depth is as follows:

[0037]

[0038]

[0039] Where N f is the stress concentration coefficient of the rock formation, f is the friction coefficient of the soft layer, m is the thickness of the soft layer, γ is the average density of the overlying rock formation, H is the burial depth, and δ is the tensile strength of the rock;

[0040] S53: Assume that the drilling depth is L3, and the drilling depth L3 is within the concentrated stress zone, according to the limit equilibrium zone width and coefficient N g The value of drilling depth L3 is calculated as follows:

[0041]

[0042] In the formula, the coefficient N g The value range of is 1.2 to 1.8; according to the drilling depth L3 and the hydraulic fracturing radius R hy Get the hydraulic fracturing initiation point location.

[0043] In the above invention, further, the high-pressure pump is placed at a distance of 30-100 meters from the excavation working face.

[0044] The beneficial effects of the present invention are:

[0045] 1. The present invention provides a hydraulic pre-splitting rock mass method for improving the rock breaking efficiency of a tunnel boring machine. By drilling a fracturing hole and performing multiple hydraulic fracturing operations, hard rock is pre-splitting, thereby improving the cutting performance of the hard rock mass, improving the rock breaking efficiency of the tunnel boring machine, and reducing the loss of pick teeth.

[0046] 2. The present invention also drills observation holes around the fracturing holes, and stops hydraulic fracturing in time by observing whether water is coming out of the observation holes, thereby reducing unnecessary fracturing time, improving fracturing, and preventing the crack network caused by excessive hydraulic fracturing from weakening the structure of the roadway roof and floor, thereby ensuring that the cracks are controlled within a safe range;

[0047] 3. Secondly, the present invention can select the model and performance parameters of the hydraulic pre-fracture equipment according to the fracture initiation pressure. The equipment selection by this method can ensure that the equipment performance parameters match the actual working conditions, thereby optimizing the hydraulic pre-fracture process and realizing the rapid excavation of hard rock tunnels based on hydraulic pre-fracture technology;

[0048] 4. The present invention can also determine whether to adopt a single-hole fracturing method or a double-hole fracturing method according to the actual situation of the hard rock tunnel, so as to achieve a hydraulic fracturing network to fully weaken the rock mass to be excavated in the hard rock tunnel and improve the rock breaking efficiency of the comprehensive excavation machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the hydraulic fracturing range of the present invention;

[0050] Figure 2 It is a schematic diagram of the arrangement scheme of hydraulic fracturing drilling of the present invention;

[0051] Figure 3 This is a schematic diagram of the hydraulic fracturing drilling depth and fracturing point design of the present invention;

[0052] Figure 4 The spatial position of the hydraulic pre-splitting rock mass fast excavation technology equipment of the present invention;

[0053] Figure 5 It is a schematic diagram comparing the daily advance of the tunnel boring machine before and after fracturing according to the present invention. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] A method for hydraulic pre-fracture of rock mass for improving the rock breaking efficiency of a tunnel boring machine. The method adopts methods such as on-site investigation, drilling, and on-site fracturing range detection test to grasp the original rock stress conditions of the hard rock tunnel excavation working face, determine the physical and mechanical parameters of the rock mass to be excavated, and provide basic data for subsequent research; by simplifying the stress analysis in hydraulic fracturing of the hard rock tunnel excavation working face to the problem of a circular hole on an infinitely large hole peeping at a plate, the stress distribution of any point around the circular hole is calculated using the theory of elastic mechanics, and the solution is used to estimate the pressure conditions for the initiation and expansion of the crack.

[0056] The specific steps include:

[0057] S1: After the tunnel section is temporarily supported by knocking the top and top to confirm that the surrounding rock of the working face is stable, the center position of the hard rock tunnel section is determined as the preliminary location of the fracturing hole, and the stress distribution and related physical and mechanical parameters of any point around the fracturing hole are calculated by on-site measurement and elastic mechanics theory;

[0058] The stress distribution and related physical and mechanical parameters measured on site include plumb stress, lateral stress coefficient, rock mass tensile strength, and height and cross-sectional area of ​​hard rock tunnels.

[0059] S2: Calculate the fracturing pressure according to the stress distribution and related physical and mechanical parameters, and select the model and performance parameters of the hydraulic pre-fracture equipment that match the actual working conditions according to the fracturing pressure; Based on the performance parameters of the hydraulic pre-fracture equipment, use the hydraulic fracturing radius calculation formula to obtain the theoretical fracturing radius R1, as shown in the attached figure. Figure 1 As shown; step S2 comprises:

[0060] S21: The fracture initiation pressure is calculated based on the measured plumb stress, lateral stress coefficient and rock mass tensile strength. The calculation formula for the fracture initiation pressure is as follows:

[0061] P c =min{(3-λ)q0+R t , (3λ-1)q0+R t}

[0062] Where P c is the crack initiation pressure, q0 is the plumb stress, λ is the lateral stress coefficient, R t is the tensile strength of rock mass;

[0063] Assume that the plumb stress q0=12.5Mpa, the lateral stress coefficient λ=1.2, and the rock mass tensile strength R t =4.4Mpa, the cracking pressure can be calculated by the above formula to be 26.9Mpa;

[0064] S22: According to the cracking pressure P cSelect the model and performance parameters of hydraulic pre-fracture equipment, which includes key components such as high-pressure pumps, high-pressure hoses and hole sealers. This method of equipment selection can ensure that the equipment performance parameters match the actual working conditions, thereby optimizing the hydraulic pre-fracture process and realizing rapid excavation of hard rock tunnels based on hydraulic pre-fracture technology;

[0065] The model and performance parameters of the high-pressure pump and high-pressure hose include rated flow, pumping time, elastic modulus and fracture liquid pressure. If a high-pressure pump with a rated fracturing pressure of 40 MPa can be selected according to the fracturing pressure of 26.9 MPa, the high-pressure hose can be selected with a maximum fracturing pressure of 50 MPa or more. Then, through the selected high-pressure pump, its rated flow Q = 100 L / min, pumping time t = 30 min, elastic modulus E = 2.9 Gpa, fracture liquid pressure σ = 20 MPa, etc. are determined;

[0066] The theoretical fracturing radius R1 is calculated in combination with the performance parameters, and the calculation formula is as follows:

[0067]

[0068] Where Q is the pumping flow rate, t is the pumping time, E is the elastic modulus, σ is the fluid pressure in the fracture, and h is the fracture height. Since the fracturing range needs to reach most places in the space, the fracture height h here directly uses the tunnel height as a reference value to estimate the approximate value of the hydraulic fracturing radius. In the third step, further field tests are carried out to determine the actual hydraulic fracturing radius.

[0069] Since the spatial geometry of hydraulic fracturing cracks is affected by objective conditions such as formation stress and rock properties, the direction of crack expansion gradually turns to the direction of maximum principal stress. Therefore, the actual expansion range of hydraulic fracturing cracks in the vertical and horizontal directions of the excavation working face is not consistent. In order to achieve sufficient pre-fracture weakening of the hard rock to be excavated by the hydraulic fracture network, the next step is to conduct on-site fracturing range detection tests based on the theoretical calculation results of the hydraulic fracturing radius.

[0070] S3: Setting observation holes around the fracturing holes, analyzing the actual expansion radius of the hydraulic fracturing cracks in the hard rock tunnel according to the theoretical fracturing radius R1 and the on-site fracturing range detection test, and taking the minimum value; the specific steps of the on-site fracturing range detection test are as follows:

[0071] S31: With the fracturing hole as the center, pre-construct observation holes in the vertical and horizontal directions according to the theoretical fracturing radius R1;

[0072] S32: Observe whether there is water discharge from the observation hole. If there is no water discharge from the observation hole, gradually shorten the distance between the observation hole and the fracturing hole in the radial direction until water discharge occurs in the observation hole. The distance at this time is the fracturing distance.

[0073] S33: Record the vertical fracturing distance R H and horizontal fracturing distance R h , select the minimum value as the sufficient hydraulic fracturing radius R hy , the sufficient hydraulic fracturing radius R hy The calculation formula is as follows:

[0074] R hy =min(R H , R h )

[0075] According to the vertical fracturing distance R H and the horizontal fracturing distance R h The minimum value in is used to determine the hydraulic fracturing radius in the drilling layout design, which can ensure that the range of hydraulic fracturing meets the pre-fracture requirements and is controlled within a safe and effective range.

[0076] S4: Calculate the sufficient hydraulic fracturing area according to the minimum value of the actual expansion radius of the hydraulic fracturing crack, and determine the number of drill holes, drill hole spacing and observation hole arrangement plan for the hydraulic pre-fractured hard rock tunnel to be excavated according to the size of the sufficient hydraulic fracturing area; the specific process is as follows:

[0077] S41: According to the hydraulic fracturing radius R hy Calculate the sufficient hydraulic fracturing area S hy , the sufficient hydraulic fracturing area S hy The calculation formula is as follows:

[0078]

[0079] S42: The fully hydraulically fractured area S hy and the cross-sectional area S of the hard rock tunnel d For comparison, the cross-sectional area of ​​the hard rock tunnel S d It can be calculated by measuring the length and width of the hard rock tunnel section. If the hydraulic fracturing area S is sufficient hy Proportion of hard rock tunnel cross-sectional area S d If the water fracturing rate is more than 80%, it means that the cross-sectional area of ​​the hard rock tunnel excavation working face is small, and single-hole fracturing can be used; otherwise, it means that the cross-sectional area of ​​the hard rock tunnel excavation working face is large. If only single-hole fracturing is not enough to fully fracture the hard rock, it will increase the working difficulty of the tunneling machine and increase the degree of pick wear. In this case, double-hole fracturing is more appropriate to reduce the difficulty of excavation and improve the excavation efficiency.

[0080] S43: After the number of fracturing holes is determined according to the above steps, the sufficient hydraulic fracturing area S hy Determine the arrangement of drilling locations, drilling spacing and observation holes.

[0081] In the above embodiment, preferably, when the cross-sectional area S of the hard rock tunnel is d When the size is small, single-hole fracturing is used. Figure 2 As shown, the specific steps of arranging the drilling positions and observation holes are as follows:

[0082] The center position of the hard rock tunnel section is used as the drilling position of the fracturing hole, which is the initial position of the fracturing hole in S1. In order to prevent the hydraulic fracture network from weakening the structure of the tunnel roof and floor, observation holes G1 and G2 are set at a distance of 0.1 meters from the roof and floor respectively in the same vertical direction of the fracturing hole. During the fracturing operation, observe whether water comes out of the observation hole. If water comes out of the observation hole, it means that the fracture network has expanded to the tunnel roof and floor, and the fracturing operation should be stopped immediately. This can prevent the fracture network caused by excessive hydraulic fracturing from weakening the structure of the tunnel roof and floor, thereby ensuring that the cracks are controlled within a safe range.

[0083] In the above embodiment, preferably, when the cross-sectional area S of the hard rock tunnel is d When the size is large, double-hole fracturing is used. Figure 2 As shown in the figure, the specific steps for arranging the drilling positions, drilling spacing and observation holes are as follows:

[0084] Assume that the fracturing holes used for double-hole fracturing are K1 and K2, and the fracturing holes K1 and K2 are located at the same vertical height as the center of the hard rock tunnel section. The fracturing holes K1 and K2 are symmetrically arranged about the central axis of the hard rock tunnel section, and the drilling spacing between the fracturing holes K1 and K2 is half the width of the hard rock tunnel section; and observation holes G1 and G2 are arranged on the central axis line of the hard rock tunnel section at a distance of 0.1 meters from the top plate and the bottom plate respectively; when performing fracturing operations, observe whether water comes out of the observation holes. If water comes out, stop the fracturing operation immediately.

[0085] The fracturing process implements high-pressure water injection through the fracturing holes to form a hydraulic fracture network in the rock to be excavated. Fracturing will continue until the predetermined time limit of 30 minutes is reached, or it will be terminated when water is detected in the observation hole, so as to ensure that the cracks are controlled within a safe range, thereby completing the effective weakening of the hard rock.

[0086] S5: After the excavation working face is disturbed by mining activities, three areas will be formed in front: pressure relief zone, concentrated stress zone and original rock stress zone. Figure 3 As shown, a concentrated stress zone is selected as the hydraulic fracturing range, and the drilling depth of the fracturing hole and the observation hole and the hydraulic fracturing starting point position in the borehole are determined according to the length of the concentrated stress zone. The specific steps are as follows:

[0087] S51: Parameters related to the friction coefficient of the soft layer, the thickness of the soft layer, the stress concentration factor, the average density of the overlying rock layer, the burial depth and the tensile strength of the rock are obtained based on field measurements;

[0088] S52: The pressure relief zone width L1 and the limit balance zone width L2 can be calculated by using the limit balance zone depth calculation formula of the limit balance theory in combination with the above measured related parameters. The limit balance zone depth calculation formula is as follows:

[0089]

[0090] Where N f is the stress concentration coefficient of the rock formation, f is the friction coefficient of the soft layer, m is the thickness of the soft layer, γ is the average density of the overlying rock formation, H is the burial depth, and δ is the tensile strength of the rock;

[0091] S53: Assume that the drilling depth is L3, and the drilling depth L3 is within the concentrated stress zone, according to the limit equilibrium zone width and coefficient N g The value of drilling depth L3 is calculated as follows:

[0092]

[0093] In the formula, the coefficient N g The value range of is 1.2~1.8;

[0094] Because a large number of cracks will be generated in the rock mass in the pressure relief zone, in order to ensure that high-pressure water will not leak from the working surface during hydraulic fracturing, the hydraulic fracturing point should be greater than the pressure relief zone depth L1. The specific depth can be determined based on the drilling depth L3 and the hydraulic fracturing radius R. hy Determine the location of the hydraulic fracturing initiation point.

[0095] S6: After the drilling is completed, the backward high-pressure water injection fracturing technology is used to fractur e the hard rock to be excavated; the clean water purified by the filtration system is pressurized by the emulsifier pump and injected into the borehole. The water injection pressure must be greater than the theoretical minimum fracture pressure of the rock mass to ensure that the high-pressure water can generate sufficient internal water pressure inside the borehole to promote the directional expansion and development of the cracks in the rock mass to be excavated. The specific arrangement of hydraulic fracturing is as follows Figure 3 shown.

[0096] In the above embodiment, preferably, the high pressure pump is placed at a distance of 30-100 meters from the excavation working face. Figure 4 As shown, ensure that the normal operation of the tunnel boring machine will not be interfered with.

[0097] By implementing the backward hydraulic fracturing technology to pre-crack the rock to be excavated, the strength of the hard rock is significantly reduced under the action of hydraulic fractures and the increase in water content. After completing the pre-crack process, the small-diameter sealer and high-pressure hose are retracted, and then the conversion process is carried out to use a comprehensive mechanized excavator to cut the rock to be excavated.

[0098] As attached Figure 5 As shown in the figure, the number of daily excavation cycles within 10 days before and after fracturing was counted. Before hydraulic fracturing, the number of excavation cycles in hard rock tunnels was generally 2-3; calculated at 1.2m per cycle, the daily excavation footage in hard rock tunnels was 2.4m to 3.6m. After fracturing, due to the weakening of rock mechanical properties, the damage rate of picks was reduced by more than 20%, and the cutting efficiency of the tunneling machine was increased by more than 30%. The number of operation cycles increased from 2-3 to 4-5 (the number of operation cycles was less in the initial stage of the test), and the daily excavation footage increased to 4.8m to 6.0m, which effectively improved the rock breaking efficiency of the tunneling machine, reduced the loss of picks, and increased the production capacity of the mine.

[0099] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by the terms "up", "down", "left", "right", etc. are based on the directions or positional relationships shown in the accompanying 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 a limitation on the present invention.

[0100] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A hydraulic pre-splitting rock mass method for improving the rock breaking efficiency of a tunnel boring machine, characterized in that: The following steps are involved: S1: Determine the center position of the hard rock tunnel section as the initial location of the fracturing hole, and measure the stress distribution and related physical and mechanical parameters of any point around the fracturing hole on site; S2: Calculate the fracturing pressure according to the stress distribution and related physical and mechanical parameters, and select the model and performance parameters of the hydraulic pre-fracture equipment that match the actual working condition requirements according to the fracturing pressure; and obtain the theoretical fracturing radius R1 using the hydraulic fracturing radius calculation formula based on the performance parameters of the hydraulic pre-fracture equipment; S3: setting observation holes around the fracturing holes, analyzing the actual expansion radius of the hydraulic fracturing cracks in the hard rock tunnel according to the theoretical fracturing radius R1 and the on-site fracturing range detection test, and taking the minimum value; S4: calculating a sufficient hydraulic fracturing area according to the minimum value of the actual expansion radius of the hydraulic fracturing fissure, and determining the number of drill holes, the drill hole spacing and the arrangement of the observation holes for hydraulic pre-fractured hard rock tunnel to be excavated according to the size of the sufficient hydraulic fracturing area; S5: Analyze the range of stress concentration zone of the rock mass to be excavated, determine the depth of the fracturing hole and the location of the hydraulic fracturing starting point in the borehole; S6: After the drilling is completed, the backward high-pressure water injection fracturing technology is used to fractur e the hard rock to be excavated.

2. A method for hydraulic pre-splitting rock mass for improving rock breaking efficiency of a tunnel boring machine according to claim 1, characterized in that: In step S1, the stress distribution and related physical and mechanical parameters measured on site include plumb stress, lateral stress coefficient, rock mass tensile strength, and height and cross-sectional area of ​​the hard rock tunnel.

3. A method for hydraulic pre-splitting rock mass for improving rock breaking efficiency of a tunnel boring machine according to claim 2, characterized in that: Step S2 includes: S21: The fracture initiation pressure is calculated based on the measured plumb stress, lateral stress coefficient and rock mass tensile strength. The calculation formula for the fracture initiation pressure is as follows: P c =min{(3-λ)q0+R t ,(3λ-1)q0+R t } Where P c is the crack initiation pressure, q0 is the plumb stress, λ is the lateral stress coefficient, R t is the tensile strength of rock mass; S22: According to the cracking pressure P c The model and performance parameters of the hydraulic pre-fracture equipment are selected. The hydraulic pre-fracture equipment includes a high-pressure pump and a high-pressure hose. The model and performance parameters of the high-pressure pump and the high-pressure hose include rated flow, pumping time, elastic modulus and fluid pressure in the fracture. The theoretical fracturing radius R1 is calculated in combination with the performance parameters. The calculation formula is as follows: Where Q is the pumping flow rate, t is the pumping time, E is the elastic modulus, σ is the fluid pressure in the fracture, and h is the fracture height, where the fracture height h is the height of the hard rock tunnel.

4. A method for hydraulic pre-splitting rock mass for improving rock breaking efficiency of a tunnel boring machine according to claim 3, characterized in that: In step S3, since the actual hydraulic fracturing fracture space is different from the theoretical hydraulic fracturing fracture space, it is necessary to measure it through a field fracturing range detection test. The specific steps of the field fracturing range detection test are as follows: S31: Pre-constructing observation holes in the vertical and horizontal directions with the fracturing hole as the center; S32: Observe whether there is water discharge from the observation hole. If there is no water discharge from the observation hole, shorten the distance between the observation hole and the fracturing hole in the radial direction until water discharge occurs in the observation hole. The distance at this time is the fracturing distance. S33: Record the vertical fracturing distance R H and horizontal fracturing distance R h , select the minimum value as the sufficient hydraulic fracturing radius R hy , the sufficient hydraulic fracturing radius R hy The calculation formula is as follows: R hy =min(R H ,R h ) 5. A method for hydraulic pre-splitting rock mass for improving rock breaking efficiency of a tunnel boring machine according to claim 4, characterized in that: Step S4 specifically includes: S41: According to the hydraulic fracturing radius R hy Calculate the sufficient hydraulic fracturing area S hy , the sufficient hydraulic fracturing area S hy The calculation formula is as follows: S42: The fully hydraulically fractured area S hy and the cross-sectional area S of the hard rock tunnel d For comparison, if the hydraulic fracturing area S hy Proportion of hard rock tunnel cross-sectional area S d If the pressure is more than 80%, single-hole fracturing is used; otherwise, double-hole fracturing is used; S43: After the number of fracturing holes is determined according to the above steps, the sufficient hydraulic fracturing area S hy Determine the arrangement of drilling locations, drilling spacing and observation holes.

6. A method for hydraulic pre-splitting of rock mass for improving rock breaking efficiency of a tunnel boring machine according to claim 5, characterized in that: In step S43, if single-hole fracturing is adopted, the specific steps of arranging the drilling position and observation hole are as follows: The center position of the hard rock tunnel section is used as the drilling position of the fracturing hole, and observation holes G1 and G2 are set at a distance of 0.1 meters from the top plate and bottom plate respectively in the same vertical direction of the fracturing hole; when performing fracturing operations, observe whether water comes out of the observation holes. If water comes out, stop the fracturing operation immediately.

7. The method for hydraulic pre-splitting of rock mass for improving the rock breaking efficiency of a tunnel boring machine according to claim 5, characterized in that: In step S43, if dual-hole fracturing is adopted, the specific steps of arranging the drilling positions, drilling spacing and observation holes are as follows: When double-hole fracturing is adopted, the fracturing holes are K1 and K2 respectively. The fracturing holes K1 and K2 are located at the same vertical height as the center position of the hard rock tunnel section. The fracturing holes K1 and K2 are symmetrically arranged about the central axis of the hard rock tunnel section, and the drilling spacing between the fracturing holes K1 and K2 is half of the width of the hard rock tunnel section; and observation holes G1 and G2 are arranged on the central axis line of the hard rock tunnel section at a distance of 0.1 meter from the top plate and the bottom plate respectively; when performing fracturing operations, observe whether water comes out of the observation holes. If water comes out, the fracturing operation is stopped immediately.

8. The method for hydraulic pre-splitting of rock mass for improving the rock breaking efficiency of a tunnel boring machine according to claim 5, characterized in that: In step S5, after the excavation working face is disturbed by mining activities, three areas, namely, a pressure relief zone, a concentrated stress zone, and an original rock stress zone, are formed in front. Among them, the concentrated stress zone is selected as the hydraulic fracturing range, and the drilling depths of the fracturing holes and the observation holes and the hydraulic fracturing initiation point position in the borehole are determined according to the length of the concentrated stress zone. The specific steps are as follows: S51: Parameters related to the friction coefficient of the soft layer, the thickness of the soft layer, the stress concentration factor, the average density of the overlying rock layer, the burial depth and the tensile strength of the rock are obtained based on field measurements; S52: The calculation formula of the limit equilibrium zone depth of the limit equilibrium theory is used to calculate the pressure relief zone width L1 and the limit equilibrium zone width L2. The calculation formula of the limit equilibrium zone depth is as follows: Where N f is the stress concentration coefficient of the rock formation, f is the friction coefficient of the soft layer, m is the thickness of the soft layer, γ is the average density of the overlying rock formation, H is the burial depth, and δ is the tensile strength of the rock; S53: Assume that the drilling depth is L3, and the drilling depth L3 is within the concentrated stress zone, according to the limit equilibrium zone width and coefficient N g The value of drilling depth L3 is calculated as follows: In the formula, the coefficient N g The value range of is 1.2 to 1.8; according to the drilling depth L3 and the hydraulic fracturing radius R hy Get the hydraulic fracturing initiation point location.

9. The method for hydraulic pre-splitting of rock mass for improving the rock breaking efficiency of a tunnel boring machine according to claim 3, characterized in that: The high-pressure pump is placed 30-100 meters away from the excavation working face.

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