Pre-fracturing method of rock mass with ultra-high BQ value and application

Abstract

This invention provides a pre-fracture method for ultra-high BQ value rock masses, comprising the following steps: First, several blasting holes are opened at the working face, penetrating the ultra-high BQ value rock mass, with the blasting holes distributed in a vortex pattern around the center of the working face; second, explosives are filled into the blasting holes; third, the ends of the blasting holes are sealed; finally, the blasting holes are detonated one by one from the outside to the inside along the vortex pattern. This invention fully considers the effects of high ground stress and the characteristics of high BQ value rock masses, employing specific detonation paths, explosive structures, and sealing methods. This ensures that under the action of the explosion, the rock mass forms fissures between the blasting holes and cracks around the blasting holes, controlling the peak value of the explosive load while guaranteeing the pre-fracture effect. This method solves the technical problem of the difficulty in pre-fracture of ultra-high BQ value rock masses and is suitable for pre-fracture construction of rock masses under conditions of high ground stress and high integrity coefficient, offering advantages of high construction efficiency and low cost.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, specifically relating to a pre-fracture method for ultra-high BQ value rock masses, and the application of the pre-fracture method for ultra-high BQ value rock masses in tunnel engineering. Background Technology

[0002] This invention relates to the field of rock engineering, and particularly to a pre-fracture tunneling method using tunnel boring machines (TBMs) in rock masses with extremely high BQ (Basic Quality Index) values. TBMs offer significant advantages in rock excavation, with their high efficiency stemming from their continuous operation capability, eliminating the need for downtime between excavation and support, thus greatly improving tunnel construction efficiency, especially in long tunnels. Secondly, TBMs produce tunnels of excellent quality; the uniform distribution and precise control of the cutters result in smooth tunnel surfaces, requiring almost no secondary processing. However, when encountering rock masses with extremely high BQ values, TBM excavation performance is poor, efficiency is low, and it cannot meet engineering requirements.

[0003] The basic quality index (BQ) of rock mass is determined based on the uniaxial saturated compressive strength Rc (MPa) and the rock mass integrity coefficient Kv. It is an important parameter reflecting the compressive strength and integrity of rock. An ultra-high BQ value usually indicates good rock integrity and high compressive strength. Such rock characteristics make it difficult for TBMs to tunnel efficiently, because the TBM's cutting tools have limited ability to break up such high-strength rock.

[0004] Therefore, to address the problem of low efficiency in TBM excavation of ultra-high BQ value rock masses, a new blasting method is urgently needed to create stable pre-fractures within the high BQ value rock mass. This would effectively improve construction efficiency and ensure rock stability after construction, meeting the needs of deep-earth engineering. Patent application number 201911067836.2 discloses a water jet-assisted rock-breaking system and method installed on a tunnel boring machine (TBM). This system utilizes a water supply mechanism to provide a fluid source and filters and softens the fluid, thereby forming a high-pressure jet to assist the TBM cutterhead in rock breaking. Patent application number 201810502773.8 introduces a laser-assisted rock-breaking method for TBMs. This method mounts a laser head on the TBM cutterhead and distributes it evenly in the radial direction between the cutterheads. During TBM excavation, laser-assisted irradiation is first used to generate thermal cracks or thermal fracturing, reducing the rock hardness, before the cutterheads perform rock-breaking excavation. However, the aforementioned laser and high-pressure water flow-assisted rock breaking methods have some problems in actual operation: on the one hand, it is difficult to modify these methods on the existing cutterhead design; on the other hand, the depth and effect of these assisted rock breaking methods are poor.

[0005] Therefore, finding a method to assist TBMs in efficient rock breaking under high BQ value rock mass conditions is of great significance for the efficient construction of tunnel projects under high-strength rock mass geological conditions, and is also a technical problem that urgently needs to be solved. Summary of the Invention

[0006] One of the objectives of this invention is to provide a pre-fracture method for ultra-high BQ value rock masses that has high construction efficiency, low construction cost, and good pre-fracture effect.

[0007] The second objective of this invention is to provide a pre-fracture method for ultra-high BQ value rock masses and its application in tunnel engineering.

[0008] One of the technical solutions adopted by this invention to achieve its objective is to provide a pre-fracture method for rock masses with ultra-high BQ values, comprising the following steps:

[0009] S1. Several blasting holes are opened at the working face to penetrate the rock mass with ultra-high BQ value inside. The blasting holes are distributed in a vortex shape around the center of the working face.

[0010] S2. Fill the blast hole with explosives;

[0011] S3. Seal the end of the blast hole, with the sealing length being 30 to 50 times the diameter of the blast hole;

[0012] S4. Detonate the blasting holes one by one from the outside to the inside following a vortex-shaped path.

[0013] The general idea of ​​the pre-fracture method for ultra-high BQ value rock masses provided by this invention is as follows: First, the drilling locations are determined according to the required pre-fracture range, and several blasting holes are drilled in the working face. Considering the effects of high ground stress and the characteristics of high BQ value rock masses, a specific arrangement of blasting holes is set, so that the blasting holes are distributed in a vortex shape. The post-blast fracture network and the original fracture network are interconnected, which controls the peak value of the explosive load while ensuring the pre-fracture effect. Second, explosives are filled into each blasting hole. Under the action of the explosives, the rock mass is fractured through the blasting holes and cracks are formed around the blasting holes. In order to ensure the fracture formation effect, this invention uses a relatively long plug, with the plug length set to 30 to 50 times the diameter of the blasting hole, so that the explosive gas can fully interact with the rock mass inside. Finally, the detonation method is to detonate the holes one by one from the outside to the inside along the vortex-shaped route. The gas generated by the blasting of adjacent blasting holes fully couples and forms cracks. The post-blast fracture network and the original fracture network are interconnected, effectively reducing the strength and integrity of the rock mass. The pre-fracture method provided by this invention can create a fracturing effect within the excavated base surface and form ring-shaped cracks within the tunnel face, reducing the difficulty of subsequent tunneling construction and improving construction efficiency.

[0014] Furthermore, the working face mentioned in this invention refers to the initial face in tunnel engineering that corresponds to the working face that is continuously advanced as the tunnel is excavated.

[0015] Furthermore, the ultra-high BQ value rock mass described in this invention refers to rock mass with a BQ (basic quality index of rock mass) value greater than 350. This type of rock mass includes rock masses with basic quality levels I, II, and III. These rock masses generally possess characteristics of hardness, high compressive strength, good integrity, and resistance to breakage.

[0016] Furthermore, in step S1, the vortex pattern formed by the blasting holes is centered on the center of the working face, and its coverage area accounts for 30% to 50% of the total excavation area of ​​the working face.

[0017] Further, in step S1, the diameter of the blasting hole is 76-110 mm; the spacing between the blasting holes is 0.5-1.5 m; and the drilling depth of the blasting hole is 6-30 m.

[0018] Preferably, the drilling depth of the blasting hole is 15-30m. The pre-fracture method provided by the present invention, compared with the conventional blasting method, sets a longer blasting hole length to increase the linear charge density and total charge of the explosive, ensuring that the rock mass strength and integrity can be effectively reduced within a 30m range.

[0019] Furthermore, in step S2, considering the initial ground stress and the effect of internal explosion forming a crack, the linear charge of the explosive is set to 800-5000 g / m; preferably, the linear charge of the explosive is 2500-5000 g / m. This invention increases the explosive load peak value by increasing the charge amount, thereby obtaining a better pre-fracture effect.

[0020] Furthermore, the explosive can be an emulsion explosive, a porous granular ammonium nitrate explosive, etc. Preferably, for the emulsion explosive, its charge density is 900–1100 kg·m³. -3 The detonation velocity is 3300–4900 m / s. -1 For porous granular ammonium nitrate explosives, the charge density is 780–880 kg·m³. -3 Explosion speed 3000~3200m·s -1 .

[0021] Furthermore, in step S2, the length of the explosive charge in the blast hole accounts for 75% to 85% of the length of the blast hole.

[0022] Furthermore, in step S3, considering the safety of the engineering equipment and construction efficiency, a sealing material with good sealing properties should be used and the sealing length should be increased to ensure that the sealing material cannot be thrown out, allowing the explosive load to fully expand the interior of the high BQ value rock mass into a fracture network. Preferably, the sealing material is selected from clay materials, which have better sealing performance. In this invention, a sufficiently long sealing length is set with the diameter of the blast hole as a reference, significantly increasing the duration of the explosive load.

[0023] Preferably, the sealing material is selected from clay-sand mixtures or cement products with a porosity of 15%–25% after compaction. In this invention, using a sealing material with excellent sealing performance can achieve a better sealing effect. Combined with a vortex-shaped detonation path and detonation network, the gas generated by the blasting acts as a wedging agent within the blast hole and rock mass, causing the rock mass to pre-fracture and form a fracture network, thereby significantly reducing the strength of ultra-high BQ rock mass.

[0024] Furthermore, in step S4, the initiation time difference for each hole is 20–50 ms. In this invention, a hole-by-hole initiation method is adopted, creating a continuous crack network between the blasting holes and establishing a crack network around each hole. After the blast, the crack network and the original crack network are interconnected, controlling the peak value of the explosive load while ensuring the pre-fracture effect. In addition, the initiation time setting comprehensively considers the initiation path, the diameter and spacing of the blasting holes. By adjusting the internal crack formation and the blasting time difference, the safety of the construction site is ensured while maintaining blasting efficiency.

[0025] The second technical solution adopted by the present invention to achieve the objective is to provide an application of the pre-fracture method described in the first objective of the present invention in tunnel engineering.

[0026] The pre-fracture method provided by this invention is applicable to rock breaking construction under high BQ value conditions. It is used as an auxiliary method before and / or during the construction of tunnel boring machines (TBMs) or other rock masses requiring pre-fracture. This method can form an interconnected fracture network within the excavation surface, improving the fracturing effect and solving the problem of difficult fracturing and excavation faced by TBMs when dealing with high BQ value rock masses in tunnels. With the assistance of this pre-fracture method, TBMs can achieve rock fracturing with only relatively small forces during subsequent excavation, significantly reducing the construction difficulty of TBMs and improving their construction efficiency.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) This invention provides a pre-fracture method for ultra-high BQ value rock masses. This method creates fissures within the working face and utilizes the characteristic that the tensile and shear strengths of the rock are lower than its compressive strength to fracture the ultra-high BQ value rock mass. This method can solve the technical problem of the difficulty in pre-fracture of ultra-high BQ value rock masses and has the characteristics of high construction efficiency and low cost.

[0029] (2) The pre-fracture method for ultra-high BQ value rock masses provided by this invention is applicable to construction projects requiring pre-fracture of rock masses under conditions of high ground stress and high integrity coefficient, including tunnel excavation projects for ultra-high BQ value rock masses. This method significantly improves excavation efficiency and operational safety by precisely adjusting blasting parameters and construction methods, effectively solving the problems of high cost, low efficiency, and environmental pollution that may occur with non-blasting excavation methods (such as TBMs) when dealing with ultra-high BQ value rock masses. The pre-fracture method provided by this invention effectively compensates for the low efficiency of TBMs in handling ultra-high BQ value rock masses, providing a new pre-fracture method for efficient and safe tunnel excavation, and has broad prospects for promotion and application. Attached Figure Description

[0030] Figure 1 This is a plan view of the pre-fracture construction method provided in an embodiment of the present invention;

[0031] Figure 2 This is a schematic cross-sectional view of the blast hole in Embodiment 1 of the present invention;

[0032] Wherein, 1-working face; 2-blast hole layout line; n1, n2, n3, n4, n5, n6, n7, n8, n9, n 10 - blast hole; 3- detonating cord; 4- sealing material; 5- electric detonator; 6- blast hole; 7- explosive. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0035] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0036] Example 1

[0037] like Figure 1As shown, the tunnel in a certain project has a diameter of 10m and a cross-sectional area of ​​78.54m². 2 The rock mass BQ value inside the tunnel is 400-450. The construction using the technical solution of this invention involves the following specific steps:

[0038] (1) As Figure 1 As shown, 10 blasting holes were opened at the tunnel face, arranged in a vortex pattern from the outside to the inside around the center of the tunnel face. In this construction, the diameter of the blasting holes was set to 105mm, the spacing between the holes was set to 1.2m, and the drilling depth along the tunnel axis was 20m.

[0039] (2) Considering that high BQ rock masses are often located in areas with high burial depth, a linear charge of 3000 g / m was selected. This charge level ensures sufficient explosive load to create fissures within the high BQ rock mass. The explosive section is 16 m long, and emulsion explosive (density ρ0 = 1100 kg·m³) is used. -3 ,explosion speed D=4800m·s -1 ).

[0040] (3) To ensure the explosives could be effective inside the rock mass, 4m of sealing material was used in the blast hole. The cross-section of the blast hole after sealing is shown below. Figure 2 As shown. The sealing material selected is a clay-sand mixture with good sealing performance (initial porosity of 40%, and porosity of 25% after compaction) to ensure that the explosive force of the explosive does not leak out prematurely, so that the explosive load can be fully applied to the rock mass while ensuring the safety of equipment and personnel at the construction site.

[0041] (4) After the explosives were placed, a sequential detonation method was adopted. This detonation method allows the post-explosion fracture network and the existing fracture network to interconnect, controlling the peak value of the explosive load while ensuring the pre-fracture effect. The detonation sequence is as follows: Figure 1 As shown, detonations n1-n are sequentially initiated from the outside to the inside along a vortex-shaped path. 10 The time interval is set to 25ms to ensure that the peak load in the rock mass is controlled within a safe range, ensuring the safety of construction equipment and personnel while breaking through the rock.

[0042] (5) After pre-fracture, the high BQ rock mass is formed by the through-holes and cracks around the blast holes, which greatly reduces the compressive strength and integrity of the high BQ rock mass, making it easier for subsequent construction.

[0043] Example 2

[0044] A certain engineering project has a tunnel with a diameter of 13m and a cross-sectional area of ​​132.73m². 2 The rock mass BQ value inside the tunnel is 530-580. The construction using the technical solution of this invention involves the following specific steps:

[0045] (1) Twelve blasting holes are made at the working face, arranged in a vortex pattern from the outside to the inside around the center of the working face (see the arrangement method). Figure 1 In this construction project, the diameter of the blasting holes was set to 100mm, the hole spacing was set to 1.5m, and the drilling depth along the tunnel axis was 25m.

[0046] (2) Considering that high BQ rock masses are often located in areas with high burial depth, a linear charge of 4500 g / m was selected. This charge level ensures sufficient explosive load to create fissures within the high BQ rock mass. The explosive section length is 20.8 m, and emulsion explosive (density ρ0 = 1100 kg·m³) was used. -3 ,explosion speed D=4800m·s -1 ).

[0047] (3) To ensure the explosives could be effective inside the rock mass, 4.2m of sealing material was used in the blast hole. The cross-section of the blast hole after sealing is shown below. Figure 2 As shown. The sealing material selected is a clay-sand mixture with good sealing performance (initial porosity of 40%, and porosity of 20% after compaction) to ensure that the explosive force of the explosive will not leak out prematurely, so that the explosive load can be fully applied to the rock mass while ensuring the safety of equipment and personnel at the construction site.

[0048] (4) After the explosives were placed, a sequential detonation method was adopted. This detonation method allows the post-explosion fracture network and the existing fracture network to interconnect, controlling the peak value of the explosive load while ensuring the pre-fracture effect. The detonation sequence is referenced... Figure 1 Twelve blasting holes were detonated sequentially from the outside to the inside along a vortex-shaped route, with a detonation time interval set at 45ms. This ensures that the peak load within the rock mass is controlled within a safe range, guaranteeing the safety of construction equipment and personnel while breaking through the rock.

[0049] (5) After pre-fracture, the high BQ rock mass is formed by the through-holes and cracks around the blast holes, which greatly reduces the compressive strength and integrity of the high BQ rock mass, making it easier for subsequent construction.

[0050] Example 3

[0051] like Figure 1 As shown, the tunnel in a certain project has a diameter of 8m and a cross-sectional area of ​​50.27m². 2 The rock mass BQ value inside the tunnel is 580-620. The construction using the technical solution of this invention involves the following specific steps:

[0052] (1) As Figure 1As shown, nine blasting holes are drilled at the working face, arranged in a vortex pattern from the outside to the inside around the center of the working face (see reference for arrangement). Figure 1 In this construction project, the diameter of the blasting holes was set to 76mm, the hole spacing was set to 0.6m, and the drilling depth along the tunnel axis was 15m.

[0053] (2) Considering that high BQ rock masses are often located in areas with high burial depth, a linear charge of 2500 g / m was selected. This charge level ensures sufficient explosive load to create fissures within the high BQ rock mass. The explosive section is 12 m long, and emulsion explosive (density ρ0 = 1100 kg·m³) is used. -3 ,explosion speed D=4800m·s -1 ).

[0054] (3) To ensure the explosives could be effective inside the rock mass, a 3m long sealing material was used in the blast hole. The cross-section of the blast hole after sealing is shown below. Figure 2 As shown. The sealing material selected is a cement product with good sealing performance to ensure that the explosive force does not leak out prematurely, allowing the explosive load to fully act on the rock mass while ensuring the safety of equipment and personnel at the construction site.

[0055] (4) After the explosives were placed, a sequential detonation method was adopted. This detonation method allows the post-explosion fracture network and the existing fracture network to interconnect, controlling the peak value of the explosive load while ensuring the pre-fracture effect. The detonation sequence is referenced... Figure 1 Nine blasting holes were detonated sequentially from the outside to the inside along a vortex-shaped route. The blasting time interval was set to 20ms. This ensured that the peak load in the rock mass was controlled within a safe range, guaranteeing the safety of construction equipment and personnel while breaking through the rock.

[0056] (5) After pre-fracture, the high BQ rock mass is formed by the through-holes and cracks around the blast holes, which greatly reduces the compressive strength and integrity of the high BQ rock mass, making it easier for subsequent construction.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A pre-fracture method for ultra-high BQ value rock mass, used as an auxiliary construction method before and / or during the construction of a tunnel boring machine (TBM), wherein the BQ value of the ultra-high BQ value rock mass is greater than 350, characterized in that, The pre-fracture method includes the following steps: S1. Several blasting holes are made at the working face to penetrate the rock mass with ultra-high BQ value inside. The blasting holes are distributed in a vortex shape around the center of the working face. The drilling depth of the blasting holes is 15~30m. S2. Fill the blast hole with explosives; the linear charge of the explosives is 2500~5000g / m; the filling length of the explosives accounts for 75%~85% of the length of the blast hole; S3. Seal the end of the blast hole, with the sealing length being 30 to 50 times the diameter of the blast hole; S4. Detonate the blasting holes one by one from the outside to the inside according to the vortex-shaped route. The detonation time difference for each hole is 20~50ms.

2. The pre-fracture method according to claim 1, characterized in that, In step S1, the vortex pattern formed by the blasting holes is centered on the center of the working face, and its coverage area accounts for 30% to 50% of the total excavation area of ​​the working face.

3. The pre-fracture method according to claim 1, characterized in that, In step S1, the diameter of the blasting hole is 76~110mm, and the spacing between the blasting holes is 0.5~1.5m.

4. The pre-fracture method according to claim 1, characterized in that, In step S3, the sealing material is selected from clay mixed with sand and cement products with a porosity of 15% to 25% after compaction.

5. The application of a pre-fracture method according to any one of claims 1-4 in tunnel engineering.

6. The application according to claim 5, characterized in that, The pre-fracture method is used as an auxiliary construction method before and / or during the construction of a tunnel boring machine (TBM).

Images