A mine-based roof sandblasting jet axial roof cutting pressure relief method

Abstract

The present application belongs to the technical field of mine exploitation, and discloses a roof sanding jet flow axial roof cutting pressure relief method based on a mine, which comprises the following steps: drilling a hole in the roof of a mine tunnel; spraying two high-pressure water flows containing abrasive onto the hole wall, the two high-pressure water flows are both sprayed radially along the hole, the spraying directions of the two high-pressure water flows are perpendicular to each other on the hole cross section, and the spraying positions are moved at a constant speed along the hole axis, thereby forming two initial cracks on the hole wall, which are perpendicular to each other and parallel to the hole axis; sealing the upper and lower ends of the two initial cracks to form a sealed sealing section; injecting water into the sealing section to continuously expand the two initial cracks along their depth direction, thereby forming a three-dimensional crack network in the target rock stratum; and effectively solving the problem that the existing technology causes the roof to collapse in a plate shape and the pressure relief to have a blind area due to the initial cracks being located in a single plane.

Description

Technical Field

[0001] This invention belongs to the field of mining technology, specifically relating to a method for axial roof cutting and pressure relief using a grinding jet on the roof of a mine. Background Technology

[0002] Roof cutting and pressure relief is an important means of controlling hard roofs and preventing rockbursts in mining operations. Currently, deep-hole blasting and hydraulic fracturing are common methods for roof cutting and pressure relief. Although deep-hole blasting has a direct and controllable effect, it has problems such as large engineering workload, complex process, easy generation of harmful gases, and susceptibility to safety management issues. Hydraulic fracturing has a relatively simple construction process and low safety risks, but in conventional fracturing, the roof is not pre-treated with fracture surfaces, making it difficult for the fracture surface to expand along the optimal direction of roof weakening during fracturing, thus compromising the pressure relief effect.

[0003] To address this, existing technologies have proposed methods for directional roof cutting and pressure relief. For example, Chinese patent CN111255454A discloses a method for directional roof cutting and pressure relief in mines with hard roofs. This method involves hydraulically cutting a fissure within a borehole to create a crack surface parallel to the borehole axis on each side. A sealing device is then used to seal both ends of the crack surface, and high-pressure water is injected into the sealed section to cause the crack to expand directionally. In this scheme, the two nozzles inside the jet injector are positioned 180° opposite each other on both sides of the casing. Therefore, the two cracks formed on the borehole cross-section are on the same diameter and are symmetrical cracks within the same plane. However, during implementation, because the initial cracks are distributed along only a single plane, subsequent fracturing primarily extends along this plane, resulting in a plate-like roof collapse. The triangular overhang plate at the working face end may still provide support, leading to insufficient collapse, a blind zone in pressure relief, and difficulty in completely destroying the lateral support effect of the end overhang. Therefore, existing technologies suffer from the problem of plate-like roof collapse due to the initial cracks being located only in a single plane, and a blind zone in pressure relief. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for axial roof cutting and pressure relief using a grinding jet in mines, which solves the problems in existing technologies where the roof collapses in a plate-like manner due to initial cracks located only in a single plane, and where there are blind spots in pressure relief.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for axial roof-cutting pressure relief using a grinding jet in a mine includes the following steps: Drilling holes in the roof of the mine roadway; Two jets of high-pressure water containing abrasive are sprayed onto the borehole wall. Both jets are sprayed radially along the borehole and their spray directions are perpendicular to each other on the borehole cross-section. At the same time, the spraying position is moved at a constant speed along the borehole axis, forming two initial cracks that are perpendicular to each other and parallel to the borehole axis on the borehole wall at one time. The two initial cracks are sealed at their upper and lower ends to form a sealed section. Water is injected into the sealing section, causing the two initial fractures to continue to expand along their depth direction, thereby forming a three-dimensional fracture network within the target rock layer.

[0006] Furthermore, when spraying two jets of high-pressure water containing abrasive into the borehole wall, a segmented cutting method is used for construction, forming two mutually perpendicular axial cracks on the borehole wall of each segment.

[0007] Furthermore, when two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, the cutting pressure is 45MPa to 50MPa and the cutting speed is 6m / h to 8m / h.

[0008] Furthermore, when spraying two jets of high-pressure water containing abrasive into the borehole wall, the nozzle diameter used is 1.5 mm, and the mass fraction of abrasive in the high-pressure water jet containing abrasive is 6.5%.

[0009] Furthermore, when sealing the upper and lower ends of the two initial cracks to form a sealed section, the specific steps include: Move the sealing device to the upper and lower ends of the two initial cracks; High-pressure water is injected into the sealing device to cause it to expand and seal the upper and lower ends of the two initial cracks.

[0010] Furthermore, when injecting water into the sealing section, the fracturing pressure is 25 MPa to 35 MPa, and the fracturing time is 30 min to 45 min.

[0011] Furthermore, when water is injected into the sealing section, the two mutually perpendicular initial cracks guide the high-pressure water to expand simultaneously along both the direction and dip of the roadway, cutting the thick, hard roof into a block structure and destroying the plate-like cantilever structure that is fixed at both ends.

[0012] Furthermore, after the three-dimensional crack network is formed, the process also includes a step of detecting and analyzing the top-cutting effect. The detection and analysis adopts one or more of the following methods: electromagnetic wave CT, microseismic monitoring, and support pressure monitoring.

[0013] The beneficial effects of this invention are: By setting the jet directions of two high-pressure water jets to be perpendicular to each other at a 90° angle on the borehole cross-section, two initial cracks perpendicular to each other and parallel to the borehole axis are formed on the borehole wall. This allows the high-pressure water to precisely expand in both strike and dip directions during subsequent fracturing, forming a three-dimensional fracture network within the target rock strata. This solves the technical problem in existing technologies where 180° opposed nozzles can only form two symmetrical cracks in a single plane, leading to plate-like roof collapse and blind spots in pressure relief. It achieves the technical effects of cutting the thick, hard roof into block structures, completely destroying the plate-like suspended roof structure fixed on both sides of the working face end, making the roof collapse in the goaf more complete, shortening the pressure step distance, reducing the additional dynamic load, changing the support stress mode from constant resistance to increased resistance, reducing the static load on the surrounding rock foundation, and significantly reducing the probability of rockburst. This achieves the goal of precise pressure relief. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall process of the top plate abrasive jet axial cutting pressure relief method of the present invention; Figure 2 This is a comparison diagram of the microseismic activity between the axial cutting zone of the abrasive jet and the deep hole blasting zone in an embodiment of the present invention; Figure 3 This is a schematic diagram of the top plate structure without cutting and depressurizing in an embodiment of the present invention; Figure 4 This is a schematic diagram of the top plate structure after depressurization in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, a method for axial roof cutting and pressure relief using a grinding jet in a mine includes the following steps: Drilling holes in the roof of the mine roadway; Two jets of high-pressure water containing abrasive are sprayed onto the borehole wall. Both jets are sprayed radially along the borehole and their spray directions are perpendicular to each other on the borehole cross-section. At the same time, the spraying position is moved at a constant speed along the borehole axis, forming two initial cracks that are perpendicular to each other and parallel to the borehole axis on the borehole wall at one time. The two initial cracks are sealed at their upper and lower ends to form a sealed section. Water is injected into the sealing section to allow the two initial cracks to continue to expand along their depth direction, thereby forming a three-dimensional crack network within the target rock layer, achieving full collapse of the roof and depressurization of the surrounding rock; To address the technical problems in patent CN111255454A, where two nozzles are positioned 180° apart, resulting in only two symmetrical cracks in a single plane, leading to roof collapse into a plate-like structure, the potential for triangular suspension plates at the end area to still provide support, and the existence of blind spots in pressure relief, this solution employs a design where the jet directions of two high-pressure water streams are perpendicular to each other at a 90° angle on the borehole cross-section. This creates two initial cracks on the borehole wall that are perpendicular to each other and parallel to the borehole axis in a single operation. These two initial cracks extend along the tunnel's direction and dip, respectively. During subsequent fracturing, high-pressure water precisely extends along these two predetermined directions, forming a three-dimensional fracture network within the target rock strata composed of strike-and dip fractures. This network cuts the thick, hard roof into block structures, completely destroying the plate-like cantilever structure fixed on both sides of the working face end. This results in more complete roof collapse in the goaf, a shorter pressure step distance, reduced additional dynamic load, a change in the support stress mode from constant resistance to increased resistance, and a reduction in the static load on the surrounding rock foundation. This solves the technical problems of insufficient collapse and blind spots in pressure relief in existing technologies, achieving precise pressure relief.

[0018] When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, a segmented cutting method is used for construction, and two mutually perpendicular axial cracks are formed on the borehole wall of each segment. The construction method adopts a segmented slit cutting method, in which two mutually perpendicular axial cracks are formed in each segment. The three-dimensional crack network formed by multiple segments overlaps and connects with each other in the borehole axis, expanding the weakened area from isolated points to a continuously distributed weakened zone, avoiding pressure relief blind spots, and enhancing the fullness of roof collapse and the uniformity of surrounding rock pressure relief.

[0019] When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, the cutting pressure is 45MPa to 50MPa and the cutting speed is 6m / h to 8m / h. Under these parameters, the abrasive jet can form a clear and regular initial crack, which ensures both cutting depth and crack quality, while avoiding excessive pressure leading to equipment wear or excessive speed leading to low efficiency, thus achieving a balance between cutting effect and construction efficiency.

[0020] When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, the nozzle diameter is 1.5 mm and the mass fraction of abrasive in the high-pressure water jet is 6.5%.

[0021] When sealing the upper and lower ends of the two initial cracks to form a sealed section, the specific steps include: Move the sealing device to the upper and lower ends of the two initial cracks; High-pressure water is injected into the sealing device to expand it and seal the upper and lower ends of the two initial cracks. The expansion of the sealing device seals both ends of the fracture, making the operation simple and the seal reliable. This ensures that the high-pressure water is confined within the sealed section during subsequent fracturing and acts on the fracture propagation, preventing the high-pressure water from leaking along the borehole axis and causing the fracturing energy to disperse. This ensures that the fracture fully expands along the pre-fabrication direction and reaches the predetermined fracturing radius.

[0022] When water is injected into the sealing section, the fracturing pressure is 25MPa to 35MPa and the fracturing time is 30min to 45min. Under these parameters, the fracturing radius can reach more than 10m. The initial fractures fully expand along the prefabrication direction to form a large-scale fracture network, which ensures that the fractures fully expand in both the strike and dip directions, while avoiding excessive pressure that could lead to uncontrolled fractures or equipment overload, thus achieving a balance between fracturing effect and construction safety.

[0023] When water is injected into the sealing section, two mutually perpendicular initial cracks guide the high-pressure water to expand simultaneously along both the direction and dip of the roadway, cutting the thick, hard roof into a block structure and destroying the plate-like cantilever structure fixed at both ends. The two mutually perpendicular initial cracks play a key guiding role in this step. The high-pressure water preferentially expands along the tips of the two pre-fabricated cracks and extends simultaneously along both the direction and dip of the roadway, cutting the thick, hard roof into a block structure and completely destroying the plate-like cantilever structure fixed on both sides. This allows the roof to collapse more fully, shortens the pressure step distance, reduces the additional dynamic load, changes the support stress mode from constant resistance to increased resistance, reduces the static load of the roadway surrounding rock foundation, significantly reduces the probability of rockburst, and achieves precise pressure relief.

[0024] After the three-dimensional crack network is formed, the process also includes the detection and analysis of the roof cutting effect. The detection and analysis adopts one or more of the following methods: electromagnetic wave CT, microseismic monitoring, and support pressure monitoring. The electromagnetic wave CT method can visually display the changes in the electromagnetic wave absorption capacity of the roof in the pressure relief zone to verify the roof pre-cracking effect. The microseismic monitoring method can compare and analyze the microseismic frequency, total energy, and energy release stability to evaluate the pressure relief and anti-impact effect. The support pressure monitoring method can analyze the changes in the working resistance of the support to verify whether the roof breaks in time and transmits the load. The above detection and analysis methods provide multi-dimensional data support for the optimization of construction parameters and the verification of effects, ensuring the quality and reliability of the roof cutting and pressure relief project.

[0025] The invention will now be described in detail with reference to the accompanying drawings and embodiments. In this embodiment, the boreholes are arranged along the roadway direction, with an azimuth of 270°, an inclination of 75°, a borehole diameter of 75mm, and a borehole depth of 35m. The jet injector has two built-in abrasive nozzles with a 90° included angle. Each borehole is divided into four slits, each slit being 1.0m long. The slit pressure is 45-50MPa, the slit speed is 6-8m / h, the nozzle diameter is 1.5mm, and the abrasive mass fraction is 6.5%. After cutting, two axial cracks with a 90° included angle are formed in the borehole wall, with a crack surface width of 4-6mm. A controllable packer is used to seal the borehole. After the sealing pressure reaches 20MPa, it automatically switches to fracturing mode, with a fracturing pressure of 25-35MPa and a fracturing time of 30-45min. Field tests show that the slit radius can reach over 300mm, and the fracturing radius can exceed 10m.

[0026] like Figure 2 As shown, microseismic monitoring was conducted at 490m advances in both the deep-hole blasting zone and the axial cutting zone of the grinding jet on the working face roof. The results indicate that the microseismic frequency, total energy, and energy release are relatively higher in the axial cutting zone of the grinding jet. Support pressure monitoring results show that the support's working resistance increases, the stress mode changes from constant resistance to increased resistance, and the bearing capacity of the surrounding rock in the roadway decreases.

[0027] like Figure 3 As shown, this is the roof structure before the roof is cut and pressure is relieved. A large area of ​​suspended plate structure is formed near the end of the working face. The static load of the surrounding rock increases sharply. When the roof suddenly breaks, a strong dynamic load is formed, which is prone to rockburst.

[0028] like Figure 4 As shown, this is the roof structure after the method was used to cut the roof. Due to the formation of a network of cracks along the direction and dip, the plate-like cantilever structure with fixed supports on both sides was destroyed, the roof fractured in time, the goaf collapsed more fully, the pressure step distance was shortened, the static and dynamic loads were significantly reduced, and the probability of rockburst was significantly reduced.

[0029] In summary, this invention employs a 90° bidirectional slit cut to form a three-dimensional crack network, cutting the thick, hard roof into a block structure. This completely destroys the plate-like cantilever structure fixed on both sides of the working face end, resulting in more complete roof collapse in the goaf, shorter pressure step distance, reduced additional dynamic load, a change in the support stress mode from constant resistance to increased resistance, and reduced static load on the surrounding rock foundation. This solves the technical problems of insufficient collapse and blind spots in pressure relief in existing technologies, achieving precise pressure relief. It has broad application prospects in areas such as rockburst and dynamic pressure disaster management, and goaf retention.

[0030] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for axial roof cutting and pressure relief using a grinding jet in a mine, characterized in that, Includes the following steps: Drilling holes in the roof of the mine roadway; Two jets of high-pressure water containing abrasive are sprayed onto the borehole wall. Both jets are sprayed radially along the borehole and their spray directions are perpendicular to each other on the borehole cross-section. At the same time, the spraying position is moved at a constant speed along the borehole axis, forming two initial cracks that are perpendicular to each other and parallel to the borehole axis on the borehole wall at one time. The two initial cracks are sealed at their upper and lower ends to form a sealed section. Water is injected into the sealing section, causing the two initial fractures to continue to expand along their depth direction, thereby forming a three-dimensional fracture network within the target rock layer.

2. The method for axial roof cutting and pressure relief using a grinding jet in a mine, as described in claim 1, is characterized in that... When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, a segmented cutting method is used for construction, and two mutually perpendicular axial cracks are formed on the borehole wall of each segment.

3. The axial roof-cutting pressure relief method based on a grinding jet in a mine, as described in claim 2, is characterized in that... When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, the cutting pressure is 45MPa to 50MPa and the cutting speed is 6m / h to 8m / h.

4. The axial roof-cutting pressure relief method based on mine roof grinding jet according to claim 3, characterized in that, When two jets of high-pressure water containing abrasive are sprayed onto the borehole wall, the nozzle diameter is 1.5 mm and the mass fraction of abrasive in the high-pressure water jet is 6.5%.

5. The method for axial roof cutting and pressure relief using a grinding jet in a mine, as described in claim 1, is characterized in that... When sealing the upper and lower ends of the two initial cracks to form a sealed section, the specific steps include: Move the sealing device to the upper and lower ends of the two initial cracks; High-pressure water is injected into the sealing device to cause it to expand and seal the upper and lower ends of the two initial cracks.

6. The method for axial roof cutting and pressure relief using a grinding jet in a mine, as described in claim 1, is characterized in that... When injecting water into the sealing section, the fracturing pressure is 25MPa to 35MPa, and the fracturing time is 30min to 45min.

7. The method for axial roof cutting and pressure relief using a grinding jet in a mine, as described in claim 6, is characterized in that... When water is injected into the sealing section, two mutually perpendicular initial cracks guide the high-pressure water to expand simultaneously along both the direction and dip of the roadway, cutting the thick, hard roof into a block structure and destroying the plate-like cantilever structure that is fixed at both ends.

8. The method for axial roof cutting and pressure relief using a grinding jet in a mine, as described in claim 1, is characterized in that... After the three-dimensional crack network is formed, the step of detecting and analyzing the top cutting effect is also included. The detection and analysis adopts any one or more of the following methods: electromagnetic wave CT, microseismic monitoring, and support pressure monitoring.

Images