Construction method for tunneling, pressure relief and scour prevention of coal seam containing hard dirt band

Abstract

The invention discloses a construction method for tunneling, pressure relief and scour prevention of a coal seam containing a hard dirt band. The construction method comprises the following steps: firstly, drilling a construction long drill hole in a front hard dirt band layer; a cutting groove is constructed in the hole wall of the long drill hole and used as an initial fracture initiation point of subsequent hydraulic fracturing; then, the long drill hole is subjected to segmented sealing isolation and segmented hydraulic fracturing; in the fracturing process, the pressure and flow of injected high-pressure water are controlled, so that fractures are cracked from all the cutting grooves, and the expansion range and degree of the fractures developed into the surrounding coal seam are controlled; after one-time fracturing is completed, the fracturing effect is detected through a monitoring means, fracturing is stopped until the required requirement is met, and hard dirt band breaking and coal seam area pressure relief and scour prevention can be achieved at the same time through the mode; then low-pressure water is continuously injected into the long drill hole, so that permeation softening of the coal seam and the hard dirt band layer is achieved; after the process is completed, tunneling construction is carried out from the roadway tunneling head-on to the front, so that the tunneling efficiency is effectively improved on the premise of ensuring safety.

Description

Technical Field

[0001] This invention belongs to the field of coal mine underground roadway excavation and disaster prevention technology, specifically a construction method for excavating and depressurizing coal seams containing hard interbedded gangue. Background Technology

[0002] Many existing coal mines contain hard interbedded rock layers within their coal seams. These hard interbedded rock layers are typically distributed in layers along the coal seam's strike, mainly composed of argillaceous rock and sandstone. Their extremely high hardness and integrity cause severe wear on tunneling machines and slow tunneling speeds, posing a significant challenge to roadway excavation. Currently, many coal mines still have to use traditional blasting tunneling (blasting) techniques for such conditions. This technique suffers from cumbersome procedures, long operation cycles, poor safety, and low tunneling efficiency, often leading to tight coordination between mining and excavation, becoming a bottleneck restricting safe and efficient production. On the other hand, in high-stress mining areas, rockburst hazards are a serious threat. To prevent rockbursts, it is usually necessary to construct a large number of dense, large-diameter pressure relief boreholes in front of the coal seam before roadway excavation. While this method can achieve pressure relief in front of the excavation, it involves a large amount of work, high costs, and the construction of pressure relief boreholes interferes with the tunneling operation, further affecting tunneling efficiency.

[0003] Therefore, there is an urgent need for a new method that can integrate efficient tunneling with disaster prevention and control. By combining hydraulic fracturing with directional long drilling, it is possible to simultaneously break up hard rock inclusions and relieve regional pressure to prevent scour, thereby effectively improving tunneling efficiency while ensuring safety. This is the direction that this invention aims to research. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a construction method for tunneling and pressure relief and scour prevention in coal seams containing hard interbedded rock. By combining hydraulic fracturing with directional long boreholes, it can simultaneously achieve the breaking of hard interbedded rock and pressure relief and scour prevention in the coal seam area. It can also achieve controllable fracture initiation and propagation in the hard interbedded rock layer. Furthermore, it can perform the triple functions of rock breaking, softening, and pressure relief within the same long borehole, ultimately effectively improving tunneling efficiency while ensuring safety.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a construction method for tunneling and depressurizing / anti-scour of coal seams containing hard interbedded gangue, comprising the following steps: Step 1: Construction of a long borehole: A long borehole is constructed in the coal and rock mass ahead of the tunnel face, and the borehole is drilled within a hard interlayer of rock.

[0006] Step 2, Construction of Grooves: Multiple pre-planned groove locations are planned within the long borehole. High-pressure jets or mechanical cutters are used to sequentially construct grooves on the borehole wall at each pre-planned location. These grooves serve as the initial fracture initiation points for subsequent hydraulic fracturing. This not only reduces the initiation pressure of hydraulic fracturing but also allows the fractures generated by fracturing to propagate directionally to the surrounding coal seam.

[0007] Step 3, hydraulic fracturing: The long borehole is sealed and isolated in sections using a sealing device, and high-pressure water is injected into each sealed section through a hydraulic fracturing pump system to perform segmented hydraulic fracturing.

[0008] Step 4, Fracture Control: During the segmented hydraulic fracturing process, the pressure and flow rate of high-pressure water injected into the borehole by the hydraulic fracturing pumping system are controlled to cause fractures to initiate from each cut point, and the extent and degree of fracture development into the surrounding coal seam are controlled, thereby avoiding excessive fracture expansion that could affect the subsequent roadway formation.

[0009] Step 5: Fracturing effect verification: After completing one hydraulic fracturing operation, the fracturing effect is verified by monitoring. If the required requirements are met, the hydraulic fracturing process is completed; otherwise, steps 3 and 4 are repeated to continue hydraulic fracturing until the required requirements are met. This verification method ensures that hydraulic fracturing can achieve the required pressure relief and weakening effect, preventing damage to the roadway formation during subsequent tunneling.

[0010] Step 6, Water Injection Softening: After fracturing is completed, low-pressure water is continuously injected into the long borehole for no less than 30 minutes to achieve permeation and softening of the coal seam and hard interbedded gangue, thereby reducing the dust from subsequent tunneling and the load and wear on the cutting head of the roadheader.

[0011] Step 7, Tunneling Construction: After softening and depressurizing the hard interbedded rock layer and the surrounding coal, a roadheader is used to tunnel forward from the roadway face.

[0012] Step 8: Segmented construction: If the hard interbedded gangue layer is long along the coal seam, segmented construction shall be carried out and the construction length of each long borehole shall be set until the hard interbedded gangue layer is penetrated; Steps 1 to 7 shall be repeated for each segment to achieve the tunneling construction of the coal seam containing the hard interbedded gangue layer.

[0013] The core innovative principle of this invention is as follows: Existing hydraulic fracturing technology is mostly used for gas extraction or roof weakening, typically involving the construction of fracturing holes in the sides or roof of an already formed roadway to increase permeability or relieve pressure. The inventors of this application, through research, discovered that before tunneling through coal seams containing hard interbedded rock, a long borehole is first constructed into the hard interbedded rock layer ahead. Then, hydraulic fracturing technology is used to fracture the borehole. By controlling the direction, extent, and degree of the fractures generated by the fracturing, not only can the hard interbedded rock be broken and weakened, but also, because the generated fractures can extend into the surrounding coal seam to provide regional pressure relief and scour prevention, only one long borehole is needed to simultaneously achieve the two objectives of breaking the hard interbedded rock and regional pressure relief and scour prevention. Under the premise of ensuring safety, roadway tunneling can be carried out directly, and tunneling efficiency can be effectively improved.

[0014] Furthermore, the groove is a circumferential annular groove (cutting a circle around the hole wall in a circumferential direction) or a directional groove (cutting two or more symmetrical straight grooves in a specific direction on the hole wall); the groove depth is 10% to 200% of the hole diameter; the groove width is 1 to 6 mm; and the length of the directional groove is not less than 1.5 times the hole diameter.

[0015] Furthermore, in step two, the high-pressure jet is either an abrasive jet or a pulsed water jet.

[0016] Furthermore, the segmented hydraulic fracturing in step three is a segmented retreat hydraulic fracturing, starting from the deepest part of the long borehole as the initial fracturing segment, and proceeding sequentially towards the drill mouth in segments; and the spacing of the sealing devices, the pressure and flow rate parameters of the high-pressure water during the segmented fracturing process are determined based on the physical and mechanical properties of the hard interbedded rock layer and the geostress field conditions of the surrounding coal seam.

[0017] Furthermore, in step four, the method for controlling the degree of crack propagation is to use alternating constant pressure water injection and pulse water injection, or to support the cracks by injecting sand-carrying fluid, in order to control the degree of crack propagation.

[0018] Furthermore, the specific steps for verifying the fracturing effect in step five are as follows: observation holes are set up on one or both sides of the long borehole, and the observation holes are parallel to the long borehole; stress monitoring or borehole television monitoring is used to verify the fracturing effect by comparing the water flow, stress changes or borehole viewing images before and after fracturing.

[0019] Furthermore, the long boreholes are constructed using conventional tunnel drilling rigs or directional drilling rigs.

[0020] Furthermore, in step six, the pressure of the low-pressure water is ≤10MPa. Within this pressure range, the softening effect of the water on the coal seam and hard interbedded gangue layers can be effectively guaranteed.

[0021] Compared with the prior art, the present invention has the following advantages: 1. One hole, multiple uses, integrated and efficient: This invention only requires one long borehole combined with hydraulic fracturing, which solves the two core problems of "hard rock inclusions that are difficult to cut" and "high ground stress that requires pressure relief". It combines pre-fracturing and weakening before tunneling with disaster prevention engineering, which greatly reduces the amount of special engineering work in the well and avoids mutual interference between processes.

[0022] 2. Active and controllable, precise weakening: This invention achieves effective guidance and control of the fracture initiation location and expansion range by pre-cutting grooves and controlling the parameters of hydraulic fracturing, avoiding the problem of roadway profile damage caused by fracturing blind spots or excessive fracturing, and ensuring the weakening effect and roadway forming quality.

[0023] 3. Improve efficiency and reduce costs: This invention effectively breaks up hard rock inclusions through advanced hydraulic fracturing and softens the coal and rock mass through water injection, reducing the overall strength and cutting resistance of the coal and rock mass, significantly improving the tunneling speed of the roadheader, and reducing the wear of cutting teeth and equipment maintenance costs; at the same time, the above methods also have the effect of regional pressure relief and anti-scour, which can replace or reduce traditional dense pressure relief drilling projects, effectively improving tunneling efficiency while ensuring safety.

[0024] 4. Safety and environmental protection: This invention eliminates the safety risks of blasting operations; the water penetration during the softening stage effectively reduces the dust concentration during tunneling, improves the working environment, and protects the health of workers. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the on-site construction principle of hydraulic fracturing in this invention.

[0026] Figure 2 yes Figure 1 A schematic diagram of the medium-length borehole trenching construction and hydraulic fracturing section.

[0027] Figure 3 This is a schematic diagram of the fracture propagation after hydraulic fracturing in this invention.

[0028] Figure 4 This is a schematic diagram of the layout of the observation holes in this invention.

[0029] Figure 5 This is a monitoring data chart after construction using the present invention.

[0030] In the diagram: 1-coal seam, 2-hard interbedded gangue layer, 3-long borehole, 4-groove, 5-fracture, 6-sealing device, 7-directional drilling rig, 8-water pump, 9-digital intelligent monitoring equipment, 10-manual pump, 11-observation hole. Detailed Implementation

[0031] The present invention will be further described below.

[0032] like Figure 1 As shown, the present invention includes the following steps: Step 1: Construction of long boreholes: In the coal and rock mass ahead of the tunnel face, use a conventional tunnel drilling rig or a directional drilling rig 7 to construct long boreholes 3, and these boreholes are drilled within a hard interbedded rock layer 2.

[0033] Step 2, Construction Grooving: (e.g.) Figure 2 As shown, multiple pre-set slot positions are planned within the long borehole. High-pressure jets (abrasive jets or pulsed water jets) or mechanical cutters are used to sequentially construct slots 4 on the borehole wall at each pre-set position. The slots 4 are either circumferential annular slots (cutting a circle around the borehole wall in a circumferential direction) or directional slots (cutting two or more symmetrical straight slots in a specific direction on the borehole wall). The slot depth is 10% to 200% of the borehole diameter; the slot width is 1 to 6 mm; and the length of the directional slot is not less than 1.5 times the borehole diameter, used as the initial fracture initiation point for subsequent hydraulic fracturing. This not only reduces the initiation pressure of hydraulic fracturing but also allows the fractures 5 generated by fracturing to extend directionally to the surrounding coal seam 1.

[0034] Step 3, Hydraulic Fracturing: The long borehole 3 is sealed in sections using a sealing device 6, and high-pressure water is injected into each sealed section via a hydraulic fracturing pump system to perform segmented hydraulic fracturing. Figure 3 As shown, this segmented hydraulic fracturing is a segmented retreating hydraulic fracturing method. The fracturing begins at the deepest part of the long borehole 3 and proceeds sequentially towards the borehole. The spacing of the sealing devices 6 and the pressure and flow rate parameters of the high-pressure water during the segmented fracturing process are determined based on the physical and mechanical properties of the hard interbedded rock layer 2 and the geostress field conditions of the surrounding coal seam 1. The aforementioned hydraulic fracturing pumping system includes a water pump 8, a digital intelligent monitoring device 9, and a manual pump 10. The water pump 8 is used to inject water into the long borehole 3, the digital intelligent monitoring device 9 is used to monitor the injection pressure and flow rate, and the manual pump 10 serves as an auxiliary pressurization device.

[0035] Step 4, Fracture Control: During the segmented hydraulic fracturing process, the pressure and flow rate of high-pressure water injected into the borehole by the hydraulic fracturing pump injection system are controlled to cause fractures 5 to initiate from each cut 4, and to control the extent and degree of fracture expansion into the surrounding coal seam 1. The method of controlling the degree of fracture expansion is to use constant pressure water injection and pulse water injection alternately, or to support the fracture by injecting sand-carrying fluid, so as to control the degree of fracture expansion; thereby avoiding excessive fracture expansion that would affect the subsequent roadway formation.

[0036] Step 5: Fracturing Effect Verification: After completing one hydraulic fracturing operation, the fracturing effect is verified through monitoring methods, such as... Figure 4As shown, specifically: one or more observation holes 11 are arranged on one or both sides of the long borehole 3, and the observation holes 11 are parallel to the long borehole 3. If there are multiple observation holes 11, the distance between adjacent observation holes 11 is 2~6m. Stress monitoring or borehole television monitoring is used to verify the fracturing effect by comparing the water flow, stress changes or borehole viewing images in the observation holes 11 before and after fracturing. If the required requirements are met, the hydraulic fracturing process is completed. Otherwise, steps three and four are repeated to continue hydraulic fracturing until the required requirements are met and then stopped. This verification method ensures that hydraulic fracturing can achieve the required depressurization and weakening effect, preventing damage to the roadway formation during subsequent tunneling.

[0037] Step 6, Water Injection Softening: After fracturing is completed, low-pressure water is continuously injected into the long borehole 3 at a pressure ≤10MPa for a time of not less than 30 minutes to achieve permeation and softening of coal seam 1 and hard interbedded gangue layer 2, thereby reducing subsequent tunneling dust and the load and wear on the cutting head of the roadheader.

[0038] Step 7, Tunneling Construction: After softening and depressurizing the hard interbedded rock layer 2 and the surrounding coal, a roadheader is used to tunnel forward from the roadway face.

[0039] Step 8, Segmented Construction: If the hard interbedded rock layer 2 is relatively long along the strike of coal seam 1, segmented construction shall be carried out and the construction length of each long borehole 3 shall be set (the specific length shall be determined according to the type of drilling rig used and the geological conditions on site) until the hard interbedded rock layer 2 is penetrated; Steps 1 to 7 shall be repeated for each segment to achieve the tunneling construction of the coal seam containing the hard interbedded rock layer.

[0040] Effect verification: To verify the effectiveness of the method of this invention, in the same coal seam containing hard interbedded gangue, the existing method was first used for tunnel excavation. After a certain distance, the method of this invention was then used for tunnel excavation. The excavation speed, cutting tooth consumption, dust concentration, and micro-vibration and stress monitoring indicators of the existing and new methods were recorded and compared in detail. Based on these comparative data, the rapid excavation and stress relief effects were evaluated from three dimensions: excavation speed improvement rate, dust reduction, and stress relief degree. Figure 5Taking a mining face as an example, after tunneling to the fracturing area constructed using this invention, the wear of cutting teeth decreased by more than 40% compared to before the pretreatment, dust reduction was 65%, and the tunneling footage increased from 5-6m per day to 8-9m per day. After hydraulic fracturing pretreatment, the total energy, frequency, and maximum energy of micro-vibrations were significantly reduced, and no high-energy events exceeding 5E3 J occurred. The above monitoring data shows that the method of this invention has significant improvements in all three dimensions compared to existing methods. This demonstrates that this invention, by combining long borehole construction with hydraulic fracturing technology, can simultaneously achieve three functions: advanced fracturing and weakening of hard interlayers, permeation and softening of coal to reduce dust, and creation of a fracture network for regional pressure relief and prevention of rockbursts. Under the premise of ensuring safety, it effectively improves tunneling efficiency.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded gangue, characterized in that, Includes the following steps: Step 1: Construction of a long borehole: A long borehole is constructed in the coal and rock mass ahead of the tunnel face, and the borehole is drilled within a hard interlayer of gangue. Step 2, Construction of Grooves: Plan multiple pre-set groove positions within the long borehole, and use high-pressure jets or mechanical tools to sequentially construct grooves on the borehole wall at each pre-set position, which will serve as the initial fracture initiation points for subsequent hydraulic fracturing. Step 3, hydraulic fracturing: The long borehole is sealed and isolated in sections using a sealing device, and high-pressure water is injected into each sealed section through a hydraulic fracturing pump system to carry out segmented hydraulic fracturing; Step 4, Fracture Control: During the segmented hydraulic fracturing process, the pressure and flow rate of high-pressure water injected into the borehole by the hydraulic fracturing pump injection system are controlled to cause fractures to initiate from each cut, and to control the extent and degree of fracture development into the surrounding coal seam. Step 5: Fracturing effect verification: After completing one hydraulic fracturing operation, the fracturing effect is verified by monitoring. If the required requirements are met, the hydraulic fracturing process is completed; otherwise, repeat steps 3 and 4 to continue hydraulic fracturing until the required requirements are met and then stop. Step 6, Water Injection Softening: After fracturing is completed, low-pressure water is continuously injected into the long borehole for no less than 30 minutes to achieve permeation and softening of the coal seam and hard interbedded gangue. Step 7, Tunneling Construction: After softening and depressurizing the hard interbedded rock layer and the surrounding coal, a roadheader is used to tunnel forward from the roadway face. Step 8: Segmented construction: If the hard interbedded gangue layer is long along the coal seam, segmented construction is carried out and the construction length of each long borehole is set. Steps 1 to 7 are repeated for each segment to achieve the tunneling construction of the coal seam containing the hard interbedded gangue layer.

2. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, The groove is a circumferential annular groove or a directional groove; the groove depth is 10% to 200% of the hole diameter; the groove width is 1 to 6 mm; and the length of the directional groove is not less than 1.5 times the hole diameter.

3. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, In step two, the high-pressure jet is either an abrasive jet or a pulsed water jet.

4. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, In step three, the segmented hydraulic fracturing is a segmented retreat hydraulic fracturing, starting from the deepest part of the long borehole as the initial fracturing segment, and proceeding segmented fracturing towards the borehole in sequence; and the spacing of the sealing devices, the pressure and flow rate of the high-pressure water during the segmented fracturing process are determined based on the physical and mechanical properties of the hard interbedded rock layer and the geostress field conditions of the surrounding coal seam.

5. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, In step four, the method to control the degree of crack propagation is to use alternating constant pressure water injection and pulse water injection, or to support the cracks by injecting sand-carrying fluid, in order to control the degree of crack propagation.

6. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, The specific steps for verifying the fracturing effect in step five are as follows: observation holes are set up on one or both sides of the long borehole, and the observation holes are parallel to the long borehole; stress monitoring or borehole television monitoring is used to verify the fracturing effect by comparing the water flow, stress changes or borehole viewing images before and after fracturing.

7. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, The long boreholes are constructed using conventional tunnel drilling rigs or directional drilling rigs.

8. The construction method for tunneling and depressurization / scour prevention in coal seams containing hard interbedded rock as described in claim 1, characterized in that, In step six, the pressure of the low-pressure water is ≤10MPa.

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