Roof cutting pressure relief method based on intensive drilling
Technical Field
The invention relates to a drilling top-cutting pressure relief method, in particular to a top-cutting pressure relief method based on intensive drilling.
Background
By 2020, the coal yield in China can reach 39 hundred million tons, and the coal yield is increased by 9.57 hundred million tons compared with the prior art. To meet the demand for coal, the mining depth is increasing every year. On one hand, along with the increase of the depth of a coal seam, the mine pressure is continuously increased, and in order to meet production requirements, the tunneling of the gate way of the working face of the lower section must be carried out while the mining of the working face of the upper section is carried out, and the surrounding rock of the gob-side roadway is in a high stress state under the influence of the mining of the upper section. On the other hand, 38% of the fully mechanized mining working surfaces in China belong to hard top plates with high pressure intensity, after the working surfaces are mined, the hard top plates are difficult to collapse in time, a cantilever structure is easy to form, the cantilever structure can be caused to rotate and sink after the basic roof is broken, the stress of surrounding rocks around an adjacent roadway is increased, the roadway adjacent to the working surfaces is seriously deformed, and the dynamic disasters such as severe vibration and impact mine pressure of rock masses of the working surfaces, coal and gas outburst and the like are caused.
Aiming at the problems of serious gob-side entry driving surrounding rock deformation and high roof control difficulty, the deformation of the surrounding rock cannot be effectively controlled by means of the traditional anchor rod and anchor cable for reinforcing and supporting the roadway, and the stress concentration of the gob-side roadway surrounding rock can be fundamentally reduced only by cutting off the mechanical connection between the basic top cantilever rock beam of the gob-side basic top and the gob-side roadway roof plate and releasing the elastic potential energy accumulated in the roof plate, so that the stability of the gob-side roadway surrounding rock is improved. The existing common technical methods comprise a blasting top-cutting pressure relief technology, a hydraulic fracturing weakening top-cutting pressure relief technology and a composite perforation top-cutting pressure relief technology. However, explosive blasting is adopted in both blasting top-cutting pressure relief technology and composite perforation top-cutting pressure relief technology, explosive blasting is only suitable for low-gas mines, high-gas mines need strict use technical requirements, and top-cutting blasting may cause the roof in a roadway to be cut down in advance, so that roof management is difficult. The hydraulic fracturing weakening roof-cutting pressure relief technology has the problems of complex equipment process, poor adaptability to roadway natural conditions and the like.
Disclosure of Invention
The invention aims to provide a roof cutting pressure relief method based on dense drilling, which is characterized in that dense drilling is carried out on a top plate through reasonably designing drilling parameters, and roof cutting pressure relief is carried out; the problem of overlarge rock burst during mining of small coal pillars in the process of coal mine deep mining gob-side entry retaining can be effectively solved; the roof cutting and pressure relief can be carried out in time under the conditions that a hard roof of the goaf cannot be collapsed in time and the elastic potential energy in the roof is accumulated in a large amount; in order to reduce the number of drilling holes as much as possible to improve the labor efficiency under the condition of ensuring the roof cutting and pressure relief, drilling parameters need to be calculated to obtain an optimal value.
The invention discloses a roof cutting and pressure relief method based on dense drilling, which comprises the following steps of:
s1: determining a borehole arrangement area: the drill holes are positioned on the top plate of the gate way along the upper section and are adjacent to the lower section, and the arrangement direction of the drill holes is the same as the direction extending along the gate way;
s2: determining drilling parameters required by top cutting, including the diameter, the interval, the angle and the depth of a drill hole;
diameter of the drilled hole: according to the size damage condition of the plastic damage area around the drill holes with different diameters, values are taken through calculation of a mechanical formula and numerical simulation;
the distance between the drilled holes: solving the stress state of the rock mass around the drill hole according to an elastic theory, obtaining an approximate boundary line equation of the plastic zone of the rock mass around the drill hole according to the elastic mechanics theory, the stress balance condition of the elastic-plastic zone and a Moire intensity criterion, and calculating and determining a reasonable drill hole interval by substituting mine geological data so as to connect the weakening zones outside the adjacent drill hole plastic zones to form the weakening zones;
drilling angle: selecting an included angle between a drill hole and a roadway top plate in the horizontal direction from a lower section to an upper section according to a masonry beam theory and a surrounding rock structure S-R stabilization principle;
drilling depth: after the artificial rock mass structure weakening zone is constructed through the intensive drilling, the self weight of the direct roof and the basic roof and the mining stress caused by the extraction of a working face can stride and fall only by overcoming the residual shear strength of the artificial rock mass structure weakening zone, so that the drilling depth is determined;
s3: drilling construction: and (4) outside the forward-supporting section of the working face of the upper section, which is close to the lower section, of the gateway, and drilling a row of holes above the section obliquely upwards along the direction of the working face according to the drilling parameters determined in the step S2 at the position selected in the step S1.
Further, in step S1, the position of the drill hole is located on the gate board along the next lower section of the upper section, and is located on the side of the coal pillar reserved between the upper section and the lower section.
Preferably, the diameter of the drilled hole is 10-100 mm.
Preferably, the distance between the drill holes is 100-500 mm.
Preferably, the drilling depth is not less than 7 m.
Preferably, the drilling angle is 70-90 degrees.
According to the roof cutting and pressure relief method based on the intensive drilling, provided by the invention, based on the surrounding rock loosening circle theory, drilling parameters can be determined, weakening zones formed by drilling and excavation are mutually overlapped and communicated to form an artificial rock mass structure weakening zone, and a hard top plate of a goaf is broken along an artificial structure weakening plane, namely the artificial rock mass structure weakening zone at an expected position in the stoping process, so that the aim of roof cutting and pressure relief is fulfilled. The problem of overlarge impact ground pressure during small coal pillar mining in the process of coal mine deep mining gob-side entry retaining can be effectively solved; and the roof cutting and pressure relief can be carried out in time under the conditions that the hard roof of the goaf cannot be collapsed in time and the elastic potential energy in the roof is accumulated in a large amount.
Drawings
FIG. 1 is a plan view of a borehole layout for a compact borehole based roof cutting pressure relief method of the present invention;
FIG. 2 is a sectional view taken along line I-I of FIG. 1;
FIG. 3 is a schematic view of the collapse of the top plate of FIG. 1 after cutting the top of the drilled hole at II-II;
FIG. 4 is a diagram of the distribution of the area of influence of the borehole;
FIG. 5 is a schematic view of a pressure relief stack for a tight-gauge borehole;
in the figure, 1, gate; 2. an upper section; 3. naturally caving the top plate; 4. top cutting and roof caving; 5. a lower section; 6. drilling; 7. a crushing zone; 8. a plastic region; 9. a weakening zone.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and a mineral case.
The invention provides a roof cutting and pressure relief method based on dense drilling, which comprises the following steps:
s1: determining the arrangement area of the drill holes 6: as shown in fig. 1 and 2, the bore 6 is located along the roof of the gate 1 immediately adjacent to the lower section 5 in the upper section 2; the arrangement direction of the drill holes 6 is the same as the extending direction along the gate 1; thereby determining various parameters of the rock formation in the arrangement area of the borehole 6 and providing a basis for the selection of the parameters of the borehole 6. Preferably, the bore 6 may be arranged at a position on the side of the coal pillar reserved between the upper section 2 and the lower section 5.
S2: determining parameters of the drill hole 6 required by top cutting, including the diameter, the interval, the angle and the depth of the drill hole 6;
diameter of the bore 6: according to the size damage condition of the plastic damage area around the drill holes 6 with different diameters, the values are calculated through a mechanical formula and are obtained through numerical simulation: the range of the selection can be 10-100 mm;
spacing of the drilled holes 6: the fracture area 7, the plastic area 8 and the stressed state of a single drill hole 6 are shown in fig. 4, and the fracture area 7, the plastic area 8 and the weakened zone 9 of the drill hole 6 are arranged from the center of the drill hole 6 to the outside in sequence. Solving the stress state of the rock mass around the drill hole 6 according to the elastic theory, obtaining an approximate boundary line equation of the plastic zone 8 of the rock mass around the drill hole 6 according to the elastic mechanics theory, the elastic plastic zone stress balance condition and the Moire strength criterion, and connecting the weakening zones 9 outside the plastic zones 8 of the adjacent drill holes 6 by determining the reasonable distance between the drill holes 6; as shown in fig. 5. The distance between the drill holes 6 can be determined to be 100-500 mm by integrating the actual conditions of all coal mines;
drilling 6 angles: according to the masonry beam theory and the surrounding rock structure S-R stabilization principle, selecting a drilling hole 6 according to an included angle of 70-90 degrees with a horizontal direction from a lower section 5 to an upper section 2 of a roadway roof through calculation; i.e. the angle as shown in fig. 2.
Depth of the drilled hole 6: after the artificial rock mass structure weakening zone is constructed through the intensive drilling 6, the weights of the direct roof and the basic roof and the mining stress caused by the stoping of a working face can stride and fall only by overcoming the residual shear strength of the artificial rock mass structure weakening zone; therefore, an equilibrium equation is derived, and the depth of the borehole 6 is determined by substituting the in situ formation specific parameters. The depth of the bore 6 in a mine is taken to be not less than 7 m.
S3: and (6) drilling 6: in the position close to the reserved coal pillar side, a row of drill holes 6 are drilled obliquely upward from the section 2 along the working face direction according to the parameters of the drill holes 6 determined in the step S2 outside the forepoling section of the gate 1 close to the lower section 5 of the working face of the upper section 2, so as to form dense drill holes 6, as shown in fig. 1 and 2.
If roof cutting and pressure relief are not carried out, the top plate of the goaf naturally collapses after the working face of the upper section 2 is pushed forwards, the top plate above the crossheading 1 adjacent to the lower section 5 forms a cantilever structure, and when the roadway is excavated along the air below the cantilever structure again, the roadway pressure is large, and maintenance is difficult. After the holes 6 are drilled according to the parameters of the holes 6, the superposition state of the weakening zones 9 of the holes 6 is shown in fig. 5, the multiple holes 6 form dense-level holes 6, the weakening zones 9 are superposed, under the influence of mining disturbance and high surrounding rock stress, the dense holes 6 are mutually connected and communicated to form an artificial rock mass structure weakening zone structure, under the influence of self weight and mining movement of a rock mass, the top plate can be cut along the weakening zone, as shown in fig. 3, the top plate in a goaf collapses to form a naturally-collapsed top plate 3, and the top plate above the gateway 1 collapses to form a top-cut collapsed top plate 4.
If the roof cutting work is finished and the working face of the upper section 2 is completely mined, the tunneling work of the working face gateway 1 of the lower section 5 can be immediately carried out, and as the basic top cantilever structure of the mining side is damaged, as shown in fig. 3, the influence of the basic top cantilever structure of the working face of the upper section 2 on the working face gateway 1 of the lower section 5 is small in the process of gob-side entry driving, the control difficulty of the surrounding rock of the roadway is reduced, and the supporting is relatively easy. If the excavation connection work is relatively tense, the excavation work of the crossheading 1 of the working face of the lower section 5 can be carried out after the small coal pillar mining side of the working face of the upper section 2 is cut and subjected to pressure relief. In the period of the gob-side excavation of the stope face, unstable bearing pressure stress increasing areas are generated in front of and behind the working face under the severe influence of overlying strata of the mining space after the working face of the upper section 2 is mined, in order to reduce the difficulty of roadway maintenance, the excavation of the gob-side roadway needs to be stopped in the mining-influenced severe areas of the working face of the upper section 2, only the stope of the working face of the upper section 2 and roof cutting pressure relief work are carried out, and the re-excavation work of the gob-side roadway is carried out after the mining of the working face of the upper section 2 exceeds the area. Because the violent mining influence area of the working surface of the upper section 2 is avoided, and the basic top cantilever structure of the mining side is damaged in the gob-side entry driving process of the working surface gate way 1 of the lower section 5, the influence of the mining dynamic pressure of the working surface of the upper section 2 is small, the control difficulty of surrounding rocks of the roadway is reduced, and the support is relatively easy.
According to the roof cutting and pressure relief method based on the intensive drilling, provided by the invention, based on the surrounding rock loosening circle theory, drilling parameters can be determined, weakening zones formed by drilling and excavation are mutually overlapped and communicated to form an artificial rock mass structure weakening zone, and a hard top plate of a goaf is broken along an artificial structure weakening plane, namely the artificial rock mass structure weakening zone at an expected position in the stoping process, so that the aim of roof cutting and pressure relief is fulfilled. The problem of overlarge impact ground pressure during small coal pillar mining in the process of coal mine deep mining gob-side entry retaining can be effectively solved; and the roof cutting and pressure relief can be carried out in time under the conditions that the hard roof of the goaf cannot be collapsed in time and the elastic potential energy in the roof is accumulated in a large amount.