CN112031772A - Method for inducing overall damage of overlying residual coal pillars by using high-pressure water jet - Google Patents
Method for inducing overall damage of overlying residual coal pillars by using high-pressure water jet Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21C—MINING OR QUARRYING
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- E21C41/16—Methods of underground mining; Layouts therefor
- E21C41/18—Methods of underground mining; Layouts therefor for brown or hard coal
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- E—FIXED CONSTRUCTIONS
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- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
- E21F17/00—Methods or devices for use in mines or tunnels, not covered elsewhere
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Abstract
The invention discloses a method for inducing the overall damage of an overlying residual coal pillar by using high-pressure water jet, which comprises the following steps of firstly determining the width of an elastic core area of the residual coal pillar so as to determine the damage range of the high-pressure water jet; then, dividing the residual coal pillar elastic nuclear area into regions which can destroy the residual coal pillar elastic nuclear area in different modes, drilling the high-pressure water jet destruction region after determining the basic parameters of the high-pressure water jet to destroy the residual coal pillar, weakening the high-pressure water jet by using an ultrahigh-pressure hydraulic slotting device to enable the high-pressure water jet destruction nuclear region to become a plastic region, and then enabling the residual non-water jet destruction elastic nuclear region to be automatically destroyed under the action of mine pressure; and repeating the step four, and finally, damaging all the residual coal pillars on the length. The method can destroy the residual coal pillars of the overlying goaf in a time-saving and labor-saving manner. The method has no limit on the damage form of the left coal pillar, and has wider application range.
Description
Technical Field
The invention relates to the technical field of damage of residual coal pillars in a goaf above a mine stope, in particular to a method for inducing overall damage of overlying residual coal pillars by using high-pressure water jet.
Background
In the process of mining the upper coal seam of the close-distance coal seam group, in order to prevent air leakage of the working face, water accumulation in the goaf and guarantee the stability of a roadway, 20-40 m wide protective coal pillars are reserved between the working faces, and after the stoping of the working face is finished, most of the protective coal pillars are influenced by mining conditions and are reserved in the goaf, and the coal pillars are called residual coal pillars. When a lower coal seam is mined, under the influence of stress transmission of residual coal pillars in an overlying goaf, the mine pressure in the working face area below the residual coal pillars appears violently, and a safety valve of a support is opened frequently, so that the safe and efficient production of a coal mine is seriously hindered, and the influence on the safe mining of the working face and the economic loss are caused.
At present, for solving the influence of the residual coal pillars in the overlying goaf on the working face of the lower part, the residual coal pillars are usually weakened and damaged by the technologies such as blasting, hydraulic fracturing, water injection softening and the like, for example:
chinese patent publication No. CN 110359909A discloses a softening method for a hard coal seam remaining coal pillar, which combines a shallow hole presplitting blasting technology with a hydraulic slotting technology to soften the remaining coal pillar, but the method relates to flammable and explosive articles such as gunpowder, detonator, etc., an explosive storage chamber needs to be reserved underground, and professional management needs to be arranged, so that potential safety hazards exist, and the method is not beneficial to safe, efficient and economic production of a mine.
Chinese patent publication No. CN110230493A discloses a corner cut destruction method for a left coal pillar, which mainly changes the coal pillar destruction form by determining the coal pillar destruction angle and cutting the top angle and the bottom angle of the coal pillar, so as to realize the conversion from the coal pillar pressure destruction to the shear destruction. According to the method, for narrow left-over coal pillars, the left-over coal pillars are changed from pressure damage to shear damage, but for the left-over coal pillars with the width of more than 30m, after the top angle and the bottom angle of the coal pillars are cut, the middle parts of the left-over coal pillars have large areas which are not damaged, and under the action of mine pressure, the left-over coal pillars are still in a pressed state and are not easy to shear damage, so that the method has certain limitation.
Chinese patent publication No. CN 108894787 a discloses a fracture relieving method for stress concentration of a remaining pillar in an overlying gob, which is characterized in that the stress of a roof is optimized by directional fracturing of the roof, and the source of the force is reduced; secondly, the coal pillar is fractured by pulse to generate a gap network, so that the rigidity of the coal pillar is weakened, and the bearing capacity of the coal pillar is reduced; and finally, pulse fracturing of the coal pillar bottom plate rock stratum weakens the capability of transmitting stress concentration. In the construction process of the method, high-pressure water easily flows into the goaf along the left coal pillar crack or the joint weak surface, and an ideal destruction effect cannot be achieved.
The invention discloses a coal pillar destruction method for weakening a potential destruction surface of a left coal pillar, which is similar to the technology of the invention, namely Chinese patent publication No. CN 110130895A. Firstly, drilling a rock core on an upper-layer left coal pillar, processing the rock core into a test piece with the same height-diameter ratio as the left coal pillar, performing a uniaxial compression test, determining whether the failure mode of the test piece meets the shearing failure mode, if so, performing the next step (see step S1), which indicates that the technology disclosed by the user is only suitable for the shearing failure coal pillar, and is not suitable for the tensile failure coal pillar, so that the use is limited greatly; secondly, the position of the weakened coal pillar is selected at the center of the coal pillar, the weakened drilling hole divides the left coal pillar into two small coal pillars, the two small coal pillars are used as supporting points to bear the pressure of the overlying strata together, when the left coal pillar is narrow, the divided two small coal pillars can not bear the pressure of the overlying strata, and then the left coal pillar is damaged, but when the left coal pillar is wide, the divided two small coal pillars can bear the pressure of the overlying strata, and the left coal pillar can not be damaged under the action of mine pressure, so that the most suitable narrow left coal pillar is determined, just as the coal pillars with the height a and the width b of 3m and 5m respectively listed in the specific implementation mode, if the weakened coal pillar is used for the wide left coal pillar, the possibility that the whole left coal pillar can not be damaged exists.
Disclosure of Invention
In order to accurately and effectively destroy the residual coal pillars in the overlying goaf and not influence the safe mining of the lower coal seam, the invention provides a design method for integrally destroying the residual coal pillars in the goaf by using high-pressure water jet, wherein the method is not limited in destruction form.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for inducing the integral damage of an overlying residual coal pillar by using high-pressure water jet is characterized by comprising the following steps:
firstly, determining the width B of an elastic nuclear area of a residual coal pillar1To determine the high-pressure water jet destruction range
Analyzing the range of the elastic plastic zone of the residual coal pillar based on the limit balance theory, and obtaining the width B of the elastic core zone of the residual coal pillar through formulas (1) to (3)1And determining the high-pressure water jet damage range, namely the high-pressure water jet damage area is positioned in the residual coal pillar elastic core area.
B1＝B-2B0 (3)
In the formula:
p-load per residual coal column length, kN/m
H, burying depth of residual coal pillar, m;
h, collapse height of rock stratum in the goaf, m;
-caving angle, degree, of overlying strata in the goaf;
gamma-overburden average volume weight, kN/m3。
B, the width of the residual coal pillar, m;
B0-sum of the widths of the damaged zone and the plastic zone, m;
B1-elastic nucleus area width, m;
m represents the mining thickness of the coal bed, M;
q1-concentrated load, MPa, above the residual coal pillars;
c-coal cohesion, MPa;
g-the coefficient of stress in the three axes,
f-friction factor;
p1-resistance of the support to the coal slope, MPa.
Secondly, dividing the residual coal pillar elastic nuclear area into areas which can destroy the residual coal pillar elastic nuclear area in different modes
According to mine pressure and rock stratum control theory, only when an elastic nuclear area is damaged, the load transferred by the bottom plate of the overlying residual coal pillar can be reduced, and normal exploitation of the working surface at the lower part of the residual coal pillar can not be influenced. Based on the above mechanism: the coal pillar is weakened by high-pressure water jet, so that on one hand, a defect body is manufactured on the elastic core, the coal body around the defect body is damaged, and the integrity of the coal pillar is reduced; then, the whole coal pillar containing the defect body is destroyed by using the mine pressure, and the method further comprises the following steps:
2.1: designing the zone of the elastic nucleus of the residual coal pillar
The central line of the elastic nucleus area is taken as a symmetry axis, and two sides of the central line of the elastic nucleus area are respectively divided into two areas from near to far, namely: a non-water jet breaks the elastic nucleus region and a high-pressure water jet breaks the elastic nucleus region;
and 2.2: determining the width of a non-water-jet-destroyed elastic nucleus region and a high-pressure water-jet-destroyed elastic nucleus region
The determination principle is as follows: firstly, destroying the coal body in the elastic core area by adopting high-pressure water jet to destroy the high-pressure water jet so as to change the coal body into a plastic area, losing the bearing capacity and transferring the overlying load to the non-water jet to destroy the elastic core area; if the remaining non-water jet flow damages the elastic core area to a certain extent (can be regarded as small coal pillars), plastic damage occurs under the action of mine pressure, so that the whole coal pillars are damaged, and the residual coal pillars lose the bearing capacity;
based on the principle, the following steps are provided:
B2-1and B2-2The widths m of the elastic nucleus areas damaged by the high-pressure water jet on the two sides of the central line of the elastic nucleus area;
B3-1and B3-2The widths m of the elastic nucleus area damaged by the non-water jet on two sides of the central line of the elastic nucleus area respectively;
q' is when the width of the coal pillar is B3-1+B3-2Load above residual coal column of (g), and q'>q1(this is because the concentrated load above the coal pillar is inversely proportional to the residual coal pillar width at the same burial depth),
to ensure complete destruction of the elastic nucleus region of the residual coal pillar, the width B under the load q' should be determined before the elastic nucleus region is destroyed by non-water jet3-1+B3-2The maximum value of all plastic fracture of the non-water jet fracture elastic core region can be obtained according to the formulas (4) to (5) by obtaining q' and B under the load3-1Or B3-2The plastic zone width is:
in the formula:
p-load per residual coal column length, kN/m
H, burying depth of residual coal pillar, m;
h, collapse height of rock stratum in the goaf, m;
-caving angle, degree, of overlying strata in the goaf;
gamma-overburden average volume weight, kN/m3。
M represents the mining thickness of the coal bed, M;
c-coal cohesion, MPa;
g-the coefficient of stress in the three axes,
f-friction factor;
then according to the formula (6), the width B of the elastic nucleus area damaged by the high-pressure water jet at two sides of the central line of the elastic nucleus area can be obtained2-1Or B2-2；
Thirdly, determining basic parameters of residual coal pillars damaged by high-pressure water jet
The basic parameters include: seam groove radius, single drilling seam groove interval, drilling number, drilling angle, single drilling seam groove number, coal pillar length direction high pressure water jet construction interval, wherein:
3.1: in order to obtain the seam groove radius and the coal pillar length direction high-pressure water jet construction interval when the high-pressure water jet damages the residual coal pillar, a field pre-test is needed to be carried out in the same coal layer area with the residual coal pillar, and the seam groove radius and the coal pillar length direction high-pressure water jet construction interval are obtained through the field pre-test and by combining a field monitoring means; the empirical value of the distance between the single-drilled-hole slots is generally 3-5 m;
3.2: determining high-pressure water jet flow construction parameters in width direction of coal pillar
Determining the number of drill holes, the drill hole angle and the number of single drill hole slots according to the position relationship (namely the vertical distance and the horizontal distance between the stoping roadway of the lower coal seam working face and the residual coal pillars of the overlying goaf) and the basic parameters of damaging the residual coal pillars by the high-pressure water jet determined in the step 3.1;
fourthly, destroying the whole residual coal pillar
During construction, firstly drilling the high-pressure water jet damaged elastic core area according to the site construction parameters determined in the third step, then weakening the high-pressure water jet by using an ultrahigh-pressure hydraulic slotting device to enable the high-pressure water jet damaged elastic core area to become a plastic area, and then enabling the residual non-water jet damaged elastic core area to be automatically damaged under the action of mine pressure; and repeating the step four, and finally, damaging all residual coal pillars on the length M.
The invention has the positive effects that:
1. according to the method, firstly, the high-pressure water jet is utilized to perform gridding local weakening on the residual coal pillars in the overlying goaf, the wide residual coal pillars are changed into narrow residual coal pillars, the narrow residual coal pillars are used as single supporting points for bearing the pressure of the overlying rock stratum, and then the narrow residual coal pillars are integrally destroyed under the action of the mine pressure.
2. According to the method, the high-pressure water jet damage area is determined by adopting theoretical calculation before the high-pressure water jet weakens the coal pillar, and after the high-pressure water jet weakens the coal pillar, the residual coal pillar is completely plastically damaged under the action of mine pressure, so that the whole coal pillar is damaged, the residual coal pillar loses the bearing capacity, and the method can be used for ensuring that the residual coal pillar in the overlying goaf can be damaged in a time-saving and labor-saving manner.
3. The weakening area is obtained through stress analysis, the damage form of the left coal pillar is not limited, and the application range is wider.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
FIG. 1 is a mechanical model of determining the elastic nucleus region width of a residual coal pillar;
FIG. 2 is a mechanical model for determining the width of a non-water jet damaged elastic nucleus region and a high-pressure water jet damaged region;
FIG. 3 is a schematic view of an on-site pre-test drilling arrangement;
FIG. 4 is a schematic view of FIG. 3A-A;
FIG. 5 is a schematic view of FIGS. 3B-B;
FIG. 6 is a width-wise drilling arrangement of the residual coal pillar;
FIG. 7 is a residual coal pillar length direction drilling arrangement;
FIG. 8 is a top view of a gridding slot after hydraulic slotting of a residual coal pillar.
In the figure: 1-residual coal pillars; 2-working surface of coal bed; 3-laying a coal seam working face; 4-mining a roadway on the working face of the lower coal seam; 5-slot sewing; 6, drilling; 7-pre-experiment slotting and drilling; 8, installing a drill hole by using a drill hole stress meter; 9-borehole stressmeter; 10-preliminary slot radius.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
Taking a certain coal mine as an example, the working face 3 of the lower coal seam of the coal mine is 2540m long, 180m wide, 400m average buried depth, 5.0m average coal thickness, 2m average coal seam inclination angle, the upper coal seam working face 3 is covered with a goaf of the upper coal seam working face 2, the average spacing is 25m, the residual coal pillars 1 between the working faces 2 of the upper coal seam are positioned above the working face 3 of the lower coal seam,the width B of the residual coal pillar 1 is 38m, the horizontal distance between the residual coal pillar 1 and the mining roadway 4 of the lower coal seam working face is 30m, wherein the height of the mining roadway 4 of the lower coal seam working face is 5m, and the width of the mining roadway 4 of the lower coal seam working face is 4 m. The thickness M of the coal seam on the working surface 2 of the upper coal seam is 6M, the burial depth H is 375M, the caving height H of the rock stratum of the goaf is 70M, the caving angle of the overlying rock stratum of the goaf is 60 degrees, and the average bulk density gamma of the overlying rock stratum is 26kN/M3The cohesive force c of the coal body is 1.76MPa, and the internal friction angle of the coal body
The friction factor f of the contact surface of the coal bed and the top and bottom plates is 22 degrees and is 0.4, and the resistance p of the bracket to the coal side1Is 0.
The method for integrally destroying the mine remaining coal pillar by using the method of the invention comprises the following steps:
firstly, determining the width B of an elastic nuclear area of a residual coal pillar1To determine the high-pressure water jet destruction range
Analyzing the range of the elastic plastic zone of the residual coal pillar 1 based on the limit balance theory, and obtaining the width B of the elastic core zone of the residual coal pillar 1 remained on the working surface 2 of the upper coal layer shown in figure 1 through formulas (1) to (3)1And determining the damage range of the high-pressure water jet.
B1＝B-2B0 (3)
In the formula:
p-load per residual coal column length, kN/m
H, burying depth of residual coal pillar, m;
h, collapse height of rock stratum in the goaf, m;
-caving angle, degree, of overlying strata in the goaf;
gamma-overburden average volume weight, kN/m3。
B, the width of the residual coal pillar, m;
B0-sum of the widths of the damaged zone and the plastic zone, m;
B1-elastic nucleus area width, m;
m represents the mining thickness of the coal bed, M;
q1-concentrated load, MPa, above the residual coal pillars;
c-coal cohesion, MPa;
g-the coefficient of stress in the three axes,
f-friction factor;
p1-resistance of the support to the coal slope, MPa;
the sum B of the widths of the destructive zone and the plastic zone on one side of the residual coal pillar 1 in the figure 1 is obtained by the formula0About 4.2m, elastic nucleus region B1About 29.6 m.
Secondly, dividing an elastic nuclear area of the residual coal pillar 1 into different modes to destroy the elastic nuclear area of the residual coal pillar 1
According to the mine pressure and rock stratum control theory, the load transferred by the bottom plate of the overlying residual coal pillar 1 can be reduced only when the elastic nuclear area is damaged, and the normal exploitation of the working surface at the lower part of the residual coal pillar 1 can not be influenced. Based on the above mechanism: the coal pillar is weakened by high-pressure water jet, so that on one hand, a defect body is manufactured on the elastic core, the coal body around the defect body is damaged, and the integrity of the coal pillar is reduced; then, the mine pressure is utilized to destroy the whole coal pillar containing the defect body, and the specific method comprises the following steps:
2.1: designing the zone of the elastic nucleus of the residual coal pillar
The central line of the elastic nucleus area is taken as a symmetry axis, and two sides of the central line of the elastic nucleus area are respectively divided into two areas from near to far, namely: non-water jet destructionAn elastic nucleus area and a high-pressure water jet damage area; as shown in fig. 2, width B2-1And B2-2The parts shown represent the high-pressure water jet destruction zones on either side of the centre line of the elastic nucleus region, respectively, the width B3-1And B3-2The portions shown represent the regions of the elastic nucleus where non-water jets on either side of the center line of the elastic nucleus region break down.
And 2.2: determining the width of the non-water jet-disrupted elastic nucleus region and the high-pressure water jet-disrupted region
The concentrated load above the coal pillar is inversely proportional to the width of the residual coal pillar 1 due to the same burial depth. Suppose that when the pillar width is B, the load above the residual pillar is q1(ii) a When the width of the coal pillar is B3-1+B3-2In this case, the load above the residual coal pillar 1 is q '(q'>q1) As shown in fig. 2. In order to ensure that the elastic nuclear area of the residual coal pillar 1 is completely destroyed, the high-pressure water jet is used for destroying the B2-1、B2-2Before the region, determining B under the action of a load q3-1+B3-2The maximum width at which plastic failure occurs throughout. According to the formulas (4) to (5), q', B under the load can be obtained3-1Or B3-2The plastic zone width is:
i.e. B3-1Or B3-2Has a width value of 4.4m, i.e. B3-1+B3-2The width value of (2) is 8.8 m.
Then according to the formula (6), obtaining high-pressure water jet damaged areas B at two sides of the central line of the elastic nucleus area2-1Or B2-2Width of (d):
i.e. B2-1Or B2-2The width value of (2) is 10.4 m.
Thirdly, determining basic parameters of residual coal pillars damaged by high-pressure water jet
The basic parameters include: 5 radiuses of seam groove, 5 intervals of single drilling seam groove, 6 numbers of drilling, 6 angles of drilling, 5 numbers of seam groove, coal pillar length direction high pressure water jet construction interval, wherein:
3.1: in order to obtain the radius of a slot 5 and the construction distance of high-pressure water jets in the length direction of a coal pillar when the high-pressure water jets damage the residual coal pillar, a field pre-test is required, and the specific method comprises the following steps:
3.1.1 test sites: in order to ensure the accuracy of parameters obtained by the field pre-test, the field pre-test is carried out in the same coal seam area with the residual coal pillars;
3.1.2 Experimental drill placement:
determining the position of a pre-experimental slotting drill hole: arranging 4 pre-experiment slotting drill holes 7 at intervals of 3m, 4m and 5m and 2.5m away from the bottom plate, wherein the depth of the pre-experiment slotting drill holes 7 is 6 m; determining the position of a borehole stress meter installation borehole 8: arranging a borehole stress meter installation borehole 8 between the pre-experiment slotting boreholes 7, wherein 3 borehole stress meter installation boreholes 8 are arranged in total, the interval is 3.5m, 4.5m and the distance from the bottom plate is 1m, and the depth of the borehole stress meter installation borehole 8 is 6m, as shown in figures 3-5;
firstly, drilling a borehole stress meter installation borehole 8 and installing a borehole stress meter 9 at a design position by using a geological drilling rig; and then drilling an A # pre-experiment slotting drill hole 7 at the design position by using a geological drilling machine, slotting after drilling the pre-experiment slotting drill hole 7, adopting 90MPa jet pressure and 5min slotting time, calculating the radius 10 of a pre-experiment slotting groove according to the slag discharge amount of the pre-experiment slotting drill hole 7 during slotting, drilling a B # pre-experiment slotting drill hole 7, a C # pre-experiment slotting drill hole 7 and a D # pre-experiment slotting drill hole 7 at intervals of 3m, 4m and 5m by using the geological drilling machine after determining the radius 10 of the pre-experiment slotting groove, and slotting by adopting 90MPa jet pressure and 5min slotting time after drilling.
After the slotting of each pre-experimental slotting drill 7 is finished, collecting the data of each drilling stress meter 9 for analysis, and obtaining the optimal coal pillar length direction high-pressure water jet construction interval.
According to the monitoring result of the on-site pre-test, the radius of the pre-test seam groove 10 is determined to be 0.75m, the optimal construction interval of high-pressure water jet in the length direction of the coal pillar is 4m, and in addition, for the interval of a single drilling seam groove, the empirical value obtained according to related research is generally 3-5 m.
3.2: determining high-pressure water jet construction parameters in width direction of coal pillar
Designing high-pressure water jet construction parameters (6 drilling holes, 6 drilling angles and 5 slots) in the width direction of the coal pillar according to the position relation (vertical distance and horizontal distance) of a stoping roadway 4 of a lower coal seam working face and the residual coal pillar 1 of the overlying goaf and the basic parameters of destroying the residual coal pillar 1 of the high-pressure water jet determined in the step 3.1, determining and arranging 6 drilling holes 6 by combining with the field engineering profile, wherein the drilling holes are respectively a 1# drilling hole, a 2# drilling hole, a 3# drilling hole, a 4# drilling hole, a 5# drilling hole and a 6# drilling hole (see figure 6), and the specific implementation parameters of each drilling hole are as shown in the following.
TABLE 1 residual coal pillar Width Direction drilling layout parameters
Fourthly, destroying the whole residual coal pillar
During construction, firstly, drilling is carried out on the high-pressure water jet damaged area according to the site construction parameters determined in the third step, then, high-pressure water jet weakening is carried out by using an ultrahigh-pressure hydraulic slotting device, so that the high-pressure water jet damaged area becomes a plastic area, then, the residual non-water jet damaged elastic core area is automatically damaged under the action of mine pressure, and then, the whole residual coal pillar 1 is damaged, and the residual coal pillar 1 loses the bearing capacity. And repeating the step four, and finally damaging the residual coal pillars 1 on all the lengths M, as shown in FIGS. 7-8.
The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of through the inventive work should be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
Claims (2)
1. A method for inducing the integral damage of an overlying residual coal pillar by using high-pressure water jet is characterized by comprising the following steps:
firstly, determining the width B of an elastic nuclear area of a residual coal pillar1Determining the high-pressure water jet flow damage range, analyzing the range of the elastic plastic zone of the residual coal pillar based on the limit balance theory, and obtaining the width B of the elastic core zone of the residual coal pillar through formulas (1) to (3)1Determining the damage range of the high-pressure water jet;
B1＝B-2B0 (3)
in the formula:
p-load per residual coal column length, kN/m
H, burying depth of residual coal pillar, m;
h, collapse height of rock stratum in the goaf, m;
-caving angle, degree, of overlying strata in the goaf;
gamma-overburden average volume weight, kN/m3；
B, the width of the residual coal pillar, m;
B0-sum of the widths of the damaged zone and the plastic zone, m;
B1-elastic nucleus area width, m;
m represents the mining thickness of the coal bed, M;
q1-concentrated load, MPa, above the residual coal pillars;
c-coal cohesion, MPa;
g-the coefficient of stress in the three axes,
f-friction factor;
p1-resistance of the support to the coal slope, MPa;
secondly, dividing the residual coal pillar elastic nuclear area into areas which can destroy the residual coal pillar elastic nuclear area in different modes
The coal pillars are weakened by high-pressure water jet, so that on one hand, a defect body is manufactured in the elastic core area, the coal bodies around the defect body are damaged, and the integrity of the coal pillars is reduced; secondly, the coal pillar containing the defect body is integrally damaged by using the mine pressure;
thirdly, determining basic parameters of residual coal pillars damaged by high-pressure water jet
The basic parameters include: seam groove radius, single drilling seam groove interval, drilling number, drilling angle, single drilling seam groove number, coal pillar length direction high pressure water jet construction interval, wherein:
3.1: in order to obtain the seam groove radius and the coal pillar length direction high-pressure water jet construction interval when the high-pressure water jet damages the residual coal pillar, a field pre-test is needed to be carried out in the same coal layer area with the residual coal pillar, and the seam groove radius and the coal pillar length direction high-pressure water jet construction interval are obtained through the field pre-test and by combining a field monitoring means; the distance between the single drilling slot and the single drilling slot is 3-5 m;
3.2: determining high-pressure water jet flow construction parameters in width direction of coal pillar
Determining the number of drill holes, the drill hole angle and the number of single drill hole slots according to the position relation between the stoping roadway of the lower coal seam working face and the residual coal pillars of the overlying goaf and the basic parameters of damaging the residual coal pillars by the high-pressure water jet determined in the step 3.1;
fourthly, destroying the whole residual coal pillar
During construction, firstly drilling a high-pressure water jet damage area according to the site construction parameters determined in the third step, then weakening high-pressure water jet by using an ultrahigh-pressure hydraulic slotting device to enable the high-pressure water jet damage nuclear area to become a plastic area, and then enabling the residual non-water jet damage elastic nuclear area to be automatically damaged under the action of mine pressure; and repeating the step four, and finally, damaging all the residual coal pillars on the length.
2. The method for inducing the overall damage of the overlying residual coal pillar by using the high-pressure water jet as claimed in claim 1, wherein the method for damaging the elastic nucleus area of the residual coal pillar in different modes in the elastic nucleus area of the residual coal pillar in the second step comprises the following steps:
2.1: designing the zone of the elastic nucleus of the residual coal pillar
The central line of the elastic nucleus area is taken as a symmetry axis, and two sides of the central line of the elastic nucleus area are respectively divided into two areas from near to far, namely: a non-water jet breaks the elastic nucleus region and a high-pressure water jet breaks the elastic nucleus region;
and 2.2: determining the width of a non-water jet destruction region and a high-pressure water jet destruction elastic nucleus region
The determination principle is as follows: firstly, destroying the coal body in the elastic core area by adopting high-pressure water jet to destroy the high-pressure water jet so as to change the coal body into a plastic area, losing the bearing capacity and transferring the overlying load to the non-water jet to destroy the elastic core area; if the residual non-water jet flow damaged elastic core area reaches a certain degree and can be regarded as a small coal pillar, plastic damage is generated under the action of mine pressure, so that the whole coal pillar is damaged, and the residual coal pillar loses the bearing capacity;
based on the principle, the following steps are provided:
B2-1and B2-2The width m of the elastic nucleus area damaged by high-pressure water jet is respectively;
B3-1and B3-2Respectively, the width m of the non-water jet flow damaged elastic nucleus area;
q' is when the width of the coal pillar is B3-1+B3-2Load above residual coal column of (g), and q'>q1；
In order to ensure that the elastic core area of the residual coal pillar is completely destroyed, the elastic core area is destroyed by destroying non-water jetFirst, the width B under load q' is determined3-1+B3-2The maximum value of all plastic fracture of the non-water jet fracture elastic core region can be obtained according to the formulas (4) to (5) by obtaining q' and B under the load3-1Or B3-2The plastic zone width is:
B3-1or
In the formula:
p-load per residual coal column length, kN/m
H, burying depth of residual coal pillar, m;
h, collapse height of rock stratum in the goaf, m;
-caving angle, degree, of overlying strata in the goaf;
gamma-overburden average volume weight, kN/m3；
M represents the mining thickness of the coal bed, M;
c-coal cohesion, MPa;
g-the coefficient of stress in the three axes,
f-friction factor;
then according to the formula (6), the width B of the elastic core area damaged by the high-pressure water jet on the two sides of the center line of the elastic core area can be obtained2-1Or B2-2：
B2-1Or
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| CN112983420A (en) * | 2021-03-31 | 2021-06-18 | 神华神东煤炭集团有限责任公司 | Coal mining method |
| CN114542005A (en) * | 2022-02-17 | 2022-05-27 | 山东科技大学 | Hard thick top coal hydraulic fracturing is with pressing-penetrating integration packer device |
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| CN105114038A (en) * | 2015-08-04 | 2015-12-02 | 太原理工大学 | System and method for increasing drainage quantity of coal bed gas of ground well drainage goaf |
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