A method for reducing the scope of coal pressure under buildings and structures under thick loose layer conditions

Abstract

The present invention relates to the field of methods for handling coal pressure under structures, and in particular to a method for reducing the scope of coal pressure under structures under thick loose layer conditions. The present invention forms an isolation zone by grouting after constructing isolation grouting drilling, thereby isolating the loose layer in the protected area from the external loose layer. When the coal seam outside the protective coal pillar is mined, the external loose layer is stretched and separated from the isolation zone. The loose layer in the protected area will not be affected due to the isolation effect of the isolation zone, and the stretched cracks are filled by constructing grouting drilling. The method for reducing the scope of coal pressure under structures under thick loose layer conditions proposed by the present invention eliminates the influence of the loose layer on the setting of the protective coal pillar by constructing isolation grouting drilling, so that there is no need to consider the thickness of the loose layer when setting the protective coal pillar, greatly reducing the amount of protective coal pillars, and improving the coal recovery rate and resource utilization rate. The isolation grouting drilling is mainly constructed in the loose layer, with fast construction speed, short cycle and low cost.

Description

Technical Field

[0001] The present invention relates to the field of coal pressure treatment methods under buildings and structures, and in particular to a method for reducing the range of coal pressure under buildings and structures under thick loose layer conditions. Background Art

[0002] Coal mining can cause surface subsidence. When there are structures on the surface, it is necessary to coordinate the relationship between coal mining and the maintenance of surface structures. One approach is to use backfill mining, which can achieve both coal mining and the protection of surface structures. However, underground backfill mining requires replacing the entire set of fully mechanized mining equipment, especially the dedicated hydraulic supports. The cost of backfill hydraulic supports is huge, and the backfill mining speed is slow, far from meeting the mine production capacity requirements. It can only be used as a supporting mining surface. Moreover, the surface will still sink and deform to a certain extent during backfill mining, which is not very suitable for structures with high ground protection levels.

[0003] Another approach is to leave the coal beneath structures as protective pillars, meaning the underlying coal is not mined. However, due to the characteristics of rock strata movement and unconsolidated strata movement, the area of ​​coal covered by structures is much larger than the structure itself. This means that mining coal not directly beneath the structure will also cause subsidence and deformation in the area surrounding the structure. The angle of bedrock movement is generally around 70°, while the angle of unconsolidated strata movement is generally around 45°. This indicates that the impact of unconsolidated strata movement is greater than that of bedrock movement. Furthermore, the amount of coal covered increases with the depth of the coal seam. Therefore, when encountering thick unconsolidated strata, the required protective pillar area becomes very large, resulting in significant coal resource losses. Relocating surface structures is one possible solution, but not all surface structures meet relocation policy requirements. Furthermore, relocation requires extensive coordination, a long timeframe, and high costs. Therefore, industry professionals are eager to find ways to reduce the scope of protective pillars in thick unconsolidated strata. Summary of the Invention

[0004] To address the problem of a large range of protective coal pillars under structures in traditional thick and loose strata, the present invention isolates the movement transmitted by the loose strata by constructing isolation grouting drillings, thereby greatly reducing the range of protective coal pillars. Specifically, the present invention proposes a method for reducing the range of coal pressure under structures in thick and loose strata, comprising the following steps:

[0005] Step 1: Draw two straight lines parallel to the strike and dip of the coal seam through the outermost corners of the structure or group of structures. The intersection of the four straight lines encloses a rectangular protected area for the structure or group of structures; the structure or group of structures is completely located within the rectangular protected area.

[0006] Step 2: Set up a protective belt of a certain width outside the rectangular protected area to form a rectangular annular protective belt abcd; on the one hand, the protective belt can be used to isolate the grouting drilling construction area to form a loose layer grouting isolation belt; on the other hand, it can offset the errors in the calculation of the size and position of the protective coal pillar caused by the selection of the bedrock movement angle and the loose layer movement angle, the coal rock layer occurrence angle and the depth exploration error when setting the protective coal pillar.

[0007] Preferably, the entire enclosure has a uniform width.

[0008] The third step is to construct a first isolation grouting borehole from the ground in the middle of the retaining belt to a certain depth in the bedrock, and the first isolation grouting borehole is vertical; near the rectangular protected area of ​​the retaining belt, a second isolation grouting borehole is constructed from the ground to the top surface of the bedrock (i.e., the interface between the loose layer and the bedrock), and the intersection of the second isolation grouting borehole and the top surface of the bedrock is located directly below the outer boundary of the retaining belt; injecting a cementing slurry into the stratum from the isolation grouting borehole to form a circumferential grouting isolation zone surrounding the rectangular protected area, and the grouting isolation zone isolates the loose layer of the rectangular protected area from the loose layer outside the grouting isolation zone;

[0009] Preferably, the first isolation grouting borehole and the second isolation grouting borehole are arranged at intervals.

[0010] Preferably, the slurry with cementitious properties is cement slurry.

[0011] Step 4: Project the four endpoints a, b, c, d of the rectangular enclosure or the rectangular enclosure vertically to the top surface of the bedrock to form four endpoints a1, b1, c1, d1 projected to the top surface of the bedrock; for the two endpoints b1 and c1 close to the upper part of the dip, first draw straight lines in the upward direction based on the bedrock uphill movement angle β, forming two intersections with the coal seam, and the straight lines passing through the two intersections are the first straight line; for the two endpoints a1 and d1 close to the lower part of the dip, first draw straight lines in the downward direction based on the bedrock downhill movement angle γ, forming two intersections with the coal seam, and the straight lines passing through the two intersections are the second straight line; for the two endpoints a1 and b1 close to one side of the strike, first draw straight lines in the downward direction based on the bedrock downhill movement angle γ, forming two intersections with the coal seam, and the straight lines passing through the two intersections are the second straight line. Draw a straight line in the direction of the strike direction based on the bedrock movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the third straight line; for the two endpoints c1 and d1 close to the other side of the strike, first draw a straight line in the direction of the other side based on the bedrock movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the fourth straight line; the area enclosed by the intersection of the first straight line, the second straight line, the third straight line, and the fourth straight line is the coal compression range A1B1C1D1 of the structure or structure group, that is, the protective coal pillar, where the first straight line intersects with the third straight line and the fourth straight line at B1 and C1 respectively, and the second straight line intersects with the third straight line and the fourth straight line at A1 and D1 respectively;

[0012] Preferably, the fourth step can also be determined by the following method: the four endpoints a, b, c, d of the rectangular enclosure or the rectangular enclosure are vertically projected to the top surface of the bedrock to form four endpoints a1, b1, c1, d1 projected to the top surface of the bedrock; for the two endpoints b1 and c1 close to the upper part of the inclination, first draw straight lines in the upward direction based on the bedrock uphill movement angle β to form two intersections with the coal seam, and then project these two intersections vertically to the top surface of the bedrock to form b2 and c2, and then move them respectively based on the bedrock strike. Draw a straight line in the opposite direction of the strike angle δ to form two intersections B1 and C1 with the coal seam; for the two end points a1 and d1 near the lower part of the dip, first draw a straight line in the downward direction based on the downward movement angle γ of the bedrock to form two intersections with the coal seam, and then project these two intersections vertically to the top surface of the bedrock to form a2 and d2, and then draw a straight line in the opposite direction of the strike angle δ to form two intersections A1 and D1 with the coal seam. The coal pressing range of the structure is the area enclosed by A1B1C1D1, which is the protective coal pillar area.

[0013] The fifth step is to mine the coal seam outside the coal compression range A1B1C1D1 of the structure or the group of structures and close to the coal compression range A1B1C1D1 of the structure or the group of structures, construct filling boreholes from the ground downward at the outer boundary of the retaining belt, and flush filling materials into the tensile cracks of the loose layer through the filling boreholes.

[0014] Preferably, the grouting filling material is initially injected with loose materials such as sand, and later injected with bonding materials such as cement slurry.

[0015] The inventive points and beneficial effects of the present invention are as follows: 1. The present invention forms an isolation zone by grouting after constructing isolation grouting drilling, thereby isolating the loose layer in the protected area from the external loose layer. When the coal seam outside the protective coal pillar is mined, the external loose layer is stretched and separated from the isolation zone. The loose layer in the protected area will not be affected by the isolation effect of the isolation zone, and the stretched cracks will be filled by constructing grouting drilling.

[0016] 2. The isolation grouting drilling of the present invention includes: constructing a first isolation grouting drilling hole vertically from the ground to a certain depth in the bedrock in the middle of the protective belt, and constructing a second isolation grouting drilling hole from the ground to the top surface of the bedrock in the protective belt near the rectangular protected area, and the intersection of the second isolation grouting drilling hole and the top surface of the bedrock is located directly below the outer boundary of the protective belt; in this way, in the first isolation grouting drilling hole, an isolation section is formed at the upper part of the intersection with the second isolation grouting drilling hole, and a support section is formed at the lower part of the intersection with the second isolation grouting drilling hole; in the second isolation grouting drilling hole, a guarantee section is formed at the upper part of the intersection with the first isolation grouting drilling hole, and a transition section is formed at the lower part of the intersection with the first isolation grouting drilling hole; when the coal seam outside the protective coal pillar is mined, the inclined transition section plays a transition role and forms a connection with the inclined bedrock movement angle, the support section supports the transition section, improves the stability of the transition section, the isolation section isolates the loose layer in the protected area from the external loose layer, and the guarantee section plays a secondary isolation role.

[0017] 3. The method proposed in the present invention for reducing the scope of coal pressure under buildings under thick loose layer conditions eliminates the influence of loose layers on the installation of protective coal pillars by constructing isolation grouting drilling holes, so that there is no need to consider the thickness of the loose layer when installing protective coal pillars, which greatly reduces the amount of protective coal pillars and improves coal recovery rate and resource utilization rate. The isolation grouting drilling holes are mainly constructed in the loose layer, with fast construction speed, short cycle and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] When considered in conjunction with the accompanying drawings, the present invention can be more completely and better understood and many of the accompanying beneficial effects can be easily known by referring to the following detailed description. However, the drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0019] Figure 1 —A schematic diagram of the direction of coal under a building using a vertical section method in the prior art;

[0020] Figure 2 —Schematic diagram of the range of coal pressure under a building determined by vertical section method in the prior art;

[0021] Figure 3 —Schematic diagram of the range of coal pressure under a building determined by the present invention;

[0022] Figure 4 —Schematic diagram of the range of coal pressure under a building determined by the present invention;

[0023] Figure 5 — Figure 3 A partial enlarged view of the isolation drilling arrangement;

[0024] Figure 6—Schematic diagram of the existing technology and the present invention for determining the area of ​​coal pressure under a building;

[0025] Figure 7 —Schematic diagram of the coal compression tendency range determined by the vertical section method in the prior art;

[0026] Figure 8 —Schematic diagram of determining the coal compression tendency range in Example 2 of the present invention;

[0027] Figure 9 — Figure 8 A partial enlarged view of the isolation drilling arrangement;

[0028] Figure 10 —Schematic diagram of the coal pressing range determined by the prior art and the present invention in Example 2;

[0029] Description of the accompanying drawings: first isolation grouting borehole 1; isolation section 1-1; support section 1-2; second isolation grouting borehole 2; guarantee section 2-1; transition section 2-2; filling borehole 3; protected area of ​​building group 4-1; building group enclosure belt 4-2; protected area of ​​railway track 5-1; railway track enclosure belt 5-2; loose layer 6, bedrock 7, coal seam 8. DETAILED DESCRIPTION

[0030] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings. In the present invention, various aspects of the present invention are described with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present invention are not limited to those described in the accompanying drawings. It should be understood that the present invention is implemented by any of the various concepts and embodiments introduced above, as well as the concepts and implementation methods described in detail below, because the concepts and embodiments disclosed in the present invention are not limited to any implementation method. In addition, some aspects disclosed in the present invention can be used alone or in any appropriate combination with other aspects disclosed in the present invention.

[0031] First embodiment

[0032] A certain building complex is relatively dense, with high floors and important buildings. The relocation is difficult, expensive and time-consuming. Therefore, a protective coal pillar is left under the building complex to protect the ground buildings. The loose layer thickness of the building complex is 250m, the coal seam dip is 10°, the bedrock uphill movement angle β = 70°, the bedrock downhill movement angle γ = 70°, the bedrock strike movement angle δ = 70°, and the loose layer movement angle

[0033] refer to Figure 1-2 、 Figure 6The steps to determine the coal compression range of the building using the existing vertical section method are as follows: Determine the rectangular protected area a'b'c'd' through the outermost corner points of the building group, with a length of 400m and a width of 200m. Set a 20m wide enclosure belt 4-2, and determine that the length ad and bc of the enclosure belt along the strike is 440m long, and the length ab and cd along the dip is 240m wide. Figure 2 As shown in the figure, the lowest depth of the coal compression range determined based on the loose layer movement angle and the uphill movement angle is 376m, and the deepest depth of the coal compression range determined based on the loose layer movement angle and the downhill movement angle is 533m. The coal compression range is 903m long along the dip. Figure 1 As shown in the figure, the lowest depth of the coal compression range corresponding to the upper coal seam 8 is 376m, and the deepest depth of the coal compression range corresponding to the lower coal seam 8 is 533m. Based on the loose layer movement angle and strike movement angle, the length BC at the lowest depth of the coal compression range is 1032m, and the length AD at the deepest depth is 1146m. That is, the coal compression area reaches 983367m 2 , the coal seam is 5m thick and the density is 1.3 tons / m 3 The amount of coal pressed reached 6.392 million tons. Based on the price of 500 yuan per ton of coal, the economic loss was about 3.2 billion yuan.

[0034] As a comparison, the method for reducing the scope of coal pressure under buildings designed according to the present invention has the following specific steps: Figure 6 As shown, the first step is to draw two straight lines parallel to the strike and dip of the coal seam through the outermost corner of the structure group. The intersection of the four straight lines forms a rectangular protected area a'b'c'd' for the structure group, which is 400m long and 200m wide.

[0035] Step 2: Set up a 20m wide enclosure belt 4-2 around the rectangular protected area a'b'c'd' to form a rectangular ring enclosure belt abcd. The length ad and bc of the enclosure belt along the strike direction is 440m long, and the length ab and cd along the dip direction is 240m wide.

[0036] The third step, such as Figure 3-5 As shown, a first isolation grouting borehole 1 is constructed from the ground to 20m into the bedrock in the middle of the retaining belt 4-2. The first isolation grouting borehole 1 is vertical and has a length of 270m. A second isolation grouting borehole 2 is constructed from the ground to the top surface of the bedrock near the rectangular protected area 4-1 in the retaining belt 4-2. The intersection of the second isolation grouting borehole 2 and the top surface of the bedrock is located directly below the outer boundary of the retaining belt 4-2 and has a length of 251m. Cement slurry is injected into the stratum from the isolation grouting borehole to form a circumferential grouting isolation zone surrounding the rectangular protected area 4-1. The grouting isolation zone isolates the loose layer inside the rectangular protected area 4-1 from the loose layer outside the grouting isolation zone. The first isolation grouting borehole 1 and the second isolation grouting borehole 2 are arranged at intervals.

[0037] In this way, in the first isolation grouting borehole, an isolation section 1-1 is formed at the upper part of the intersection with the second isolation grouting borehole, and a support section 1-2 is formed at the lower part of the intersection with the second isolation grouting borehole; in the second isolation grouting borehole, a guarantee section 2-1 is formed at the upper part of the intersection with the first isolation grouting borehole, and a transition section 2-2 is formed at the lower part of the intersection with the first isolation grouting borehole; when the coal seam outside the protective coal pillar is mined, the inclined transition section 2-2 plays a transition role, forming a transition connection with the inclined bedrock movement angle, the support section 1-2 plays a supporting role for the transition section, and improves the stability of the transition section 2-2, the isolation section 1-1 plays a role in isolating the loose layer in the protected area from the external loose layer, and the guarantee section 2-1 plays a secondary isolation role.

[0038] Step 4: Project the four endpoints a, b, c, d of the rectangular enclosure 4-2 or the rectangular enclosure 4-2 vertically to the top surface of the bedrock to form four endpoints a1, b1, c1, d1 projected to the top surface of the bedrock; Figure 4 As shown, for the two endpoints b1 and c1 close to the upper part of the dip, first draw straight lines in the upward direction based on the bedrock upward movement angle β, forming two intersections with the coal seam, and the straight line passing through the two intersections is the first straight line; for the two endpoints a1 and d1 close to the lower part of the dip, first draw straight lines in the downward direction based on the bedrock downward movement angle γ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the second straight line; as shown Figure 3 As shown, for the two endpoints a1 and b1 close to one side of the strike, first draw a straight line in the direction of the strike based on the bedrock strike movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the third straight line; for the two endpoints c1 and d1 close to the other side of the strike, first draw a straight line in the direction of the other side of the strike based on the bedrock strike movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the fourth straight line; as shown Figure 6 As shown, the area enclosed by the intersection of the first straight line, the second straight line, the third straight line and the fourth straight line is the coal compression range A1B1C1D1 of the building group, that is, the protective coal pillar, wherein the first straight line intersects with the third straight line and the fourth straight line at B1 and C1 respectively, and the second straight line intersects with the third straight line and the fourth straight line at A1 and D1 respectively.

[0039] The fourth step can also be to determine the scope of coal pressure of buildings and structures by the following methods: Figure 3-4 、 Figure 6As shown, the four endpoints a, b, c, d of the rectangular enclosure 4-2 or the rectangular enclosure 4-2 are vertically projected to the top surface of the bedrock to form four endpoints a1, b1, c1, d1 projected to the top surface of the bedrock; for the two endpoints b1 and c1 close to the upper part of the inclination, first draw straight lines in the upward direction based on the bedrock uphill movement angle β to form two intersections with the coal seam, and then project these two intersections vertically to the top surface of the bedrock to form b2 and c2, and then project them in the opposite direction of the strike direction based on the bedrock strike movement angle δ. Draw a straight line to form two intersections B1 and C1 with the coal seam; for the two end points a1 and d1 near the lower part of the dip, first draw a straight line in the downward direction based on the downhill movement angle γ of the bedrock to form two intersections with the coal seam, and then project these two intersections vertically to the top surface of the bedrock to form a2 and d2, and then draw a straight line in the opposite direction of the strike based on the strike movement angle δ of the bedrock to form two intersections A1 and D1 with the coal seam. The coal compression range of the building group is the area enclosed by A1B1C1D1, that is, the protective coal pillar area.

[0040] In the fifth step, when mining the coal seam outside and near the building cluster pressure zone A1B1C1D1, fill boreholes 3 are drilled from the ground downward at the outer boundary of the retaining belt 4-2, with a length of approximately 20-200 meters. Multiple rows of fill boreholes can be constructed parallel to the boundary of the rectangular protected area 4-1. Filling material is injected into the tensile cracks in the loose layer through the fill boreholes 3 to fill the tensile cracks. The filling material is initially injected with loose materials such as sand, and later injected with a cementing material such as cement slurry.

[0041] like Figure 4 As shown, the lowest depth of the coal compression range determined by the present invention is 418m, and the deepest depth of the coal compression range determined based on the loose layer movement angle and the downhill movement angle is 486m. The coal compression range is 395m long along the dip. Figure 3 As shown in the figure, based on the loose layer movement angle and strike movement angle, the length B1C1 of the lowest depth of 418m (upper coal seam) in the coal compression range is 534m, and the length A1D1 of the deepest depth of 486m (lower coal seam) is 648m. That is, the coal compression area reaches 233445m 2 , the coal seam is 5m thick and the density is 1.3 tons / m 3 The coal compression volume was only 1.517 million tons, a savings of 4.875 million tons compared to the existing vertical profile method, representing only 24% of the coal compression volume determined by the existing vertical profile method. At a cost of 500 yuan per ton of coal, this reduced economic losses by approximately 2.44 billion yuan. Because the first isolation grouting borehole 1, the second isolation grouting borehole 2, and the backfill borehole 3 were essentially all constructed in the unconsolidated stratum, the total cost of drilling, grouting, and backfilling was only approximately 20 million yuan, ultimately reducing economic losses by 2.42 billion yuan.

[0042] Second embodiment

[0043] A mine is crossed by a ground railway track (structure) along its strike. Since the railway track cannot be relocated, a protective coal pillar is left under the railway track to protect the ground railway track. The railway track covers an area of ​​60m wide. The thickness of the loose layer in the area is 200m. The coal seam has a dip angle of 10°, the bedrock uphill movement angle β = 70°, the bedrock downhill movement angle γ = 70°, the bedrock strike movement angle δ = 70°, and the loose layer movement angle

[0044] refer to Figure 7 、 Figure 10 , according to the existing vertical section method, the general steps for determining the coal pressure range of the railway track are as follows: Since the railway track crosses the entire mine along the strike, the strike coal pressure range is the strike length of the entire mine, which is 5000m. What needs to be determined is the coal pressure range along the dip. The rectangular protected area a'b'c'd' is determined across the outermost boundary of the railway track, which is 5000m long and 60m wide. Since the railway track has a higher ability to resist sinking and deformation than buildings, a 10m wide retaining belt 5-2 is set, and the length ad and bc of the retaining belt along the strike are determined to be 5000m long, and the length ab and cd along the dip are 80m wide. As Figure 7 As shown in the figure, the lowest depth of the coal compression range determined based on the loose layer movement angle and the uphill movement angle is 335m, and the deepest depth of the coal compression range determined based on the loose layer movement angle and the downhill movement angle is 444m. The coal compression range is 627m long along the dip. That is, the coal compression area reaches 3135000m 2 , the coal seam is 5m thick and the density is 1.3 tons / m 3 The amount of coal pressed reached 20.378 million tons. Based on the price of 500 yuan per ton of coal, the economic loss reached about 10.19 billion yuan.

[0045] As a comparison, the method for reducing the scope of coal pressure under the structure designed according to the present invention has the following specific steps: Figure 10 As shown, the first step is to draw two straight lines parallel to the coal seam through the outermost corner of the railway track, and the intersection with the boundary of the mine to enclose the rectangular railway track protected area a'b'c'd', which is 5000m long and 60m wide;

[0046] Step 2: Set up a 10m wide enclosure belt around the periphery of the rectangular railway track protected area a'b'c'd' inclination, forming an enclosure belt abcd. The length ad and bc of the enclosure belt along the strike is 5000m, and the width ab and cd along the inclination is 80m.

[0047] The third step, such as Figure 8-9As shown, a first isolation grouting borehole 1 is constructed from the ground to 20m into the bedrock in the middle of the retaining belt 5-2. The first isolation grouting borehole 1 is vertical and has a length of 220m. A second isolation grouting borehole 2 is constructed from the ground to the top surface of the bedrock near the rectangular protected area 5-1 in the retaining belt 5-2. The intersection of the second isolation grouting borehole 2 and the top surface of the bedrock is located directly below the outer boundary of the retaining belt 5-2, with a length of 200.3m. Cement slurry is injected into the stratum from the isolation grouting borehole to form a grouting isolation zone in the protected area along the length direction of the railway track. The grouting isolation zone isolates the loose layer of the protected area of ​​the railway track from the loose layer outside the grouting isolation zone. The first isolation grouting borehole 1 and the second isolation grouting borehole 2 are arranged at intervals.

[0048] In this way, in the first isolation grouting borehole, an isolation section 1-1 is formed at the upper part of the intersection with the second isolation grouting borehole, and a support section 1-2 is formed at the lower part of the intersection with the second isolation grouting borehole; in the second isolation grouting borehole, a guarantee section 2-1 is formed at the upper part of the intersection with the first isolation grouting borehole, and a transition section 2-2 is formed at the lower part of the intersection with the first isolation grouting borehole; when the coal seam outside the protective coal pillar is mined, the inclined transition section 2-2 plays a transition role and forms a connection with the inclined bedrock movement angle, the support section 1-2 plays a supporting role for the transition section, improves the stability of the transition section 2-2, the isolation section 1-1 serves to isolate the loose layer in the protected area from the external loose layer, and the guarantee section 2-1 plays a secondary isolation role.

[0049] Step 4: Project the four endpoints a, b, c, d of the retaining belt 5-2 or the retaining belt 5-2 vertically to the top surface of the bedrock to form four endpoints a1, b1, c1, d1 projected to the top surface of the bedrock; Figure 8 、 10 As shown, for the two endpoints b1 and c1 close to the upper part of the dip, straight lines are drawn in the upward direction based on the upward movement angle β of the bedrock, forming two intersection points B1 and C1 with the coal seam. For the two endpoints a1 and d1 close to the lower part of the dip, straight lines are drawn in the downward direction based on the downward movement angle γ of the bedrock, forming two intersection points A1 and D1 with the coal seam, forming the coal compression range A1B1C1D1, that is, the protective coal pillar.

[0050] In the fifth step, when mining the coal seam outside and near the compressed coal range A1B1C1D1, fill boreholes 3 are drilled from the ground downward at the outer boundary of the retaining belt 5-2, with a length of approximately 20-180 meters. The fill boreholes are parallel to the length of the railway and are constructed in multiple rows. Filling material is injected into the tensile cracks in the loose layer through the fill boreholes 3 to fill the tensile cracks. The filling material is initially injected with loose materials such as sand, and later with cementing materials such as cement slurry.

[0051] like Figure 8As shown in the figure, the lowest depth of the coal compression range determined by the present invention is 368m, and the deepest depth of the coal compression range determined based on the loose layer movement angle and the downhill movement angle is 406m. The coal compression range is 221m long along the dip. Since the railway track crosses the entire mine along the strike, the strike coal compression range is the strike length of the entire mine, which is 5000m. In other words, the coal compression area reaches 1105000m 2 , the coal seam is 5m thick and the density is 1.3 tons / m 3 The coal compression volume was only 7.18 million tons, a savings of 13.198 million tons compared to the existing vertical profile method, representing only 35.2% of the coal compression volume determined by the existing vertical profile method. At a cost of 500 yuan per ton of coal, this reduced economic losses by approximately 6.6 billion yuan. Because the first isolation grouting borehole 1, the second isolation grouting borehole 2, and the backfill borehole 3 were essentially all constructed in the unconsolidated stratum, the total cost of drilling, grouting, and backfilling was only approximately 40 million yuan, ultimately reducing economic losses by 6.58 billion yuan.

[0052] Of course, the above description is only a preferred embodiment of the present invention, and the present invention is not limited to the above-mentioned embodiments. It should be noted that all equivalent substitutions and obvious deformation forms made by any technician familiar with this field under the guidance of this specification fall within the substantive scope of this specification and should be protected by the present invention.

Claims

1. A method for reducing the extent of coal pressure under buildings and structures under thick loose layer conditions, characterized in that: The steps include: Step 1: Draw two straight lines parallel to the strike and dip of the coal seam through the outermost corners of the structure or group of structures. The intersection of the four straight lines encloses the rectangular protected area of ​​the structure or group of structures. Step 2: Set a certain width of enclosure belt outside the rectangular protected area to form a rectangular ring enclosure belt abcd; The third step is to construct a first vertical isolation grouting borehole from the ground in the middle of the retaining belt to a certain depth in the bedrock, and construct a second isolation grouting borehole from the ground to the top surface of the bedrock near the rectangular protected area of ​​the retaining belt, with the intersection of the second isolation grouting borehole and the top surface of the bedrock being located directly below the outer boundary of the retaining belt; inject a cementing slurry into the stratum from the isolation grouting borehole to form a circumferential grouting isolation belt surrounding the rectangular protected area; Step 4: Project the four endpoints a, b, c, and d of the retaining belt vertically to the top surface of the bedrock, forming four endpoints a1, b1, c1, and d1 accordingly; for the two endpoints b1 and c1 close to the upper part of the inclination, first draw straight lines in the upward direction based on the uphill movement angle β of the bedrock, forming two intersections with the coal seam, and the straight lines passing through these two intersections are the first straight lines; for the two endpoints a1 and d1 close to the lower part of the inclination, first draw straight lines in the downward direction based on the downhill movement angle γ of the bedrock, forming two intersections with the coal seam, and the straight lines passing through these two intersections are the second straight lines. Line; for the two endpoints a1 and b1 close to one side of the strike, first draw a straight line in the direction of the strike based on the bedrock strike movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the third straight line; for the two endpoints c1 and d1 close to the other side of the strike, first draw a straight line in the direction of the other side of the strike based on the bedrock strike movement angle δ, forming two intersections with the coal seam, and the straight line passing through the two intersections is the fourth straight line; the area enclosed by the intersection of the first straight line, the second straight line, the third straight line, and the fourth straight line is the coal compression range A1B1C1D1; Alternatively, the coal compression range is determined in the following manner: the four endpoints a, b, c, and d of the retaining belt are vertically projected to the top surface of the bedrock to form four endpoints a1, b1, c1, and d1 respectively; for the two endpoints b1 and c1 close to the upper part of the dip, straight lines are first drawn in the upward direction based on the uphill movement angle β of the bedrock to form two intersections with the coal seam, and then these two intersections are vertically projected to the top surface of the bedrock to form b2 and c2, and then straight lines are drawn in the opposite direction of the strike based on the bedrock strike movement angle δ to form two intersections B1 and C1 with the coal seam; for the two endpoints a1 and d1 close to the lower part of the dip, straight lines are first drawn in the downward direction based on the downhill movement angle γ of the bedrock to form two intersections with the coal seam, and then these two intersections are vertically projected to the top surface of the bedrock to form a2 and d2, and then straight lines are drawn in the opposite direction of the strike based on the bedrock strike movement angle δ to form two intersections A1 and D1 with the coal seam to form the coal compression range A1B1C1D1; The fifth step is to mine the coal seam outside the coal compression range A1B1C1D1 and close to the coal compression range A1B1C1D1, construct filling boreholes from the ground downward at the outer boundary of the retaining belt, and inject filling materials into the tensile cracks of the loose layer through the filling boreholes.

2. The method for reducing the extent of coal pressure under buildings according to claim 1, characterized in that: In the second step, the entire enclosure is made uniform in width.

3. The method for reducing the extent of coal pressure under buildings according to claim 1, characterized in that: In the third step, the first isolation grouting borehole and the second isolation grouting borehole are arranged at intervals.

4. The method for reducing the extent of coal pressure under structures according to claim 1, characterized in that: In the fifth step, sand is injected in the initial stage and cementing material is injected in the later stage.

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