Method for repairing fractured stratum after coal seam sandstone roof mining by grouting

Abstract

The application provides a coal seam sandstone roof post-mining broken stratum grouting repair method, which comprises the following steps: determining a target grouting layer according to the broken stratum after the coal seam roof is mined; performing first grouting on a lower layer in the target grouting layer to form a cushion layer, the grouting material of the first grouting is aggregate slurry, and the grouting pressure is a first pressure; after the first grouting is completed, performing second grouting on an upper layer in the target grouting layer to form a sealing layer, the grouting material of the second grouting is rapid-setting slurry, and the grouting pressure is a second pressure; after the second grouting is completed, performing third grouting on a middle layer in the target grouting layer to form a partition layer, the grouting material of the third grouting is fine-grained slurry, and the grouting pressure is a third pressure, wherein the first pressure and the second pressure are both less than the third pressure. The coal seam sandstone roof post-mining broken stratum grouting repair method provided by the application is simple and convenient, safe, and resource-saving.

Description

Technical Field

[0001] This application relates to the field of coal mine management technology, and in particular to a method for grouting repair of fractured strata in the sandstone roof of a coal seam after mining. Background Technology

[0002] During coal mining, the water-conducting fracture zones in the roof strata often extend to the bottom of the overlying aquifer, causing water from the aquifer to flow along these fracture zones into the underground goaf or roadways, creating a potential for roof water inrush. In severe cases, this can lead to large-scale water inrushes in the mine. This not only threatens safe coal mine production but also causes significant loss of groundwater resources, resulting in environmental water resource damage and surface ecological problems. Without special measures, the aquitardant strata above the coal seam are often damaged after mining, significantly reducing their water-blocking properties and making it difficult to prevent aquifer water from seeping downwards.

[0003] To address the impact of coal mining disturbance on regional hydrogeology and protect valuable groundwater resources, the concept of water-conserving coal mining has been proposed. This involves preserving the integrity of aquifers and aquifer structures as much as possible while mining coal, thereby reducing mine drainage. One important approach is to implement artificial intervention and reinforcement of aquifers or aquitards before or after mining, such as grouting to fill fissures and rebuilding aquitards.

[0004] Existing water-conserving coal mining techniques include: mining protective layers, limiting mining height to control the height of water-conducting fracture zones, filling goaf areas, and pre- or post-mining grouting modifications to aquifers. However, under conditions where the roof aquifer is extremely water-rich or the water-blocking layer is weak, the effectiveness of a single measure is limited. In particular, traditional grouting techniques often employ methods such as curtain grouting around the mining face or injecting grout into the fractured roof strata in a single drilling operation. However, due to the complex structure of the roof's water-conducting fracture zones and the varying fracture sizes, single-stage, single-material grouting often yields minimal results. Large fractures are prone to rapid grout leakage and are difficult to fill, while fine fractures are difficult for high-viscosity grout to penetrate, resulting in unsatisfactory water-blocking effects after grouting. Meanwhile, the degree of rock strata damage and water-bearing characteristics vary at different depths: near the coal seam, there may be mining-induced delamination voids and large fractures; in the middle strata, there are primary inter-layer fractures and mining-induced propagation fractures; and in the upper part near the aquifer, there are mostly secondary joint networks and micro-fractures. If the same grout is used for continuous grouting from bottom to top, it is very likely that the lower grout will be lost to the goaf, and the upper grout will be diluted by water or even enter the aquifer, failing to form an effective water barrier at the intended location. Therefore, there is an urgent need for a grouting repair method that can improve grouting efficiency and reduce grout loss. Summary of the Invention

[0005] In view of this, the purpose of this application is to propose a method for grouting repair of fractured strata in the sandstone roof of coal seams after mining in order to solve the above-mentioned technical problems.

[0006] This application provides a method for grouting repair of fractured strata in a coal seam sandstone roof after mining, comprising: determining a target grouting layer based on the fractured strata in the coal seam roof after mining; performing a first grouting on the lower strata within the target grouting layer to form a cushion layer, wherein the grouting material for the first grouting is aggregate slurry and the grouting pressure is a first pressure; after the first grouting is completed, performing a second grouting on the upper strata within the target grouting layer to form a sealing layer, wherein the grouting material for the second grouting is quick-setting slurry and the grouting pressure is a second pressure; after the second grouting is completed, performing a third grouting on the middle strata within the target grouting layer to form a partition layer, wherein the grouting material for the third grouting is fine-grained slurry and the grouting pressure is a third pressure, wherein both the first pressure and the second pressure are less than the third pressure.

[0007] Furthermore, the lower layer, the middle layer, and the upper layer are stacked sequentially, with the lower layer having a thickness of 4m to 10m, the middle layer having a thickness of 16m to 34m, and the upper layer having a thickness of 2m to 6m.

[0008] Furthermore, the aggregate slurry has a particle size of 2 mm to 10 mm, the fine-particle slurry has a particle size of less than or equal to 5 mm, and the rapid-setting slurry has an initial setting time of 30 s to 60 s.

[0009] Furthermore, the first pressure is less than or equal to 1.8 MPa, the second pressure is less than or equal to 1 MPa, and the third pressure is less than or equal to 6 MPa.

[0010] Further, the step of forming a partition layer by performing a third grouting on the middle layer within the target grouting layer includes: performing filling grouting on the middle layer, wherein the grouting pressure for the filling grouting is a fourth pressure; after the filling grouting is completed, performing splitting grouting on the middle layer, wherein the grouting pressure for the splitting grouting is a fifth pressure; after the splitting grouting is completed, performing compaction grouting on the middle layer to form the partition layer, wherein the grouting pressure for the compaction grouting is a sixth pressure, wherein the fourth pressure is less than the fifth pressure and the sixth pressure.

[0011] Furthermore, the fourth pressure is 1 MPa to 3 MPa, the fifth pressure is 3 MPa to 5 MPa, and the sixth pressure is 4 MPa to 6 MPa.

[0012] Furthermore, the grouting material for the filling grouting is a high-viscosity slurry with added aggregate, wherein the aggregate has a particle size of 2 mm to 5 mm and the aggregate content is 10% to 20%; the grouting material for the splitting grouting is a high-viscosity clay-cement slurry or an anti-erosion long-flowing cement slurry; and the grouting material for the compaction grouting is an ultrafine sulfoaluminate cement slurry or a high-viscosity clay-cement slurry.

[0013] Furthermore, the grouting flow rate of the filling grout is 40L / min to 80L / min, the grouting flow rate of the fracturing grout is 30L / min to 80L / min, and the grouting flow rate of the compaction grout is less than or equal to 30L / min.

[0014] Furthermore, the conditions for completing each grouting operation are that the grouting pressure reaches the preset pressure, the grouting flow rate is less than or equal to the preset flow rate, and the pressure stabilization time reaches the preset time.

[0015] Furthermore, the method for grouting and repairing the fractured strata after mining of the sandstone roof of the coal seam also includes: after the third grouting is completed, when the water inflow of the coal seam roof is less than or equal to the preset water inflow, the grouting and repair of the fractured strata is completed.

[0016] As can be seen from the above, this application provides a method for grouting repair of fractured strata in the sandstone roof of a coal seam after mining, comprising: determining the target grouting layer based on the fractured strata in the coal seam roof after mining; performing a first grouting on the lower strata within the target grouting layer to form a cushion layer, wherein the grouting material for the first grouting is aggregate slurry and the grouting pressure is a first pressure; after the first grouting is completed, performing a second grouting on the upper strata within the target grouting layer to form a sealing layer, wherein the grouting material for the second grouting is quick-setting slurry and the grouting pressure is a second pressure; after the second grouting is completed, performing a third grouting on the middle strata within the target grouting layer to form a partition layer, wherein the grouting material for the third grouting is fine-grained slurry and the grouting pressure is a third pressure, wherein both the first pressure and the second pressure are less than the third pressure. The first grouting creates a cushion layer at the bottom to prevent large amounts of grout from leaking into the mining-induced fractures or goaf below. The second grouting creates a sealing layer at the top, quickly sealing the upper fractures of the roof to prevent grout from leaking upwards during intermediate grouting. The third grouting creates a partition layer in the middle, cementing the water-conducting fractures into a dense rock mass with high compressive strength and low permeability. This bottom-up-middle grouting method, combined with different grouting materials, has been tested and proven to effectively plug water-conducting fractures in the roof and rebuild the aquitard, achieving water-conserving coal mining and mine water hazard prevention. It also effectively reduces grout loss and lowers costs. This post-mining grouting repair method for fractured strata in coal seams and sandstone roofs is simple, convenient, safe, and resource-saving. Through multi-layered, multi-material grouting, it restores the integrity and low permeability of the fractured roof rock mass, thereby protecting the overlying aquifer from large-scale water leakage due to mining activities. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the grouting repair method for the post-mining fractured strata of the sandstone roof in the embodiments of this application;

[0019] Figure 2 This is a schematic diagram of the structure for grouting repair of the fractured strata in the coal seam roof after mining, as described in this application embodiment.

[0020] Figure 3 This is a schematic diagram of the structure for the third grouting in an embodiment of this application.

[0021] Attached diagram labels: 1. Coal seam roof; 2. Target grouting layer; 3. Subbase; 4. Sealing layer; 5. Interlayer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0023] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] Existing water-conserving coal mining techniques include: mining protective layers, limiting mining height to control the height of water-conducting fracture zones, filling goaf areas, and pre- or post-mining grouting modifications to aquifers. However, under conditions where the roof aquifer is extremely water-rich or the water-blocking layer is weak, the effectiveness of a single measure is limited. In particular, traditional grouting techniques often employ methods such as curtain grouting around the mining face or injecting grout into the fractured roof strata in a single drilling operation. However, due to the complex structure of the roof's water-conducting fracture zones and the varying fracture sizes, single-stage, single-material grouting often yields minimal results. Large fractures are prone to rapid grout leakage and are difficult to fill, while fine fractures are difficult for high-viscosity grout to penetrate, resulting in unsatisfactory water-blocking effects after grouting. Meanwhile, the degree of rock strata damage and water-bearing characteristics vary at different depths: near the coal seam, there may be mining-induced delamination voids and large fractures; in the middle strata, there are primary inter-layer fractures and mining-induced extended fractures; and in the upper part near the aquifer, there are mostly secondary joint networks and micro-fractures. If the same grout is used for continuous grouting from bottom to top, it is very likely that the lower grout will be lost to the goaf, and the upper grout will be diluted by water or even enter the aquifer, making it impossible to form an effective water barrier at the intended location.

[0025] Therefore, it is necessary to develop a layered and graded grouting method for water-conducting fracture zones in mine roofs. By grouting the fractured rock mass in layers, and using different grout materials and processes for different fracture sizes within each layer, all levels of fractures can be effectively and densely filled, thereby maximizing the restoration of the roof's water-tightening performance. Key technical issues that this method needs to address include: how to prevent grout loss to non-target areas (such as lower goafs or upper aquifers) during grouting; how to design appropriate grout formulations and grouting parameters for fractures of different sizes; and how to determine the criteria for grout saturation termination.

[0026] The following describes specific embodiments in conjunction with... Figures 1 to 3 The technical solution of this application will be described in detail below.

[0027] Some embodiments of this application provide a method for grouting repair of fractured strata in the sandstone roof of a coal seam after mining, such as... Figure 1 As shown, the process includes the following steps: S1, determining the target grouting layer based on the fractured strata after mining of the coal seam roof.

[0028] After coal seam mining, fractures will form in the sandstone roof, creating a broken stratum. Surveying the broken strata after mining can determine the extent of water-conducting fracture zones. The uppermost aquitard within this zone can be used as the target grouting layer. Surveying can employ methods such as borehole television testing or fiber optic sensor testing. Test results, for example, include borehole television images, which visually indicate the actual extent of the water-conducting fracture zone. Alternatively, fiber optic sensing can detect fracture signals; the continuity of these signals indicates whether the water-conducting fracture zone has developed to the main aquifer.

[0029] The target grouting layer is the layer where grouting will be carried out subsequently. Grouting can be performed using surface directional drilling technology to arrange the grouting holes. The borehole diameter can be, for example, 90 mm to 130 mm, and the hole depth can reach the target grouting layer. Multiple vertical grouting holes can be used, with an overlap of 0.5 m to 1.0 m between adjacent grouting holes to ensure that the grouting layers are interconnected and form a unified whole.

[0030] S2. A first grouting is performed on the lower layer within the target grouting layer to form a cushion layer. The grouting material for the first grouting is aggregate slurry, and the grouting pressure is a first pressure.

[0031] The thickness of the lower layer is, for example, 4m to 10m, the particle size of the aggregate slurry is, for example, 2mm to 10mm, and the first pressure is less than or equal to 1.8MPa.

[0032] In the lower strata, a grouting material mainly composed of aggregate slurry is injected into the branch grouting holes. The aggregate slurry contains hard aggregates (crushed gangue, coarse sand, etc.) as well as stone powder, fly ash, and other components. When the water pressure is greater than 2 MPa, cementitious materials such as cement can also be added at a mass fraction of 8% to 15%. Specifically, the aggregate slurry used includes 30 to 70 parts by weight of crushed gangue or coarse sand aggregate, 20 to 40 parts by weight of clay, 20 to 40 parts by weight of fly ash, and 0 to 10 parts by weight of cement. The water-cement ratio is, for example, 0.8:1 to 1.5:1. It has the characteristics of high initial viscosity, low strength after solidification, and a certain degree of flexibility to adapt to the deformation of the bottom mining-induced fractures and prevent slurry leakage.

[0033] The initial pressure can be set in stages. During the initial filling stage, the initial pressure can be 0.4 MPa to 0.8 MPa, allowing the grout to "flow by itself" to fill pores and large cracks and form bridges. During the stabilization stage, the initial pressure can be 0.8 MPa to 1.2 MPa, continuously replenishing the grout and pushing the aggregate to fill deeper. During the final pressure locking stage, the initial pressure can be 1.2 MPa to 1.8 MPa, compacting the aggregate pile to form a solidified cushion layer to prevent grout and water from leaking to lower layers.

[0034] S3. After the first grouting is completed, a second grouting is performed on the upper layer within the target grouting layer to form a sealing layer. The grouting material for the second grouting is a quick-setting grout, and the grouting pressure is the second pressure.

[0035] The thickness of the upper layer is, for example, 2m to 6m, the initial setting time of the quick-setting grout is, for example, 30s to 60s, and the second pressure is less than or equal to 1MPa.

[0036] Inject grouting material, mainly quick-setting grout, into the branch grouting holes in the upper layer. The quick-setting grout can be a single-component grout with added quick-setting agent to cement grout or a cement-water glass double-component grout. For example, when using cement-quick-setting agent single-component grout, the quick-setting agent dosage is 3% to 8% of the cement weight, and the initial setting time is about 30 seconds. When using cement-water glass double-component grout, the water-cement ratio of cement grout is 1:1 to 1.5:1, the volume ratio of cement grout to water glass is 2:1 to 1:1, and the initial setting time is 10 seconds to 60 seconds, which can quickly gel and seal leaks.

[0037] Slow grouting is performed under a lower second pressure, allowing the grout to fill and solidify immediately, blocking the cracks in the upper part of the top slab and forming a top cushion layer to prevent the grout from flowing upward into the overlying aquifer during grouting in the middle layers.

[0038] S4. After the second grouting is completed, a third grouting is performed on the middle layer within the target grouting layer to form a partition layer. The grouting material for the third grouting is fine-grained slurry, and the grouting pressure is the third pressure. The first pressure and the second pressure are both less than the third pressure.

[0039] The thickness of the middle layer is, for example, 16m to 34m, the particle size of the fine slurry is less than or equal to 5mm, which is smaller than the particle size of the aggregate slurry, and the third pressure is less than or equal to 6MPa, forming a solid interlayer.

[0040] The intermediate layer can complete the full coverage of "coarse-medium-fine" cracks and the evolution of intensity gradient within the same space. It can use a three-stage slurry material of "dilute-thick-fast" to gradually densify the material, so that the early high-permeability cracks are first penetrated and sealed, and then gradually split and diffused, and finally compacted into a fine network.

[0041] The grouting process in this embodiment is as follows: Figure 2As shown, the lower cushion layer is located at the bottom of the impermeable layer (target grouting layer), filling larger cavities and bottom fissures, providing a base and support for the subsequent interlayer, cementing the bottom fractured rock mass into a foundation cushion layer, preventing grout leakage, and initially stabilizing the bottom rock mass. After solidification, the cushion layer reinforces the top bedrock fissures, improves the bearing capacity of the surrounding rock, and creates a stable bearing surface for the interlayer. The upper sealing layer is located at the top of the impermeable layer, sealing the top boundary fissures, cutting off the overlying aquifer, forming a "counter-pressure cap," and preventing the high-pressure grout in the middle layer from flowing upwards. The middle interlayer bears the main water pressure resistance, and through a relatively thick grouting consolidation zone, it cements the water-conducting fissures into a dense rock mass. The solidified main layer has high compressive strength and low permeability coefficient. This layered structure aims to "support from below and seal from above, concentrate the main layer": the lower layer stabilizes the foundation, the upper layer seals the top edge, and the thick middle layer stops the water.

[0042] This embodiment follows a grouting sequence of "bottom → top → middle," conforming to the optimal mechanism of fluid-structure interaction and seepage control: low-pressure aggregate grout first fills the large cracks and voids at the bottom (5mm to 20mm), forming a "bottom plate" with flexible support to block downward seepage; rapid-setting grout quickly sets at the top, sealing the top boundary cracks, severing the connection with the overlying aquifer, forming a "back pressure cover" to prevent the upward escape of the high-pressure grout in the middle layer. After the establishment of the upper and lower non-permeable boundaries, the subsequent high-pressure fine-grained grout in the middle layer diffuses in a confined manner within the closed cavity, splitting the crack network and instantly solidifying to achieve complete filling and densification of the fracture system.

[0043] If the grouting sequence is "bottom → middle → top", there will be a lack of top resistance. During high-pressure grouting of the middle layer, the grout can easily seep upwards along the cracks into the aquifer. The subsequent upper sealing layer can only fill the cavity and cannot sever the connection with the overlying aquifer. If the grouting sequence is "top → middle → bottom", the lower cavity will not be pre-filled, and the grout in the middle layer will flow downwards, making it difficult to form a complete water-resistant zone.

[0044] Furthermore, the selection of grouting materials for each layer in this embodiment is also optimized. If a quick-setting grout is used in the lower layer, it may cause "clogging" when encountering coarse cracks, leaving the internal pores empty. If an aggregate grout is used in the middle layer, large particles may be unable to enter the 0.1mm to 1mm micro-cracks, resulting in high permeability of the interlayer, easy "bridging" and early blockage under pressure, and poor pressure resistance. If a fine-grained grout is used in the upper layer, the grout will set slowly, be diluted by the backflush of the upper water head, prolong the sealing time, force the middle layer grouting window to be delayed, have low early strength, and may be ruptured by the high pressure of the middle layer, leading to upward flow and other problems.

[0045] This post-mining grouting repair method for fractured strata in coal seams and sandstone roofs effectively prevents grout loss. By pre-constructing the bottom and top, the area to be reinforced is sealed off vertically, creating a relatively enclosed grouting space and preventing the unrestricted diffusion of grout from the middle layer to both ends. This not only improves grout utilization and reduces material waste but also ensures that the grout can fully function within the target fracture zone.

[0046] This post-mining grouting repair method for fractured strata in coal seams and sandstone roofs can preserve aquifer water resources. By rebuilding the roof aquitard, it can significantly reduce the amount of water leakage downwards from the aquifer within the mining-affected area, keeping mine water inflow within a safe and controllable range. From an environmental and resource perspective, this effectively protects the water reserves of the overlying aquifer, preventing severe damage to the groundwater system due to mining, and achieving a win-win situation for coal and water resources.

[0047] This post-mining grouting repair method for fractured strata in coal seam sandstone roofs achieves a coupling of strength and permeability. The high thickness and multi-stage consolidation of the central interlayer design ensure optimal compressive and permeability resistance. The upper sealing layer emphasizes rapid setting and low permeability, while the lower cushion layer emphasizes bridging and load-bearing capacity with relatively relaxed permeability requirements. This method effectively solves the problem of reconstructing aquifers in coal seam roof aquifers, protecting the groundwater environment while ensuring safe coal mine production.

[0048] In some embodiments, the step of forming a partition layer by performing a third grouting on the middle layer within the target grouting layer includes:

[0049] S401. Grouting is performed on the middle layer, and the grouting pressure is the fourth pressure.

[0050] Filling grouting targets wider mining-induced fractures and bedding separation fractures in water-conducting fracture zones caused by coal mining. The grouting material for filling grouting is, for example, a high-viscosity slurry with added aggregates such as crushed gangue and coarse sand, with a particle size of 2mm to 5mm. These finer particles facilitate secondary compaction within the sealed cavity. The aggregate content is, for example, 10% to 20%, which improves rheology and preserves space for subsequent fracturing; the high content primarily acts as a bridging agent. The grouting flow rate is, for example, 40L / min to 80L / min, and the pressure is, for example, 1MPa to 3MPa, which can quickly fill large fractures and cavities and reduce water inflow. After injecting a certain amount of grout, if the grout absorption rate does not decrease, the grout concentration can be gradually increased to enhance the plugging effect.

[0051] S402. After the filling grouting is completed, the middle layer is subjected to splitting grouting, and the grouting pressure of the splitting grouting is the fifth pressure.

[0052] Fracture grouting targets primary structural fractures and medium-width interlayer fractures in the top strata. The grouting material used is, for example, a high-viscosity clay-cement grout or an erosion-resistant, long-flowing cement grout, which further opens and connects the fine fractures in the rock strata and allows the grout to penetrate along the bedding depth. The grouting flow rate is, for example, 30 L / min to 80 L / min, and the fifth pressure is, for example, 3 MPa to 5 MPa. Grouting is continued until the pressure begins to rise and the grout absorption significantly decreases. If the pressure fails to rise during the process, intermittent grouting (repeatedly stopping and starting) or a fast-setting two-component grout can be used to accelerate the sealing process.

[0053] S403. After the splitting grouting is completed, the middle layer is compacted by grouting to form the interlayer. The grouting pressure of the compaction grouting is the sixth pressure, the fourth pressure is less than the fifth pressure, and the fifth pressure is less than the sixth pressure.

[0054] The compaction grouting process addresses residual network-like secondary fractures and micro-fractures within the intermediate layer. The grouting material used is, for example, ultrafine sulfoaluminate cement grout or high-viscosity clay-cement grout, injected as a fine-grained, high-strength material for final compaction and reinforcement. The grouting flow rate is less than or equal to 30 L / min, and the sixth pressure is, for example, 4 MPa to 6 MPa. This allows the fine grout to penetrate and fill even the smallest-scale fractures under high pressure, compacting the surrounding rock mass. Grouting continues until the pressure at this stage reaches the designed final pressure and stabilizes.

[0055] The third grouting is specifically as follows: Figure 3 As shown, grouting was performed in stages to seal fractures across the entire range of the intermediate strata. This allowed for targeted treatment of fractures of all sizes: large fractures were rapidly filled and bridged by aggregate grout, significantly reducing the permeability of water-conducting channels; medium-sized fractures were further opened and filled with grout under high pressure, eliminating potential leakage channels; and micro-fractures were compacted by high-pressure fine grout, eliminating residual seepage networks in the rock mass. Compared to a single-stage grouting method, this approach achieves more thorough and uniform filling and compaction of water-conducting fracture zones, resulting in superior grouting and water-stopping effects.

[0056] The first stage of the third grouting process targets larger fractures and bedding separation joints generated by mining, using high-viscosity grout mixed with aggregate for filling and grouting. The second stage targets primary fractures and fine interlayer fractures in the surrounding rock, employing a splitting grouting technique to force the grout into and extend it to the depth of the fractures. The third stage targets network-like secondary fractures and micro-fractures, using high-pressure compaction grouting to allow fine-grained grout to penetrate and compact the fractures. Grouting construction involves directional drilling on the ground, with different grout ratios selected for different layers and stages. The grouting pump flow rate and grout specific gravity are dynamically adjusted to ensure that the grout fully penetrates into each level of fracture and solidifies in a timely manner to stop water flow. The upper sealing layer and lower cushion layer limit the vertical flow loss of the grout, while the intermediate interlayer compacts the fractures in stages. The combination of these three layers achieves comprehensive filling and reinforcement of the water-conducting fracture zone in the roof, rebuilding the roof aquitard, and effectively stopping water flow and protecting the water resources of the overlying aquifer from mining disturbance.

[0057] In addition, during the three-stage grouting construction in the middle layer, the first stage was carried out every 20m. 3 up to 50m 3 The slurry concentration was gradually increased by one level, and the slurry density increased from approximately 1.20 g / cm³. 3 Increased to approximately 1.50 g / cm³ 3 The second stage mainly uses clay-modified cement grout for single-liquid grouting. When the cumulative amount of grout injected in the second stage exceeds the design value or the pressure is difficult to increase, cement-water glass double-liquid grout is used to seal the remaining channels. The ultrafine cement used in the third stage has a water-cement ratio of 0.5:1 to 1:1 to ensure that it can penetrate the finest cracks and solidify into a high-strength solidified body.

[0058] In some embodiments, the completion conditions for each grouting operation are that the grouting pressure reaches a preset pressure, the grouting flow rate is less than or equal to a preset flow rate, and the pressure stabilization time reaches a preset time.

[0059] The termination criteria for the first, second, and third grouting, as well as filling grouting, fracturing grouting, and compaction grouting, can be determined according to the following conditions: the grouting pressure reaches the preset pressure, which is generally 1.5 to 2.0 times the hydrostatic pressure of the roof; the grouting flow rate is less than or equal to the preset flow rate, which is, for example, 30 L / min; and the pressure stabilization time reaches the preset time, which is, for example, 20 to 30 minutes. If these conditions are met, it is considered that the rock mass fissures in that section have been basically filled and saturated, and grouting can be stopped and the borehole sealed.

[0060] In addition, the grouting pump used has a rated maximum pressure of not less than 5 MPa and a rated maximum flow rate of not less than 70 L / min; the water glass liquid pump has a rated maximum pressure of not less than 5 MPa and a rated maximum flow rate of not less than 40 L / min; the grouting pipeline uses steel wire reinforced high-pressure hoses, and the orifice pressure and grout flow rate are monitored in real time during construction so as to adjust the grouting parameters according to the changes in pressure and flow rate.

[0061] In some embodiments, the post-mining grouting repair method for fractured strata in the sandstone roof of a coal seam further includes:

[0062] S5. After the third grouting is completed, when the water inflow of the coal seam roof is less than or equal to the preset water inflow, the grouting repair of the fractured strata is completed.

[0063] After the third grouting is completed, the water pressure and inflow of the roof aquifer can be monitored through a dedicated detection borehole or mine drainage system. If the inflow is found to be less than or equal to the preset inflow, for example, 5 m³, the system will detect any changes. 3 If the flow rate is / h, it means the sealing is effective; if the flow rate is found to be greater than the preset flow rate, it means that there are still weak sections in the target grouting layer, and supplementary grouting treatment is required.

[0064] This post-mining grouting repair method for fractured strata in coal seams and sandstone roofs offers safe and efficient construction. Utilizing surface directional drilling technology, it eliminates the need for underground high-risk areas to reinforce and treat the roof, reducing construction risks. The multi-layer grouting mode using directional drilling improves construction efficiency and reduces costs. The grouting materials are mainly cement and industrial waste (fly ash, gangue, etc.), which are low-cost and utilize industrial waste resources, resulting in economic and environmental benefits. Through online monitoring and phased control, the construction process is highly controllable, and quality standards are clearly defined.

[0065] It should be noted that the above description describes some embodiments of this application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0066] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application (including the claims) is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in the details for the sake of brevity.

[0067] Additionally, to simplify the description and discussion, and to avoid obscuring the embodiments of this application, well-known power / ground connections to other components may or may not be shown in the provided drawings. Furthermore, the apparatus may be illustrated in block diagram form to avoid obscuring the embodiments of this application, and this also takes into account the fact that the details of implementation of these block diagram apparatuses are highly dependent on the platform on which the embodiments of this application will be implemented (i.e., these details should be entirely within the understanding of those skilled in the art). While specific details have been set forth to describe exemplary embodiments of this application, it will be apparent to those skilled in the art that the embodiments of this application may be implemented without these specific details or with variations thereof. Therefore, these descriptions should be considered illustrative rather than restrictive.

[0068] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. The embodiments of this application are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A method for grouting repair of fractured strata in the sandstone roof of a coal seam after mining, characterized in that, include: Determine the target grouting layer based on the fractured strata in the coal seam roof after mining; The lower layer within the target grouting layer is grouted to form a cushion layer. The grouting material for the first grouting is aggregate slurry, which contains hard aggregate, stone powder, and fly ash. The grouting pressure is a first pressure. After the first grouting is completed, a second grouting is performed on the upper layer within the target grouting layer to form a sealing layer. The grouting material for the second grouting is a quick-setting grout, which is either a single-liquid grout with a quick-setting agent added to cement grout or a cement-water glass double-liquid grout. The grouting pressure is the second pressure. After the second grouting is completed, a third grouting is performed on the middle layer within the target grouting layer to form a partition. The grouting material for the third grouting is fine-grained grout, and the grouting pressure is the third pressure. The lower layer, the middle layer, and the upper layer are stacked sequentially. The thickness of the lower layer is 4m to 10m, the thickness of the middle layer is 16m to 34m, and the thickness of the upper layer is 2m to 6m. The particle size of the fine-grained grout is smaller than that of the aggregate grout, which has a particle size of 2mm to 10mm. The particle size of the fine-grained grout is less than or equal to 5mm. The initial setting time of the quick-setting grout is 30s to 60s. The first pressure and the second pressure are both less than the third pressure. The first pressure is less than or equal to 1.8MPa, the second pressure is less than or equal to 1MPa, and the third pressure is less than or equal to 6MPa.

2. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 1, characterized in that, The step of forming a third grouting layer in the middle layer within the target grouting layer includes: The middle layer is filled with grout, and the grouting pressure is the fourth pressure. After the filling grouting is completed, the middle layer is subjected to splitting grouting, and the grouting pressure of the splitting grouting is the fifth pressure; After the splitting grouting is completed, the middle layer is compacted by grouting to form the interlayer. The grouting pressure of the compaction grouting is the sixth pressure, and the fourth pressure is less than the fifth pressure, which is less than the sixth pressure.

3. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 2, characterized in that, The fourth pressure is 1 MPa to 3 MPa, the fifth pressure is 3 MPa to 5 MPa, and the sixth pressure is 4 MPa to 6 MPa.

4. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 2, characterized in that, The grouting material for the filling grouting is a high-viscosity slurry with added aggregate, wherein the aggregate has a particle size of 2 mm to 5 mm and the aggregate content is 10% to 20%; the grouting material for the splitting grouting is a high-viscosity clay-cement slurry or an anti-erosion long-flowing cement slurry; the grouting material for the compaction grouting is an ultrafine sulfoaluminate cement slurry or a high-viscosity clay-cement slurry.

5. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 2, characterized in that, The grouting flow rate for the filling grouting is 40 L / min to 80 L / min, the grouting flow rate for the splitting grouting is 30 L / min to 80 L / min, and the grouting flow rate for the compaction grouting is less than or equal to 30 L / min.

6. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 1, characterized in that, The conditions for completing each grouting operation are that the grouting pressure reaches the preset pressure, the grouting flow rate is less than or equal to the preset flow rate, and the pressure stabilization time reaches the preset time.

7. The method for grouting and repairing fractured strata in the sandstone roof of a coal seam according to claim 1, characterized in that, Also includes: After the third grouting is completed, when the water inflow from the coal seam roof is less than or equal to the preset water inflow, the grouting repair of the fractured strata is completed.

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