Top plate series support method for crossing fault and preventing roof fall

Abstract

The invention relates to the field of mining engineering, and discloses a top plate series support method for crossing a fault and preventing roof caving, which comprises the following steps: before a stope face advances to the fault, obtaining fault occurrence and a fracture range through detection, and planning a support path which penetrates through a fracture zone and goes deep into a deep stable rock stratum; a high-strength hollow grouting anchor cable is installed in the drill hole, full-length under-pressure grouting is carried out, and the loose rock mass is cemented through grout; and after the slurry is solidified, axial pre-tightening force is applied, and the broken rock stratums are connected in series and pressed tightly to form a combined bearing structure. According to different fault fall and stoping working conditions, a bidirectional series connection and deep extension dynamic compensation or side protection linkage strategy is adopted, and a hydraulic support under-pressure top rubbing measure is adopted in a matched mode. Through rock mass modification and deep and shallow part cooperative bearing, the problems of fault fracture zone anchoring foundation deficiency and support failure are solved, surrounding rock deformation is effectively controlled, roof fall accidents are prevented, and stoping safety is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of mining engineering technology, specifically to a method for cascade roof support for crossing faults and preventing roof collapse. Background Technology

[0002] Coal mining often encounters geological structures such as faults. The surrounding rock in fault fracture zones typically exhibits characteristics such as well-developed joints and fissures, loose and fractured rock masses, and weak interlayer bonding. During longwall mining across faults, to ensure smooth progress, operating procedures often employ methods such as roof breaking or floor penetration to force passage. Currently, roof control technology in fault fracture zones mainly relies on increasing support strength, such as increasing the density of anchor bolts, erecting I-beam supports, or simply relying on the high initial support force of hydraulic supports to passively support the roof.

[0003] However, the existing support technologies have limitations in complex geological conditions such as fault fracture zones. Firstly, because the roof rock structure in the fault-affected zone is already damaged, exhibiting a discontinuous, loose medium state, traditional end-anchoring or extended anchoring methods mainly rely on mechanical friction or resin bonding between the anchoring section and the borehole wall. In loose, fractured surrounding rock, the borehole wall integrity is poor, the anchoring agent is easily lost, and it is difficult to form an effective bond, resulting in unreliable anchoring foundations. The support components cannot effectively transfer the self-weight load of the shallow fractured rock layers to the deep, stable rock layers, making overall collapse highly likely.

[0004] Secondly, existing support systems are insufficient to effectively constrain fractured rock masses. The fractured rock blocks are discrete, and passive suspension or bottom support alone is insufficient to limit expansion deformation and delamination, failing to establish sufficient normal stress within the rock layers to increase interlayer frictional resistance. The lack of active axial compression prevents the loose, fractured rock blocks from forming a self-supporting composite structure, making the roof strata highly susceptible to progressive failure and plastic zone expansion under its own weight and mining stress.

[0005] Furthermore, traditional support designs often employ a single vertical arrangement, failing to adequately consider the shear effects of the fault slip surface and the dynamic damage to the support structure caused by the coal mining machine's roof-breaking operation. Standard vertically arranged anchor cables are insufficient to resist the shear forces generated by fault activation, making them prone to shear breakage. Simultaneously, when the coal mining machine performs roof-breaking operations, it directly cuts off parts of the support components, resulting in insufficient effective anchorage length. Existing technologies lack adaptive designs for shear slippage and cutting losses, making the support system prone to failure during critical periods when crossing faults, thereby triggering safety accidents such as roof falls or rockbursts. Summary of the Invention

[0006] This invention provides a method for tandem roof support to prevent roof falls when crossing fault zones. It aims to solve technical problems such as roof falls, spalling, and support failure caused by loose and fractured roof rock and weak interlayer bonding when the longwall face crosses a fault fracture zone. This method achieves effective control of the fractured surrounding rock and ensures the safe operation of longwall mining by constructing an integrated support system that incorporates rock mass modification, long-span tandem support, active constraint, and dynamic coordination.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides a method for tandem roof support for crossing faults and preventing roof collapse, which mainly includes advanced detection and assessment, hole location arrangement and drilling, installation of tandem components and full-length grouting, application of pre-tightening force and initial support force, and coordination measures during fault mining.

[0008] First, addressing the uncertainty of geological conditions in fault areas, this invention employs advanced detection methods to obtain fault orientation elements and the fracture range of the overlying strata. By combining physical drilling and core sampling with digital imaging, the location of fault fracture zones or delamination areas is accurately identified, and the theoretical radius of the overlying fracture zone is determined accordingly. This process provides a geological basis for the design of subsequent support parameters, ensuring that the support structure can traverse the plastic failure zone and penetrate deep into the stable strata of the elastic zone.

[0009] Secondly, based on the detection results, a series support path is planned to construct a physical connection framework. Holes are drilled along the determined path, penetrating the top strata of the fault fracture zone and reaching deep, stable rock layers. For loose, fractured, or muddy areas, wall-supported drilling or staged reaming techniques are employed to ensure borehole quality. On this basis, high-strength hollow grouting anchors and grout stoppers are installed into the borehole, and pressurized grouting is performed along the entire length from the bottom to the opening using the central channel of the anchor. This step uses grout to fill the rock fractures and wrap the anchor rod. After the grout solidifies, it binds the loose, fractured rock blocks into a whole, improving the strength and integrity of the surrounding rock and forming a composite load-bearing structure integrating rock, grout, and the rod.

[0010] Next, after the grout has solidified to the design strength, axial preload is applied to the high-strength hollow grouting anchor cables. By installing trays and locking devices, and employing a staged loading and over-tensioning locking process, the preload is effectively transferred to the series-connected fractured rock strata. This process transforms the fractured rock mass, which was originally in a passive stress state, into a load-bearing beam or arch subjected to active axial pressure. The axial compressive force is used to suppress delamination and displacement between rock strata, achieving series anchoring of the fractured rock mass into deeper stable rock strata.

[0011] Finally, dynamic coordination measures are adopted when the longwall face passes through areas with tandem supports. The integrity of the roof is maintained by adjusting the cutting parameters of the coal mining machine and the support status of the hydraulic supports. In particular, the use of pressurized roof-scraping support shifting and controlling the minimum initial support force can balance the direct roof weight and overcome the unloading effect of the anchor cable preload, preventing support failure caused by mining activities.

[0012] As a further improvement to the technical solution of this invention, targeted enhancement strategies have been formulated for different fault displacements and mining conditions: When the fault displacement is large, a two-way series structure is adopted. This includes a vertical suspension group and an inclined collapsing group. The vertical suspension group mainly bears the self-weight load of the fractured rock strata on the top plate; the inclined collapsing group sets the deflection angle according to the fault dip angle and the optimized shear resistance range, so that it passes through the main slip surface of the fault fracture zone and penetrates into the intact rock mass of the fault's opposing plate, thereby establishing a shear-resistant connection structure between the two plates of the fault and effectively curbing the slip failure caused by fault activation.

[0013] When the longwall face is in the area of ​​full-rock roof breaking, a deep extension and advanced reinforcement strategy is adopted. Dynamic compensation is reserved in the length design of high-strength hollow grouting anchor cables to ensure that after the coal mining machine cuts off part of the roof rock, the remaining effective anchor length of the anchor cables can still penetrate into the stable rock layer above the cut surface, avoiding failure of the support structure due to roof breaking operations.

[0014] When the longwall face is in the undercut zone, a strategy of combined side protection and root reinforcement is adopted. By adjusting the installation angle of the anchor cables close to the coal face and cooperating with the hydraulic support side protection plates, the lateral displacement of the roof on the coal face side is limited, preventing buckling damage caused by excessive overhang.

[0015] This invention provides a method for series support of the roof slab across faults and to prevent roof collapse. It has the following beneficial effects: 1. This invention utilizes high-strength hollow grouting anchor cables to perform full-length pressurized grouting. The grout fills and cements the rock fissures within the fault fracture zone, transforming the originally loose and discontinuous fractured rock mass into a continuous composite load-bearing body. Combined with the arrangement of anchor cables extending into deep, stable rock strata, the deep stable zone is used as the anchoring foundation, transferring the self-weight load of the shallow fractured rock strata to the deeper layers. This solves the problem of the lack of reliable anchoring points in fault fracture zones due to low rock strength, thereby improving the overall stability of the surrounding rock.

[0016] 2. In this invention, after the grout has solidified to the design strength, an axial preload is applied to the anchor cable. The high-strength anchor cable applies active compression constraint to the series of fractured rock layers, increasing the normal stress and frictional resistance between the rock layers, effectively inhibiting the development of delamination and interlayer slippage of the fractured rock layers. This active reinforcement mechanism constructs loose fractured rock blocks into a composite structure with load-bearing capacity, limiting the vertical deformation and plastic zone expansion of the top plate.

[0017] 3. This invention provides an adaptive support strategy for fault displacement and mining processes. For faults with large displacements, inclined anchor cables are arranged to pass through the main slip surface to resist shear failure. In the whole-rock roof breaking area, dynamic compensation for anchor cable length is reserved to cope with cutting losses. During the mining through the fault, hydraulic supports are used to assist with pressurized roof rubbing. These measures ensure that the support structure can maintain effective anchorage length and shear resistance under fault activation and strong mining disturbance, preventing roof collapse accidents caused by support failure. Attached Figure Description

[0018] Figure 1 This is an overall process flow diagram of the method of the present invention; Figure 2 This is a schematic diagram of the stiffness enhancement model of the composite beam on the top plate of the fault fracture zone according to the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see the appendix Figure 1 - Appendix Figure 2 This method constructs a linear, continuous load-bearing structure that penetrates multiple layers of fractured rock mass along the stratigraphic normal or a predetermined dip angle in the fault fracture zone region, connecting the discrete top rock layers cut by the fault into a composite load-bearing beam with overall bending and shear resistance. The method includes the following steps: The fault attitude parameters are determined through geological exploration; a series support path is planned based on the fault attitude parameters; grouting anchor cable holes are drilled along the series support path to penetrate the fractured roof rock layer and reach the stable rock layer; hollow grouting anchor cables are installed into the grouting anchor cable holes; full-length pressurized grouting is performed on the grouting anchor cable holes to fill the rock layer fissures and wrap the hollow grouting anchor cables; after the grout solidifies, axial preload is applied to the hollow grouting anchor cables.

[0021] This method utilizes hollow grouting anchor cables as axial tie elements, combined with a cemented body formed by full-length grouting, to establish a reinforced zone with continuous stress transmission within the fault fracture zone. The reinforced zone, through the axial preload P applied by the hollow grouting anchor cables and the bonding force generated by the grouting cementation, alters the contact state between fractured rock blocks, transforming it from uniaxial compression to triaxial compression, thereby increasing the friction angle and cohesion within the rock mass. This structural form eliminates the interruption of stress transmission at the fault in point supports, allowing horizontal tectonic stress and vertical gravity loads to smoothly pass through the fault region, avoiding stress concentration that could lead to dynamic instability of the rock mass.

[0022] Based on the Mohr-Coulomb criterion and the mechanical properties of the reinforced body, a calculation model for the shear strength of a series support structure is established. The equivalent shear strength of the fault fracture zone rock mass after series support is calculated. A preset safety threshold must be met, calculated using the following formula: ; in: This represents the equivalent shear strength (MPa) of the rock mass in the fault fracture zone after series support. This represents the residual cohesion of the fractured rock mass (MPa). This represents the increase in rock mass cohesion due to grouting (MPa). This represents the normal stress (MPa) acting on the top rock stratum. The equivalent internal friction angle (°) of the fractured rock mass after grouting reinforcement. This indicates the number of hollow grouting anchor cables arranged per unit area; This indicates the axial working resistance (N) provided by a single hollow grouting anchor cable. Indicates the area of ​​the roof support in the calculation region ( ); This indicates the angle (°) between the installation angle of the hollow grouting anchor cable and the normal to the rock stratum.

[0023] The formula shows that this method improves the cohesion parameter through full-length grouting. And by applying active axial force Provide incremental support. When the hollow grouting anchor cable penetrates the top rock layer, the tensile strength of the steel strand provides a reverse restraint force, and the grouting solidification body restricts the rock block from overturning and delamination.

[0024] In areas where the fault drop exceeds the thickness of the coal seam, a high-density mesh-like series arrangement is adopted, which involves laying metal mesh and steel strips between hollow grouting anchor cables. The steel strips connect adjacent hollow grouting anchor cables, allowing local loads to be transferred to the deep anchoring ends of adjacent anchor cables through the steel strips, thus distributing the self-weight load of the fractured rock mass into the deep, stable rock mass.

[0025] In unsupported fault fracture zones, stress waves propagate to the fracture interface and are reflected and attenuated, causing energy to accumulate at the fracture tip. This method uses high-pressure grouting to inject grout into micro-fractures. After the grout solidifies, the resulting concreted mass has acoustic impedance and elastic modulus close to that of rock, restoring the continuous medium properties of the rock mass. High stress within the surrounding rock passes through the reinforced zone as a continuous wave, eliminating the stress-blocking effect of the fault plane.

[0026] In this embodiment, hollow grouting anchors are arranged perpendicular to the bedding direction of the top strata or at a preset angle determined by the fault dip angle. These hollow grouting anchors, acting as penetrating linear connecting components, physically connect the discretely distributed fractured rock blocks and weak rock layers within the fault fracture zone in the longitudinal direction. The hollow grouting anchors, in conjunction with the grout solidification body formed by high-pressure grouting, construct a multi-layered load-bearing structure within the fractured top strata. When axial preload is applied, the anchor ends of the hollow grouting anchors compress against the surface trays, forcing the connected fractured rock blocks to generate normal compressive stress, increasing the frictional resistance between the bedding planes and fracture surfaces, and restricting the lateral sliding and displacement of the fractured rock blocks along the bedding planes.

[0027] A composite beam stiffness enhancement model is used to describe the improvement of the overall bending resistance of the roof strata by the tandem support structure. After applying the tandem support and grouting, the roof strata are transformed into an integral composite beam, whose equivalent bending stiffness is... Defined by the following formula: ; in: This represents the equivalent flexural stiffness of the composite beam of the roof slab after tandem support and grouting reinforcement, expressed in Newtons per square meter. ; This indicates the number of rock strata or the number of broken rock blocks that are connected and penetrated by a single high-strength hollow grouting anchor cable. Indicates the first The equivalent elastic modulus of the rock strata after grouting reinforcement and filling of fractures, expressed in Pascals (Pa). Indicates the first For the first rock layer cross section The moment of inertia of the neutral axis of the rock strata themselves, expressed in fourth-degree meters (m²). ); This represents the interlayer shear transfer coefficient, which reflects the degree of constraint exerted by the high-strength hollow grouting anchor cable and the grout solidified body on interlayer slippage. The value ranges from 0 to 1, where 0 represents a completely unbonded slippage state and 1 represents a completely rigid connection state. In the tandem support structure of this invention, high preload and full grouting filling are applied along the entire length. The value of is designed to be close to 1; Indicates the first The cross-sectional area of ​​the rock strata is expressed in square meters. ; Indicates the first The vertical distance between the neutral axis of the rock strata and the common neutral axis of the overall composite beam, in meters. .

[0028] The formula introduces an incremental term for structural stiffness, indicating that the connected rock strata possess collaborative bearing capacity. Furthermore, the hollow grouting anchor cable, as a ductile metal component, acts as a pin when the roof is subjected to dynamic loads or undergoes minor displacement. The hollow grouting anchor cable generates shear resistance on the shear surface, and the solidified grout forms a bonded network, restoring the physical continuity of the rock mass.

[0029] The tandem components are hollow grouting anchor cables. They consist of a steel rod with a central through-hole, which serves as a grout delivery channel. A continuous corrugated thread structure is provided on the outer surface of the rod for screwing in the drilling and mixing resin cartridge, and to increase the mechanical interlocking force between the rod and the solidified grout after solidification.

[0030] The length of the hollow grouting anchor cable must adhere to the principle of effective penetration and be calculated based on the normal thickness of the fault fracture zone and the drilling angle. Effective length The following calculation formula must be met to ensure that the skewers have sufficient physical span to support the candied hawthorn skewers: ; in: The total length of the selected high-strength hollow grouting anchor cable is indicated in meters (m). This indicates the maximum vertical development height of fault fracture zones or disordered bedding areas as determined by ground-penetrating radar or drilling, expressed in meters (m). This indicates the angle between the borehole axis of the high-strength hollow grouting anchor cable and the horizontal plane, in degrees (°). This indicates the effective anchorage length of the high-strength hollow grouting anchor cable, extending deep into stable, intact rock strata above the fault fracture zone, expressed in meters (m). This parameter is crucial for ensuring the rooting of the tandem structure and is typically required to... The anchorage should be at least 1.5 meters long to ensure that the anchoring end can provide sufficient pull-out resistance and prevent the entire tandem structure from sinking along with the fractured rock strata. This indicates the length of the exposed tension section of the high-strength hollow grouting anchor cable on the surface of the roof slab. It is used for installing trays, locks, and applying preload. The unit is meters (m).

[0031] The material used is high-strength, low-relaxation steel strand or precision-rolled threaded steel with a tensile strength of not less than 1860MPa and an elongation of more than 3.5%. Grout outlet holes are set at preset intervals along the axial direction of the rod or grout stop plugs are set at the ends to achieve grout filling from the inside out.

[0032] The grouting binder is configured based on the degree of rock fracture development in the fault fracture zone. Ultrafine cement grout or polymeric chemical grout is used in micro-fracture zones; early-strength ordinary silicate cement grout is used in large fracture zones. The effective diffusion radius of the grouting binder is also considered. Controlled by Bingham's fluid diffusion formula: ; in: This indicates the effective diffusion radius of the grouting cementing material within the rock strata fissures centered on the high-strength hollow grouting anchor cable, expressed in meters (m). It represents the difference between the effective grouting pressure applied by the grouting pump and the pore water pressure and friction resistance inside the fracture, and is expressed in Pascals (Pa). This indicates the average aperture of rock fractures within the fault fracture zone, expressed in meters (m). This indicates the duration of maintaining effective grouting pressure, measured in seconds (s). This represents the dynamic viscosity coefficient of the grouting binder in the liquid state, expressed in Pascal-seconds (Pa·s).

[0033] According to the above formula, the dynamic viscosity coefficient can be reduced by adjusting the water-cement ratio or chemical composition of the grouting binder. Alternatively, by increasing the output pressure of the grouting system. This can increase the effective diffusion radius. When actually arranging a string-of-pearls-style support structure, the spacing between two adjacent high-strength hollow grouting anchor cables should be set to less than [a certain value]. This ensures that adjacent grouting areas overlap spatially. This overlap effect guarantees that the area between two anchor cables is also filled with solidified grouting cementitious material, thus avoiding the existence of gaps. The solidified grouting cementitious material not only wraps around the rod of the high-strength hollow grouting anchor cable, forming a three-in-one load-bearing structure of rock, grout, and rod, but also seals the water-conducting fissures inside the rock, isolates the gas escape channels, and further enhances the stability of the surrounding rock during fault crossings. This dense cemented network allows the originally loose fractured zone to transmit mining forces like a complete rock slab, effectively preventing roof collapse accidents caused by local rock fragment detachment.

[0034] Step one, advance detection and assessment, is the prerequisite and parameter design basis for implementing the string-of-pearls support structure. This step aims to accurately obtain fault occurrence elements, the fracture range of the roof strata, and the occurrence strata of deep stable strata before the working face is mined into the fault-affected area. This provides quantitative geological data support for the selection of the length of high-strength hollow grouting anchor cables, the setting of grouting parameters, and the planning of borehole angles.

[0035] In practice, when the working face is 30 to 50 meters away from the fault at a predetermined distance, an advance detection procedure is initiated. The detection method combines physical core drilling with digital borehole imaging. First, a high-powered pneumatic side-rock drilling rig or hydraulic drilling rig is used to drill detection boreholes at different dip angles in the roadway roof. During drilling, the drilling speed and the color and particle size of the returned rock powder are monitored and recorded in real time. When the drilling speed suddenly increases (due to drill bit suction) or the returned rock powder is in clumps or muddy form, it is determined that the fault fracture zone or delamination development zone has been entered. Subsequently, a high-precision mining borehole sighting instrument is inserted into the detection borehole. A wide-angle camera is used to capture panoramic video of the borehole wall, allowing for direct observation of the location of fractures, fracture opening, delamination location, and the specific depth of lithological changes within the roof rock mass.

[0036] Based on the rock mechanics parameters and geological information obtained from the aforementioned exploration, in order to determine the theoretical boundary of the loose and fractured zones (plastic zones) that need to be connected in series in the "string of candied hawthorns" structure, this invention introduces a modified Castner formula to calculate the plastic failure radius of the tunnel roof under fault influence. The calculation result directly determines the minimum depth that the high-strength hollow grouting anchor cable must penetrate to ensure that its anchoring end can be rooted outside the plastic failure radius. : ; in: This represents the theoretical limit radius of the fault-fractured roof plate, with the tunnel axis as the origin, where plastic yielding and loosening failure occur. The unit is meters (m). The rock mass within this radius is the part of the candied hawthorn that needs to be connected and reinforced in the candied hawthorn structure. The equivalent radius of the roof control zone of a roadway or working face is expressed in meters (m). This represents the vertical geostress load borne by the top plate of the fault zone. This value takes into account both the original rock stress and the tectonic stress concentration factor, and the unit is megapascal (MPa). This parameter represents the cohesion of the roof rock mass in the detection area under ungrouted conditions. It is obtained by laboratory rock mechanics testing of core samples taken from the borehole and is measured in megapascals (MPa). The internal friction angle of the roof rock mass in the detection area in the ungrouted state is expressed in degrees (°). This represents the original support resistance on the roadway surface (such as the radial resistance provided by ordinary anchor bolts). When making a conservative assessment, this value can be taken as 0 to calculate the maximum easily damaged range. The unit is megapascal (MPa).

[0037] Through the above evaluation steps, if the calculated... If the anchorage length exceeds the existing support length, or if borehole inspection results show obvious delamination cracks within the existing support area, the area is immediately identified as a high-risk area, and the cascade support method of this invention must be implemented. Simultaneously, based on the detected fault dip angle... A fault space model was constructed, and the drilling trajectory of the high-strength hollow grouting anchor cable was planned to allow it to pass through the main fracture surface or bedding plane at an angle close to 90 degrees as easily as possible to obtain the maximum shear resistance component. This evaluation process ensured that the support scheme was tailored to the objective geological conditions, avoiding inadequate support or material waste caused by blind construction.

[0038] In step two, the arrangement and drilling of the "string of candied hawthorns" (a type of rock formation) holes, based on the geological survey data obtained in step one, the physical construction of high-strength hollow grouting anchor cable boreholes is carried out in the fault zone of the roadway roof or mining face. The core of this step lies in establishing the skeleton shape of the "string of candied hawthorns" structure through a specific geometric array arrangement, ensuring that the subsequently installed linear connecting components can intercept and penetrate potential delamination rock blocks within the fault fracture zone to the greatest extent.

[0039] In practice, the main control zone and transition zone are first determined within the influence area of ​​the fault fracture zone. The main control zone covers the fault outcrop and an area of ​​5 to 10 meters on both sides. Within this zone, a high-density rectangular or staggered (quincunx) borehole pattern is used. The borehole diameter must match the diameter of the selected high-strength hollow grouting anchor cable. Typically, the borehole diameter is set 6 to 10 millimeters larger than the anchor cable diameter to allow sufficient annular clearance for grout flow. For example, for a 22-millimeter diameter high-strength hollow grouting anchor cable, a drill bit with a diameter of 28 to 32 millimeters is used.

[0040] To address the abrupt changes in the attitude of rock strata in fault zones, a multi-dimensional locking strategy is employed in the borehole angle design. For relatively horizontal rock strata located on the hanging wall or footwall of the fault, the borehole axis is perpendicular to the top strata, i.e., the borehole inclination angle is 90 degrees, to achieve vertical suspension of the layered rock slabs. For areas that directly traverse the fault plane, the borehole axis needs to be adjusted according to the fault dip angle, ensuring that the angle between the borehole trajectory and the fault plane is... The angle is maintained between 45 and 90 degrees. This large-angle cross arrangement ensures that the high-strength hollow grouting anchor cable mainly bears the combined effect of tensile and shear loads when passing through the fault plane, avoiding the failure of the anchor cable when the rock strata shift due to the arrangement parallel to the fault plane.

[0041] To prevent borehole collapse and stuck drill bits during drilling in loose, fractured rock masses, this invention employs a wall-supported casing drilling or staged reaming process. In extremely fractured muddy zones, a drill rod with an outer casing is first used for directional drilling. After drilling to a predetermined depth, the casing is retained as temporary borehole wall support. The casing is then removed after a high-strength hollow grouting anchor cable is inserted. Simultaneously, a lockhole structure is installed at the borehole opening. This involves reaming the borehole within a 0.5-1.0 meter range from the opening and pre-embedding a borehole casing. Quick-setting cement is used to seal the gap between the casing and the coal and rock mass, creating a closed grout-stopping barrier for subsequent high-pressure grouting, preventing grout from flowing back or overflowing from the fractured fissures around the borehole opening.

[0042] The spacing of the boreholes (including row spacing and column spacing) is a key parameter determining the overall load-bearing capacity of the "string of candied hawthorns" structure. Excessive spacing can lead to a blind spot between the two anchor cables, causing rock to fall (i.e., spalling), while insufficient spacing results in wasted engineering work and can easily damage the integrity of the rock mass. Based on suspension theory and the principle of combined arches, this invention calculates the maximum allowable row spacing of high-strength hollow grouting anchor cables using the following formula. : ; in: This indicates the maximum permissible center-to-center distance (including row spacing and column spacing) between two adjacent high-strength hollow grouting anchor cables, in meters (m). The ultimate breaking tensile force of a single high-strength hollow grouting anchor cable is expressed in Newtons (N). This represents the working efficiency coefficient of the anchor cable, which is typically taken as 0.7 to 0.85, taking into account the influence of drilling deviation and installation quality. This represents the safety factor during fault crossing, taking into account dynamic loads and the risk of rock bursts. The value ranges from 2.0 to 3.0. This indicates the average unit weight of the rock at the top of the fault fracture zone, expressed in Newtons per cubic meter (N / m³). ; This indicates the effective thickness of the fractured rock strata that need to be suspended or connected in series; this value is taken as the plastic failure radius calculated in step one. The larger of the heights of the fracture zones from geological surveys, expressed in meters (m).

[0043] Calculated based on the above formula This serves as the upper limit for borehole placement. In practice, to further enhance defense against rock bursts, the calculated spacing between boreholes is typically reduced by 10% to 15% during construction. In the core area with the largest fault displacement, a dual-control, denser layout is adopted. This involves adding a reinforcing borehole at the geometric center of four adjacent boreholes, creating a pentagonal pattern. This halves the control area of ​​a single support unit, improving the ability to capture and control small, fractured rock fragments. This refined borehole placement provides a precise spatial channel for subsequently connecting discrete rock masses into a cohesive structure.

[0044] In step three, the installation of the tandem components and the full-length grouting, a combination of physical placement and chemical filling is used to achieve substantial coupling between the linear connecting components and the fractured rock mass in the string-of-pearls structure. The quality of this step directly determines whether the support system can consolidate the discrete rock blocks within the fault fracture zone into a whole.

[0045] In practice, the drill cuttings and accumulated water inside the borehole are first cleared to ensure unobstructed access. Then, the artificial resin cartridge for the high-strength hollow grouting anchor is pushed into the bottom of the hole. Next, pneumatic or hydraulic outriggers are used to insert the rod of the high-strength hollow grouting anchor into the borehole to the predetermined depth. During this process, the resin cartridge is stirred by rotating the high-strength hollow grouting anchor to achieve resin anchoring at the anchor end. This anchored section primarily provides suspension force to the foundation in the initial stage before grout solidification, preventing the anchor from detaching under its own weight.

[0046] After the anchor cable ends are anchored, a grout stopper (or borehole sealer) is immediately installed at the borehole opening. The grout stopper expands and compresses the borehole wall, forming a high-pressure sealed cavity. This sealed cavity is a critical boundary condition for achieving full-length pressurized grouting. If the borehole seal fails, the grout will flow out along the borehole wall, failing to establish sufficient diffusion pressure at depth, leading to cascade failure. After installing the grout stopper, connect the grouting connector at the tail of the high-strength hollow grouting anchor cable to the grout outlet pipe of the high-pressure grouting pump, and start the grouting pump to begin grouting operations.

[0047] The grouting process employs a filling path from the inside out and from the bottom up. Driven by a high-pressure grouting pump, the grout flows through the central through-hole inside the high-strength hollow grouting anchor cable, reaching the bottom of the hole. It then exits from the grout outlet at the end of the cable or on the side wall, first filling the space at the bottom of the hole. Subsequently, under the continuous action of grouting pressure, it flows back towards the borehole opening along the annular space between the high-strength hollow grouting anchor cable and the borehole wall. When the grout fills the entire annular space and is blocked by the grout stop plug at the borehole opening, the internal pressure of the borehole begins to rise sharply.

[0048] This marks the beginning of the crucial infiltration and diffusion stage. The high-pressure grouting pump continues to operate, maintaining the hydrostatic pressure within the borehole at the designed grouting pressure range of 2.0 MPa to 4.0 MPa. Driven by high pressure, the grout is forced to infiltrate and diffuse from the borehole wall into the fissures, bedding planes, and delamination voids of the surrounding fractured rock mass. The grout flows, fills, and eventually chemically solidifies within the fissures, binding the rock fragments, originally separated by the fault, tightly around the high-strength hollow grouting anchor cable—like the fruit on a candied hawthorn skewer—through the grout's coating.

[0049] To ensure that the grout volume can fully cover the fractured network without excessive waste of grout, this invention sets a theoretical grout volume. The calculation model is used. In actual construction, the actual grouting volume should not be less than the theoretical grouting volume. Theoretical grouting volume Calculate using the following formula: ; in: This represents the theoretical grouting volume required for a single high-strength hollow grouting anchor cable, expressed in cubic meters. This indicates the diameter of the borehole, in meters (m). The diameter of the high-strength hollow grouting anchor rod is indicated by meters (m). This indicates the depth of the borehole, which is the length that needs to be filled with grout, and is expressed in meters (m). This represents the filling coefficient of the grout in the borehole and fracture. Considering the roughness of the rock surface and the shrinkage of the grout, this value is usually taken as 1.1 to 1.3. This indicates the fracture ratio and grout diffusion loss coefficient of the rock mass in the fault fracture zone. This parameter reflects the proportion of grout that needs to penetrate into the rock mass fractures; for general fracture zones, The value ranges from 0.3 to 0.5; for extremely fractured or porous fault zones, The value can range from 0.8 to 1.5; this parameter needs to be dynamically adjusted based on the borehole inspection results in step one. If the inspection shows a large fracture aperture and high density, then the value should be increased. value.

[0050] The completion of grouting is determined by a dual-control standard: grouting pressure control as the primary factor and grouting volume control as a secondary factor. When the pressure gauge reading of the grouting pump stably reaches the design final pressure (e.g., 4.0 MPa) and remains stable for 3 to 5 minutes or more, and the grout intake significantly decreases, the full-length grouting is considered complete, and the grouting valve is closed. This high-pressure full-length grouting process ensures that the high-strength hollow grouting anchor cable is not merely a suspension component but also a reinforcement component. Through the physical placement and cementing effect of the grout, it improves the overall strength and deformation resistance of the fractured surrounding rock.

[0051] In step four, by applying prestressing and initial support, the "string of candied hawthorns" structure, which had been grouted and filled in step three but was in a passive load-bearing state, is transformed into a high-prestressed load-bearing structure with active restraint. This step applies axial tension to the high-strength hollow grouting anchor cable, forcing the loose rock blocks within the fault fracture zone to undergo elastic compression deformation under the clamping action of the anchor points at both ends of the high-strength hollow grouting anchor cable. This eliminates the separation gaps between rock strata and establishes an active support resistance capable of resisting roof collapse.

[0052] In practice, the first step is to set a curing time after grouting. Tensioning cannot be performed immediately after grouting; the grouting binder must be allowed to grow to 70% to 80% of its design strength. At this point, the grout has formed a solidified body with certain shear and compressive strength within the rock fissures and the annular space surrounding the high-strength hollow grouting anchor cable, capable of withstanding the shear forces during tensioning.

[0053] Once the grout has solidified to the required strength, clean the surface of the exposed section of the high-strength hollow grouting anchor cable of laitance and debris. Then, assemble the high-strength arched tray, adjusting washer, and tensioning lock in sequence. The selection of the adjusting washer is crucial. Because the drilling trajectory in step two is prone to being at a non-perpendicular angle to the top surface, the spherical contact of the adjusting washer must be used to ensure that the bearing surface of the lock remains perpendicular to the axis of the high-strength hollow grouting anchor cable. This prevents the steel strand from breaking due to bending during tensioning and also ensures that the preload is transmitted axially along the anchor cable to the deep rock mass without loss.

[0054] After installation, a large-tonnage pneumatic tensioning jack or hydraulic tensioning device is used to secure the tail end of the high-strength hollow grouting anchor cable, and the tensioning equipment is started for tensioning operations. The tensioning process adopts a staged loading and over-tensioning locking technique. First, the load is increased to 50% of the design preload for initial tensioning to eliminate slack gaps in the steel strands and the support; then, the load is increased to 110% of the design preload for over-tensioning, held for 30 to 60 seconds to overcome the frictional resistance of the high-strength hollow grouting anchor cable in the hole and the instantaneous plastic deformation of the rock mass; finally, the load is lowered back to the design preload value, and the clamps of the locking device are locked to complete the preload locking.

[0055] To ensure the candied hawthorn skewer structure can provide sufficient initial support to balance the self-weight and structural stress of the fault top plate, the axial preload of the high-strength hollow grouting anchor cable is... Strict mechanical calculation requirements must be met. Insufficient preload will fail to compact the fractured rock layer, while excessive preload will cause the anchor cable material to yield or even break. This invention sets the axial preload applied during construction based on the material yield limit and active support efficiency requirements of high-strength hollow grouting anchor cables. It must conform to the following formula: ; in: This represents the construction setting value of the axial preload applied to the high-strength hollow grouting anchor cable, in Newtons (N). This indicates the yield strength limit of the high-strength hollow grouting anchor rod material, which is usually taken as 1860 MPa or higher, with the unit being MPa. This represents the effective cross-sectional area of ​​the high-strength hollow grouting anchor rod, expressed in square meters (m²). ; This indicates the strength utilization coefficient of the high-strength hollow grouting anchor cable. In order to retain sufficient deformation margin to cope with the roof subsidence during mining, the value of this coefficient is set to a range of 0.4 to 0.6, that is, the pre-tightening force is usually set to 40% to 60% of the breaking tensile force to ensure a continuous active support state. This represents the prestress loss compensation coefficient. Considering the slight retraction of the tensioning lock at the moment of locking and the creep characteristics of the rock mass, this coefficient is taken as 1.05 to 1.15, which means that appropriate over-tensioning is required during construction.

[0056] The high axial preload applied through the above steps The stress is transferred to the roof surface through a high-strength arched tray, forming a conical compressive stress distribution zone (i.e., a compressive stress bubble) centered on the anchor cable axis within the rock mass. When the spacing between adjacent high-strength hollow grouting anchor cables is reasonable, the adjacent compressive stress distribution zones overlap spatially, forming a continuous compressive stress reinforcement zone within the fault fracture zone. Within this reinforcement zone, the fractured rock blocks, originally under uniaxial stress or in a loose state, are forced into a triaxial compressive state, and their lateral deformation is strictly limited. This active initial support force not only directly balances the gravity of the immediate roof below the roof, but more importantly, it increases the normal stress between the bedding layers. According to the friction law, the interlayer shear friction resistance increases significantly. This allows the "string of candied hawthorns" structure to immediately exert maximum support effectiveness in the early stages of the longwall mining face advancement and the increase in the exposed roof area, preventing delamination and displacement of the fractured rock layers in the early stages of mine pressure manifestation, thereby effectively preventing roof collapse accidents.

[0057] In the coordination measures during the fault-crossing mining phase in step five, to ensure that the cascading roof support structure constructed in the aforementioned steps does not fail during the dynamic advancement of the coal face and to maintain the stability of the fault fracture zone roof, a collaborative mining control method based on support strength coupling is implemented. This method dynamically matches the cutting parameters of the coal mining machine, the support status of the hydraulic supports, and the active constraint force of the high-strength hollow grouting anchor cables to minimize the secondary damage caused by mining disturbances to the already grouted and solidified fault fractured rock mass.

[0058] In practice, the cutting process parameters of the coal mining machine are first adjusted with constraints. When passing through fault fracture zones, the traction speed of the coal mining machine is reduced to 40% to 60% of the normal mining speed to reduce the low-frequency vibration wave energy generated when the drum cuts the rock, preventing micro-cracks in the rock mass at the anchoring end of the high-strength hollow grouting anchor cable caused by vibration. At the same time, the cutting depth of the coal mining machine (i.e., the depth to which the drum cuts into the coal wall) is adjusted from the conventional 0.8 to 1.0 meters to 0.5 to 0.6 meters. Reducing the cutting depth directly reduces the gap between the front end of the hydraulic support top beam and the coal wall, thereby reducing the bending moment of the roof strata in the exposed state.

[0059] In terms of hydraulic support control, an operational strategy combining pressurized roof-rubbing support movement and advanced support is adopted. After the coal shearing machine drum cuts the coal, the hydraulic support is immediately moved within a range of 3 to 5 supports behind the drum. During the support movement, the hydraulic system's supply pressure is controlled so that the top beam of the hydraulic support does not completely detach from the roof, but maintains a preset residual support force (usually 10% to 15% of the working resistance) and slides forward while closely rubbing against the roof surface. This operation eliminates the zero-load time window of the roof force during the hydraulic support lowering and moving process, ensuring that the roof strata are always under bidirectional pressure from the axial preload of the high-strength hollow grouting anchor cables and the vertical support force of the hydraulic support.

[0060] To quantitatively determine the minimum initial support force required for hydraulic supports during fault crossings, ensuring their effective joint load-bearing system with the truncated concrete support structure and preventing delamination during roof recompaction, this invention sets the initial support force of the hydraulic supports based on the roof composite beam theory. The calculation model requires that the initial support force of the hydraulic support must be able to balance the gravity of the direct jacking and overcome the unloading effect of the preload of the high-strength hollow grouting anchor cable in the vertical direction. Minimum initial support force of the hydraulic support. The calculation formula is as follows: ; in: This indicates the minimum initial support force that the hydraulic support must be set, in kilonewtons (kN). This represents the safety factor for roof management, which, taking into account the non-uniformity of stress in the fault area, ranges from 1.2 to 1.5. This indicates the average unit weight of rocks within the fault fracture zone, expressed in kilonewtons per cubic meter. ; This represents the thickness of the rock layer directly above the hydraulic support, or the plastic failure radius calculated in step one. The unit is meters (m); This indicates the effective jacking length of a single hydraulic support beam, expressed in meters (m). This indicates the width of a single hydraulic support, in meters (m). This indicates the number of high-strength hollow grouting anchor cables distributed within the jacking range of a single hydraulic support, expressed in units of cables. Indicates the first The actual axial preload applied to the high-strength hollow grouting anchor cable is expressed in kilonewtons (kN). Indicates the first The angle between the installation angle of a high-strength hollow grouting anchor cable and the vertical direction, in degrees. .

[0061] The initial support force of the hydraulic support was calculated and set using the above formula, ensuring the mechanical complementarity between mechanical support and anchor cable support. If, during the mining process, mine pressure monitoring reveals a risk of roof collapse in a localized area or minor cracks in the "string of candied hawthorns" structure, supplementary chemical grouting measures are immediately implemented. Short holes are drilled at the gaps in the high-strength hollow grouting anchor cables, and rapid-expanding polyurethane or phenolic resin material with a reaction time of less than 60 seconds is injected. This material rapidly expands and fills the gap between the support beam and the broken roof, forming a flexible cushion layer. This transforms the point-line contact of the hydraulic support into surface contact, further improving the stress state of the fault-broken roof and ensuring the safe and rapid passage of the working face through the fault geological structure zone.

[0062] This invention addresses geological conditions where the fault displacement exceeds the coal seam thickness or surpasses 3.0 meters. Under such conditions, a single vertical, cascading structure is insufficient to effectively resist the immense shear forces and slippage tendencies generated between the hanging wall and footwall of the fault. Therefore, this embodiment employs a bidirectional, cascading structure. This involves arranging two sets of high-strength hollow grouting anchor cables that intersect at a specific angle in space to construct a three-dimensional reinforcement network that resists both tension and shear.

[0063] Specifically, the two-way series structure consists of two core components: a vertical suspension group and an inclined collapsing group. The vertical suspension group comprises multiple high-strength hollow grouting anchor cables arranged perpendicular to the surface of the tunnel roof. Its main function is to bear the self-weight load of the fractured rock strata of the roof, connecting the loose rock mass vertically to the deeper rock strata and maintaining the basic integrity of the roof. The inclined collapsing group consists of multiple high-strength hollow grouting anchor cables arranged at a predetermined deflection angle to the vertical line of the roof. The drilling trajectory of the inclined collapsing group is designed to directly pass through the main slip surface (Fault Plane) of the fault fracture zone and penetrate deep into the intact rock mass of the fault's hanging wall (footwall or footwall).

[0064] To maximize the resistance of high-strength hollow grouting anchors against fault slip, the installation angle of the inclined locking and collapsing assembly must follow the principle of shear optimization. Studies show that the shear resistance provided by the anchor cable is strongest when the angle between the anchor cable axis and the rock slip surface (fault plane) is close to 90 degrees; while when they are parallel, the anchor cable provides virtually no shear resistance. Therefore, the installation deflection angle α of the inclined locking and collapsing assembly needs to be precisely calculated and set based on the detected fault dip angle θ to ensure the intersection angle between the high-strength hollow grouting anchor cable and the fault plane. It is within the optimal shear resistance range (typically 45 to 90 degrees). The installation deflection angle α (i.e., the angle between the borehole axis and the vertical line of the top plate) of the high-strength hollow grouting anchor cable of the inclined locking group is determined according to the following geometric formula: ; in: The angle of installation deflection of the high-strength hollow grouting anchor cable of the inclined locking group relative to the vertical line of the top plate is expressed in degrees (°); if the deflection is above the fault plane, it is positive, and if it is below, it is negative. The geological dip angle of the fault plane is expressed in degrees (°). This indicates the optimal shear angle between the designed high-strength hollow grouting anchor cable and the fault plane. In order to make full use of the tensile and shear properties of the anchor cable, this value is usually set to 60 to 80 degrees. This indicates the apparent dip angle of the roof strata of the tunnel, expressed in degrees (°).

[0065] Besides the angle setting, the high-strength hollow grouting anchor cable of the inclined locking group must be long enough to ensure it can penetrate the wide fault fracture zone and provide sufficient anchoring force. Its length... The following crossing formula must be satisfied: ; in: The total length of the inclined locking group high-strength hollow grouting anchor cable is indicated in meters (m). This indicates the normal width (thickness) of the fault fracture zone. In faults with large drops, this value is often large, and the unit is meters (m). This indicates the actual angle between the axis of the high-strength hollow grouting anchor cable and the cross-section, in degrees (°). This indicates the anchorage length of the high-strength hollow grouting anchor cable within the stable rock strata of the same block (such as the mining side) before it crosses the fault plane, and the unit is meters (m). This indicates the anchorage length of the high-strength hollow grouting anchor cable after it crosses the fault plane and penetrates deep into the stable rock strata of the opposite side (such as the non-mining side). This section is crucial for stitching up the fault and should not be less than 2.0 meters. The unit is meters (m). This indicates the length of the tensioning section exposed outside the orifice, in meters (m).

[0066] Through the interwoven arrangement of the vertical suspension groups and the inclined locking groups, a truss-like load-bearing structure is formed within the fault fracture zone. When the vertical suspension groups apply preload, they generate an upward active support force; when the inclined locking groups apply preload, they generate an oblique tensile force. This tensile force is decomposed at the fault plane into a normal compressive force perpendicular to the fault plane and an anti-sliding force in the opposite direction along the fault plane. This bidirectional load-bearing state not only compacts the fractured rock blocks but also increases the frictional resistance of the fault plane and the nearby fracture surfaces. Subsequent bidirectional full-length grouting allows the grout to penetrate the fracture network from different angles, eliminating the shadow zone that is prone to occur with unidirectional grouting. This solidifies the truss structure into a robust reinforced concrete bidirectional series load-bearing body, effectively curbing the common phenomena of top plate subsidence and rotational instability in large-drop faults.

[0067] For these two special working conditions that alter the boundary conditions of the surrounding rock, adaptive adjustments were made to the string-of-pearls support structure to ensure that the support system remains effective after the geometry of the surrounding rock changes.

[0068] When the fault drop is small or the coal seam rises upwards, the coal mining machine drum needs to cut through part of the roof rock to facilitate a smooth transition; this is known as roof breaking. This operation essentially reduces the thickness of the roof strata, directly resulting in the removal of the lower anchoring section of the originally designed high-strength hollow grouting anchor cable. Without adjustment, this will lead to insufficient effective anchoring length and may even cause the composite beam structure, which was originally reinforced in series, to break due to the reduced thickness.

[0069] For roof-breaking operations, this invention employs a deep extension and advanced reinforcement strategy. First, high-strength hollow grouting anchors must be installed and grouted in the advanced support area before the coal mining machine begins roof-breaking and cutting. This means that the grouting binder must have already penetrated and solidified in the deep rock mass above the intended cut rock layer before the roof rock is cut.

[0070] At this point, the design length of the high-strength hollow grouting anchor cable is... Dynamic compensation must be implemented based on the existing structure. The principle of compensation is: after deducting the thickness of the rock cut off by the coal mining machine, the effective anchorage length remaining on the high-strength hollow grouting anchor cable must still meet the suspension requirements of the plastic zone. The adjusted length of the high-strength hollow grouting anchor cable... Calculate using the following formula: ; in: The total adjusted length of the high-strength hollow grouting anchor cable used in the breached area is indicated in meters (m). This represents the minimum effective rock layer thickness required to maintain roof stability as determined in step one (i.e., the effective length of the anchor cable that must remain within the rock mass). This value is typically not less than 2.5 to 3.0 meters, expressed in meters (m). Indicates the horizontal distance from the fault slope change point At this point, the vertical thickness of the roof rock that the coal mining machine needs to cut to meet the set transition slope is specified in meters (m); this value changes linearly or curvilinearly with the change of the transition slope. This indicates the angle between the installation angle of the high-strength hollow grouting anchor cable and the plumb line, expressed in degrees (°). This indicates the excess length of the exposed tension section and anchorage end, in meters (m).

[0071] According to this formula, at the deepest point of the breach, extended high-strength hollow grouting anchor cables or extended rod technology are used to ensure that the anchoring end of the cable is always rooted in the stable rock strata above the cut surface. Furthermore, since breaching the roof will damage the integrity of the top strata and induce new fractures, the grouting pressure in the breach area needs to be increased by 15% to 20% to force the grout to diffuse deeper, forming a new, dense artificial false roof above the cut surface.

[0072] When the bottom-cutting process is implemented, the floor rock is cut downwards to accommodate the coal seam descent. Although the roof is not directly cut, the effective height (mining height) of the roadway increases. The increase in mining height leads to an increase in the support height of the hydraulic supports, which reduces the stability of the supports. It also increases the displacement of the roof strata relative to the floor, making it easier to induce spalling (coal wall spalling) and thus expand the area of ​​roof unsupported.

[0073] For the undercut working conditions, the key adjustments in this embodiment focus on the linkage between the sidewall and the root reinforcement. In the "string of candied hawthorns" support structure, a row of high-strength hollow grouting anchor cables near the coal face is particularly reinforced. The installation angle of this row of anchor cables is designed to be inclined at 15 to 25 degrees towards the coal face, so that it can not only suspend the roof, but also generate lateral restraint force on the triangular rock mass above the coal face, preventing roof collapse caused by coal face flakes due to increased mining height. At the same time, in the undercut area, due to the increased mining space, in order to prevent buckling failure of the high-strength hollow grouting anchor cables due to excessive exposure, it is necessary to strictly control the fastening quality of the end trays, and cooperate with the sidewall plates of the hydraulic support to limit the lateral displacement of the roof on the coal face side, ensuring that the high-strength hollow grouting anchor cables are always in an ideal tensile working state. Through this targeted parameter correction, whether it is roof thinning caused by roof breaking or mining height increase caused by bottoming, the string-of-pearls structure can maintain the stability of the surrounding rock in the fault transition zone through adaptive adjustment of geometric dimensions and mechanical parameters.

[0074] In the comparison of monitoring data, comparative tests under actual field conditions verified the advantages of the proposed roof series support method over traditional support techniques in controlling the deformation of the surrounding rock in fault fracture zones. The figure details the mine pressure manifestation patterns of two adjacent longwall faces applying different support schemes under the same geological structural background (i.e., similar fault displacement, dip angle, and lithological parameters). The horizontal axis represents the distance of the longwall face's advance position relative to the fault core line (negative values ​​indicate proximity to the fault, zero values ​​indicate being at the fault center, and positive values ​​indicate moving away from the fault), in meters (m); the vertical axis represents the cumulative vertical subsidence of the roof surface and the amount of delamination within the roof strata, in millimeters (mm).

[0075] The comparative results show that the control group (curve A) using conventional anchor cable support experienced a rapid deterioration in roof control after entering the fault-affected zone. Data shows that when the working face advanced to approximately -20 meters from the fault center, the roof subsidence rate began to increase non-linearly and exponentially. Particularly when traversing the fault's core fracture zone (range -5 meters to +5 meters), the peak cumulative roof subsidence exceeded 500 millimeters, and the curve exhibited severe sawtooth-like fluctuations. This fluctuation pattern physically corresponds to multiple local collapses and instantaneous shear slips in the roof strata. Simultaneously, multi-point displacement gauges buried deep within the roof detected delamination voids exceeding 80 millimeters in the stratum range of 2.0 meters to 6.0 meters above the roof. This indicates that the point anchoring method of conventional anchor cables cannot restrain the expansion deformation of loose, fractured rock masses; the immediate roof and the basic roof have completely separated, making large-scale roof collapses highly likely.

[0076] In stark contrast, the experimental group (curve B) applying the string-of-pearls-style roof support method of this invention exhibited extremely high structural stability throughout the fault crossing period. Monitoring curves show that the cumulative settlement of the roof increased gradually and convergently. Even in the fault center region where stress was most concentrated, the maximum cumulative settlement was strictly controlled within 120 mm, only 20% to 25% of the deformation under conventional support conditions. More importantly, the deep delamination monitoring data remained consistently at a trace level of 0 to 10 mm, directly confirming that the full-length pressurized grouting process implemented in step three successfully bonded the originally loose and discrete broken rock blocks with high-strength hollow grouting anchor cables into a rigid, integral composite load-bearing beam. The grout filled the fissures, and the high pre-tightening force eliminated the free movement space between the rock blocks, causing the roof strata to exhibit the mechanical behavior of a continuous medium on a macroscopic scale.

[0077] To quantitatively evaluate the degree to which this invention improves the stability of the fault fractured roof, this embodiment introduces a roof stability enhancement factor. As an evaluation index, this factor comprehensively reflects the support system's ability to inhibit surrounding rock deformation and the uniform stability of the support components under stress. Its calculation model is as follows: ; in: This represents the roof stability enhancement factor. The larger the value, the higher the safety margin of the roof during fault crossing. This represents the maximum cumulative subsidence of the roof during the fault crossing period monitored in the control group (conventional support), expressed in millimeters (mm). The first term of the formula represents the maximum cumulative subsidence of the roof slab monitored by the experimental group (support of this invention), in millimeters (mm); the first term of the formula reflects the deformation control efficiency. The average working resistance of the high-strength hollow grouting anchor cable group during the monitoring period is expressed in kilonewtons (kN), reflecting the active bearing capacity of the support structure. The standard deviation of the stress monitoring value of the high-strength hollow grouting anchor cable is expressed in kilonewtons (kN). This value reflects the fluctuation of the anchor cable stress. The smaller the fluctuation, the more uniform the stress of the candied hawthorn structure, and the absence of overload breakage or loosening failure of a single anchor cable. To prevent tiny constants with a denominator of zero.

[0078] The roof stability enhancement factor was calculated by substituting on-site measured data into the above formula after applying this invention. This method achieves an improvement of approximately 4.2 times compared to traditional methods. It physically demonstrates that the "string of candied hawthorns" structure, through a dual reinforcement mechanism of physical linkage and chemical grouting, effectively cuts off the evolution path of deformation and instability of the surrounding rock in the fault fracture zone, ensuring the safe, continuous, and efficient passage of the mining face through complex geological structures.

[0079] The roof series support system constructed in this invention fundamentally changes the instability mechanism of the surrounding rock in the fault fracture zone, transforming the traditional passive defense into active consolidation, thereby reducing the safety risks during the mining face crossing the fault.

[0080] Specifically, traditional fault support often relies on passive support (such as hydraulic supports or ordinary anchor cables). Once a local roof collapse occurs in the fractured rock mass, it can easily trigger a domino effect, causing the upper rock layers to lose support and continuously collapse. The "string of candied hawthorns" structure of this invention utilizes high-strength hollow grouting anchor cables as a highly resilient backbone, combined with the muscle formed by full-length grouting, giving the fractured roof extremely strong impact resistance and self-healing ability. Even under strong dynamic loads generated by fault activation, the rock blocks connected by the high-strength hollow grouting anchor cables will not separate into smaller pieces, avoiding the vicious chain of accidents involving roof collapse, open roofs, and roof falls.

[0081] To quantify the effect of this technology on suppressing the risk of roof collapse, this embodiment constructs a safety factor for roof collapse resistance across fault lines. The calculation model not only considers static load balance, but also focuses on incorporating the shear resistance increment provided by the grouting solidified body. The calculation formula is as follows: ; in: This represents the safety factor against roof collapse in fault zones. According to coal mine safety regulations and engineering experience, this value must be greater than 1.5 to be considered safe and reliable. This indicates the number of high-strength hollow grouting anchor cables that are effectively working within the potential collapse arch area; Indicates the first The ultimate tensile strength that a high-strength hollow grouting anchor cable can provide when breaking is expressed in Newtons (N). This represents the average shear strength of the fault fracture zone rock mass along the most unfavorable slip surface after grouting modification. This value is determined by the bond strength between the grout and the rock, and is usually 3 to 5 times higher than that of the ungrouted rock mass. The unit is Pascal (Pa). This indicates the shear failure area of ​​the potential rock mass along its perimeter, expressed in square meters (m²). ; The dynamic load coefficient during fault crossing reflects the impact effect of coal mining machine cutting vibration and fault stress release, and its value ranges from 1.2 to 1.4. This indicates the weight of rock mass that is prone to collapse within a fault fracture zone, expressed in Newtons (N).

[0082] Applying this formula to calculate the operating conditions of the embodiments, after adopting the technology of this invention, even in Under the unfavorable condition that the weight of the rock mass increases due to fault fracturing, the numerator term... The increase in (grouting shear strength) and The efficient use of (anchor cable tension) increases the safety factor. It has consistently remained at a high level above 2.0.

Claims

1. A method for series support of the roof slab for crossing faults and preventing roof collapse, characterized in that, Includes the following steps: S1. Advanced Detection and Assessment: Before the mining face advances to the fault-affected area, geological exploration is conducted to obtain fault occurrence elements, the fracture range of the roof strata, and the occurrence strata of deep stable strata, and the theoretical radius of the roof fracture zone is determined accordingly. S2. Hole location layout and drilling: Based on the fault occurrence elements and the theoretical radius of the fractured zone of the top plate, plan the series support path, and drill high-strength hollow grouting anchor cable boreholes that penetrate the top plate rock layer of the fault fracture zone and go deep into the stable rock layer on the series support path. S3. Installation of tandem components and full-length grouting: Install high-strength hollow grouting anchors and grout stoppers into the borehole of the high-strength hollow grouting anchors, and use the central channel of the high-strength hollow grouting anchors to perform full-length pressurized grouting from the bottom of the hole to the opening of the hole, so that the grout fills the rock fissures and wraps the high-strength hollow grouting anchor rod. S4. Apply pre-tightening force and initial support force: After the injected grout has solidified to the design strength, install trays and locks on the surface of the roadway roof, apply axial pre-tightening force to the high-strength hollow grouting anchor cable, and compress the series of broken rock layers. S5. Coordination measures during fault-crossing mining: When the mining face passes through an area with implemented series support, adjust the cutting parameters of the coal mining machine and the support status of the hydraulic supports to maintain the integrity of the roof.

2. The method for series support of roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, In step S1, the specific method for advanced detection and evaluation is as follows: The method combines physical drilling and core sampling with digital imaging. The drilling rig is used to construct a detection borehole. The location of the fault fracture zone or delamination development zone is determined based on the changes in drilling speed and the properties of the returned rock powder. A borehole sight is sent into the detection borehole to observe the location of fracture development and the depth of lithological changes inside the roof rock mass. Based on the rock mechanics parameters and geological information obtained from the detection, the plastic failure radius of the roadway roof under the influence of the fault is calculated. The plastic failure radius is used as the theoretical radius of the roof fracture zone to determine the minimum depth that the high-strength hollow grouting anchor cable must penetrate, ensuring that the anchoring end of the high-strength hollow grouting anchor cable is located in the elastic zone outside the plastic failure radius.

3. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, In step S2, the specific arrangement of hole positions and drilling method is as follows: Within the influence range of the fault fracture zone, the main control zone and the transition zone are determined, and a rectangular or staggered hole arrangement is adopted in the main control zone. When drilling, for loose, broken, and muddy areas, use wall-supported drilling and casing drilling or staged hole enlargement process. That is, first use a drill rod with an outer casing for guiding drilling, retain the casing as a temporary support, and then pull it out after the high-strength hollow grouting anchor cable is sent in. A lock hole structure is set at the borehole opening. The gap between the borehole opening pipe and the coal and rock mass is sealed by enlarging the hole and pre-embedding the opening pipe with quick-setting cement.

4. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, When the fault drop is greater than the coal seam thickness, the series support path in step S4 adopts a two-way series structure arrangement. The bidirectional series structure includes a vertical suspension assembly and an inclined locking assembly; The vertical suspension assembly includes multiple high-strength hollow grouting anchor cables arranged perpendicular to the surface of the roadway roof, which are used to bear the self-weight load of the fractured rock layer on the roof and connect the fractured rock mass in the vertical direction to the deep rock layer. The inclined locking group includes multiple high-strength hollow grouting anchor cables arranged at a preset deflection angle to the vertical line of the top plate, used to pass through the main slip surface of the fault fracture zone and penetrate into the intact rock mass of the fault opposite plate.

5. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 4, characterized in that, The arrangement parameters of the inclined locking group meet the following requirements: The installation deflection angle of the high-strength hollow grouting anchor cable of the inclined locking group is determined according to the detected fault dip angle and the preset optimal intersection shear angle, so that the angle between the axis of the high-strength hollow grouting anchor cable and the fault plane is in the shear optimization range. The total length of the high-strength hollow grouting anchor cable of the inclined locking group is determined according to the normal width of the fault fracture zone, ensuring that the high-strength hollow grouting anchor cable can penetrate the fault fracture zone, and has a first anchorage length in the stable rock layer of the main block before crossing the fault plane, and a second anchorage length in the stable rock layer of the opposite block after crossing the fault plane.

6. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, When the longwall face is in the area of ​​total rock breach, steps S2 and S3 adopt a deep extension and advanced reinforcement strategy: Before the coal mining machine performs roof-breaking and cutting, the installation and grouting of high-strength hollow grouting anchor cables are completed in the advanced support area; The length of the selected high-strength hollow grouting anchor cable includes a dynamic compensation amount, which is determined based on the vertical thickness of the roof rock that the coal mining machine needs to cut. This ensures that after deducting the thickness of the cut rock, the remaining effective anchoring length on the high-strength hollow grouting anchor cable can still penetrate into the stable rock layer above the cut surface.

7. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, When the longwall face is in the undercut zone, step S2 employs a combination of side protection and root reinforcement strategies: The installation angle of a row of high-strength hollow grouting anchor cables near the coal face is designed to be inclined towards the coal face, generating lateral restraint force on the triangular rock mass above the coal face. At the same time, the protective plates of the hydraulic support restrict the lateral displacement of the roof of the coal wall and prevent the high-strength hollow grouting anchor cables from buckling due to excessive exposure.

8. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, The specific process of full-length pressurized grouting in step S3 is as follows: Insert the rod of the high-strength hollow grouting anchor cable into the borehole to the predetermined depth, and install a grout stop plug at the borehole opening to seal the annular space of the borehole. High-pressure grouting pumps are used to pump grout into the central channel of high-strength hollow grouting anchor cables. The grout flows out from the end of the rod or the grout outlet, fills the bottom of the hole and flows back to the hole opening along the annular space. Once the grout fills the annular space, maintain the grouting pressure to allow the grout to penetrate and diffuse into the fissures and delamination voids of the surrounding fractured rock mass. The type of grouting cementing material is selected based on the degree of rock fissure development in the fault fracture zone. Ultrafine cement grout or polymer chemical grout is used in micro-fissure areas, while early-strength ordinary silicate cement grout is used in large fissure areas.

9. A method for series support of the roof slab for crossing faults and preventing roof collapse according to claim 1, characterized in that, The specific process for applying the preload and initial support force in step S4 is as follows: After the grouting operation is completed and the strength of the grouting bonding material has increased to the design strength, the exposed section of the high-strength hollow grouting anchor cable is cleaned. The arched tray, the angle-adjusting washer, and the tensioning lock are assembled in sequence. The angle-adjusting washer is used to adjust the pressure-bearing surface of the lock to be perpendicular to the axis of the high-strength hollow grouting anchor cable. The process employs a graded loading and over-tensioning locking technique. First, the load is applied to a portion of the design preload for initial tensioning. Then, the load is applied to exceed the design preload for over-tensioning and holding the load. Finally, the load is returned to the design preload value to lock the locking device.

10. A method for series support of the roof slab across faults and preventing roof collapse according to claim 1, characterized in that, The specific details of the coordinating measures in step S5 include: Reduce the traction speed of the coal mining machine and decrease the cutting depth of the coal mining machine to reduce the gap between the front end of the hydraulic support top beam and the coal wall. The hydraulic support adopts a pressurized rubbing top moving method. During the moving process, the hydraulic system supply pressure is controlled so that the top beam of the hydraulic support maintains residual support force and slides forward while closely rubbing the top plate surface. Setting the minimum initial support force of the hydraulic support can balance the direct jacking gravity and overcome the unloading effect of the pre-tightening force of the high-strength hollow grouting anchor cable; if a risk of roof leakage is detected in a local area, supplementary chemical grouting is carried out at the gap of the high-strength hollow grouting anchor cable.

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