Construction method of grouting anchor cable for coal seam reinforcement

Abstract

The invention discloses a grouting anchor cable construction method for coal seam reinforcement, and belongs to the technical field of coal mine tunnel supporting, the method abandons a fixed linear construction sequence, emphasizes a closed loop process logic of evaluation, execution, feedback and adjustment, and is characterized in that a grouting anchor cable is constructed according to real-time response of surrounding rock at each stage of construction. And specific parameters and opportunity of subsequent process steps are dynamically decided, so that optimal cooperation of anchoring and grouting in time and space is achieved, and the reinforcing effect and reliability in the soft and broken coal seam are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of coal mine roadway support technology, and more specifically, to a method for constructing grouting anchor cables for coal seam reinforcement. Background Technology

[0002] In deep coal mining, controlling the surrounding rock of soft and fractured coal seams is a major technical challenge. These coal seams (often referred to as "three-soft" seams) have low strength and poor self-stabilizing ability. Traditional support methods, such as U-shaped support, suffer from cumbersome construction, passive load-bearing, and susceptibility to deformation and failure. Grouting and anchoring technology, by combining anchoring and grouting, can actively reinforce the surrounding rock and has become an effective solution.

[0003] Existing grouting anchor cable construction methods typically follow a linear process of "drilling-hole cleaning-anchor cable insertion-grouting-tensioning". For example, current methods involve drilling a hole with a specialized drilling rig, inserting the assembled anchor cable, and injecting micro-expansion high-strength grout. After the grout solidifies, a pre-tightening force is applied. Another improvement is to try binding the anchor cable and the grouting pipe together and sending them to the bottom of the hole to achieve bottom grouting, and adding a protective sleeve to the free section to prevent grout from flowing in. Recently, there has also been exploration of "synchronous cable threading and grouting", which uses a hollow drill rod to push the anchor cable to the bottom of the hole while grouting is being performed, aiming to improve efficiency.

[0004] However, after in-depth research and practice, the applicant discovered that the existing technology still has the following shortcomings: For example, the process is rigid and has poor adaptability. Most methods are sequential construction with fixed parameters, which do not fully consider the dynamic changes in soft coal seams during construction, such as the difficulty of drilling, the easy collapse of the borehole wall, and the uncontrollable diffusion of grout. For example, in extremely broken coal bodies, the borehole wall is severely damaged after conventional drilling, which directly affects the anchoring quality and uniformity of the subsequent grouting body. The grouting has poor coupling with the surrounding rock. The timing, pressure and amount of grouting are often preset and cannot be dynamically adjusted according to the real-time fracture status of the surrounding rock and the grout absorption characteristics revealed by the borehole. This results in either a large amount of grout leakage that cannot effectively reinforce the rock, or premature sealing of the cracks that fails to penetrate to the deep part that needs reinforcement. The lack of effect-based closed-loop control means that the evaluation of reinforcement effect is relatively delayed after the construction process is completed. Once the support strength is found to be insufficient, only costly passive reinforcement can be carried out. It is not convenient to optimize process parameters in real time through monitoring and feedback during the construction process. Therefore, there is an urgent need for a construction method that can dynamically adapt to coal seam conditions, achieve coordinated anchoring depth, and perform iterative optimization based on real-time feedback. Thus, we propose a grouting anchor construction method for coal seam reinforcement to solve the aforementioned problems. Summary of the Invention

[0005] 1. Technical problems to be solved To address the problems existing in the prior art, the present invention aims to provide a grouting anchor cable construction method for coal seam reinforcement. This method abandons the fixed linear construction sequence and instead emphasizes a closed-loop process logic of evaluation, execution, feedback, and adjustment. Its core lies in dynamically deciding the specific parameters and timing of subsequent process steps based on the real-time response of the surrounding rock at each stage of construction, thereby achieving optimal synergy between anchoring and grouting in time and space, and significantly improving the reinforcement effect and reliability in soft and fractured coal seams.

[0006] 2. Technical Solution To solve the above problems, the present invention adopts the following technical solution.

[0007] A method for constructing grouting anchor cables for coal seam reinforcement includes the following steps performed cyclically: Step S1, Dynamic assessment and pretreatment of surrounding rock condition: Before drilling, the working face is sealed, and drilling parameters and slag return are analyzed in real time during the drilling process to dynamically assess the degree of breakage and stability level of the coal body at the drilling location. Step S2, Anchor Cable Hole Drilling and Instant Response Wall Protection: After the hole is formed, based on the stability level assessed in Step S1, the first stage of wall protection slurry is selectively injected into the hole through the drill pipe to perform instant wall protection and consolidation. Step S3, Integrated installation of anchor cable and grouting system and dynamic grouting: The hollow grouting anchor cable and the dual-channel grouting pipe are installed as a whole, and the grouting pressure and flow rate are dynamically adjusted and intermittent re-grouting is implemented based on the real-time changes in grouting pressure and flow rate to complete the second stage of high-pressure grouting; Step S4, Prestressing application in stages and grouting effect feedback loop: After the grout in the second stage of high-pressure grouting in step S3 reaches a certain strength, the first prestress is applied. Based on the feedback from subsequent prestress loss and surrounding rock deformation monitoring, a decision is made to perform a second tensioning or to start a feedback loop with local reinforcement grouting as the core.

[0008] Furthermore, in step S1, the stability level is divided into at least three levels: Level I is basically intact, Level II is slightly broken, and Level III is severely broken and seeping water. The evaluation criteria include the drilling speed mutation point, the abnormal vibration frequency of the drill pipe, the proportion of powdery matter in the returned slag, and the water output from the borehole.

[0009] Furthermore, in step S2, the immediate wall consolidation specifically involves: when the stability level is I and the structure is basically intact, no wall grouting is performed; when the stability level is II and the structure is slightly broken or III and the structure is severely broken and leaking, a low-viscosity, slightly expanding modified silicate slurry is injected through the hollow channel of the drill pipe that has not been withdrawn as the first stage of wall grouting, and the grouting pressure is controlled at 0.5-2.0 MPa.

[0010] Furthermore, in step S3, the dynamic adjustment of grouting pressure and flow rate and the implementation of intermittent re-grouting specifically include: initially using grouting at a pressure of 1-3 MPa, gradually increasing the pressure to 5-15 MPa when the pressure-flow curve is stable to implement fracturing and permeation grouting, pausing grouting in the hole when the pressure suddenly increases and the flow rate sharply decreases, and switching to grouting in an adjacent borehole, returning to the original hole for re-grouting after a period of time.

[0011] Furthermore, in step S3, the central channel of the dual-channel grouting pipe is used to inject the second section of high-pressure grout, and the side wall channel is used to monitor the grout return status at the orifice. When the grout return is pure grout, it serves as one of the signals to stop grouting.

[0012] Furthermore, in step S4, the first prestressing tensioning is carried out 12-36 hours after the second grouting is completed and the strength of the grouting body has developed to 60%-70% of the design value, and the tensioning force is 50%-70% of the design prestressing force.

[0013] Furthermore, in step S4, the decision logic of the feedback loop is as follows: when the preload loss rate after the first tensioning is less than the set threshold and the surrounding rock deformation rate tends to stabilize, then the second tensioning is performed to the designed preload; when the preload loss rate is greater than the set threshold or the surrounding rock deformation is obvious, then the feedback loop is started to perform local reinforcement grouting on the affected area.

[0014] Furthermore, the local reinforcement grouting includes: taking the abnormal loss point of preload as the center, within a radius of 2-3 times the designed anchor cable spacing, repeating the dynamic high-pressure grouting process in step S3 for existing anchor cable holes or newly added auxiliary grouting holes.

[0015] 3. Beneficial Effects Compared with the prior art, the advantages of this invention are: (1) This scheme transforms the construction from a static operation sequence to a dynamic decision tree. The execution method and parameters of each step of wall protection, grouting, and tensioning depend on the real-time response of the surrounding rock in the previous step, such as the borehole evaluation level, grouting pressure-flow curve, and prestress loss rate, thereby improving the adaptability of the construction method. (2) In this scheme, the differentiated instant wall protection effectively solves the core pain points of difficult hole formation and poor hole shape in soft coal seams. The dynamic grouting strategy greatly improves the grout utilization rate and reinforcement uniformity. The prestress loss feedback loop mechanism transforms post-event remediation into in-process proactive optimization, fundamentally improving the final quality of the support system and the long-term stability of the roadway. Moreover, this construction method does not rely on specific new devices, but reconstructs the process logic of conventional drilling rigs, grouting pumps, tensioning equipment and monitoring instruments, making it easy to implement and promote on site. It is particularly suitable for soft and broken coal seam roadways with complex and varied geological conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the construction method architecture of the present invention. Detailed Implementation

[0017] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Example 1: Please refer to the accompanying drawings in the instruction manual. Figure 1 A method for constructing grouting anchor cables for coal seam reinforcement includes the following steps performed cyclically: Step S1: Dynamic assessment and pretreatment of surrounding rock condition: Based on the preliminary design of anchor cable parameters and spacing according to the geological survey data of the tunnel, before the drilling rig is in place, the surface of the face and the area to be drilled is pre-treated by spraying a thin layer of mortar mixed with a quick-setting agent to form a preliminary sealed shell. During the drilling process, the drilling speed, drill rod vibration frequency, slag return characteristics and water volume are recorded and analyzed in real time to dynamically evaluate the degree of breakage and stability level of the coal body at the drilling location. The stability level is divided into Level I basically intact, Level II slightly broken, and Level III severely broken and water-seeping.

[0019] Step S2, Anchor Hole Drilling and Immediate Response Wall Protection: Using medium-compressed air or atomized water as the drilling medium, drill to the designed depth. After drilling, do not immediately remove the drill pipe. Instead, perform differentiated immediate wall protection operations based on the stability level assessed in step S1. Specifically: If the assessment is Level I and the product is basically intact, proceed directly to step S3. When the assessment is Class II mild fracture or Class III severe fracture with water seepage, a first stage of low-viscosity, micro-expansion modified silicate grout is injected into the hole through the hollow channel of the drill pipe. The grouting pressure is controlled at 0.5-2.0 MPa, and the grouting volume is stopped when there is slight grout return at the hole opening or when the predetermined volume is reached. This stage of grout aims to penetrate the micro-fractures in the borehole disturbance zone, achieve preliminary consolidation and wall protection, and form a guiding channel for subsequent main grouting.

[0020] Step S3: Integrated installation of anchor cables and grouting system, and dynamic grouting: After the wall-protecting grout has initially set, the drill pipe is removed. Then, the hollow grouting anchor cable and the dual-channel grouting pipe are bundled together as a single unit and quickly inserted into the hole. The central channel of the dual-channel grouting pipe is used for high-pressure grouting, and the side channel is used for low-pressure air return or grout return. After the anchor cable is in place, the second stage of high-pressure grouting immediately begins through the dual-channel grouting pipe. The key to this stage is dynamic control. Initially, a pressure of 1-3 MPa was used to inject nano-silicon-based composite grout, and the changes in grouting pressure and flow rate were monitored in real time. If the pressure and flow rate are stable, gradually increase the pressure to 5-15 MPa and implement fracturing-penetration composite grouting to force the grout into deeper fissures. If the pressure rises sharply and the flow rate drops sharply, it indicates that the local area is saturated. In this case, stop grouting in the hole and switch to grouting in the adjacent hole. After an interval of 30-60 minutes, return to the hole for re-grouting to achieve the flow of grout around the area and full filling. The grout return situation at the orifice is monitored through the side wall channel. When the returned grout is pure grout, grouting is stopped and the orifice is sealed.

[0021] Step 4: Prestressing graded application and grouting effect feedback loop: After the second grouting is completed, instead of waiting for the grout to fully reach its final strength, the first prestressing tensioning is carried out when its strength develops to 60%-70% of the design value (usually 12-36 hours after grouting). The tensioning force is 50%-70% of the design prestressing force. After the tensioning is completed, temporary locking devices are installed. 24-48 hours after the initial tensioning, measure the preload loss using a pressure sensor installed under the anchor cable tray or by using a torque wrench, and observe the roadway surface deformation monitoring data. Based on this feedback: If the preload loss rate is less than 15% and the surrounding rock deformation rate tends to stabilize, then a second tensioning is performed to the design preload (usually not less than 200kN), and the final locking is completed. If the preload loss rate is greater than 15% or the surrounding rock deformation is obvious, it is determined that the coupling strength between the grout and the surrounding rock in this area has not met expectations. At this time, the feedback loop is started: record the coordinates of the location, and take it as the center. Within a radius of 2-3 times the anchor cable spacing, start the re-grouting process in step S3 for adjacent existing anchor cables or newly added auxiliary grouting holes to perform local reinforcement. After reinforcement, re-evaluate and complete the final tensioning.

[0022] Example 2: Based on the above embodiment 1, the following description, combined with the actual application scenario of a coal mine, will provide further details: Application in the construction of a deep, soft coal seam mining roadway The 1203 mining roadway in a coal mine has a depth of 820m and traverses a Jurassic soft coal seam with a uniaxial compressive strength of only 3.2MPa, classifying it as a typical "three-soft" coal seam (soft coal, soft roof, and soft floor). The roadway's designed cross-section is rectangular (4.5m wide × 3.0m high). When U-shaped support was originally used, the roof and floor converged by 280mm within 30 days of excavation, and the sidewalls converged by 160mm, resulting in severe support failure. The grouting anchor cable construction method of this invention is now being used for support, and the specific implementation is as follows: 1. Pre-construction preparation Based on the tunnel geological survey report, the grouting anchor cable design parameters are as follows: the anchor cable adopts Φ22mm hollow threaded steel, with a length of 6.5m, a row spacing of 1.5m, and a spacing of 1.2m; Materials required: Modified silicate wall grout (viscosity 15-25 mPa·s, expansion rate 3%-5%), nano-silica-based composite grout (compressive strength ≥40 MPa). Equipment configuration: medium-pressure drilling rig, dual-liquid grouting pump (maximum pressure 20MPa), pressure and flow monitoring instrument, anchor cable tensioning machine (rated tension 300kN), and roadway surface displacement monitoring points (1 set every 5m).

[0023] 2. Step S1: Dynamic assessment and pretreatment of surrounding rock condition Before the drilling rig is in place, a thin layer of mortar mixed with 3% quick-setting agent is sprayed onto the face of the drilling rig, with a thickness of 50mm, to form a surface sealing shell. During the drilling process, real-time monitoring showed that the drilling speed suddenly changed from 0.8 m / min to 1.5 m / min (indicating a broken interface), the abnormal vibration frequency of the drill rod was ≥3 Hz, the proportion of powdery material in the returned slag reached 45%, and some boreholes showed trace water seepage (single borehole water output ≤5 L / min). Comprehensive assessment: The coal seam in the 30-50m section of the roadway is classified as Class II slightly broken, while the 50-70m section is classified as Class III severely broken and water-seeping due to water seepage and the proportion of powdery matter rising to 60%.

[0024] 3. Step S2: Anchor cable hole drilling and immediate responsive wall protection Atomized water was used as the drilling medium, and the hole was drilled to the designed depth of 6.5m. The drill rod was not removed after the hole was completed. Level II slightly fractured area (30-50m section): Inject the first section of modified silicate slurry through the hollow channel of the drill pipe. The grouting pressure is controlled at 1.2MPa, and the grouting volume is 8-10L per hole. Stop when there is slight slurry return at the hole opening to achieve consolidation of microcracks in the hole wall. For Class III severely fractured and seepage-prone areas (50-70m section): increase the grouting pressure to 1.8MPa, increase the grouting volume to 12-15L, and add 2% anti-seepage agent. After grouting, let it stand for 30 minutes to ensure that the grout initially sets and forms a stable hole wall.

[0025] 4. Step S3: Integrated installation of anchor cable and grouting system and dynamic grouting. After the wall-protecting grout has initially set (about 2 hours), remove the drill rod, bind the hollow grouting anchor cable and the dual-channel grouting pipe together, and quickly insert them into the hole to ensure that the anchor cable is in place at the bottom of the hole. Initiating the second stage of high-pressure grouting: Initially, a nano-silicon-based composite grout was injected at a pressure of 2 MPa. Monitoring showed that the pressure and flow rate were stable (approximately 8 L / min). The pressure was gradually increased to 8 MPa, and fracturing-penetration composite grouting was implemented. After grouting for 15 minutes, the pressure in the borehole at 52m increased sharply (from 8 MPa to 12 MPa) and the flow rate decreased sharply (to 1.5 L / min). Grouting at this hole was paused, and grouting was switched to the adjacent hole at 51.5m. After an interval of 45 minutes, the hole at 52m was returned for re-grouting. The re-grouting pressure was maintained at 6MPa for 8 minutes. After the sidewall channel was monitored and clean grout was detected, grouting was stopped and the hole was sealed.

[0026] 5. Step S4: Prestressing graded application and grouting effect feedback loop 24 hours after the second grouting is completed, the grout strength is tested and found to be 65% of the design value. The first prestressing tensioning is then carried out, and the tensioning force is controlled at 60% of the design preload (200kN), i.e., 120kN. Temporary locking devices are then installed. Thirty-six hours after the first tensioning, monitoring by pressure sensors showed that the preload loss rate in the 30-45m section was 12%, and the deformation rate of the surrounding rock dropped to 0.3mm / d, tending to stabilize; the preload loss rate in the 50-70m section reached 18%, and the deformation rate at some monitoring points was still 0.7mm / d. Decision execution: The 30-45m section is tensioned a second time to 200kN to complete the final locking; the 50-70m section initiates the feedback loop; Local reinforcement grouting: Centered on 52m (the point of maximum preload loss), within a radius of 3m (twice the anchor cable spacing of 1.5m), repeat the dynamic high-pressure grouting process of step S3 for the original 5 anchor cable holes and the newly added 2 auxiliary grouting holes, and control the reinforcement grouting pressure at 7-9MPa. 24 hours after reinforcement, the preload loss rate was tested again and found to be reduced to 9%, and the surrounding rock deformation rate was stabilized at 0.2 mm / d. The second tensioning was carried out to 200 kN to complete all support.

[0027] Construction effect verification After the tunnel was constructed using this method, it was continuously monitored for 60 days: the convergence of the top and bottom plates was controlled within 45mm, the convergence of the two sides was ≤30mm, and the anchoring force of the grouting anchor cables was ≥220kN, meeting the design requirements. The stability of the tunnel was significantly improved, and no support failure occurred. Compared with traditional support methods, the support life was extended by more than 3 times, and the construction efficiency was improved by 25%.

[0028] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a grouting anchor cable for reinforcing a coal seam, characterized by, The method comprises the following steps which are cyclically executed: Step S1, dynamic evaluation and pretreatment of surrounding rock state: before drilling, the surface of the working face is closed, and drilling parameters and back slurry are analyzed in real time during drilling to dynamically evaluate the fragmentation degree and stability grade of the coal body at the drilling position; Step S2, anchor hole drilling and immediate responsive wall protection: after the hole is formed, according to the stability grade evaluated in step S1, the first section of wall protection slurry is selectively injected into the hole through the drill rod to perform immediate wall protection consolidation; Step S3, integrated placement of anchor and grouting system and dynamic grouting: the hollow grouting anchor and the double-channel grouting pipe are placed as a whole, and based on the real-time grouting pressure and flow changes, the grouting pressure, flow and intermittent re-injection are dynamically adjusted to complete the second section of high-pressure grouting; Step S4, pre-stress graded application and grouting effect feedback cycle: after the slurry in step S3 reaches a certain strength, the first pre-stress is applied, and according to the subsequent pre-tightening force loss and surrounding rock deformation monitoring feedback, the second tensioning or the feedback cycle with local reinforced grouting as the core is started.

2. The grouting anchor cable construction method for coal seam reinforcement according to claim 1, characterized in that: In step S1, the stability grade is at least divided into three levels: level I is basically complete, level II is slightly broken, and level III is severely broken and seepage, and the evaluation is based on drilling speed mutation point, abnormal vibration frequency of drill rod, proportion of powdery matter in back slurry and water outflow of the hole.

3. The grouting anchor cable construction method for coal seam reinforcement according to claim 2, characterized in that: In step S2, the immediate wall protection consolidation is specifically: when the stability grade is level I, no wall protection grouting is performed, when the stability grade is level II or level III, low viscosity and micro-expansion modified silicate slurry is injected as the first section of wall protection slurry through the hollow channel of the drill rod, and the grouting pressure is controlled at 0.5-2.0MPa.

4. The grouting anchor cable construction method for coal seam reinforcement according to claim 1, characterized in that: In step S3, the dynamic adjustment of grouting pressure, flow and intermittent re-injection specifically includes: initially, the pressure grouting is performed at 1-3MPa, when the pressure-flow curve is stable, the pressure is gradually increased to 5-15MPa for splitting permeation grouting, when the pressure suddenly rises and the flow sharply decreases, the hole grouting is suspended and switched to adjacent hole grouting, and after a period of time, the original hole is returned for re-injection.

5. The grouting anchor cable construction method for coal seam reinforcement according to claim 1, characterized in that: In step S3, the center channel of the double-channel grouting pipe is used for injecting the second section of high-pressure slurry, and the side wall channel is used for monitoring the hole back slurry state, and when the back slurry is pure slurry, it is one of the signals for stopping grouting.

6. The grouting anchor cable construction method for coal seam reinforcement according to claim 1, characterized in that: In step S4, the first pre-stress tensioning is performed 12-36 hours after the second section of grouting is completed, and the strength of the grouting body develops to 60%-70% of the design value, and the tensioning force is 50%-70% of the design pre-tightening force.

7. The grouting anchor cable construction method for coal seam reinforcement according to claim 1, characterized in that: In step S4, the decision logic of the feedback cycle is: when the pre-tightening force loss rate is less than the set threshold and the surrounding rock deformation rate tends to be stable after the first tensioning, the second tensioning to the design pre-tightening force is performed, and when the pre-tightening force loss rate is greater than the set threshold or the surrounding rock deformation is obvious, the feedback cycle is started, and local reinforced grouting is performed in the affected area.

8. The grouting anchor cable construction method for coal seam reinforcement according to claim 7, characterized in that: The local reinforcement grouting includes: taking the pre-tightening force abnormal loss point as the center, in the range of a radius of 2-3 times the anchor cable design row distance, repeatedly performing the dynamic high-pressure grouting process in the step S3 on the existing anchor cable hole or the newly added auxiliary grouting hole.

Images