Large-section broken rock mass advanced roof control safe and efficient excavation method

Abstract

The application discloses a kind of large section broken rock mass advance roof control safe and efficient excavation method, belong to broken rock mass technical field.The application includes the following steps: S1, along the large section broken area excavation contour line is measured;S2, grouting sequence is two sides to middle construction, full hole once injection type;S3, for large section broken area engineering adopts partition step reverse intersection point method construction;S4, according to the effect of site grouting reinforcement, select appropriate support parameters;S5, along the large section broken area engineering excavation contour line inside position place roof protection empty hole;S6, after blasting, using steel tape or other length measuring tool, measure the large section broken area engineering contour size after blasting;S7, according to the above steps, carry out 15-35 times field blasting test;S8, the roadway section deviation measured in steps S6, S7, using regression analysis method.The application improves the service life of large section area engineering, improves the safety efficiency and economic benefits of underground space production operation.

Description

Technical Field

[0001] This invention relates to the field of fractured rock technology, and in particular to a safe and efficient method for pre-controlling the roof of large-section fractured rock masses. Background Technology

[0002] According to public reports from local emergency management and mine safety management departments, as of the first half of 2022, a total of 87 accidents occurred in mines nationwide, resulting in 132 deaths and 35 injuries. Among these accidents, roof collapses and landslides were the most frequent, accounting for 30.7% and 28.9% of the total, respectively. This not only brought misfortune to employees and their families but also impacted the development of these enterprises.

[0003] Analysis of accident data in underground mines reveals that roof falls have become increasingly frequent in recent years, accounting for nearly 30% of all mine accidents. Serious injuries resulting from roof falls are also common, exceeding 30% of all roof fall accidents. Therefore, roof safety is a key focus of underground mine safety management. Existing mining technologies must be utilized, and strict construction design must be implemented to minimize damage to the roof during construction.

[0004] Due to the needs of underground mine construction, facilities such as bottom shaft yards, central substations, and central pump rooms are often installed, all of which are large-section facilities. Because of the large cross-section and depth of the excavation area, the stress field of the surrounding rock changes after excavation, making it difficult to maintain roadways in fractured or relatively fractured areas, increasing their susceptibility to collapse and impacting safe production. The large excavation cross-section also increases the difficulty of roof support and the significant impact of blasting operations on the original rock. Blasting vibrations adversely affect the rock mass in the excavated area, damaging the stability of the original rock mass structure. To ensure the safety and stability of these large-section facilities, the amount of support and shotcreting required increases accordingly. However, under long-term blasting loads, the stability of the already supported fractured or relatively fractured rock mass structure is affected, resulting in high maintenance costs in the later stages. Summary of the Invention

[0005] The purpose of this invention is to provide a safe and efficient method for advanced roof control in large-section fractured rock masses, which aims to reduce damage and destruction to the roof of roadways in large-section fractured and relatively fractured areas, reduce the safety risks of roof and face collapse, control the forming effect of engineering in large-section fractured areas, improve the service life of engineering in large-section areas, and improve the safety efficiency and economic benefits of underground space production operations.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A safe and efficient method for pre-controlled excavation of large-section fractured rock masses includes the following steps:

[0008] S1. Conduct point surveying along the excavation outline of the large-section fractured area, strictly controlling the elevation and orientation of the tunnel top and bottom to ensure accuracy. Surveying work should be conducted according to the progress of the working face, establishing different directional control lines before establishing the construction control lines. Based on the site's geological conditions, select an appropriate excavation length and use a rock drilling rig or grouting machine to construct grouting holes with a depth of 40m-50m. The drilling angle should be parallel to the excavation face direction, and the bottom of the hole should fall on the excavation section. At a position 1m outside; the hole spacing is 0.6m to 1m, the hole diameter is 60mm, and a 60mm diameter grout stop plug is installed, with a grout stop plug length of 1.5 to 2.0m; when the rock mass in the large cross-section area is particularly broken, a water exploration drilling rig is used to drill φ75mm holes, and a 9m diameter 60mm steel pipe is pre-embedded. A 7m diameter perforation hole is cut at the front end of the steel pipe, and grout is injected into the surrounding rock through the steel pipe. The steel pipe spacing is 1m, the drilling angle is 10 to 20° in the direction of the excavation face, and the bottom of the hole is 0.8m outside the excavation cross-section;

[0009] S2. To ensure grouting effectiveness, the grouting sequence is from both sides towards the middle, with a single injection of the entire hole. The grouting material is primarily a two-component cement grout, using P.O42.5 ordinary Portland cement, with an additional 0.5% by weight of cement as an admixture. The admixture provides rapid setting and early strength. If the rock is fractured, or the water inflow or grout absorption is large, a two-component grout can be used, or a two-component grout can be injected first and then used for sealing. After grouting, excavation can only begin 8 hours later.

[0010] S3. For projects in large-section fractured areas, the zoned step-back reverse intersection method is adopted for construction. The specific construction sequence is as follows:

[0011] S301. The step-type excavation method is adopted for construction. First, the "entry tunnel" half-section is constructed with an advance of 2m. After the roof and top and sides reach the design dimensions, anchor mesh cable spraying support is carried out.

[0012] S302, Lateral excavation to the entire large cross-section design size, and top and side anchor mesh cable spraying support;

[0013] S303, the left and right sections of the upper step construction are excavated alternately, with an advance of 2.0m per cycle (adjusted and optimized in a timely manner according to the site rock conditions); after the left and right sections of the upper step are leveled to the bottom slab, the lower step construction begins.

[0014] S304, Excavation and support of the entire cross section is completed;

[0015] S4. Based on the on-site grouting reinforcement effect, select appropriate support parameters. The optimized support parameters are as follows: ① The entire cross-section uses HRB400 φ18mm*2400mm threaded steel resin anchors with a spacing of 800*800mm; the metal mesh is welded with φ6.0mm steel bars, with a mesh size of 2100mm*1050mm and a mesh size of 100mm*100mm. The mesh panels are connected with 14# iron wire, with an overlap length of 100mm; ② The anchor cable uses φ=17. 8mm, L=6300mm resin seven-core steel strand, the support plate is made of 15mm thick steel plate, the specification is 300mm*300mm, the anchor cable design spacing is 1600*1500mm; to ensure the integrity of the anchor cable construction, the anchor cable is supported by mining W-shaped steel strip; the mining W-shaped steel strip model is 2000mm (length)*280mm (width)*4.75mm (thickness); ③ the initial shotcrete thickness is 100mm, the secondary shotcrete thickness is 100mm, and the total shotcrete thickness is 200mm;

[0016] S5. To reduce the impact of blasting vibration and shock waves on the top rock mass of the large-section fractured area (pre-grouting reinforcement), protective holes are arranged at positions S1 = (0.1~0.2) m inside the excavation outline of the large-section fractured area, with a spacing of S2 = (8~15) d. 孔 The slotting holes, auxiliary holes, and peripheral holes are detonated in sequence. To reduce the impact of blasting vibration on the surrounding rock of the excavation area and to control the maximum charge in a single simultaneous blast, digital electronic detonators are designed to achieve micro-delay interval detonation of each hole. The interval delay time of each hole (10, 20 ms, etc.) is optimized and adjusted according to the layout of the tunneling section.

[0017] S6. After blasting, use a steel tape measure or other length measuring tools to measure the outline dimensions of the large-section fractured area after blasting.

[0018] S7. Following the steps above, conduct 15 to 35 field blasting tests to improve the reliability of the experimental data; it is best to perform regression analysis on the roadway cross-sectional deviation S; too few tests will affect the accuracy and reliability; too many tests will result in long field test times and high costs.

[0019] S8. The roadway cross-sectional deviation S measured in steps S6 and S7 is used to perform regression analysis to obtain the patterns of the depth, angle, spacing, and delay time of the roof reinforcement holes.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) This invention targets the top of the large-section fractured area in underground space for advanced pre-grouting reinforcement, which consolidates the fractured rock mass into a whole, improves the overall stability of the fractured rock mass roadway roof area, and provides favorable conditions for controlling the formation of the roadway excavation section.

[0022] (2) Based on the overall stability of the fractured area of ​​the large cross section after reinforcement, the present invention divides the tunneling area into multiple zones (zone 1, zone 2, zone 3, etc.), reduces the exposed area of ​​the large cross section, and provides active support for some local roofs in advance, which is conducive to controlling the collapse of the roof rock and maintaining the integrity of the surrounding rock, thereby making full use of the bearing capacity of the surrounding rock itself. By optimizing the construction organization sequence, the safety and efficiency of construction operations are improved.

[0023] (3) The present invention arranges dense protective holes along the excavation outline of the large cross-section fractured area. The initial pre-splitting holes formed can effectively block the propagation of blasting vibration generated by the subsequent blasting holes, reducing the damage and disturbance of blasting vibration to the roof of the large cross-section area.

[0024] (4) The present invention uses digital electronic detonators, which can realize micro-differential detonation of each hole, control the maximum amount of explosives in one burst, reduce the impact of blasting vibration on the surrounding rock of the excavation area, and improve the overall stability of the large-section fractured area.

[0025] (5) The present invention effectively controls the forming effect of the tunnel section in the large section fracture area, reduces the deviation of the tunnel section size, reduces the workload and support cost of the tunnel section shotcrete support, and improves the safety efficiency and economic benefits of underground space production operations. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the plane projection and cross section of a large-section fractured rock mass for efficient excavation according to the present invention;

[0027] Figure 2 This is a reverse construction sequence diagram for efficient excavation of large-section fractured rock mass according to the present invention;

[0028] Figure 3 This is a diagram of advanced pre-grouting reinforcement of a large-section fractured rock mass excavation face according to the present invention;

[0029] Figure 4 This invention relates to a layout diagram of blast holes for efficient excavation of large-section fractured rock mass.

[0030] In the diagram: 1. Pre-grouting hole; 2. Dual-liquid solidified grout; 3. Grouting equipment; 4. High-pressure grouting pipe; 5. Area to be excavated; 6. Curtain reinforcement area; 7. Excavation outline; 8. Roof support hole; 9. Cutting hole; 10. Auxiliary hole; 11. Peripheral hole. Detailed Implementation

[0031] The technical solutions of 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.

[0032] This invention provides a safe and efficient method for pre-grouting and reinforcing the roof of large-section fractured rock masses. To reduce damage to the roof of large-section, fractured, or heavily fractured tunnels in underground spaces, and to extend the service life of large-section projects, this method optimizes the pre-grouting and reinforcement-vibration-reduction construction sequence for fractured tunnels. It innovates a safe and efficient construction process for pre-grouting and reinforcement of fractured rock tunnels. This process pre-grouts and seals the fractured areas of the tunnel, consolidating the fractured rock mass into a unified whole, ensuring the stability of the tunnel. After the pre-grouting and reinforcement of the fractured rock tunnel is completed, the excavation area is divided into different blasting zones, and pre-wall protection holes are arranged along the tunnel excavation outline. These pre-wall protection holes are detonated first, forming pre-cracks, reducing the impact of the explosion pressure from subsequent blasting holes on the stability of the preserved rock mass side structure, thereby achieving the desired tunnel formation effect in large-section fractured areas. Therefore, for the excavation of large-section fractured rock masses underground, effective advanced pre-grouting reinforcement and zoned advanced wall protection blasting techniques are adopted. On the one hand, this improves the overall stability of the large-section fractured rock mass, and on the other hand, it ensures the smoothness of the tunneling and blasting section outline, reduces the over-excavation and under-excavation rate of the section, reduces the support and subsequent maintenance costs, and extends the service life of the project in the large-section fractured area.

[0033] Figure 1 This invention provides a schematic diagram of the plan projection and cross-section of a large-section fractured rock mass for efficient excavation. Considering the characteristics of large-section fractured rock masses, the excavation area is divided into reverse construction sequences, and is further divided into different construction zones (Zone 1, Zone 2, Zone 3, etc.) according to the progress of each cycle. See details below. Figure 2 The pre-grouting holes 1 are evenly arranged inside the excavation outline 7 (0.2-0.3m) according to the design requirements, and the size of the pre-grouting holes 1 is adjusted according to the drilling equipment. Based on the engineering geological and hydrogeological conditions of the large-section fractured area, a suitable dual-liquid solidification grout 2 is selected. The grouting equipment 3 uses a pneumatic or hydraulic device, and the dual-liquid solidification grout 2 is pumped into the pre-grouting holes 1 through the high-pressure grouting pipe 4. Under high pressure, the dual-liquid solidification grout 2 seeps into the fissures of the area to be excavated 5, solidifies the fractured rock mass, and forms a curtain reinforcement zone 6 with a certain diffusion range at the top of the excavation area 5, improving the overall safety and stability of the top of the excavation area 5. After the grouting reinforcement is completed, the curtain reinforcement thickness is further strengthened before tunneling construction can resume. See the schematic diagram for the specific layout. Figure 3 .

[0034] Outrigger holes 8 are arranged along the designed excavation outline 7 inwards (0.1-0.2m), with a spacing of 8-15 times the borehole diameter. The depth of the outrigger holes 8 is adjusted according to each cycle of advance, exceeding the depth of the top perimeter holes by 0.1-0.3m. The outrigger holes 8 are not loaded with explosives and are used to isolate the impact of blasting shock waves on the overall structure of the upper rock mass. The cut holes 9 adopt a wedge-shaped cut according to the design, with a hole spacing of 0.45-0.5m, a row spacing of 1.5-1.8m, and a borehole inclination angle of 81°. The designed detonation sequence is first the middle and then the outer side, with micro-delay detonation of each hole (interval time of 20ms). The upper borehole spacing of auxiliary borehole 10 is designed to be 1.0–1.2 m, the lower borehole spacing is designed to be 0.6–0.7 m, and the row spacing is 0.5–0.7 m. The borehole arrangement direction is perpendicular to the working face. The designed detonation sequence is first the middle, then the outer side, with micro-delay detonation for each borehole (interval time of 30 ms). The upper area spacing of peripheral borehole 11 is designed to be 350 ± 100 mm, and the spacing between the peripheral boreholes on the straight wall is designed to be 450 ± 100 mm. The design adopts a smooth blasting process to evenly distribute the explosive energy in the borehole, and transfer the detonation energy through the detonating cord. The designed detonation sequence is first the bottom, then the top, with micro-delay detonation for each borehole (interval time of 40 ms). See the detailed layout diagram. Figure 4 .

[0035] This invention designs a method for pre-grouting reinforcement of the top of a large-section fractured area, consolidating the fractured rock mass into a unified whole. This improves the overall stability of the roadway roof area and provides favorable conditions for controlling the formation of the roadway excavation cross-section. Dense wall-supporting holes are arranged in the roof above the excavation outline of the large-section fractured area. These initial pre-splitting holes effectively block the propagation of blasting vibrations generated by subsequent blasting holes, reducing damage to the roof of the large-section area caused by blasting vibrations.

[0036] To facilitate on-site construction operations, the digital electronic detonator and detonating cord are inserted together into the bottom charge cartridge of the upper peripheral borehole, avoiding connection between the digital electronic detonator and the detonating cord. After the bottom charge cartridge detonates, the detonating cord detonates the explosive in the borehole and transfers it to the borehole opening, achieving reverse detonation at the bottom of the borehole and increasing energy utilization. The design uses digital electronic detonators, which can achieve micro-delay interval detonation of each hole, control the maximum charge in a single burst, reduce the impact of blasting vibration on the surrounding rock of the excavation area, improve the flatness of the excavation section wall, cycle advance and half-hole ratio, and improve the overall stability of the large-section fractured area.

[0037] In summary, the proposed method for safe and efficient excavation of large-section fractured rock masses with advanced roof control improves the overall stability of the roof area of ​​the roadway and provides favorable conditions for controlling the formation of the roadway excavation cross-section. By arranging dense wall-supporting holes along the upper roof of the excavation outline of the large-section fractured area, the initial pre-splitting holes effectively block the propagation of blasting vibrations generated by subsequent blasting holes, reducing damage to the roof of the large-section area from blasting vibrations. The design utilizes digital electronic detonators, enabling micro-delayed detonation of each hole, controlling the maximum charge per simultaneous blast, reducing the impact of blasting vibrations on the surrounding rock of the excavation area, improving the smoothness of the excavation cross-section wall, cycle advance, and half-hole ratio, enhancing the overall stability of the large-section fractured area, effectively controlling the formation of the excavation cross-section in the large-section fractured area, reducing roadway cross-section dimensional deviations, reducing the workload and cost of shotcrete support for the excavation cross-section, and improving the safety efficiency and economic benefits of underground space production operations.

[0038] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0039] The above description is only a preferred embodiment of the present invention, but 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 inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A safe and efficient method for pre-excavation of large-section fractured rock mass with controlled roof, characterized in that: Includes the following steps: S1. Conduct point surveying along the excavation outline of the large-section fractured area. Use a rock drilling rig or grouting machine to construct grouting holes with a depth of 40m~50m. The drilling angle is parallel to the excavation face direction, and the bottom of the hole is 1m outside the excavation face. The drilling spacing is 0.6m~1m, the hole diameter is 60mm, and 60mm diameter grout stop plugs are installed. The length of the grout stop plugs is 1.5~2.0m. When the rock mass in the large-section area is particularly fractured, use a water exploration drilling rig to construct φ75mm holes, pre-embed 9m diameter 60mm steel pipes, cut a 7m diameter notch at the front end of the steel pipe, and inject grout into the surrounding rock through the steel pipe. The steel pipe spacing is 1m, the drilling angle is 10~20° to the excavation face direction, and the bottom of the hole is 0.8m outside the excavation face. S2. To ensure the grouting effect, the grouting sequence is from both sides to the middle, and the entire hole is injected at once. The grouting uses a two-component cement grout as the main component. The two-component cement grout uses P.O42.5 ordinary Portland cement, and an admixture of 0.5% by weight of cement is added. The admixture plays a role in rapid setting and early strength. After the grouting is completed, excavation can only be carried out after 8 hours. S3. For projects in large-section fractured areas, the partitioned step reverse intersection method is adopted for construction. S4. Based on the on-site grouting reinforcement effect, the entire section adopts HRB400φ18mm*2400mm threaded steel resin anchor rods, and selects appropriate support parameters. S5. To reduce the impact of blasting vibration on the top rock mass of the large-section fractured area, protective holes are arranged at a position S1=(0.1~0.2)m inside the engineering excavation outline of the large-section fractured area, with a spacing of S2=(8~15)d holes; the slotting holes, auxiliary holes, and peripheral holes are detonated in sequence; to reduce the impact of blasting vibration on the surrounding rock of the excavation area and control the maximum charge of a single simultaneous blast, digital electronic detonators are designed to achieve micro-delay interval detonation of each hole, and the interval delay time of each hole is optimized and adjusted according to the layout of the tunneling section; S6. After blasting, use a steel tape measure or other length measuring tools to measure the outline dimensions of the large-section fractured area after blasting. S7. Following the above steps, conduct 15 to 35 on-site blasting tests to improve the reliability of the experimental data; use regression analysis to process the roadway cross-sectional deviation S; too few tests will affect accuracy and reliability; too many tests will result in long on-site test times and high costs. S8. Using regression analysis, the deviation S of the roadway cross section measured in steps S6 and S7 is used to obtain the rules of the depth, angle and spacing of the roof reinforcement holes and the delay time of each hole.

2. The method for safe and efficient excavation of large-section fractured rock mass with advanced roof control according to claim 1, characterized in that: The specific construction steps for step S3 are as follows: S301. The step-type excavation method is adopted for construction. First, the "entry tunnel" half-section is constructed with an advance of 2m. After the roof and top and sides reach the design dimensions, anchor mesh cable spraying support is carried out. S302, Lateral excavation to the entire large cross-section design size, and top and side anchor mesh cable spraying support; S303, the left and right sections of the upper step construction are excavated alternately, with an advance of 2.0m per cycle; after the left and right sections of the upper step are completed and the bottom slab is leveled, the lower step construction begins. S304, the entire cross-section forward excavation is completed.

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