CN115324623B - Advanced support method for deep broken rock mass roadway of metal ore - Google Patents

Abstract

The invention discloses a method for advanced support of a roadway of a broken rock mass in a deep part of a metal mine, which comprises the steps of firstly determining self-stabilizing time, self-stabilizing span and tunneling footage of the roadway, if the self-stabilizing time of the rock mass is insufficient to complete the support operation cycle, firstly executing the following steps 2-7, and then executing the steps 1-7 in a cycle manner; if the supporting process can be completed within the self-stabilization time, circularly executing the steps 1-6; step 1: tunneling, namely, step 2: metal mesh + sprayed concrete, step 3: erecting a prefabricated steel bar net rack, and step 4: fixing the prestressed anchor rod and the double ribs, and step 5: spraying concrete, and step 6: fixed anchor rope at bottom of mounting hole, step 7: and (5) advanced grouting of the anchor rod. The advanced support method based on rock mass self-stabilization time, self-stabilization span and full coupling of the support body and surrounding rock improves support quality, support efficiency and safety of deep broken roadway of metal ores, and provides technical guarantee for safe and efficient construction of deep roadway support of metal ores.

Description

A method for advanced support of broken rock tunnels in deep metal mines

Technical Field

The invention relates to the technical field of deep broken rock mass support, and in particular to a method for advanced support of deep broken rock mass tunnels in metal mines.

Background Art

As the mining depth of the ore deposit increases, the strata that deep mining tunnels pass through are complex and changeable, and are mostly in special conditions such as "high well depth, high ground stress, high ground temperature, and strong mining". In particular, the extremely weak and broken rock masses such as faults and broken zones that deep tunnels of metal mines pass through have the characteristics of high stress, low rock strength, cementation, and extremely poor integrity. At present, the support design for crossing complex and broken strata still adopts the pipe-roof or steel arch support design method based on the shallow "empirical method" and "engineering analogy method", which often leads to serious collapse of the excavation tunnel, short self-stabilization time, poor safety, and very difficult support construction. If improper excavation and support construction technology is adopted, it will not only affect the stability of the tunnel, the construction period, and the personal safety of the workers, but also have an adverse impact on the stability of the mining project within the area.

The existing support design for tunnels passing through complex and broken strata has a fixed support scheme, and usually does not consider the balance between self-stabilization time and construction efficiency. The process design is unreasonable, the construction efficiency is low, and the economy is poor. In addition, the existing support structure cannot be fully coupled with the tunnel surrounding rock, the support effect is poor, and the safety is low. The existing bottom-anchored anchor cables have low anchoring force, poor durability, and no connection between the support structures, resulting in poor integrity and support quality.

Summary of the invention

The technical problem to be solved by the present invention is to provide an advanced support method based on the self-stabilization time, self-stabilization span of the rock mass, and full coupling of the support body and the surrounding rock, so as to improve the support quality, support efficiency and safety of deep broken tunnels in metal mines, and provide technical guarantee for the safe and efficient construction of deep tunnel support in metal mines.

The technical solution of the present invention is as follows:

A method for advanced support of deep broken rock tunnels in metal mines, characterized by:

First, conduct engineering exploration to classify the rock mass quality, determine the tunnel self-stabilization time, self-stabilization span and excavation advance. If the rock mass self-stabilization time is not enough to complete the support operation cycle, advance support operations must be performed before tunnel excavation. First, perform the following steps 2 to 7, and then execute steps 1 to 7 in a loop. If the mine construction efficiency is high and the support process can be completed within the self-stabilization time, then execute steps 1 to 6 in a loop.

Step 1: Tunneling

The drilling and blasting method is used for excavation, and the excavation footage is not greater than the self-stabilizing span;

Step 2: Metal Mesh + Shotcrete

After the excavation is completed by the drill and blast method, metal mesh and shotcrete are immediately set up;

Step 3: Erection of prefabricated steel grid

The steel mesh frame designed according to the tunnel section shape, size, surrounding rock quality and ground pressure conditions is installed on the tunnel surrounding rock surface after shotcrete; the structure of the steel mesh frame adopts a grid structure;

Step 4: Prestressed anchor rod + double reinforcement fixing

Prestressed anchor rods + double bars are used to fix the steel grid to the surrounding rock, so that the steel grid, prestressed anchor rods, double bars and broken surrounding rock are reinforced to form an integral structure;

Step 5: Shotcrete

The prefabricated steel grid + prestressed anchor rods + double bars erected in step 3 are reinforced with shotcrete to increase the tunnel support strength, seal the tunnel surrounding rock, and improve corrosion resistance;

Step 6: Install the bottom anchor cable

In order to avoid deformation of the surrounding rock of the tunnel after reinforcement and support, fixed anchor cables are installed at the bottom of the hole to further improve the reinforced support structure and enhance the stability of the support structure;

Step 7: Pre-grouting anchors

The length of the advance grouting anchor rod is determined according to the tunnel excavation progress. The length of the advance grouting anchor rod is at least 1.5 times of the tunnel excavation progress. The advance grouting anchor rod is installed at an angle of 15° to 20° to the surface of the tunnel surrounding rock, and the spacing between anchor rods is not more than 30cm.

Preferably, in step 1, the mesh size of the metal mesh is not greater than 50 mm×50 mm, and the diameter of the metal mesh reinforcement is not less than 6 mm; the strength of the shotcrete is not less than C20, and the thickness is not less than 20 mm.

Preferably, in step 2, the steel mesh frame is composed of main bars and stirrups, wherein the diameter of the main bars is not less than 20 mm, and the diameter of the stirrups is not less than 10 mm.

Preferably, in step 3, the prestress provided by the prestressed anchor rod is not less than 8t; the double reinforcement bars are installed as close to the tunnel wall as possible; the double reinforcement bars are arranged along the tunnel excavation direction, the diameter of the double reinforcement bars is not less than 6mm, the length is consistent with the tunnel excavation footage, and they are manufactured by spot welding.

Preferably, in step 4, if water seepage occurs in a certain area, or deformation > 100 mm occurs, steel fiber shotcrete containing 2 to 3% of the material weight is used to increase the strength of the shotcrete layer and achieve a coupled support effect, so that the reinforced support structure and the tunnel surrounding rock can be deformed in coordination; the strength grade of the shotcrete is not less than C20.

Preferably, in step 5, the length of the anchor cable is not less than 6m, the bottom of the hole is fixed with an inverted wedge structure, cement slurry is injected for anchoring, the water-cement ratio of the cement slurry is not less than 0.4:1, and a push anchor is used to increase the prestress, and the prestress is not less than 15t.

Preferably, in step 6, the grouting anchor structure is a conical hollow steel pipe with a diameter of 40 mm, and holes with a diameter of 2 mm are drilled at the end thereof, and the hole spacing is not greater than 5 cm.

The method for determining the tunnel self-stabilization time, self-stabilization span and excavation progress is: according to the engineering investigation results, the rock mass quality is evaluated according to the rock mass geomechanics (RMR) classification table, and the tunnel self-stabilization time and maximum self-stabilization span are determined according to the scoring results, and the excavation progress is not greater than the maximum self-stabilization span.

Compared with the prior art, the economic effect of the present invention is:

First, advance support is very time-consuming. The present invention omits the advance support step while ensuring safety, greatly improving construction efficiency. The present invention determines the excavation advance and self-stabilization time through RMR classification. If the subsequent support process cannot be completed within the current self-stabilization time, the tunnel excavation cannot be advanced and advance support is required. If the mine construction efficiency is high (determined by the number of workers and mechanical equipment in each mine, and the cross-sectional size), the support process can be completed within the self-stabilization time, and excavation can be carried out directly, omitting advance support.

Second, the present invention optimizes the combination of support structures so that the support structures and the surrounding rock of the tunnel can be coupled with each other, which can maximize the use of the self-supporting capacity of the surrounding rock and the support capacity of the anchor rods, improve the overall stiffness of the surrounding rock, enhance the deformation resistance of the surrounding rock, strengthen the integrity of the surrounding rock, improve the support quality, support efficiency and safety of deep broken tunnels in metal mines, and provide technical guarantee for the safe and efficient construction of deep tunnel support in metal mines.

Third, unlike the U-shaped steel bracket commonly used in the prior art, the present invention uses a bracket processed from steel bars as a grid and sprays concrete. The cross section of the drilling and blasting method is usually irregular. The advantages of this method of the present invention are: the grid is easy to adjust its shape to adapt to the over-excavation and under-excavation of the tunnel, improve the coupling degree between the support structure and the surrounding rock, enhance its integrity, and improve the support quality.

Fourth, different from the hole bottom fixing method commonly used in the prior art, the present invention adopts full-length anchoring grouting. The advantages of this method of the present invention are: high anchoring force, corrosion resistance of anchor cable improves durability, and at the same time, it can play an additional grouting reinforcement role on the surrounding rock around the anchor cable.

Fifth, the present invention uses prestressed anchor rods + double ribs to fix the prefabricated steel grid so that each row of the supporting structure is interconnected, further improving the integrity and stability of the supporting structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional view of a tunnel support according to an embodiment of the present invention (vertical to the direction of the tunnel).

FIG. 2 is a cross-sectional view of the tunnel support according to an embodiment of the present invention (along the direction of the tunnel).

In the figure, 1. anchor cable, 2. anchor rod, 3. grouting anchor rod, 4. concrete, 5. steel mesh.

DETAILED DESCRIPTION

The present invention is further described below with reference to the examples.

Embodiment 1

The -1070m horizontal tunnel of an underground metal mine is located in soft and broken rock. The tunnel surrounding rock is mainly composed of epidote and marble, which has the characteristics of low rock strength, cementation and extremely poor integrity. The problems faced in the excavation and support construction of the -1070m tunnel under the influence of the tectonic belt are addressed.

The rock mass in this support area is broken. The quality of the rock mass is evaluated according to the rock mass geomechanics (RMR) classification table based on the engineering investigation results, and the tunnel self-stabilization time and maximum self-stabilization span are determined based on the scoring results. The excavation advance is not greater than the maximum self-stabilization span.

According to the RMR rock mass quality score of <20, it is Class V rock mass. From Table 1, we can know that the maximum self-stabilizing span is 1m, so the excavation advance is determined to be 1m. However, since the self-stabilizing time is only 30min, support is required in advance before drilling and blasting.

Table 1 Rock mass quality evaluation and engineering properties based on RMR total score

Rating value 100～81 80～61 60～41 40～21 ＜20 Rock mass classification I II III IV V Rock mass description very good good medium Difference Very bad Average stabilization time 15m span 20 years 10m span 1 year 5m span 1 week 2.5m span 10h 1m span 30min

Refer to Figure 1 and Figure 2 to implement the following steps.

Step 1: Tunneling

The drilling and blasting method is used for excavation, with a penetration of 1m.

Step 2: Metal mesh + shotcrete support

The diamond-shaped galvanized metal mesh is used, with a mesh size of 50×50mm and a metal mesh steel bar diameter of 7mm. The metal mesh should be installed as close to the tunnel wall as possible to maximize the role of the metal mesh. The overlap length of the two metal meshes is 100mm to ensure that the entire tunnel anchor mesh support is integrated, and the initial concrete is sprayed on the tunnel side wall, top plate and waste rock pile. The sprayed concrete strength is C20 and the thickness is 50mm for temporary support.

Step 3: Erection of prefabricated steel grid

The cross-sectional dimensions of the tunnel excavation in this design are: 3.0×3.0m; the length of a single steel mesh frame 5 is 2.1m and the width is 0.3m. Steel bars are welded on the side of the steel bar, and the leg length is 0.2m. The perimeter of the tunnel is about 8m (excluding the bottom plate). Four steel mesh frames 5 are installed on the surface of the tunnel surrounding rock after shotcrete. Each steel mesh frame 5 is tied with wire at the overlap, and the overlap is 0.5~1m. The spacing of the steel mesh frames 5 is 400mm (the distance between the center lines of the steel supports), and each group of steel mesh frames 5 is solid with the surrounding rock, and no gaps are left.

The steel mesh frame 5 is composed of main bars and stirrups, wherein the main bars have a diameter of 20 mm and the stirrups have a diameter of 10 mm. When the ground stress increases, ribs are added to the existing mesh frame to strengthen the strength of the mesh frame structure. The specific structure of the steel mesh frame 5 is: four parallel main bars form a main body with a rectangular cross-section, and the four main bars are connected together by a plurality of stirrups.

Step 4: Prestressed anchor rod + double reinforcement bar fixation

After the steel mesh frame 5 is erected, it is fixed to the surrounding rock with prestressed anchor rods + double bars. A Φ32mm drill bit is used to drill the anchor rod holes, the hole depth is 2.3m, and the exposed length of the anchor rod 2 is not allowed to exceed 150mm. The drilling should be perpendicular to the tunnel rock wall, the axial angle of the two side holes is 85°; the axial angle of the arch side hole is 75°, the radial angle of the arch center hole is 70°, and the angle of the bottom row anchor hole is 75°. The prestressed anchor rods use resin anchor rods, with a spacing of 800mm×800mm; diameter: 20mm, length: 2200mm. When installing double reinforcement bars, they must be installed from one end to the other end in sequence. When the prestressing force is applied to the anchor rod 2, the nut must be tightened to reach a prestress of more than 8t. The double reinforcement bars must be connected to each other between the staged supports to maximize the fixing effect of the prestressed anchor rods + double reinforcement bars on the prefabricated steel grid 5, so that the prefabricated steel grid 5, prestressed anchor rods, double reinforcement bars and broken surrounding rock reinforcement form an integral structure.

The installation of double reinforcement bars should be as close to the tunnel wall as possible to maximize the fixing effect of prestressed anchor rods + double reinforcement bars on the prefabricated steel mesh frame 5. The prestressed anchor rods should preferably be resin anchor rods, and their length is determined according to the depth of tunnel surrounding rock damage; the double reinforcement bars are arranged along the tunnel excavation direction, the double reinforcement bars have a diameter of 6mm, and the length is consistent with the tunnel excavation footage, and are manufactured by spot welding.

Step 5: Shotcrete

The concrete 4 with a spraying strength of C25 and a thickness of 50 mm is used to reinforce the prefabricated steel grid + prestressed anchor rods + double bars erected in the previous step, which can not only increase the support strength of the tunnel, but also seal the tunnel surrounding rock and improve the corrosion resistance.

If water seepage occurs in a certain area, or deformation > 100mm occurs, use steel fiber shotcrete containing 2-3% of the material weight to increase the strength of the shotcrete layer and achieve a coupled support effect, so that the reinforced support structure and the tunnel surrounding rock can deform synergistically.

Step 6: Install the bottom anchor cable

A Φ28mm drill bit is used to drill the anchor hole, the hole depth is 7m, and a cement slurry anchor cable is used for fixing at the bottom of the hole. The length of the anchor cable 1 is not less than 6m. An inverted wedge structure is used for fixing at the bottom of the hole, and cement slurry is used for anchoring. The water-cement ratio of the cement slurry is 0.4:1. The anchor cable 1 is tightened with an anchor cable tensioner to make the prestress reach more than 15t.

Step 7: Pre-grouting anchors

According to the tunnel excavation progress, the length of the advance grouting anchor 3 is 3200mm. The advance grouting anchor 3 is installed at an angle of 15° to the tunnel surrounding rock surface, with an anchor spacing of 150mm, a lap length of 1m, and a row spacing of 2m. The structure of the grouting anchor 3 is a conical hollow steel pipe with a diameter of 42mm. A hole with a diameter of 2mm is drilled at its end, and the hole spacing is 50mm; the grouting material is determined according to the properties of the surrounding rock.

Repeat this process in a cycle.

Embodiment 2

The -960m horizontal tunnel of an underground metal mine is located in soft and broken rock mass. The rock types are mainly pyrite sericite granite breccia and sericite granite. The rock is relatively hard and the fault structure is well developed in the area. The local rock in the alteration zone near the main section is relatively broken, the alteration is relatively strong, the cracks are well developed, and the core is relatively broken.

The rock mass in this support area is broken. The quality of the rock mass is evaluated according to the rock mass geomechanics (RMR) classification table based on the engineering investigation results, and the tunnel self-stabilization time and maximum self-stabilization span are determined based on the scoring results. The excavation advance is not greater than the maximum self-stabilization span.

According to the RMR rock mass quality score of 30, it is a Grade IV rock mass. From Table 1, it can be seen that the maximum self-stabilizing span is 2.5m and the self-stabilizing time is about 10h. Therefore, the excavation advance is determined to be 2m. The mine has a high degree of mechanization and the support process can be completed within the self-stabilizing time. Therefore, steps 1 to 6 described in Example 1 are executed in a loop.

The rock mass geomechanics (RMR) classification table described in the present invention is shown in Table 2.

Table 2 Rock mass geomechanics (RMR) classification table See Table

During classification, scores are given according to the measured data of various parameters according to the standards; then the score values of various parameters are added together to obtain the total rock mass quality score RMR value; then it is corrected according to the joint classification; finally, the rock mass is classified using the corrected RMR value.

Claims (8)

1. A method for advanced support of a roadway of a broken rock mass of a deep part of a metal mine is characterized by comprising the following steps:

Firstly, grading the rock mass by engineering exploration, and determining the self-stabilizing time, self-stabilizing span and tunneling footage of a roadway, wherein if the self-stabilizing time of the rock mass is insufficient to complete the cycle of supporting operation, the advanced supporting operation is required before the roadway tunneling, the following steps 2-7 are firstly executed, and then the steps 1-7 are circularly executed; if the mine construction efficiency is high, the supporting process can be completed in the self-stabilizing time, and the steps 1-6 are executed circularly;

step 1: tunneling of roadway

Tunneling by adopting a drilling and blasting method, wherein the tunneling footage is not greater than the self-stabilizing span;

Step 2: metal net and sprayed concrete

After tunneling by adopting a drilling and blasting method is completed, immediately erecting a metal net and spraying concrete;

Step 3: erection of prefabricated steel bar net rack

Installing a steel bar net rack designed according to the shape and the size of the section of the roadway, the quality of surrounding rock and the ground pressure condition on the surface of the surrounding rock of the roadway after concrete is sprayed; the structure of the steel bar net rack adopts a grid structure;

step 4: prestressed anchor rod and double-bar fixing

Fixing the steel bar net rack on surrounding rock by adopting a prestressed anchor rod and double ribs, so that the steel bar net rack, the prestressed anchor rod, the double ribs and the broken surrounding rock are reinforced to form an integral structure;

Step 5: sprayed concrete

The prefabricated steel bar net frame, the prestressed anchor rods and the double bars erected in the step 3 are reinforced by sprayed concrete, so that the roadway support strength is improved, the roadway surrounding rock is sealed, and the corrosion resistance is improved;

step 6: fixed anchor rope at bottom of mounting hole

In order to avoid deformation of the roadway surrounding rock after reinforcement and support, the anchor cable fixed at the bottom of the hole is installed, so that the reinforced support structure is further improved, and the stability of the support structure is enhanced;

Step 7: advanced grouting anchor rod

And determining the length of the advanced grouting anchor rod according to the tunneling footage, wherein the length of the advanced grouting anchor rod is at least 1.5 times of the tunneling footage, the installation of the advanced grouting anchor rod forms an angle of 15-20 degrees with the surface of the surrounding rock of the tunnel, and the distance between the anchor rods is not more than 30cm.

2. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 1, the mesh size of the metal mesh is not more than 50mm multiplied by 50mm, and the diameter of the steel bar of the metal mesh is not less than 6mm; the strength of the sprayed concrete is not lower than C20, and the thickness is not lower than 20mm.

3. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 2, the steel bar net rack consists of main bars and stirrups, wherein the diameter of the main bars is not less than 20mm, and the diameter of the stirrups is not less than 10mm.

4. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 3, the prestress provided by the prestress anchor rod is not less than 8t; the double ribs are arranged to be attached to the roadway wall as much as possible; the double ribs are arranged along the tunneling direction, the diameter of the double ribs is not less than 6mm, the length of the double ribs is consistent with the tunneling footage, and the double ribs are manufactured by spot welding.

5. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 4, if water seepage occurs in a certain section or deformation is more than 100mm, steel fibers with the weight of 2-3% of the material are used for spraying concrete so as to increase the strength of a sprayed layer and achieve the coupling supporting effect, and the reinforced supporting structure and the surrounding rock of the roadway are deformed cooperatively; the sprayed concrete strength grade is not lower than C20.

6. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 5, the length of the anchor cable is not less than 6m, the hole bottom is fixed by adopting a reverse wedge structure, cement slurry is injected for anchoring, and the cement slurry cement ratio is not less than 0.4:1, an anchor pusher is adopted to increase prestress, and the prestress is not less than 15t.

7. The advanced support method for the deep broken rock mass roadway of the metal ore is characterized in that: in the step 6, the grouting anchor rod structure is a conical hollow steel pipe with the diameter of 40mm, and holes with the diameter of 2mm are drilled at the end part of the grouting anchor rod structure, and the hole spacing is not more than 5cm.

8. The advanced support method for the deep broken rock mass roadway of the metal mine according to any one of claims 1 to 7, wherein the method for determining the self-stabilizing time, the self-stabilizing span and the tunneling footage of the roadway is as follows: and (3) carrying out quality evaluation on the rock mass according to the engineering investigation result and the rock mass geomechanical (RMR) classification table, and determining the self-stabilizing time and the maximum self-stabilizing span of the roadway according to the grading result, wherein the tunneling footage is not greater than the maximum self-stabilizing span.