Ground pressure theory method

Abstract

The invention belongs to the field of mining, relates to a technical project in mine ground pressure, and aims to solve the technical problem of mine ground pressure in laneway engineering. According to the method, top pressure and side pressure of the roadway are derived from dispersed soft rock mass with large plasticity. When the stress borne by the point M exceeds the strength of the point M, the survey point M can generate displacement change, and the roadway can fall, so that the surrounding rock of the roadway can be stable only when the displacement of the point M is zero. The method has the main technical characteristics that (1) the surrounding rock of the roadway is not damaged, (2) in a hard full-rock roadway, the roadway is free from support (except for evacuated soft rock mass with large plasticity), and (3) the section of the roadway is circular or semicircular arch-shaped.

Description

[0001] In the driving of rock tunnels in the mining field, the driving method used in most mines is the rock-breaking method of drilling and blasting. The depth of drilling is between 3 and 4 meters, and there are support technologies such as bolt support and shotcrete support. When breaking rocks and providing support, a lot of raw materials are consumed, such as dressed stones, cement, river sand, pit props, etc. At the same time, the rock blocks broken during rock breaking knock down the already supported brackets, resulting in too high labor intensity.

[0002] To save raw materials, a technical reform is carried out. In fully rock tunnels, the tunnel cross-section is designed into an ideal circular cross-section or a semi-circular arch cross-section tunnel (a square cross-section can also be referred to). For example, when driving in a complete rock series, the tunnel can be exempted from support. The following is an argument for this plan:

[0003] 1. Argumentation on the ground pressure theory of mine rock tunnel driving

[0004] To achieve safe and efficient operation of the mine, the phenomenon of mine ground pressure must be considered. In mine geology, two notable issues are: ① mining depth; ② geological structural stress.

[0005] Due to the movement of the earth's crust, there are tectonic stresses and elastic energies in geological structures such as fault fracture zones, folds, and soft rocks with low solidity coefficients.

[0006] In Chapter 7 of the textbook "Introduction to Coal Mining" (Coal Industry Press), there are descriptions such as "new natural balance arch" in the treatise on the roof pressure and side pressure in horizontal tunnels. This is studied from the perspective of the irregular damage of the surrounding rock after the tunnel is blasted. Through various observations, in fully rock tunnels, the reasons for the roof pressure and side pressure are that the surrounding rock is irregularly damaged after the tunnel is blasted.

[0007] When the depth of the blast hole is 3 - 4 meters, due to the problem of the blast hole direction, the influence on the surrounding rock of the tunnel is quite large. Therefore, those broken rock blocks break the support, rather than the pressure generated by the entire geological body. However, the existence of geological structural stress cannot be denied, such as in the fractured zones with loose geology and soft rock masses with low solidity coefficients. Therefore, in the driving of rock tunnels, when passing through loose fractured zones and soft rock masses, appropriate support must be provided.

[0008] In the driving of rock tunnels, the situation of the damaged surrounding rock is as follows. Please see the schematic diagram of the cross-section of the tunnel with damaged surrounding rock characteristics (Figure - 1). If the driving technology is changed and mechanical rock breaking is used to drive the tunnel cross-section into a circle, at this time the surrounding rock of the tunnel is not damaged (Figure - 2), which is the schematic diagram of the cross-section of the tunnel in a complete rock series. Then the "roof pressure" and "side pressure" of the tunnel are only likely to occur in loose and highly plastic soft rocks.

[0009] The following analyzes the distribution of geological tectonic stress when the surrounding rock of the roadway is damaged with reference to Chapter 2 of the textbook "Mine Shaft and Tunnel Engineering" (Coal Industry Press) (as shown in Figure - 3). In the geological body abcd at a depth of Z meters from the surface, an inspection point M is taken. δθ is the circumferential stress at the inspection point M, δr is the radial stress, and trθ is the shear stress. P is the vertical stress acting on the surrounding rock, q is the horizontal stress acting on the surrounding rock, r is the radial distance from the inspection point M to the center of the roadway, R0 is the radius of the roadway, and θ is the argument of the inspection point M.

[0010] When P = q, at the inspection point M, the shear stress is zero, and only the circumferential stress δθ and the radial stress δr exist.

[0011] When r = R0, the radial stress at the inspection point M is zero, and only the circumferential stress δθ is 2P.

[0012] When the surrounding rock of the roadway is not damaged and the inspection point M moves to the periphery, a circumferentially uniform stress circle with δθ = 2P is formed at the periphery (as shown in Figure - 4).

[0013] The circumferential stress being 2P only indicates an increase in the peripheral stress. The key is that there is no radial force at the inspection point M.

[0014] If the unit body M is taken out for analysis, the force - diagram is as shown in Figure - 5. When the stress on point M exceeds its own strength, the inspection point M will have displacement changes and the roadway will collapse. Therefore, when the displacement of point M is zero, the surrounding rock of the roadway can be stable.

[0015] If the cross - section adopts a circular or semi - circular arch shape, it is also a good load - bearing structure. From the perspective of engineering mechanics, this circular cross - section is just like a bridge arch, and the self - weight stress of the rock formation is solved for the stress distribution in the upper semi - circle of the cross - section.

[0016] Based on the above theoretical analysis, when driving horizontal and inclined roadways in a complete rock series, without the surrounding rock being damaged, it is possible to break through the exemption from support.

[0017] 2. Exploration of Roadway Cross - Section and Blasthole Layout

[0018] During the driving of rock roadways, the design of the roadway cross - section should make reasonable use of the load - bearing structure of the surrounding rock of the roadway. Selecting a circular or semi - circular arch shape, in order not to damage the surrounding rock of the roadway, mechanical rock breaking is ideal but costly. Smooth - wall blasting can also be used for rock breaking, and on this basis, a technical improvement can be added. First, several blastholes are drilled around the periphery of the roadway, and no explosives are loaded in the blastholes around the periphery of the roadway. The purpose is to create a crack with a circular or semi - circular arch - shaped cross - section. The middle of the roadway cross - section is a crushed area. The specific data such as the direction and depth of the blasthole layout are to be determined according to the selected blasting parameters. This blasting method must have strict technical procedures. Figure 1 It is a schematic diagram of the roadway section when the surrounding rock of the roadway is randomly damaged after blasting. Figure 2 It is a schematic diagram of the roadway section in the intact rock series when the surrounding rock of the roadway is not damaged. Figure 3 It is a distribution diagram of geological tectonic stress in the geological body abcd where the inspection point M is Z meters away from the ground surface. Figure 4 It is a schematic diagram of the circumferential stress of the inspection point M when r = R0. Figure 5 It is a schematic diagram of the circumferential stress of the inspection point M.

Claims

1. It is a technical solution for mine ground pressure in the field of mining. It mainly reveals the "top pressure" and "side pressure" of the tunnel in rock tunnel excavation (Chapter 7 of the coal mining general textbook). The article reveals that "after the tunnel is blasted, the tunnel surrounding rock is damaged irregularly", and it mainly reveals that "when the stress on point M exceeds its own strength, the observation point M will produce displacement changes, and the tunnel will fall off. Therefore, when the displacement of point M is zero, the tunnel surrounding rock can be stable", which is mainly the invention of the ground pressure theory of mine rock tunnel excavation. To implement this "method", its main technical features are: ① The surrounding rock of the tunnel is not damaged; ② In hard all-rock tunnels, tunnel support is exempted (except for evacuated soft rock with high plasticity); ③ The tunnel section is circular or semicircular arch; ④ In the discussion of "top pressure" and "side pressure" in mining rock tunnel excavation, if the tunnel surrounding rock is not damaged, the concepts of "top pressure" and "side pressure" cannot be established; ⑤ Drill several blast holes around the tunnel without explosives, in order to create a crack with a circular or semicircular arch cross section; ⑥ The "top pressure" and "side pressure" of the tunnel come from the soft rock mass with high evacuation plasticity.

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