The northeast direction of a certain tungsten ore is the direction of the maximum principal stress, which is dominated by the approximate horizontal tectonic stress. The bottom drum phenomenon is less. If the axial direction of the roadway is perpendicular to the direction of the tectonic stress, the two gangs are the most stressed, and the roadway generally presents two Helps squeeze deformation. Especially when the roadway is in a relatively broken part of the rock or the rock strength itself is very small, the deformation and destruction of the surrounding rock are caused. Because the surrounding rock of the roadway is under the horizontal stress, the mechanical properties are closely related to the area where the roadway is located [1]. This paper uses the plastic zone range to evaluate the stability of the roadway.
1 Lane location and mechanics analysis
1.1 Construction of the theoretical model In the tectonic stress field, the roadway is excavated, and the theoretical formula is constructed according to the tectonic stress [2]. Considering various factors, the structural model of the tectonic stress field is shown in Fig. 1 [3].

1.2 Theoretical range of plastic zone In the elastic zone, the surrounding rock stress of circular roadway is distributed as in formula (1) [4]:

Where λ is the lateral pressure coefficient; q is the vertical stress; a is the roadway radius; r is the distance from the center of the roadway; θ is the angle with the X axis; σr is the radial normal stress; σθ is the tangential normal stress; τrθ is Shear stress. The formula for calculating the principal stress at a certain point:

Where σr is the radial normal stress; σθ is the tangential normal stress; τrθ is the shear stress; σ1 is the maximum principal stress; σ2 is the minimum principal stress. Substituting the formula (1) into the formula (2), the formula for calculating the principal stress in the elastic region of the surrounding rock of the circular tunnel in the tectonic stress field is obtained:

In the formula:

By the Mohr-Coulomb strength criterion, the principal stress at a point in the plastic zone satisfies:

Where C is the rock mass cohesion; φ is the rock body friction angle. Therefore, from equations (3) and (5), we can get:

It can be seen from equation (6) that the curve of the solution set (r, θ) is the boundary line of the plastic zone [5], the lateral pressure coefficient λ, the vertical pressure of the surrounding rock q, the cohesion C of the rock mass and the inner part of the rock mass. The friction angle φ is the main factor affecting the range of the plastic zone in the tectonic stress field.


1.3 Factors affecting the extent of the plastic zone

(1) Side pressure coefficient λ. Suppose q=10MPa, C=4MPa, φ=30°. When the lateral pressure coefficient λ=1,3/2,2,5/2, the plastic zone distribution range of surrounding rock is shown in Fig. 2. It can be seen from Fig. 2 that in the tectonic stress field, when λ is small, only two gangs exhibit a plastic zone; when λ increases continuously, the plastic zone range is continuously reduced in the two gangs, while the plastic zone range of the top and bottom of the roadway is constantly The expansion is prominent in the corner points of the roadway. When 1<λ<2, the plastic zone only appears on the top and bottom plates; but when λ>2, the plastic zone range expands rapidly. Therefore, λ = 2 is the limit value of the roadway stability.

(2) Vertical pressure q of surrounding rock. When the vertical pressure of surrounding rock is q=5,10,15,20MPa, the distribution range is shown in Fig. 3. In the tectonic stress field, as the value of q increases, the range of plastic zone increases continuously, and the maintenance of roadway is more difficult.

(3) Cohesion of rock mass. It can be seen from Fig. 4 that as the C value becomes larger, the range of the plastic zone gradually decreases, and the stability of the roadway is improved.

(4) The internal friction angle φ of the rock mass. It can be seen from Fig. 5 that the range of the plastic zone gradually decreases as the value of φ increases; after φ<30°, the range of the plastic zone is sensitive to the change of the value of φ.

Numerical simulation analysis of 2 roadway deformation
2.1 Model construction In this study, Phase 2 was used to simulate the deformation of roadway stress [6], and the 8-line profile of the tungsten mine was selected as the modeling basis. The roadway is mainly arranged in the surrounding rock of the upper plate and the surrounding rock of the lower plate. The roadway model is shown in Figure 6.

Model boundary constraints use boundary conditions of displacement constraints. All nodes are constrained in the X and Y directions. Considering the influence of the tectonic stress field on the calculation, according to the geostress measurement results, the maximum principal stress of the middle section of 1690 is: σ1=14.167MPa, σ2=5.498MPa, σ3=1.752MPa.
2.2 Material mechanics parameter selection According to the classification of rock mass, the rock mechanics parameters are corrected. The rock integrity index (s), rock properties (M), cohesion (c), and resistance are obtained when the rock quality index (CSIR) is 100 and 60. Tensile strength (σt), compressive strength (σC) and internal friction angle (φ) (see Table 1), comparative analysis of the deformation characteristics of intact rock and incomplete rock with structural plane.

2.3 Analysis of simulation results

It can be seen from Fig. 7 that the plastic zone of the intact rock (two mica quartz schist) and the incomplete rock varies greatly. If the surrounding rock is intact, only a certain plastic zone is produced in the two gangs of the roadway, and the jet concrete is used. Support can meet the support requirements. However, the rock is not a complete structure. When the structural plane exists, the rock properties are weakened. Figure 7(b) shows that the plastic zone range is greatly increased, especially on both sides of the top of the roadway, and the plastic zone can reach or exceed the tunnel width (2m). The same explanation can be obtained according to the loose circle theory, in which the anchoring force of the anchor does not reach the hard rock and thus fails. It can be seen from Fig. 8 that the plastic zone change of the roadway in the surrounding rock has the same law, but the plastic zone of the roadway in the surrounding rock is smaller than that of the surrounding rock.

3 conclusions

(1) If the strength of the surrounding rock is higher, the stability around the roadway is more stable; when the pressure acts on the surrounding rock of the roadway, the stability of the surrounding rock changes uniformly and is positively correlated with the pressure, and the instability phenomenon is more intense. This is consistent with the problems encountered in the actual excavation roadway, that is, the deeper the excavation, the more difficult the maintenance; but the horizontal and vertical stresses act on the surrounding rock of the roadway, and the stability change has a non-uniformity, that is, the former stability. Mainly in the top and bottom of the roadway, while the latter is shown in two gangs.
(2) Numerical simulations suggest that the plastic zone of intact rock and incomplete rock varies greatly. If the surrounding rock is intact, only a certain plastic zone will be produced in the two gangs of the roadway. At this time, the support of the jet concrete can be satisfied. Support requirements, but if the rock has a structural weak surface, the rock properties are weakened, the plastic zone range is greatly increased, and may even exceed the width of the roadway, resulting in anchor bolting failure, so further support is needed in some key locations and fracture zone areas. Protection.
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Article source: Mining Technology; 2017.17(1)
Author: Xiao Guoxi; Wuzhou, Jiangxi Cathay Pacific Blasting Engineering Co., Ltd., Nanchang, Jiangxi 330038
Yu Fulin; Jiangxi Xiaolong Tungsten Industry Co., Ltd., 343723 , Ji'an, Jiangxi
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