Analysis of the influence of the shape of the roadway on the stability of the top wall along the upper plate

Jiaojia gold mine located in Laizhou City, Shandong Province, was founded in 1975, mainly on long-term use layered approach to fill stoping method [1], the method of construction along the plate approach is the main method of mechanized mining stoping layout approach In the way, along the ore body, there are mylonian veins with different thicknesses that intersect with the ore body at a small angle. The stability is poor. In the case of water, the stability is rather poor, and the ore body is inclined along the strike, or It is also present in the surrounding rock of the near ore body, which is extremely unfavorable for the exposure of the ore body and surrounding rock. If the over-exploitation or roof support is not timely, the ore body along the upper plate will cause a large loss of ore body, and the average grade of the lower ore body is relatively high. The study analyzes the stability of the top sill along the shape of the different lanes along the upper plate for the safe and efficient mining.
1Geological overview The No. 120 section of the third section of Jiaojia Mining Area is located in the middle section of -450m. The structure in the stope is mainly the ore-controlling main fault of the upper part of the ore body. Its overall trend is 39° and the inclination angle is about 28°. NW, a layer of black fault mud with a thickness of about 5 cm is developed on the fracture surface. The secondary structures developed inside the ore body are mainly NE and NW-oriented fractures and joint structures produced in a conjugated shape, followed by a gently inclined near-horizontal structure, and near-NE-trending joints tending to NW or SE. The stability of the rock in the stope is moderate, and the rock at the intersection of joint fissures is relatively broken, and its stability is relatively poor, which is easy to form a triangle. 11 120 Gold Mine focus stope middle of the disc 18 layered rock and ore sampling site found mainly containing gold iron ore mineralization altered rock, ore rock uniaxial tensile strength is generally 5.01 ~ 9.22MPa, the compressive strength is generally 53.4 ~ 134.2MPa. The physical and mechanical parameters of the materials used were obtained by laboratory analysis in the laboratory (Table 1).

2 Model establishment UDEC software is used to numerically simulate the mining process. UDEC is an ideal tool for studying the potential damage model of discontinuous features. The calculation model is 500m long and 191.3m high. The top of the model replaces the weight of its rock and tail sand body with uniform load. The lateral boundary of the model constrains the horizontal displacement. The bottom boundary of the model constrains all directions of displacement. The upper boundary of the model replaces the weight of the overburden with uniform load. The average bulk density of the upper rock is 25kN/m3. The calculation model mesh is shown in Figure 1.

3 Numerical simulation analysis According to the UDEC model modeling rules, three models were established according to the physical and mechanical parameters of Table 1. The shape of the section was selected as rectangle, trapezoid and semi-circular arch. This time, through the simulation study, the construction of the 120 stope along the upper plate is carried out in the middle section of the 11th section. The excavation of the construction road is 15m, and the exposed area of ​​the upper plate is about 15m2. The displacement of the X-axis and Z-axis of the three different shape roadways See Figure 2 to Figure 4, the specific variation parameters are shown in Table 2.

It can be seen from Fig. 2 to Fig. 4 and Table 2 that the maximum sinking value of the rectangular roadway roof is about 40 cm, and the bottom drum phenomenon is more serious, up to 55 cm, the right side inward displacement is 30 cm, and the left side displacement is 40 cm. The horizontal displacement of the X-axis of the trapezoidal roadway is obviously larger than that of the left gang, the right side is moved nearly 30cm, the left side is moved by nearly 25cm, the roof subsidence is 40.6cm, and the bottom drum is 50cm. The roadway deformation is quite serious. The ceiling of the semicircular arched roadway is 15~32.8cm, and the maximum value of the two sets of approaching is 34.4cm. It is the final position of each step of the stepping excavation of the roadway. The range is very small, most of which is 25~30cm. The large deformation is on the one hand, the geological conditions along the upper plate are relatively bad, the roof is constructed along the upper plate, the bottom plate is tail sand, the roof is relatively broken, the crack is developed, and the construction quality of the workers is poor, there is over-excavation phenomenon [2-6]; On the other hand, the corresponding bottom drum control measures have not been taken. The weaker bottom plate will become a breakthrough point for the pressure released by the surrounding rock under the action of high stress, and the damage range will continue to expand and develop to the deep, and the displacement will continue to increase.
4 Conclusion

The shape of the roadway has an important influence on the change of the top of the construction road along the upper plate; when the shape of the roadway is rectangular and trapezoidal, the displacement of the two gangs and the roof of the roadway changes greatly, and the stress is concentrated on the roof, which easily leads to the collapse of the roof; Semi-circular arched roadway, although the deformation effect of the two gangs is not obvious, it can obviously improve the top stress concentration, relieve the sinking of the roof, weaken the bottom drum, and the straight wall semi-circular arched roadway is beneficial to mining.
References [1] Jie Shijun. Underground mining of metal deposits [M]. Beijing: Metallurgical Industry Press, 2014.
[2] Lu Shiliang, Jiang Yaodong. Mechanism and prevention of roadway bottom drum [J]. China Coal, 1995 (8): 12-17
[3] Wang Weihua, Li Xibing. Discrete element method and its application in geotechnical engineering [J]. Geotechnical Engineering Technology, 2005, 19(4): 177-181.
[4] Wang Yongsheng. Safety technical measures for normal mining under large airspace [J]. Mining Express, 2002 (13): 9-11.
[5] Gao Lei. Mine rock mechanics [M]. Beijing: Mechanical Industry Press, 1988. [6] Ren Qingwen. Block element method and its application in rock mass stability analysis [J]. Journal of Hohai University, 1995(1): 1-7

Article source: "Modern Mining"; 2017.2

Author: Liu Tao, Li Xiaofei, Li Zhuang; Shandong Gold Mining (Laizhou) Co., Ltd. Jiaojia gold

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High precision double side surface grinding or fine grinding is a super finishing process performed by removing material from two surfaces of a component resulting in extremely precise geometric accuracy and surface finish. Typically, it is the last grinding step of a mechanical production chain utilized to improve and/or correct the geometry of parts coming from sintering, sawing, molding or similar operations. Depending on the application, the stock removal also can be taken from just one surface.