Abstract
This paper is aimed at the inverted arch support instability of track roadway with mining level +1100 m in Liuyuanzi Coal Mine. By means of field investigation, theoretical analysis, numerical calculation, and engineering practice, the instability reasons of inverted arch structure are expounded, the mechanical mechanism of instability of inverted arch structure is revealed, and the “sliding-rotating beam” for the instability of inverted arch structure is put forward. Based on Fenner’s formula and mechanics principle, the equilibrium equation of “sliding-rotating beam” is given. The results show the following: Firstly, the insufficient stiffness at the joint of the inverted arch structure and the U-shaped steel support on the floor is the key reason for the floor instability. Secondly, when the action stress of the “sliding-rotating beam” is less than the critical value, three kinds of instability modes of the inverted arch structure may occur, that is, sliding upward, rotating upward, or sliding-rotating upward. Each instability criterion and critical value are also different. Considering the axisymmetric condition, the critical value calculation formula of the three modes can be simplified into one formula. Thirdly, the equivalent friction factor restricts the stability of the “sliding-rotating beam,” and there is a “breaking point.” The relationship between the equivalent friction factor and the action stress of the “sliding-rotating beam” is “class hyperbola.” When the equivalent friction factor is greater than the “breaking point value,” the “sliding-rotating beam” may remain stable. Moreover, with the increase of equivalent friction factor, the action stress required for the stability of the “sliding-rotating beam” is smaller, and it tends to be more stable. The breaking point value of equivalent friction factor is 18.6. Finally, 36U-shaped steel round frame with bolt-mesh-shotcrete-combined support is applied to improve the equivalent friction factor and the foot stiffness of U-shaped support in roadway. After two months of on-site implementation, the floor heave was reduced by 69.1%. In conclusion, the theoretical analysis is correct and the control method is effective.
Highlights
Floor heave is one of the focuses concerned by scholars at home and abroad [1,2,3,4,5,6,7]
When the equivalent friction factor is greater than the “breaking point value,” ps is positive, it means that the reverse arch support of roadway is likely to be stable
After two months of monitoring, the floor heave of roadway is reduced from 246 mm to 76 mm, and the floor heave is reduced by 69.1%
Summary
Floor heave is one of the focuses concerned by scholars at home and abroad [1,2,3,4,5,6,7]. Because of the complex and changeable environment of coal mine roadway or the fact that the key points of floor heave control are different, the researches on the mechanism of floor instability under inverted arch support are relatively few or only a part of the influencing factors are studied. E original support design of the track roadway in Liuyuanzi Coal Mine is as follows: the boltmesh support is used for the first support, the shotcreting and 36U-shaped steel are used for the second support, shotcreting thickness is 200 mm, the net section is 15.7 square meter, and the driving width and height, respectively, are 4900 mm and 4500 mm.
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