trapezoidal I-steel supports were used in drawing roadways,which roof span is 4.0m, floor span is 4.9m, and hight 2.95m and spacing 0.5m. Initial resistance of the supports was almost zero because it was difficult to the support beams contact the roof, even if with high quality of installation. The trapezoidal I-steel supports would not carry load until the displacement of surrounding rock excceded 80-100 mm because the supports increased very slowly. Therefore, right after excavation, the roof would bend and subside severly. Eight hours after excavation, the roof strata would break completely, and then form rock cavity. The weight of caving rock would act on the beams of supports, which forms loose rock pressure.

By calculating, the ultimate load-bearing capacity is smaller than roof pressure whether it is uniformal or concentrated, Based on the in-situ observation, inflection value of most roof reached 200-300mm. When paired supports were used, paired beams were still bent and damaged; then midprops were added, they were also destroyed. Many roof beams were stabilized only if 2-3 props had been added. The supports were damaged completely, and most of them could not be reused. The part section of roadways had become inverted trapezoid, and the available section was far smaller than the designed section. Part of roadways was out of use because it was in the danger of serious caving.

3.Mechanism of bolt supporting

Its mechanism is to make full use of the self-load-bearing capacity of surrounding rock by bolting, and then make the surrounding rock stabilize by itself. The stability of surrounding rock depends on the equilibrium status of ground pressure, self-load-bearing capacity of surrounding rock and anchoring force of bolts. Ground pressure is to make surrounding rock deform and break; self-load-bearing capacity is the main factor to stablize surrounding rock. Anchoring force of bolts can not change the equilibrium status of the three because it is very small, compared with ground pressure and self-load-bearing capacity. And its function is to change the decreasing regularity of self-load-bearing capacity versus the deformation of surrounding rock, and balance self-load-bearing capacity against ground pressure early.

Roof pressure is the pressure acting on the roof beams when I-steel supports are used to control the roof. When roof is supported by bolts, the roof pressure change to be the pressure acting on the rock within the bolting range because this part of rock is change into self-bearing body. According to the characteristics of the roof of coal seams , bolts strata can be divided into six substrata.

编辑老师为大家整理了优秀毕业论文翻译，希望对大家有所帮助。更多详情点击进入毕业论文范文。