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Bolt Supporting of Large-Span Soft Rockway in
Shaqu Colliery
Abstract The instability of trapezoidal I-steel support is analyd for the compound roof of main coal am in Shaqu Colliery, and the mechanism of bolt supporting is studied. A scheme of bolt supporting has been given and put into practice,remarkable technical and economic benefits have been got.
产前检查 Key words :large-span,compound roof, bolt supporting, mechanism
1.Introduction
In shaqu colliery a large coal mine mining rare coking coal in China, most roadways are laid out in main coal am
除鼠 roof of coal am .The soft compound ,which is compod of mudstone and coal am
contains aboundant beddings and joints. The strength of the roof is so low that its uniaxial-saturated compressive strength is only 10.7 Mpa.RQD value of coal am and is zero ,and that of mudstone is lower than 10%. There is clay minerals in mudstone, main compositions are interbedded strata of illite and montmorillonite which will swell when soaked by water, The span of preperation roadways and gateways is wider than 4m, and that of some main roadways is over 5m. In shaqu colliery , preperation roadways and gateways were supported by trapezoidal I-steel support, the beams of which were bent and damaged, and the roadways were destroyed riously within a short period just after excavated. Roof
医助 controlling of Large-Span Soft Rockways in the coal am became the key to the production and construction of shaqu colliery.
2.supporting status and instability analysis of trapezoidal I-steel supports
画的行书写法
trapezoidal I-steel supports were ud 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 becau 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 becau the supports incread very slowly. Therefore, right after excavation, the roof would bend and subside verly. 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 loo rock pressure.
By calculating, the ultimate load-bearing capacity is smaller than roof pressure whether it is uniformal or concentrated, Bad on the in-situ obrvation, inflection value of most roof reached 200-300mm. When paired supports were ud, 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 reud. The part
ction of roadways had become inverted trapezoid, and the available ction was far smaller than the designed ction. Part of roadways was out of u becau it was in the danger of rious caving.
3.Mechanism of bolt supporting
Its mechanism is to make full u of the lf-load-bearing capacity of surrounding rock by bolting, and then make the surrounding rock stabilize by itlf. The stability of surrounding rock depends on the equilibrium status of ground pressure, lf-load-bearing capacity of surrounding rock and anchoring force of bolts. Ground pressure is to make surrounding rock deform and break; lf-load-bearing capacity is the main factor to stablize surrounding rock. Anchoring force of bolts can not change the equilibrium status of the three becau it is very small, compared with ground pressure and lf-load-bearing capacity. And its function is to change the decreasing regularity of lf-load-bearing capacity versus the deformation of surrounding rock, and balance lf-load-bearing capacity against ground pressure early.
Roof pressure is the pressure acting on the roof beams when I-steel supports are ud 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 becau this part of rock is change into lf-bearing body. According to the characteristics of the roof of coal ams
can be divided into six substrata. , bolts strata
When the value of roof subsidence is zero, roof pressure is in-situ stress; then roof pressure decreas with the increa of roof subsidence. The variation of roof pressure is analyzed by FLAC, The results are shown as curve 1 in Fig.1. Wheoof subsidence reaches 19 mm, the first roof substratum begins to bearing tensile stress, then losts lf-load-bearing capacity, and roof pressure decreas to 0.67Mpa. When roof subsidence reaches 40 mm, the cond substratum los lf-load-bearing capacity, and roof pressure decreas to 0.16Mpa. When roof subsidence reaches 100 mm, the fourth substratum los lf-load-bearing capacity, and roof pressure decreas to0.08Mpa. In the initial stage of roof subsidence, roof pressure decreas rapidly, and in the later stage of roof subsidence, roof pressure decreas slowly and then has an increasing trend.
新谷真弓
The lf-load-bearing capacity of the roof without bolting is calculated upon the theory of laminated beam, the result are shown as curve 2 in Fig.1. When roof subsidence is zero, the lf-load-bearing capacity is at its utmost value 0.0625Mpa; when roof subsidence is 100mm,roof strata have broken, most of lf-load-bearing capacity has lost, and the residual lf-load-bearing capacity is only 0.0375Mpa.The lf-load-bearing capacity of the roof with bolting is calculated upon the theory of combined beam, the result are shown as curve 3 in Fig.1. When roof subsidence is zero, the lf-load-bearing capacity is at its utmost
value 0.4Mpa; when the roof subsidence reaches 40mm the lf-load-bearing capacity decreas to 0.225Mpa,and when roof subsidence reaches 100mm, the lf-load-bearing capacity decreas to 0.1Mpa .
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