Abstract
This paper presents the engineering geological properties and roof control tecnology for a thick coal seam fully-mechanized face mining with hard roof conditions (THC) at the Jinhuagong Coal Mine (JCM), northwest China. The effective support working resistance and appropriate roof control technology are two critical factors for safe and productive mining in the THC. The load-estimate-method (LOEM) is the effective method to determine the support working resistance for normal working conditions (the mining height less than 3.5 m). In order to prevent support crushing accidents from happening and to ensure the safety and high-efficiency in the THC, the LOEM was modified based on the structure of the overlying strata in the THC. The strata which can form the voussoir beam structure in normal working conditions and will break in the form of cantilever beam in the THC is defined as the key strata in the immediate roof. Therefore, the hanging length of the key strata in the immediate roof was considered in the LOEM. Furthermore, a method for calculating the hanging length of the key strata in the immediate roof and its influencing factors were proposed using cantilever beam theory analysis of the structure of the overlying strata. Moreover, in order to fully fill the goaf area with caving roof to reduce the energy accumulation of main roof movement, it was decided to apply destress blasting technique (DEBT) at the JCM to control the large hanging length of the hard roof, so as to reduce the impact of the hard main roof movement on the working face. The key technique parameters of the roof caving borehole were also proposed. The obtained results demonstrated that the theoretical analysis is reasonable, and the chosen support type and the DEBT could meet the roof control requirements. The THC has achieved safety and high-efficiency mining.
Highlights
At present, thick seam (≥3.5 m) accounts for approximately 45% of both China’s reserves and production [1,2,3]
The roof structure in thick seam is special and it is more difficult to control the roof. It is an important issue for the working face in thick seam to find out the roof structure and determine the effective support working resistance
The most dangerous circumstance is that the key strata in the immediate roof cannot form a hinged structure and became worse when the break line of the key Ssutrstaatinaabiinlityth2e01i7m, 9m, 93e5diate roof was above the coal face
Summary
Thick seam (≥3.5 m) accounts for approximately 45% of both China’s reserves and production [1,2,3]. A method for calculating an effective support working resistance for types I and III working faces was proposed. On this basis, JU and XU [11] studied the cantilever beam of the immediate roof motion mode and its effect on the stress at thick seam working faces, according to physical modeling and measured data. JU and XU [11] studied the cantilever beam of the immediate roof motion mode and its effect on the stress at thick seam working faces, according to physical modeling and measured data They determined the calculation methods for support working resistance under different motion modes. It is of great importance to determine an effective support working resistance and support type and to develop appropriate roof control technology
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