Research On Evolution Of Stress And Structural Stability Of Surrounding Rock In The Longwall Mining Of Steeply Dipping Seam

In the process of mining steeply dipping seam, the non-definiteness of critical zone and variation of rock structure within the stope easily result in extremely complex strata movement which is hard to control. Researches on the formation and evolution characteristics of rock-mass stress field and structural stability of rock mass are theoretical foundations for safe and efficient mining and have significance to enrich mining theory and technology in such a complex condition.With a hybrid methodology including physical simulation, numerical simulation, theory analysis and in-situ application, the overburden movement and destruction mechanism, formation and evolution mechanism of rock stress field, the critical zone conversion characteristics and the rock structure stability have been done systematically. The researches indicate that:In the mining process of steeply dipping seam, roof movement has timing sequence and malconformation along the trend, the roof caving occurred first in upper area of stope with smallest caving pace, then in middle area with smaller caving pace, and last in lower area with lagest caving pace. In the tendency of coal seam, separation occurs first and then tensile failure generates at the upper position(two-thirds) of roof beams, resulting in an upper region offset of roof caving form and an asymmetric arch, the gangue slip and filled the gob with partition feature along tendency, including compaction zone in lower areas, completely filled zone in central areas, and partially filled zone in top areas.The surrounding rock stress is redistributed in mining the steeply dipping seam. Distribution of surrounding rock stress presents symmetrical arch characteristics along the trend of coal seam and presents symmetrical arch characteristics along the tendency of coal seam. It is influenced significantly by dip angle and mining height of coal seam. The abutment pressure is formed in the coal-rock mass within the stope with partition feature of distribution mode, peak, and distance and so on. The three-dimensional stress arch-shell in the steeply dipping seam mining is formed by the overlay of stress distribution along the trend and tendency of coal seam. With the working face advancing, it shifts to surrounding rock gradually and the asymmetry characteristics become more apparent.Under action of stress and caving arch in mining the steeply dipping seam, asymmetry arch shell is formed when overburden rock mass are falling. The region of arch shell called critical zone plays a decisive role on the activities of overlying rock. In tendency, critical zone would shift towards immediate roof at lower zone of the stope, and lie in lower part of main roof at middle area of the stope, and would transmit to upper part of main roof at top area of the stope. The scalar structure in tendency direction is formed by the interaction with key rocks. The instability of key rock at critical zone in different area causes dynamic instability of arch shell structure. There are six key parts of arch shell instability, including shell base, shell shoulder and shell roof in top area, shell base and shell shoulder in central area, and shell base in lower area. For the evolution of rock structure of critical zone, senior rock structure leads to impact roof weighting and lower rock structure destabilization leads to roof pushing-collapsing accident.According to conditions of No.120210 fully-mechanized sub level caving face in Zaoquan coal mine, the instability mechanism of rock mass structure is studied. The rock control technology has been established with the core technology of regional control of support loading along the tendency, regional control of top coal caving amount and well-structured safety protection system. The structural instability of surrounding rock in the stope has been controlled effectively. Beneficial technical and economic application is realized.