| Thick and hard roofs are often encountered in the process of coal mining, andinstead of fracturing they often remain steady in terms of a large area of strata that areunsupported. The breakage or slippage of hard roofs, which have gathered a largeamount of elastic energy, will generate very large shock waves, causing severedamage to stopes and even mines. The identification and control of fracture interval ofthe overlying strata, especially hard roofs, is the basis for mining design and stratacontrol; It has become essential to study the surrounding rock deformation and failureof spherical caverns as more and more spherical structures such as spherical ingates ofvertical shaft, skip loading caverns, spherical storages, underground oil cellars areconstructed. For high production and efficiency, roadways at mining area aregenerally arranged along coal seams with large rectangular section. Due to coal seamswhich are of lower strength and poorer stability compared with the overlying strata,large scale of rupture in sidewalls often occur, which has always been great threat tocoal roadways stability and safety. To ensure coal mine safety production, it has beencritical to control the deformation of complex roofs and sidewalls and improvesurrounding rock stability.To solve above problems, related researches have been carried out and the mainprogresses are as follows:(1) Based on elastic foundation beam model, analytical solutions to thedeflection and bending moment of main roof strata are proposed, and the maximumbending moment values in rock beams under various rock strata conditions as well astheir positions are analyzed, through which we can conclude that rock beams fractureeither in the middle or in coal sidewalls. Besides, the varied internal force when rockbeams fracture in coal sidewalls is calculated. This study can provide a theoreticalbasis for the determination of the initial and periodical fracture interval of main roof.(2) The strain-softening process of rock media after peak-load is simplified into kplastic flows and brittle falls, and the plastic zone of surrounding rock is divided intok spherical shells accordingly; The physico-mechanical parameters of each sphericalshell is supposed to be the function of Γi, denoting the plastic strain values ofcharacteristic points in each spherical ring. Based on the Hoek-Brown criterion andnon-associated flow rule, equations of surrounding rock deformation are set upaccording to Γi. Numerical examples show that the rock strain-softening modelproposed in this paper will be the elastic-perfectly plastic model if Γiis sufficiently low, and be the brittle-plastic model if Γiis large enough; when rupture zone occurs insurrounding rock, the linear degradation of elastic modulus will have a great influenceon the displacement of free surfaces, but less influence on insoftening radius andrupture radius relatively. This study can provide a theoretical basis for the supportdesin of underground engineering.(3) Considering rectangular roadways with horizontal layered rocks, the boltreinforcement force required to resist separation and friction sliding between the rooflayers is calculated based on the elastic rock beam model, which provides aquantitative basis for the determination of bolt pre-tightening force; According to thekey strata theory in ground control and elastic foundation beam, the analyticalsolution to pressure loading on coal roadway sidewalls is proposed and the rupturerange is determined. Then, based on the stability theory of geotechnical engineering,the anchoring force required for maintaining sidewall stability is further studied,which can provide a theoretical basis to determine supporting parameters of coalsidewalls. |
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