Structures Of Roof Strata At Longwall Mining Face With Fully-mechanized Caving In Steeply Dipping Seam

Structures of roof strata is formed in the mining face of steeply dipping seam,the strata pressure behavior of mining face is due to destabilization of these structures.As structures of roof strata at longwall mining face with fully-mechanized caving in steeply dipping seam are complex spatial structures.Its structural characteristics and stability analysis have always been a major problem in longwall mining face with fully-mechanized caving in steeply dipping seam.Therefore, the study on these structures of roof strata can improve the theory of coal mining and ground control in steeply dipping seam.Also, it has an important significance for guiding supporting structure design, ground control, safe and efficient coal mining and other engineering practices in steeply dipping seam.By the use of on-site investigation, numerical simulation, physical simulation, theoretical analysis and field measurement, to study fracture characteristics of main roof, propensity masonry structure and bearing arch structure of overburden strata at longwall mining face with fully-mechanized caving in steeply dipping seam.The results as follows:(1) The initial fracture cracks in main roof is “X-O” type at longwall mining face with fully-mechanized caving in steeply dipping seam.Although the final fracture morphology is similar to gently inclined seam main roof which is “O-X” type.But the component force of gravity which is parallel to the strata direction is large,which is lead to the fracture cracks emerging and development process is different to gently inclined seam.After the initial fracture in main roof, restriction effect and mobile space of main roof at the gob area side is different to initial fracture.Resulting in the cycle fracture cracks in main roof is “C-X”type at longwall mining face with fully-mechanized caving in steeply dipping seam.(2) After the main roof broken into rocks, which are easy to form propensity masonry structure.Which bears a part of main roof rock weight, reducing the role of the basic roof rock to transmit force of the stent.The stability of propensity masonry structure will directly affect the stress state of supports at longwall mining face with fully-mechanized caving in steeplydipping seam.propensity masonry structure may occur extrusion deformation instability and sliding instability. The upper part of propensity masonry structure in the site is most prone instability, so the hydraulic supports in the upper part of face should be strengthened and monitored.(3) Bearing arch structure is formed in overburden strata at longwall mining face with fully-mechanized caving in steeply dipping seam.Bearing arch structure in the upper strata of masonry structure, Along strike of mining face is symmetrical flat arch and along dip of mining face is asymmetric inclined arch.Instability also different between the two models, the fist one usually occurs shear failure,but the other one typically occurs the axial compressive failure.Generally the symmetrical flat arch plays a dominant role,the instability of asymmetric inclined arch result from the instability of symmetrical flat arch.Bearing arch structure with the ability to bear the weight of overburden strata and to protect strata and hydraulic supports in mining face under it, it also can prevente the strata over main roof to transmit force to masonry structure and hydraulic supports.When bearing arch structure instability, it’s power will be transferring to masonry structure under it,and leading to masonry structure instability.As a result of strata pressure behavior showing.Thesis research results consistent with site measurement of NO.120210 longwall mining face with fully-mechanized caving in Zaoquan coal mine.It can provide the basis for roadway layout,mining technology, process and equipment configuration in the follow-up mining faces.It has a great significance for safety and efficient production in Zaoquan coal mine.