Study On Stability Of Gently Dipping Rock Slope Disturbed By Composite Thin Coal Seam Mining In Karst Mountain Area

In the karst mountainous area of southwest China,there are mostly steep and thick carbonate strata in the middle and upper part,and gentle mudstone and shale strata in the lower part.The high and steep soluble carbonate rock in the upper part has developed joints and fissures under the action of long-term weathering and erosion,and the karst phenomenon is strong,forming many karst fissures and pipelines;there are usually multiple sets of minerals in the underlying mudstone,shale and other soft rock formations.The mining history has a long history,and a large area of goaf has been formed under the mountain.Therefore,in order to study the influence of the mining of composite thin coal seams in karst mountainous areas on the deformation of overlying strata and mountains,this paper relies on the "8.28" landslide case in Nayong Pusa,Guizhou,using theoretical analysis,field investigation,similar model tests,numerical simulations,etc.Method,the overlying rock deformation law,stress evolution characteristics,and formation mechanism of collapse and landslide under the mining of composite thin coal seams in karst mountainous areas in Southwest China were studied.The main research contents and results are as follows:(1)Based on the key layer theory,the overlying coal rock under the key layer is regarded as an elastic foundation,and a two-parameter Pasternak elastic foundation model that can reflect the continuity of the foundation is adopted to establish a semiinfinite length two-parameter elastic foundation upper beam mechanical model for mining under a rock slope Through calculation examples,the theoretical prediction settlement value and the numerical simulation calculation result were compared and verified,and it was found that the maximum settlement error of the two was within 10%.At the same time,the deformation trend of the overburden rock in the model test basically accorded with the prediction of the calculation theory.(2)Through similar model tests,the development of rock fissures,movement of overlying strata and stress evolution characteristics after mining of composite thin coal seams are analyzed.The results show that the lower overlying strata are characterized by the bending settlement of simple beams with a large middle and small sides on both sides.The overburden settlement is mainly characterized by the bending of the cantilever beams with large outer sides and small inner sides;after mining,the rock mass at the foot of the slope gradually slips and extrudes along the rock bed,and the rear edge of the model pulls along the deep and large fissures on the surface.Eventually,the collapse occurred in the type of "sliding and extrusion of the front edge of the mountain-tearing of the trailing edge-buckling of the front edge-overall overturning".(3)The block discrete element software UDEC was used to further study the movement law of the rock layer,the stress transfer mechanism and the instability mechanism of the Eagle Rock.The combination of lithology,rock mass structure and long-term mining of old pits,dissolution,and weathering affect the deterioration of the mountain;the main inducing factor is the large-scale mining of coal seams in recent years to accelerate the development and development of mountain cracks;the direct triggering factor is that the early heavy rainfall reduces the rock Mechanical strength of body and joint cracks.(4)Based on the previous research content,the UDEC numerical simulation software is used to carry out numerical simulation research on the mountain deformation under different mining methods.It is found that the downward mining between layers develops earlier than the upward mining between layers,and it is more likely to cause mountain cracks,which is not conducive to the stability of the mountain;Compared with the receding mining plan,the mountain's cracks are more developed and the slope deformation is larger in the conventional mining scheme;the rock mass does not appear to be broken after the filling mining,the mountain cracks are basically undeveloped,and the mountain displacement is small.