Deformation Failure Mechanism And Stability Research Of Massif Above The Mined Out Area In Gently Inclined Coal Beds

Mining-out area under the slop, always causes a lot of geological environmentalproblems, such as cracking, surface subsidence of the slop, especially for gentlyinclined slop, these problems is mostly prominent, often trigger large-scale geologicaldisasters. The slope in researched area is just a typical instance of thisThis article used Madaling landslide and Meidongpo unstable slope in Duyuncity, Guizhou province as the object of study, based on a great deal of geologicalsurvey of unstable slope in field, we studied geologic conditions, structural features ofthe slope body and the rock and soil and the deformation features of the slopecomprehensively. Through the method of qualitative and numerical simulationanalysis, it researched the deformation failure mechanism and stability of the gentlyinclined slope with mining-out area, then using limit equilibrium method makeanalysis and evaluation to the stability of the plasmodium in three different parts ofthe slope and in different working conditions. Gained the following major researchresult：(1)The slope in the study area is a typical lateral slope of gently inclined, thestructure of the slope has the characteristics of hard at the top and soft at the bottom.Their developed three mineable coal seams in a range of200m below the top of theslope, and formed large mined out area. Affected by the goaf roof breakage，thedeformation of the whole slope is very strong, joint fissure development and brokenloose in the internal slope, in generally, cracks in the top with the characteristics of wide at the top and narrow at the bottom and a visible stagger distance, alwaysdeveloped vertically along with the gob edge. At present, there are not only theMadaling landslide, a slope of already occurred structural failure, exists in theresearched area, but also a Meidongpo unstable slope，on top surface of theMeidongpo slope, there developed4intersecting deep cracks, cutting coal rakeformed3unstable slopes, whose trailing edge are already be the armchair-shape, andtheir stability is poorer.(2)Affect by the the underlying roof caving goaf damaging of the gently inclinedlayered rock slope, whose deformation can be divided into four zones, namely cavingarea, take the fissure, crack subsidence and dumping formula area, with increasingslope creep deformation and continue to develop, and ultimately formed the boundaryconditions of the landslides.(3)The results of qualitative analysis and numerical calculation shows that thedeformation failure modes of the Madaling landslide and Meidongpo slope is“Ladder-like" creep–rip-shear”, the process of the landslide can be divided into fourstages as follows:1) the stage of tension crack developed in the back of the slope,2)the stage of shear slip of the rock stratum,3) the stage of sliding surface developingand interconnect,4) the stage of integral movement of the landslide. Affected by thegoaf roof breakage，the cracks developed into different forms between rock mass ofdisparate hardness in gently inclined slopes of soft-hard lithologic groups: theydeveloped vertically in hard rock and along with the bedding in the soft stratum, thetwo cracks of different forms usually develop into the “ladder-like” middle-slidingsurface of the slope, and formed “locking block” in the middle of the slope. Finally,with the increasing of the creep deformation of the slope and promoting of the rainfall,the “locking block” was suddenly cut, formed the high-speed landslide.(4) The deformation of the whole Meidongpo slope is very strong, The result ofstability calculation shows: for unstable slope of areaⅡ, although the deformation isintensive, the prior failure is local buckling, the possibility of it along the potentialmajor slide surface occur whole failure is small; unstable slope of area Ⅲ is stableboth in the condition of nature and rainstorm, and have a certain safety stock; unstableslope of area Ⅳis the area of poorest stability in the field, the surface of area Ⅳslopeis under stable in the condition of rainstorm, it is likely to deformation and failure ofglobal or local in the condition of continuance rainstorm, in addition, all unstableslopes in the field are in the stage of creep deformation, so it is possible for the slope to occur overall instability along with the more and more severe deformation.(5) When the coal mining, filling mined-out area in a timely, implementreasonable drainage measures in slope, and put an end to the phenomenon of privatemining by the villagers can avoid large deformations in slope by mining; For the largebody of slope deformation in the current study area, strengthen the slope deformationmonitoring, build the blocking dam in Jiancaochong, and driven piles in slope toe canreduce the risk of regional geological disasters.