Study On Cantilever-fracture Instability Failure Mode Of Rock Slope In Coal Mining Subsided Area

Chongqing has a long history of coal resource development. However, theexploitation of coal resources results in a large number of coal mining subsidence andaccompanied by a large number of landslides, avalanches and other geological disasters,which have a serious impact on mine geological environment and social environment.In previous studies, more thorough understanding of soil landslide has been got whichalso has strong guidance in production. Despite the steep bedrock has been alsolaunched over the corresponding research and some achievements has made, but fortheir failure modes and understanding the failure mechanism is still not perfect. Thecurrent research on mining activities and landslide disasters often focus on one singlelandslide for the study, but lack of the awareness of their systems regularly, and thus itsguidance for subsidence prevention of geological disasters will be of limited value.According to the research report Study on Steep Bedrock Mechanism and DisasterMode in Mining Subsidence which author participated in, through the survey which thedata around Chongqing coal mine rock slope, some work is done within thisarticle.Firstly, the failure mode of mine subsidence of rock slope into typical fourcategories are proposed, and also a set of classification system is proposed beyond that.The cantilever-fracture failure mode among them is picked out as the focus of this study.Secondly, a typical example of the cantilever-fracture failure mode of subsidence slopewhich is called the Wangxia perilous rock is chosen to be analyzed. Research of thisexample is done based on its failure process, which analyzes and summarizes thecantilever-fracture failure mode. Then, the cantilever-fracture failure mode wassimplified to a numerical model and by dividingthis numerical model of slopestocomplete and defect one, mechanical characteristics of the slope under excavation isstudied. Finally, on the basis of the model by changing the conditions of the modelparameters, the impact of this type of rock slope stability and the regularpatterncausedby the impact factors are determined.Following conclusions and achievements have been made:â‘ Through field investigation and the results of analysis, main mechanical modesof Chongqing coal mining subsidence damage deformation downhill are proposed which including cantilever-fracture failure mode, extraversion-crack failure mode,introversion-pressure-induced failure mode and extrapolation-pressure-induced failuremode.According to the different impact of mining activities on the slope stability, thesteep bedrock subsidence damage is divided into mining and mining-induced type.According to the results of the field survey, three main categories of deformation anddamage of steep bedrock in local coal mining subsidence are proposed: slip form, cutform and dumping form.â‘¡By using numerical analysis, the deformation process of a particular slopeinstability is studied, which revealing the instability process and mechanism ofdeformation under mining conditions of rocky slope: the damage caused by miningactivities to the integrity of the slope is mainly manifested in two aspects, one ispromoting the original crack development, the other one is producing new cracks. Andalso, according to the study, one regular pattern has been found that gob shear stressincreases with the expand of the mined areain upper rock mining. Four stages of theevolution of slope damage under cantilever-fracture mode is found.â‘¢Focused and based on cantilever-fracture failure mode, the concept of completeslope and defect slope is proposed. And instability criterion under two conditions is alsostudied. Then law figure of the failure law is drawn after the statistics of data results.Under the complete slope conditions, to relatively hard rock, with increasing heightcantilever, the maximum length of the break trend is first ascension then flatten, andwhen the rock is relatively soft, with increasing height cantilever, the maximumbreaking length trend downward; under defect slope conditions,in different crack depthsand gob distance, the concentrated crack tip stress factors around the coal excavationvary regularly.â‘£The concept change rate of the safety factor is proposed which can be used toanalyze the factors affecting mining activity in the presence of slope stability.Bystudying the influence of various factors which influence the stability of rock slope,influence regular pattern of factors including dip of coal bed, overlying slope lithology,overlying slope inclination, mined-out area width and mined-out area position isdetermined.In this paper, some new ideas and methods for research are proposed in the courseof the study, and some conclusions are summed up on the basis of previous research results, which can play a positive effect for the promotion of research and practice ofprevention and control of geological disasters in Chongqing.