Study On The Stability Of The Waste Dump Of An Open Pit Coal Mine

In this paper, take the waste dump of an open pit coal mine which belongs to thecoal-fired power project of GH in Muara Enim, Indonesia as the research object. Onthe basis of a large number of field investigation, engineering geological prospectingand the processing and analysis of the data which comes from indoor and outdoorphysical mechanics test, the engineering geological environmental conditions ofmining area were studied, and then combining the qualitative analysis of thedeformation failure mechanism and cause of the waste dump with the quantitativecalculation used limit equilibrium method and finite difference numerical simulation,the currently stability was evaluated, the development trend was evaluateddynamically and forecasted, and two scenarios that point out the unreasonable placeof former design are put forward to contrast in order to get a reasonable design. Themain achievements obtained are as follows:(1) According to the exploration and field research, the waste dump developstwo types of weak layers. One of them is the soft plastic shaped gray and yellow clay,silty clay lower the Quaternary cohesive soil and the interface between the lower clayrock, carbonaceous mudstone and mudstone and them. Another is the muddedintercalation, which is formed of the roof between aquifer and aquifuge by thelong-term action of the groundwater. These two types of weak layers are the keystructural faces in controlling the stability of the dump slope.(2) Based on the extensive spot investigation, the main failure phenomena ofthe dump are creep sliding-tension cracking, seepage deformation, the erosion of thesurface water and so on.(3) By means of the study of the physical and mechanics parameters ofrock-soil using the in-situ test, laboratory test, engineering analogy, parameterinversion algorithm and so on, the reliable data is provided for the calculation of the stability.(4) The calculation and analysis using limit equilibrium method shows that thedump’s whole stability is good, while local stability of the single step is pooraccording to the original design in the existing parameters conditions. With theincrease of step progression，overall gradient of slope gradually slows，what is more，dump stability is also improving gradually because the platform is pressing the bottomof the next platform.The height of first step has a certain influence on the stability ofcombination step(especially the combinations of the first and the second step), and itis more reasonable when the height is about10m,in which height the stability ofcombination step is benefited.(5) The numerical simulation result has a good agreement with the resultcalculated by limit equilibrium method, the whole stability of dump slope is good, butlocal stability is poor. In the process of filling, central basement of the whole fillingrange appear the v-shape of shear stress concentration phenomenon, and the top ofsingle steps in poor stability appear the central zone of tensile stress. Dump slopeoccurs mainly downward settlement, displacement show grossly symmetricaldistribution, in the v-shape shear stress concentration belt near which is in the centralof the whole filling range, level displacement appear obviously zoning phenomenon,and the v-shape of shear stress concentration belt is corresponding, besides, it appearthe v-shape of settlement zone, after filling finished, The biggest settlement appearnear the surface of the second layer filling of the settlement zone center. The centralzone of tensile stress of the local range of plastic failure zone slope top surface andthe central zone of tensile stress of stress field is consistent.(6) On the basis of the regional meteorological and hydrological condition,engineering geological and hydrogeological condition, the possibility that a debrisflow happen in the waste dump is very large. And this debris flow may happen in twoways: one is that a landslide forms in the dump and then translates into a debris flow,another is slope debris flow.(7) Two kinds of schemes are put forward to solve the local stability of the wastedump. The first is through decreasing the height of dumping bench (scheme1),thesecond is through decreasing angle of single bench（scheme2). By comparing andanalysis of the two plans comprehensively, the scheme one is slightly better than thescheme two, so to choose the scheme one for the final plan. But comparing with theoriginal design,the dump capacity of the scheme optimized through the dumpingparameters reduces about1/4，the dump capacity is very important for the normal production of the open pit mine. Therefore, the open pit coal mine can producenormal and safely by using light retaining structures to improve the stability of thesingle step slope.