Study On Formation Mechanism Of Complex Geological Disasters Which Include Collapse And Landslide Induced By Subsidence Of Mined-out Area

Guizhou Province is famous of mineral resources in China, where there arevarieties and large reserves of mineral resources. But with the exploitation andutilization of mineral resources, the mine geological disasters are growing more inthis region. Meanwhile the covering and distribution range of mined-out area whichinduced by underground mining are also gradually expanding. Because of mined-outarea’s subsidence, sometimes there are geological disasters happened that made aserious threat to the safety of local residents.This paper is mainly making a study on Dexing mine slump in Dafang County,Guizhou Province. In order to analyze its forming mechanism and deformationevolution process, there are many ways made use of in study, such as checking out thebasic features and geological conditions,3DEC and FLAC numerical software. Onbasis of analysis, it can provide the certain reference for study on complex geologicaldisasters which include collapse and landslide induced by subsidence of mined-outarea. In this paper, main research contents and achieved research results are asfollows:(1) Dexing mine slope is the inclined slope which is consisted of Longtanformation and Changxing formation. The rock lithology are mainly limestone,sandstone and clay. There are polycyclic coal seams in Longtan formation. The coalseams mining destroy the balance of the slope stress to induce the slope top cracking,and then provide the base for the collapse.(2) Dexing mine slump is mainly composed of two parts: collapse with thecollapse direction of N45°W, and landslide with the sliding direction of N10~20°E.There are three groups of structural planes in slope, respectively Level C(N7°E/SE∠ 17°), structural plane J1(N25°E/NW∠83°), structural plane J2(N70°E/SE∠88°).(3) To simplify the structure characteristics of slope body, and establish theconceptual model of deformation of Dexing mine slump. Its deformation evolutionprocess can be divided into four stages: mining of coal seam, subsidence of mined-outarea, forming of the collapse and creep deformation of landslide.(4) The3DEC numerical simulation software is used to simulate the deformationevolution process of Dexing mine slump. The results indicate that the evolutionprocess is consistent with the conceptual model. In the process of deformation andfailure, the slope body has uneven settlement, and top maximum subsidence has up to20m, and the deformation of slope table has especially significant damage. And alsothe deformation process has obvious stage characteristics. The collapse is formed afterthe subsidence of mined-out area and it has the effect of impacting and loading toinduce the landslide.(5) The FLAC numerical analysis software is used to analyze the characteristicsof stress, displacement and plastic zones of collapse and displacement characteristicsof landslide.The results show that the slope body of collapse has both tensile failure and shearfailure after the coal seam mining. And the characteristics of stress, displacement andplastic zones have the following features:①Areas of stress concentration are mainlynear the mined-out area. In the roof and floor of the mined-out area, it formed theuninstall pressure zone, and on both ends before and after, it formed the abutmentpressure zone.②The distribution pattern of displacement is taking mined-out areaas the center, spreading of shape of the ellipse. And the closer the mined-out area, theslope displacement change is larger.③From the perspective on the distribution ofplastic zone, table of the slope, top of the slope, and the roof and floor of themined-out area show the tensile deformation, and the rock mass in the slope above themined-out area is mainly shear deformation.With the collapse, landslide gradually appears the tensile stress in the smallerclusters, and the displacement of the trailing edge of the landslide is bigger than theleading edge. From the analysis on displacement characteristics of landslide, we canknow that. At first, the collapse instantaneously impacts on the landslide’s trailingedge, to prompt landslide to start, and then forms load effect on promoting thelandslide deformation.(6) It is comparative analysis of monitoring data(from2012.7to now) of therainfall, soil moisture content in the center of landslide, and the displacement in front, center, and back of the landslide to show that the landslide is still to continue creepdeformation. And in the monitoring period, rainfall has played a vital role inthreatening the stability of the Dexing mine slump. And then it can be determined thatfrom the analysis data, if the rain washed out, it is easy to cause the collapse tohappen again, and the collapse will have the effect of impacting and loading to inducethe landslide again. So, it is necessary to strengthen the degree of real-timemonitoring on Dexing mine slump when it rains.