Study On The Deformation And Failure And Movement Characteristics Of Slope In Gently Inclined Goaf Areas

The deformation of rock mass above goaf area will result in the instability ofslope, which is one of the main engineering-geological problems affecting mining’ssafety in mountains. The deformation process of slope in gently dipping goaf areas isvery complex, and especially, the forming process of landslide’s slide-surface is morecomplex. As a result, it is very difficult to evaluate the stability of slope in those areas.Therefore, the study on the crack propagation law of rock mass in goaf areas withgently dipping strata is very important for the analysis of slope deformation andfailure mechanism and stability evaluation. This article takes Madaling landslide andJieniangping deformable body in Qingshan mining area as typical examples. Based onthe field investigation and analysis of Madaling slope’s deformation process, thedeformation and failure process of Jieniangping deformable body was predicted andthe deformation model and movement characteristic of slope in gently dipping goafareas were attained. These results will provide a theoretical basis for solving this kindof geological problems. The results are as follows:(1) Layered structure, which is gently dipping inside, is the typical structurecharacteristic of the slopes in study areas. Rock mass in upper section of slope is hardand composed of thick sandstone and thin carbonaceous shale, and rock mass in lowersection of slope is soft and composed of thick-thin carbonaceous shale and sandstoneand coal layers. Moreover, controlled by the structure characteristic, the shape ofthese slopes is concave, and the average height of these slopes is about200m. Thelower part of these slopes have two layers of coal, the average thickness of which areabout1～2m and can be excavated, and the excavation of coal leads to theappearance of large goaf areas.(2) Jieniangping slope islocated on the eastern side of Madaling landslide, andthe structure characteristic of it is similar to that of Madalinglandslide. On the effectof excavation, five wide and deep cracks appeared on the slope, and they have extended to the coal layers A10and A11. According to the deformation signs,Jieniangpingdeformable body has been moving southwest and the crack LF1andcrack LF2were the boundaries of the deformable body.(3) In this paper, mechanical parameters of sandstone, shale and coal wereacquired through numerical modeling. In this process, the broking style was similar tothat attained in laboratory tests. So, the final parameters could support the numericalmodeling of slopes.(4) Two-dimensional simulation of Madaling slope was funded, and the directionis very near the mass’s movement direction. The result indicated that, according to themicro-cracks forming curves, the deformation process of slope could divided into3stages: the stage of rapid development and expansion of cracks, the stage ofconnection of cracks and the stage of creep. In the first stage, theamount ofdeformation is the largest. In the whole deformation process, the surfacenear back edge gradually developed a crack, which was formed by tension stressandextended downward to the top of excavation area in the stage of connection of cracks.This huge crack, excavation and coal A7composed the surface of rupture. On theother hand, the results of three-dimensional modeling show that: the deposition sceneis accordant withthe corresponding results from investigation and themicro-parameters of mass, which were gotten from Madaling landslide inversion, canreflect the rock mass’s strength after slope’s deformation and failureand can also beapplied to the numerical modeling of Jieniangping slope.(5) According to the study of Madaling’s numerical modeling, the deformationand failure and movement process of Jieniangping should be similar to Madalinglandslide, so numerical modeling of Jieniangping was completed to predict theevolution process. Jieniangping has gone through two excavation stages: the stage ofexcavation of coal A7and A9and the stage of excavation of coal A10and A11. In thefirst stage, the deformation process of slope could be divided into three phases: thephase of rapid development and expansion of cracks, the phase of collapsing andcompaction and the phase of creep. And the first stage leaded to the settlement ofslope. In the second stage, the slope also went through3phases: the phase of rapiddevelopment and expansion of cracks, the phase of connection of cracks and the phaseof creep. In this process, the back edge of slope formed a large tension crack, whoseposition was similar to crack LF2, and this crack expanded downward to the top of thecoal layer A11. Finally, this tension crack reached the excavation area, and this crackand coal layer A11and excavation areas composed the surface of rupture. The resultof modeling indicated that the deformation and failure style of Jieniangping wassimilar to Madaling landslide, and the boundary of Jieniangping landslide wascomposed of crack LF1and crack LF2and coal layer A11, the deformable body has been moving southwest. And it was predicted that the formation mechanism ofJieniangping was “deep collapse-caving-subsidence-trailing edge crack-surface ofrupture forming and landslide”.(6) The three-dimension numerical modeling indicated that, Jieniangping wouldform high-speed remote landslide, which was similar to Madaling landslide. Andaccording to the study result, the process of movement could be divided into5stages:the stage of the slide of leading edge, the stage of the slide of trailing edge, the stageof debris forming, the stage of acceleration and the stage of deceleration anddeposition. And finally, the debris, which was formed by thiskind of landslide, couldreach the place which was about260m away from the estuary. According to thenumerical modeling, Jieniangping landslide would affect the safety of the way whichwas not over260m away from the estuary and the area which was near the southwestside of the slope.