The Stability Evaluation Of High Slopes Around The Cleaned-coal Bunker Of East-opencast-coal Mine

The engineering geological conditions of Pingshuo east-Opencast-Coal Mine are verycomplex and the problem of stability of slopes is quite outstanding. Therefore, an in-depthresearch on slopes is of vital significance for the optimization of slope structure design andthe long-term security of facilities. Taking the high slopes around cleaned-coal bunker ofPingshuo east-Opencast-Coal Mine as the research object, this paper aims to make anevaluation on the stability of slopes under various load conditions and put forward relevanttreatment methods, based on the analysis of deformation of slopes and development rule ofgeological hazard.The geological investigation results of East-Opencast-Coal Mine and slopes aroundshowed that there were seven landslides and one unstable slope in the study area, amongwhich the landslides from H3to H7and the unstable slope were located far apart from theproposed position of bunker and had little impact on its security, even five of landslides hadbeen leveled in July last year; H1and H2landslides lied near to the position of bunkeroriginally proposed, which should be focused on more attention. Landslides in research areawere mainly attributable to the increase of gravitational traction caused by the collapsibility ofloess and the prolonged erosion along the toe of slope. Among them, the saturation of redlayer caused by long-term entry of water in the depressions is the main external causeinducing slope instability.Combining the results of field and laboratory tests and based on the stability anddeformation analysis of the slopes under natural state and excavation sate, the conclusions canbe drawn as follows:The simulation of the proposed bunker based on supporting method and parameters ofslopes, showed that the largest vertical displacement was only300mm, even under thecombined action of earthquake and storm which was the most dangerous state. It could beseen from the distribution of the plastic zone in three dimensional models that there existedcontinuous tension fracture belt below the surface, where rainproof waterproofing measuresshould be taken.It could be drawn from the stability and deformation analysis of slopes after excavationthat the slope was unstable and would slip after excavation, especially at slope foot andstraight area where large horizontal displacement and stress concentration phenomenonappeared, these dangerous section need to be specially reinforced. According to the plasticzone in three dimensional models, shear and tensile failure may occur in the backfilling place of original channels during the process of calculation, so during the running of the bunkercertain measures should be taken to prevent them from sliding.As for the excavation slopes around coal bunker, it was better to excavate soils whilesupporting them, the joint support of anchor rod and the earth nail was suggested for inclinedwalls while combined supporting method of the steel supporting and protecting piles (caissonpiles) was suitable for straight walls; lager horizontal displacement of slopes could beeffectively reduced if a certain thickness of roof beam was set at the top of blind pass. Thecomparison of numerical simulations before and after the excavation and supporting provedthat the design of the supporting was feasible.Based on the analysis of compaction and direct shear test on modified loess, andconsidering the price of raw materials, it was proposed to mix detritus into the loess improvedby lime and combine with the use of the special belt of steel and plastic geotextile for slopesupport, so that it can meet engineering and economic requirements.The limit equilibrium analysis and finite element analysis of filled slope indicated thatthere were tension stress zones and plastic zones in the upper layer and shallow slide mayoccur, so it needs to control the degree of compaction of backfill soil and the dynamicallycompact the undisturbed soil on the surface; the plastic zones in connection section betweenbackfill soil and undisturbed soil and the bottom part of backfill soil showed that specialcompaction need be done at the connection position between different layers duringconstruction; the toe of slope and the bottom of retaining piles on the left side of the tunnel,where stress concentration appeared, were the key area of reinforcement, and it should behighly valued.