Failure Mechanism & Stability Analysis Of Liao Jiaping High-Steep Slope In Wu Shan County

Liaojiaping High-steep slope is located on the left of Changjiang River in Three Gorges Reservoir, Wu Shan county, the core of Heng Shixi Anticline, there is Siluric Shamao Group sandrock siltstone mudstone,Devonian Yun Taiguan Group quartz-sandstone,Carbonic Da Pu Group dolomitic stone and Permian Qi Xia Group limestone from the lower to the upper. The upper flat's absolute elevation is 650m in Liao Jiaping slope, there is gentle slope under the altitude of 380m, the lower layyer is changed to middle dip step by step. Because the rock in the slope is soft and hard intephase, two teams joints is developed, there are many dangerous rockmass in the cliff from the altitude of 380m to 560m, Because of slope failure, there is many rock block under the cliff, the failure is formed seriously danger to the locaed and Changjiang river waterway.The paper concludes these conclusion and congnition after field detailed survey,triaxial test and DEM analysing, These analysis offer scientific idea for controling deforming rockmass , also it has important instruction to other dangerous rockmasses study in Three Gorges reservoir.1) Detailed exploration show that there are seven soft layer in the slope, there develops two teams joints, the two teams joints are high dips and vertical to one another ,which forms many dangerous rockmass and rock columniation. Upper two soft layers is creepping, and the base of the dangerous rockmass and rock columniation in the cliff is the soft layyer.2) Using RMT-150 test system studies rock in the slope on stress-strain curves under 2-10Mpa lower confining pressure, and build the relation of peak strength,Young's modulus and confining pressure. Limstone reflects yielding plastic character in high confining pressure, in low confining pressure reflects brittleness character. In test confining pressure sandstone reflects brittleness character.Through linear regression,the paper analysis shear strength and the relation of peak strength and confining pressure. In lower confining pressure Liaojiaping Slope rock reflects brittleness character,which shows that the deforming mode reflect plastic bending possibility is not bigger than toppling failure.3) On the basis of slope structure and deformation failure phenomena, the paper concludes that the failure modes maybe have two modes, horizontal pushing and toppling falling.4) steep joint and gentle soft layyer can form horizontal pushing. According to horizontal pushing landslide failure mechanism, after calculating the critical head pressure and compares it with joint height, the paper finds that it is little possible for upper slope to horizontal push.5) the lower soft layyer failures by weathering, then it forms moment load. With the failure of the lower soft layyer seriously, the dangerous rockmass column will topple down. The field result is accorded to the failure mode. So the failure mode of Liao Jiaping slope is toppling.6) Using UDEC model, the paper make numerical analysis on the Secondary toppling mechanism of the rockmass. The simulation results show that the crack failure by Secondary toppling is reducing from the face to the back; Toppling block is controled by the soft layer, as a whole, the block don't cross the soft layer, So there is no possbile to topple as one-piece; When dangerous rockmass or rock piles are formed in secondary cliffs , there are two failure type:toppling to the front & toppling to the back. The toppling direction is relatived with belowed soft layer's failure seriously, when the toes of soft layer failure seriously the rockmass topples to the front, when the heel of soft layer failure seriously the rockmass topples to the back.7) Using Limited Equilibrium Method, the paper calculates safety factors on the whole slope, the results shows that sliding stablity factors is bigger than 1.5, the slope is in the stability conditions, the horizontal pushing sliding is lower possibility. To two presentative dangerous rockmass ,the paper calculates anti-toppling & anti-sliding factors, the results show that under eathquake the toppling safety factors fall fastly, when the horizonal eathquake factor is 0.05, the rockmass 2^nd is under stability. But the sliding factor is also bigger than 1.5, So the slope is possible to toppling, and with the failure of basis soft layer, the factor is lower. This result also matches to the failure mechanism mode.8) Basing on the character of deforming , some measure can be adopted to manage the slope, such as discarding dangerous sites,SNS softy protecting net,drainning,protecting the surface,seting forbidden waterway & building professional-location monitoring system.