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The case study was a roadside cut rock slope of a provincial trunk highway in Guangdong Province. Based on the geological investigation and joint analyses, the orientation of the maximum main stress was near south-north and an anticline was generated by the stress pattern. The slope was located in the anticline center. The orientation of highway and the maximum main stress was almost in parallel, so the maximum main stress almost had no effect on the slope stability. However the structural discontinuities generated by the anticline intersected with each other, as a result, the large unstable wedges maybe formed. The strata on the top of the slope dipped out of slope, whereas the strata at the bottom reversely dipped into slope. The range of the out-dip strata was small, it is therefore inferred that out-dip strata were caused by gravity creep. There were three failures modes, namely the plane failure, circle failure and compound slip failure caused by out-dip structural planes and water infiltration. The failure mechanism and the process were analyzed by distinct element method. It was demonstrated that the final failure mode was slip-tensile-shear, that is, the rock at the bottom slipped along the gentle structural plane dipping out of the slope, tensile cracks appeared on slope crest and the rock bridge in the middle of the slope was sheared. The slope was designed to be reinforced with anchor bars and reinforced cables and the slope surface was protected with special designed shotcrete compatible with plants for ecological and aesthetic concerns. Based on analysis with Bishop Method, the safety factor of the design satisfies the requirement of the design code. It is concluded that when slope is located near the geological structure, the geomechanical mechanism and its effect to the slope stability should be analyzed in details, and the slope stability should be evaluated including all possible situations, only based on detailed study may the reinforced scheme be decided. © 2008 Taylor & Francis Group.
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