STABILITY ASSESSMENT OF A HANGING CLIFF

Failure of a hanging cavity cliff is a rock fall geological hazard,which affects safety of road projects and housing environment. Therefore,it is critical to understand its stability and factors controlling its failures. We proposed an approach for assessing the rock mass stability of a hanging cavity cliff based on an assumption of a linear triangle distribution of the tensile stress along the wall. First,we calculated the tensile moment based on the moment balance among tensile and compression forces and in turn derived the total tensile force on the wall surface. Then we obtained the maximum tensile stress by using principle of the linear distribution of tensile stress along the wall. The failure of a hanging cavity cliff attributes to the tensile failure of rock at the top of the cliff when the maximum tensile stress exceeds the tensile strength of rock. To assess the stability of a hanging cliff,we calculated the safety factor as the ratio of the tensile strength and the maximum tensile stress. The result of the proposed approach is different from the solution for a cantilever beam from mechanics of elasticity,which demonstrates potential limitations of mechanics of elasticity in analysis of an overhanging cliff. We used a case study to assess factors that determined the magnitude of the tensile stress in a hanging cliff,including the thickness(height) H of the hanging cliff body,unit weight of rock(γ),and length(depth)(L) of the hanging cavity. The results show that the maximum resulting tensile stress is proportional to L and φ,but inversely proportional to H. A deeper/longer wall tends to have a greater possibility of tensile failure than a shallower/shorter one. As the tensile stress decreases when the wall becomes thicker,the shear failure becomes more likely than the tensile failure for a thicker wall. We also made recommendations for future studies and its applications in engineering projects and prevention of geological hazards.