Research On The Failure Mechanism Of Under-Dip Soft Rock Slopes And Stability Analysis

The failure of under-dip soft rock slopes is the consequence of intensifying bending deformation of rock layers which may include the fracture or toppling deformation.The thesis starts with the study on the structural characteristics of rock mass,based on the three-point-bending tests on semi-circular specimens and bending tests on the layered rock beams subject to thrust force on the two ends,with numerical method the fracture behavior and the evolution of bending deformation are explored,then on the basis of the analysis,failure mechanism of the under-dip soft rock slope is discussed by conducting numerical simulation.Finally,the stability assessment method and some controlling measures are proposed.The critical research works are described as follows:(1)To clarify the structural characteristics of rock mass and the failure mechanism,the onsite surveys and data collections are conducted on the actural failed rock slopes,by the method of geological analysis based on the findings,three types of failure are summarized,which include sliding-crushing-shearing,fracture induced by sliding and sliding –buckling-toppling failure(2)Considering the common fracture of rock mass the failed slope,to reveal the fracture characteristics of the rock mass,three-point-bending tests are conducted to study the effects of layer direction,bedding strength and spacing on the fracture toughness,fracture pattern of the specimens.(3)Taking the deformation characteristics of sliding-buckling on under-dip slopes into consideration,the bending tests on the layered rock beams subject to thrust force on the two ends are conducted,then the fracture strength,evolution of deformation and shear behavior between layers are revealed,combined with the finite element method,the effects of specimen dimensions,layer thickness,cohesive strength and the distribution of cross-joints between layers are discussed,which clarifies the mechanical and geological conditions for bending-induced fracture of rock layers,Finally,the mechanical models of bending deformation on single layer and multilayers are built on basis of energy theory.(4)The numerical study on the evolution of deformation on under-dip soft rock slopes is conducted and both inner and external controlling factors are discussed.The results indicate that sliding deformation on upper layers,buckling deformation on lower layers and toppling deformation at the slope toe occur in turn in the deformation process of under-dip slopes,then the influence of bedding structure,slope structure on the slope deformation are discussed and the failure types are summarized,which clarifies the conditions for occurring of each failure mode.In addition,the unloading effects caused by excavation and raining effects are studied,which reveals the influencing mechanism and is helpful for stability assessment and engineering design.(5)Taking the different failure modes of the under-dip soft rock slopes into account,stability analysis is conducted based on the “K” Method and elastic beam theory,respectively,then the formula of critical slope height and slope length for failure are derived,which contribute to the establishing of analytical solutions for stability assessment.Finally,based on the failure mechanism discovered above,several strengthening structures are proposed to controlling the deformation of the under-dip slopes and the strengthening effects are evaluated by using UDEC models.