Experimental study on deformation failure and crack propagation evolvement of jointed rock bridge under different unloading rates

Abstract

Slope excavation rate has an important influence on slope stability.It is of great significance to study the deformation and failure characteristics of locked high-steep rock slope under different excavation unloading rates and the failure mechanism of internal rock bridge. In order to simulate creep failure in front and tension cracks in back edge of landslide, a middle rock bridge is formed at the end of complete rock sample by prefabricating cracks, three kinds of biaxial unilateral unloading tests with different length of rock bridge are carried out, the strength, deformation, failure characteristics and crack propagation modes of three rock bridge length specimens under different unloading rates are analyzed, the evolution process and mechanical mechanism of fracture propagation are discussed. The results show that:① The unloading rate mainly affects the unloading strength and the number of secondary cracks, but has little effect on the crack propagation mode.② The stress-displacement curve shows the phenomenon of "steep drop of stress" and "recovery after peak", and the specimen also shows the characteristic of "multi-peak".③ With the increase of unloading rate, the failure mode of specimen gradually changes from shear failure to tensile failure, and most of the tensile cracks are concentrated near the unloading surface.④ Six types of fracture propagation are generalized:the coalescence rock bridge, the coalescence specimens upper end face, lower end face of lower crack coalescence specimens, upper end face of lower crack coalescence specimens, the coalescence specimen's left end face, the coalescence specimen's right end face. ⑤ The expression of SIF at the tip of closed crack under unloading is derived, the error of fracture initiation angle obtained by theoretical calculation and experiment is kept within 6.5%, which verifies the feasibility and rationality of the theoretical calculation results.

Keywords

• unloading rate
• central rock bridge
• crack propagation
• biaxial unloading
• initiation angle