岩质边坡阶梯状破坏及岩桥破裂机制研究

Study on the stepped failure of rock slopes and fracture mechanism of rock bridges

岩质边坡阶梯状破坏路径由节理和破裂岩桥组成,为了从地质力学模型试验的角度研究其破坏机制,开展底摩擦试验并着重分析岩桥的破裂机制。针对缓倾节理、陡缓倾节理阶梯状分布和缓倾节理平行分布的3种边坡模型,从岩桥破裂演化过程和位移场变化特征揭示阶梯状破坏机制。基于力学机制分析给出岩桥的破裂模式,并从现场岩体破坏、模型试验结果和PFC^(2D)数值分析等方面进行验证。结果表明:边坡阶梯状破坏为“多级锁固拉裂型”和“层间块体拉裂型”,而在细部上岩桥破裂为压剪–拉裂和拉剪–拉裂。前一种破坏位移增大区呈条带并向坡表扩张,而后一种破坏呈片状相并相连,均展现了岩桥张拉破裂和块体分裂的过程。相比于平面型滑坡,在岩桥的破裂路径、断裂性质和扩展方向上,阶梯状破坏均有所不同。研究成果可为阶梯状破坏岩质边坡的稳定性分析提供理论支撑。

The stepped failure path of the rock slope consists of joints and fractured rock bridges.To study the failure mechanism by geomechanical model testing,bottom friction tests were conducted.The fracture mechanism of the rock bridge was emphatically analyzed.Three slope models were examined including one with a stepped arrangement of low-inclination joints,one with a stepped arrangement of low-inclination and high-inclination joints,and one with a parallel arrangement of low-inclination joints.The stepped failure mechanism was revealed by analyzing the fracture evolution process of rock bridges and the displacement field characteristics.The fracture modes of the rock bridge were determined through the mechanical mechanism analysis.These modes were verified through in-situ rock mass failure,model test results,and PFC^(2D) numerical analysis.The slope failure occurs in two modes:the multistage locking tensile type and the interlayer block tensile type.Local rock bridges undergo tensile fracture under compressive shear stress or tensile shear stress.The displacement-increasing area of the former failure mode appears in strips and expands towards the slope surface.The displacement-increasing area of the latter failure mode is flake-like and connected.The process of rock bridge tensile fracture and block splitting is shown in these two failure models.Compared to planar rockslides,different fracture paths,fracture properties,and extension directions in the rock bridge are exhibited in the stepped failure.The research results provide theoretical support for the stability analysis of rock slopes with stepped failure.