Effects Of Rock Mass Structures On Fragmenting Movement Of Rock Avalanches

Rock avalanches have great destructive power and impact force compared with the general landslide because of their high speed,long runout,and huge volume.At present,many theories and models about rock avalanches seldom consider the effects of rock mass structures,but the rock mass structures,such as structural plane and rock block,control the deformation,failure and movement of landslides.Therefore,rock avalanches are taken as the research object in this paper.Laboratory experiments and numerical simulation were used to reproduce the processes of movement and accumulation of rock avalanches,and study the effects of rock mass structures(joint attitude,joint density,joint bond strength,and block strength)on the fragmenting movement and accumulation of landslides.The main conclusions of this study are as follows:(1)Intense fragmentation occurred at the front of block when a block impacted on the bottom plate during the experiments.The speed of the fragments were as follows:front>rear and upper>lower.Dusts concentrated in the rear of the deposits.Fragmentation was generated mainly during impact,and little fragmentation was generated in the subsequent movement process.(2)Relative breakage(B_R)increased with higher aspect ratio of the block.Thin-layered blocks cut by joints fragmented more easily than block-like blocks.In general,the relationship between L_f,L_g,Area,and B_R was not obvious.However,there was relationship between the similar joint setups:L_f increased with B_R increasing,L_g decreased with B_R increasing,and Area increased with B_R increasing.(3)The morphology of the deposits,the fragmented mode,and cracking of the block in the numerical simulation and laboratory experiments were similar by using the calibrated microscopic parameters in the numerical simulation,L_f,L_g,and Area decreased as B_R increased in the numerical simulation.The differences between the results of numerical simulation and laboratory experiments were caused by the relatively small number of particles,leading to stronger interlayer friction and interlocking,and no deflection or separation during the block movement in the numerical simulation.(4)The strength of the joints has important influence on the formation of the initial fracture surface of rock mass.Damage first occurred along the joint surface in the rock mass with low joint strength,and will occurred simultaneously in the joint surface and the rock block with high joint strength.Damage occurred more easily along the joint surface during the impact with increased B_R and decreased L_f,L_g,and Area when joint density increased.In the condition D3,in which the block was cut into thin layers by horizontal joints,relatively large breakage and more small blocks were produced by impact compared to that in condition D1 and D2 in which blocks were cut by transverse or vertical joints.Moreover,L_f,L_g,and Area were significantly reduced compared to than in D1 and D2.Individual particles formed by the fragmentation decreased,the size of the largest particle size produced increases,and B_R decreased as the strength of the block increased,.The presence of joints will aggravate the ultimate relative breakage when theblock strength is constant.