Experimental Investigation On Energy Dissipation Of Composite Prevention And Reduction Structures For High-speed Granular Flow Along Long Valley

High-altitude granular flow is one of the common geo-hazards in the region fulling with high steep mountaions which are easily failed under the heavy extra excitations,like earthquakes.Once a high slope failed,the broken rocks rapidly inburst in the valley and slide downwards.During the sliding processs,the rocks are gradually transformed into high-speed granular flow along the long running segment.In this case,the movement characteristics,final deposition mechanism,prevention and reduction are the frontiers in the academic researches on this geo-hazard.Thus,a large chute equipment with adjustable slopes in laboratory was designed and manufactured to investigate the movement characteristics and deposition mechanism of the granular flow in different particle sizes.Based on the results in the non-prevention cases and single rigid barrier cases which both are considered as the control groups,the effectiveness of prevention and reduction for the granular flow was mainly discussed in different experimental groups,such as double rigid barrier,array of baffles and multitype structures composite systems.Moreover,the final depositon characteristics of the granular flow were analyzed in different conditions,such as chute inclination,debris particle size,barrier height and key parameters of the composite systems(like array type,double barriers' height and distance).Here,there was a set of high-speed camera systems recording the movement of the granular flow in image data,which was deeply processed by different technologies,like Image Segmentation,Structure from Motion(Sf M)and Particle Image Velocimetry(PIV).The main conclusions are drawn as below.(1)Fristly,in case of non-prevention cases,the running-out distance,depositon area and width of the granular flow in control group without any prevention is in positive correlation with debris size and chute inclination,but the deposition height is in reverse relation.Besies,the deposition has outside diffusion shape with clear boundary in straight lines but has different fold structures in different regions insides and outsides of difflusion boundary.Moreover,the granular flow's velocity is in a decrease trend from the front to the end,but its decrease rate is realtaed to the chute slope and particle size.Furthermore,in cases of single rigid barrier system,the shape of the deposition in front of barrier is obviously affected by chute inclination,particle size and barrier height,but the corresponding influence degree is different.More interestingly,the movement process of the debris materials overflowing the barrier has clear stages in case of larger rate of the barrier height to the particle diameter.(2)For the double rigid barrier composite system,the prevention effectivenesss is controlled by the total height of the two barriers and approaching linear correlation.However,there is an obvious discrete zone on the prevention effectiveness,which is affected by the height distribution and distance as well.In this case,different barrier distance means different prevention mode.Compared with large distance mode,the small distance requires strict cooporation between the two barriers for the debris' s energy dispution.Besides,there is an obvious and interesting airborne phenomenon in front of the final deposits when the highspeed debris passing over the prevention strucutures.(3)In cases of array prevention system,the rectangular array has low capacity for preventing the granular flow compared with diamondoid array,especially for the medium and coarse paticles.Moreover,the multitype composite system consisting of “rigid barrier + array of baffles” has obvious prevention capacity,but its effectiveness has different performance compared with the single rigid barrier and array of baffles.Comprehensively comparing the control group without any prevention and the experimental groups,the debris depositon's center of gravity of the former is closed to the front compared with the latter's,meanwhile,the deposition end in case of control group has particle-free area and the two sides of the deposition curved outsides.In addition,the running-out distance of side deposition is larger than the central area's in case of array of baffles.