Collective Effects of Debris Flow Striking on Structure Clusters Downstream:A Case Study of the Heishui Gully Debris Flow on July 12th in Pingwu County,Sichuan Province,China
The destructive consequence of debris flow striking on structure clusters are subject to the placement of each structure downstream at gully mouth and their structural types.In the process of debris flows running through structure clusters,it exhibits several observable phenomena,such as flow diversion,amplification effect,and shielding action,which are resultants of complex fluid-solid coupling mechanism;unfortunately,there was big unknown to the processes and mechanisms of the collective effects of debris flow on grouped structures.In this study,it introduced an approach to mathematically describing the collective responses of structure clusters under striking of debris flows.It conducted field investigation,indoor experiments,and numerical simulation,then fluid stress field of debris flow was obtained for a proper interpretation of the complex process of structure damages.(1)There was an amplification effect for debris flow running through grouped structures.Under debris flow attacking,damaging structure clusters leaded to an increase of 20％in flow velocity in debris flow channel and a 46％increase inside the structures.(2)There was a flow diverging phenomenon for debris flow running through grouped structures.As debris flow traversing a structure cluster was impeded,it immediately diverged around the block in a circular pattern,leading to a localized pressure concentration at the corners of structures.(3)There was a noticeable shielding action occurred in structure cluster during debris flow running through grouped structure.Without shelter protection from upstream structures,downstream structures experienced a heavy hit of debris flow at a maximum of 120％increase in impact strength.(4)There were noticeable differences in responses of a structure cluster to debris flow striking at the positions of its periphery and interior.At the periphery of a structure cluster,affected by upstream structure ruined by debris flow striking,the immediately downstream structure had a 10 seconds earlier time of being attacked by debris flow,with an impact strength of increasing by 2.1 times.(5)The impact strength of debris flow on a structure cluster could be divided into three stages:rapid increase phase,slow increase phase,and gradual stabilization phase,which corresponded to the process of increasing debris flow depth and slow siltation.The research provide scientific references for construction layout planning and geo-disaster prevention in debris flow-prone areas of mountain villages.
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