Study On The Self-dredging Capability Of Siphon Drainage Pool In Debris Flow

Debris flows occur frequently in China, causing huge disasters and properties loss. Hydrodynamic factor is important in the outbreak of debris flows. At present, the wat er flow is moved by gravity in all the method of cutting and drainage of water in debri s flows. The technology comes with the large volume of earth works, low drainage eff iciency. Also, high carrying sediment in debris flow often makes the cut drainage stru ctures failure due to siltation. Debris flow prevention technology which combines the separation water from debris flow with self-draining siphon drainage can effectively i mprove efficiency of prevention engineer and durability. This method could reduce th e debris flow hydrodynamic conditions by setting pools which conducting flood in an d from which the water is pumped out quickly to the downstream safety zone through siphon pipes in the debris flow formation region or the valleys in circulation area. It h as several advantages,(1) It can solve the problems of governance in different scale of debris flow gully through effective control of the formation and circulation process in debris flow; (2) the construction of the siphon shunt system is simple and it can effect ively improve drainage efficiency because of the siphon makes gravity water flow int o full-pipe flow; (3) the suction of siphon can prevent pipes from siltation and effectiv ely improve durability of drainage engineering; siphon pipes without slope control ma kes convenient installation; (4) it doesn’t involve large-scale earthwork and building c onstruction, so it has low fabricating cost and little effect on environment.For a shunt structure, if the hole in drain grating is too small, it will make the drai nage structures failure due to siltation and unable the floods in valleys smoothly into t he pool; if the hole is too big, the stones in pool will unable to siphon away that leads to sedimentation in pool. Therefore, the rational design of the shunt system requires t he hydraulic performance of the siphon pool. A three-dimensional numerical model w as built to analyze the hydraulic characteristics of the pool under the siphon-lift throug h computational fluid numerical software named "FLUENT". The simulation results r evealed that a velocity field center around the siphon pipe suction appeared due to the effect of siphon in the pool. The bed shear stress (BBS) in the pool bottom correlated significantly with initial siphon head and siphon pipe diameter and there is a linear rel ationship between the BBS of pool bottom and the efficient water head, and an expon ential relationship between the BBS and the siphon pipe diameter under same efficient water head. Suction pressure reached the maximum when the distance from the sipho n pipe head to the bed was about 25% of siphon pipe diameter. Reasonable large dista nee between the outside walls of suction pipe to the side wall of the pool and a pluralit y of parallel-arranged siphon pipes can prevent the pool from sand sedimentation effic iently. The above conclusions may provide guidance in the design of siphon shunt poo 1 in the practical debris flow prevention engineering.