Experimental Study On Control Performance Of Debris Flow With Pile-Group Dam

The pile-group dam is kind of stereoscopic open-type check dam,the earliest history of using in china can be traced back to 1937.Because it has good performance on preventing and controlling debris flow,the pile-group dam has been applied well in debris flow-prone areas of China,especially in Sichuan and Tibet province Although China has established a systematic debris flow prevention and control system since the 1950s,there are few research focus on pile-group dam,and the mechanism of preventing and controlling debris flow by pile-group dam has not been revealed,theoretical research of pile-group dam lags behind its using in practical engineering,so far,designers usually design and build pile-group dam rely on their experience.Therefore,the research on the interception and control of debris flow by pile-group dam can provide theoretical basis for the practical engineering,also can improve the debris flow prevention theoriesIn order to research the interception and control of debris flow by pile-group dam,a series of flume model experiments were carried out to analyze the effect of density of debris flow and structure size of pile-group dam on the performance of pile-group dam to prevent debris flow.The research mainly includes the following conclusions(1)The flow process of debris flow would be affected by the performance of blocking rate of pile-group dam,which can be divided into three stages:climb stage,splashing stage and outflow stage from the start of debris flow contacting dam to the end of the flow.Based on the experimental data,established the mathematical relationship between the blocking rate of pile-group dam B and bulk concentration of debris flow cv,relative opening width b/d95,row number n,relative row spacing l/d95,cross section shape of pile-group dam ? through the multiple regression analysis(2)There are three blocking type of pile-group dam,including total-blocked type,part-blocked type and none-blocked type.In order to determine the blocking type of pile-group,a critical criterion for blocking of pile-group dam considered cv,b/d95,n,a is proposed.:(?)The pile-group dam manifest total-blocked type when F?2.31,manifest part-blocked type when 2.31<F<6.01,and none-blocked type when F?6.01(3)When pile-group dam is total-blocked,the form of longitudinal deposition of debris flow is characterized by convex type,liner type and concave type.and the transverse form of deposition is characterized by liner type;when the pile-group is part-blocked,the form of longitudinal deposition of debris flow is characterized by convex type and concave type,the transverse form of deposition is complex and random,which controlled by the position of dike burst;When the pile-group dam is none-blocked,the form of longitudinal deposition of debris flow is characterized by convex type,and the transverse form of deposition is characterized by liner type(4)The deposition gradient and length of debris flow is influenced by the density of debris flow,opening width of pile-group dam,row number,row spacing and cross-section shape of pile-group dam.Based on the experimental data,the empirical formulas of deposition gradient were established(5)Except for the density of the debris flow,the influence characteristics of all experimental parameters on the trapping rate P,bulk reduction rate ? and peak discharge reduction rate T were the same.Based on the experimental data,the empirical formulas of trapping rate P and peak discharge reduction rate T were established.trapping rate:(?)(6)The discharge process of debris flow can be divided into two types:single crest curve type and double crest curve type.The discharge process is single crest curve when pile-group dam is total-blocked,the discharge process is double crest curve when pile-group dam is part-blocked,and the discharge process include both single crest and double crest curve when pile-group dam is none-blocked.