Study On Burst Mode And Burst Flow Of Barrier Dam In Debris Flow Gully

Barrier dams are formed by slump-flow and debris flow that block channels and rivers.More than 100 barrier dams were formed after the Wenchuan earthquake.The burst of barrier dam results in the burst of debris flow,which has the characteristics of short disaster time,strong impact and great destructive power.Therefore,this paper took the Qipangou barrier dam,a typical blocked debris flow channel in strong earthquake area as a prototype and used indoor model test as the research means to design 26 groups of physical model tests of barrier dam burst,which were combined with different control factors such as clay content,aspect ratio of dam,upstream flow,initial water content to study the burst mode of barrier dam,the dynamic evolution process of different burst modes,the flow rate of the dam break and the flow amplification coefficient.The main conclusions are as follows:(1)Through the analysis of the burst process of the barrier dam,the burst modes of the barrier dam are divided into seepage erosion equilibrium,overtopping scour burst and permeation slip burst.Seepage scour equilibrium: water flow infiltration stage?fine particle erosion?seepage channel formation?water overflows the dam crest?water resistance and energy dissipation of large particle skeleton?seepage erosion equilibrium.Overtopping scour burst: over-dam overflow + dam slope seepage?formation of erosion pit?water cut down to form gully?retrogressive erosion of gully?formation of scarp and fall?breakthrough?toppling failure of dam body upstream of breach?dam break.Permeation and slip collapse:water infiltration at the bottom of the dam?infiltration and collapse of foot of slope?partial suspension at the foot of the slope?tensile crack on the backwater slope?slip,disintegration,breakage and liquidization of dam slope?flow overtopping?partial collapse of the dam?dam break.(2)The burst process of barrier dam can be divided into three stages: erosion initiation,rapid erosion and erosion weakening.In terms of time,the erosion rate of overtopping scour burst was small in the first stage of erosion,while the erosion rate of permeation slip burst was large in the first stage.The maximum erosion rate of the two burst modes was achieved in the second stage of erosion,and the erosion rate decreased in the third stage of erosion.The erosion rate increased to the peak at first and then decreased.In space,in the first stage of erosion,the main erosion objects of overtopping scour burst are the backwater slope and slope toe of the dam,and the erosion rate is small.In the first stage of erosion,the main erosion objects are the top of the backwater slope,the backwater slope and slope toe,and the erosion rate is relatively large.the maximum erosion rate of the two outburst modes appeared near the top of the backwater slope.In the second stage of erosion,the erosion object of the two burst modes is mainly the crest of the dam.In this stage,the hydrodynamic conditions are strong,and the erosion rate reaches the peak,and the peak occurs at the crest of the dam.The third erosion stage is mainly the erosion of the water slope.The erosion rate is low,and the maximum erosion rate appears on the water slope.Therefore,the maximum erosion rate tends to shift from the backwater slope to the water slope.(3)The anti-erosion ability of the dam body decreases first and then increases with the clay content,while the severity of the dam-break debris flow,peak discharge of flood and flow amplification coefficient first increase and then decrease with the clay content.The antierosion ability of the dam and the severity of the dam-break debris flow increase with the increase of the aspect ratio,and the peak flow rate and the flow amplification coefficient decrease with the increase of the aspect ratio.The larger the upstream flow,the stronger the hydrodynamic conditions,the stronger the flow scouring ability,and the shorter the outburst time.The severity and peak flow of debris flow increased with the increase of upstream flow,and the flow amplification coefficient decreased with the increase of incoming flow.The dam body with low initial water content has stronger resistance to water erosion,and the severity of dam-breaking debris flow,peak discharge,and flow amplification factor increase with the increase of initial water content.(4)Establishing a mathematical model of the dam-break flow amplification coefficient of the barrier dam,and selecting two blocking points in the study area and one blocking point in Yinxingpinggou for verification,which proves that the formula has certain applicability and has a certain effect on the flow amplification coefficient prediction.Due to the complexity of barrier dam failure,there are certain limitations in practical applications.