Experimental Study On Morphological Evolution Of Surge Induced By Clastic Flow Landslide In The River Channel Of Mountain Area And Its Effects On Barrier Dam Breach

Surge induced by landslide and barrier dam break are two types of secondary geohazard in the river channel of mountain area,they all feature large generation scale and wide impact range.Frequent earthquakes have resulted in the formation of a large number of barrier dams in mountainous areas of Southwest China,the barrier dams cause backwater to inundate the upstream area,which may i nduce landslide-surge events,there will be different characteristics within surge meeting with barrier dam.In order to study the characteristics of surge induced by clastic flow landslide and the breaching process of barrier dam under surge action,physical model tests have been conducted.The research presents are as follows :(1)Based on the generation,propagation and run-up stages of surge,the predicti ve models for maximum wave amplitude s,wave amplitudes attenuation and maximum wave run-up heights are obtained,and the effectiveness of the predict ve models is verified by pratical cases,the average relative deviation between the observed value of the initial surge amplitude and the predicted value of the model is only 6%.The sensitivity analysis shows that maximum wave amplitude is strongly affected by the slide impact angle and slide width,the slide impact velocity is secondary,and the water depth has a s lightly negative effect;The maximum wave run-up height is controlled by the wave amplitude near the opposite bank,slope angle in the opposite bank and the still water depth.The wave amplitude near the opposite bank is dominant,which basically determines the wave run-up height,and the other two factors have slightly negative effect.The wave amplitude attenuation in the propagation is affected by the maximum wave amplitude and wave propagation distance.T he closer to the wave source,the faster the wave amplitude attenuation is;The larger the maximum wave am plitude,the greater the wave amplitude attenuation within the equal propagation distance.The wave crest propagation velocity is lower than that of solitary wave,and the average wave crest velocity is about 90% of that of solitary wave;There is a veloci ty difference from front to back in the propagation process of the wave train,which will cause the effect of lengthening the wave train,and the effect will be more significant with the rise of wave nonlinearity.(2)According to the difference of wave run-up height,the effective classification of surge with different morphological characteristics is realized,and the boundary conditions of different wave types are defined.According to the relationship between the measured wave run-up height R and the calculated wave run-up height Rc,the types are divided into three kinds: when R≤0.45 Rc,stokes-like waves;when 0.45Rc<R≤0.9Rc,cnoidal-like waves;when R>0.9Rc,solitary-like waves.(3)There are two modes of overtopping break and non break under surge action.The first overtopping superelevation is the necessary but insufficient condition for overtopping break,the dam body will break only when the subsequent intermittent overtopping superelevation also occurs,that is,the sufficient and n ecessary condition for the dam break under surge action is : Rm a x+h-di>0 and R(t)+(h+Δh)-de>0.The overtopping break process of barrier dam under surge action is divided into initial breach formation stage and continuous overtopping flow stage.The initial breach formation stage includes two processes: the first overtopping flow and the subsequent intermittent overtopping flow;The breaching characteristics of continuous overtopping flow stage are basically consistent with those of natural overtopping flow.(4)The characteristics hydrodynamic pressure of surge on the upstream dam surface under overtopping break and non break are compared and analyzed.The oscillation attenuation process of hydrodynamic pressures under overtopping break is significantly shorter than that under non break;It is found that there are three distribution patterns of the initial peak hydrodynamic pressure of surge along the dam height under the scenarios of non overtopping,obvious overtopping superelevation a nd slight superelevation,the distribution pattern of initial peak hydrodynamic pressure surge w ith slight superelevation is the transition type between the other two scenarios,and the distribution characteristics of hydrodynamic pressure are controlled b y the change of wave run-up surface;Based on the distribution characteristics of the above three scenarios,a calculation model of the initial peak hydrodynamic pressure of surge acting on inclined dam surface is proposed.(5)Breaching mechanisms of barrier dam under surge action is discussed preliminar ily.The barrier dam break is the final result of the joint response of the inside and outside the soil of dam body under surge action.The change of pore pressure inside the dam body,the internal erosion of seepage flow and the strong scour of overflow outside the dam body are the essential causes of the dam breach.