Experimental Study On Overtopping Failure Of Dike Under Frozen Soil And Freeze-thaw Cycles

As an important part of flood control and disaster reduction system,dike plays an important role in preventing flood and resisting wind and waves.Extreme natural conditions,hidden dangers in the dike and man-made damage may lead to dike-break accidents,which will cause serious damage to water conservancy,transportation,communication and other facilities,posing a huge threat to people’s production and life.The overtopping failure process of dike involves the interaction of riverbed,dike and flow,and model test is an effective means to record the dike-break process and reveal the failure mechanism.In response to the lack of research on the mechanism of dikebreak under frozen and ice-hydrodynamic conditions,a generalized model of curved flume was constructed,dike-break tests under ice,frozen soil and freeze-thaw cycles conditions were carried out,and the expansion mode of the breach and the variation characteristics of hydraulic elements in the failure area during the process of homogeneous dike failure were analyzed.The research results can provide a scientific basis for dynamic assessment of flood risk outside the embankment and plugging of the embankment.The main contents are as follows:(1)Experiments were carried out on the failure of the homogeneous embankment under flood condition,and the development patterns of scour gully and scarp in the early stage of failure of non-cohesive dike and cohesive dike,as well as the rule of instability collapse mode in the third stage,were explained in detail.The whole process of the breach velocity and the water level of upstream and downstream of the dike from steady state to unsteady state and then to steady state was analyzed.(2)Experiments were carried out on the failure of the non-cohesive dike under ice condition,and the results showed that ice has a crushing and scraping effect on the breach and damages the breach more severely on the backwater side of the dike downstream of the main flume area.The damage intensity of the breach is related to the ice amount and the relative size of ice to the breach.With the increase of ice amount,the number of collapse and the lateral broadening rate of the breach increase,while the rate of vertical erosion and flood wave propagation decrease.(3)The influence of frozen soil depth on dike failure characteristics was studied by freezing dike at low temperature and monitoring the temperature of each layer with temperature sensor.The influence of frozen soil depth on dike-break process was analyzed.The results showed that the failure modes of the embankment are steep slope erosion and unstable collapse respectively in the backerosion stage and the lateral expansion stage,and an obvious scarp merger phenomenon occurs in cohesive dike.After freezing,the ice crystals in the soil gap and soil particles are cemented each other,and the expansion rate of the breach and the change rate of water level and velocity in the breach area decreased,which was inversely proportional to the depth of frozen soil.(4)Experiments on overtopping failure of cohesive dike under freeze-thaw cycles were carried out.The results showed that the slope damage is rapid in the early stage of the second stage and the breach is hyperbolic in shape,then the scarp is connected later.Compared with the flood condition,the expansion rate of the breach and the change rate of water level and velocity in the breach area decrease.