Research On The Impact Of Overcrest Failure Of Laterite-type Dams In Yunnan

As an important water retaining structure,earth dam plays an important role in water resource management,flood control and disaster reduction.However,due to its own characteristics and other factors,dam break may occur under certain conditions.Generally,the causes of earth dam break are overtopping,seepage failure,earthquake liquefactionand and so on.Overtopping dam break refers to a major accident that the surface particles are continuously taken away and the dam body is eroded after the water overflows the dam crest due to the flood exceeding the standard,leading to a dam breach that is continuously deepened and widened and water flows down.Yunnan Province is located in Yunnan Guizhou Plateau,and most of the shallow surface of the reservoir area is made up of laterite.When filling the dam,the principle of "taking measures according to local conditions" shall be followed,thus the dam in the water conservancy project is mostly built with laterite.The material composition and formation conditions of laterite in Yunnan are different from those of other regions,and its physical and mechanical properties have a significant impact on the laterite dam break.In addition,most of the rainfall in Yunnan is showers and rainstorms that came and went fast,therefore the flood is very destructive and sudden,which makes the dam break risk of laterite dam.The study on overtopping failure of laterite dam in Yunnan can provide theoretical basis for pre disaster warning and post disaster treatment.In the studying of the critical conditions laterite of dam break,we start up the mechanical mechanism of micro unit starting of laterite by considering the physical properties of the dam soil and establish the critical velocity of water flow and the formula of water head height by considering the scour effect of overtopping flow.We summarize the mathematical model of the formation and development of the breach by comprehensive considering that the breach of laterite dam is the result of the joint action of water and soil.Taking a dam of a reservoir in Yunnan Province as a prototype,the data of the existing prototype project are collected.Considering certain similarity conditions,the model test is carried out indoor.In the experiment,six groups of tests were completed to measure the start time of dam break,the arrival time of the maximum flood peak and the time of thelargest amount of discharged flood by grasping the main influencing factors and controlling a single variable.After the experiment,the width and depth of the breaches were measured.Compared with different slope ratios,it can be concluded that the model dam with larger slope ratio will discharge the peak discharge ahead of time and the final breach depth will be larger after overtopping breach.Compared with different water content,it can be concluded that the model dam with higher water content will break earlier,the peak discharge will be larger,and the final breach will be wider and shallower.Compared with different particle sizes,it can be concluded that the model dam with smaller particle size started to break later than the dam with larger particle size.The dam breaking speed of the group with particle size less than 0.075 mm is obviously faster than that of the other two groups,and the difference of particle size between the other two groups is not obvious.In the width of the final breach,the model dam with smaller particle size and finer particle size is significantly wider;in the depth,the test group with larger particle size is significantly deeper than the other two groups.