Experimental And Numerical Simulation Study Of Breach Process Of Concrete-faced Sand-gravel Dam By Overtopping

Due to the advantages of dam materials widely distributed in riverbed and beach,low cost,strong adaptability to complex terrain and geological conditions,CFSGD has gradually become a kind of most competitive dam type.At present,while the dam is exerting benefits,some existing face slab structures of CFSGDs have problems such as local aging,compression failure,crack and water stop failure.These problems will cause the rapid deterioration of seepage field in the dam body,which may lead to dam body is damaged by permeability.In addition,the global climate is warming gradually,and the frequency of extreme weather is increasing.The CFSGD may have excessive flood or dam crest settlement under the action of rainstorm and earthquake,and then the dam will occur breaching accident.Therefore,it is the key to improve the prevention and control of the dam break of the CFSGD to reveal the process of overtopping failure of CFSGDs,especially the failure of water stop.In this paper,the process of overtopping failure of CFSGD is studied systematically by the flume model test and numerical calculation.The main research contents are as follows:(1)Design similar requirements based on hydraulic model test.According to the scale method(similar grading method,equivalent substitution meth od and mixing method),combined with geotechnical model test,the model sand gravel materials meeting the similar requirements is selected;a large number of mortar specimens with different mix proportions are prepared,and according to the mechanical test data and the ultimate bending moment of the face slab,a model face slab with low strength,easy control and high density was developed.(2)Using the selected model sand gravel materials and model face slab,the CFSGD overtopping failure tests were carried out under the condition that the vertical seam sealing system of the face slab was intact and the water stop failed,and the overtopping failure mechanism of CFSGD is studied.Based on the test results,the evolution process of the dam transverse and longitudinal section and the evolution law of the fracture of the face slab during the overtopping process are clarified,and the mechanism of the two failure modes of the seepage surface of the downstream dam slope under the action of water stop failure and the influence of seepage on the breach process are revealed.(3)An overtopping dam failure model of CFSGD considering the erosion characteristics between vortex flow and sand-gravel materials and judging the fracture of the face slab structure is established.The flow characteristics,the interaction between sand-gravel materials and concrete face slab in the process of dam failure are described in detail.Based on numerical calculation,the differences between the flow rate,width and depth of rockfill breach,dam break duration,fracture length and fracture time of the face slab and test results were analyzed,which verified the rationality of the numerical model.(4)Taking Gouhou CFSGD as an engineering example,the overtopping process of Gouhou CFSGD is simulated by using the mathematical model established in this paper.The dam erosion process under the coupling effect of water and soil is revealed by analyzing the evolution process of dam transverse and longitudinal section,dam break duration and the evolution law of concrete face slab fracture.The results are compared with the measured results and previous research results.