| Concrete faced rockfill dam(CFRD)has been the preferred dam type for high dam construction because of the significant characteristics of small cross-section,fast construction schedule and great adaptability to complex terrain.In recent years,with the deepening of"Western Development","One Belt One Road" and other major Chinese strategies,a number of world-class high CFRD are being planned and constructed,such as the Gushui,Lawa,Dashixia and Cihaxia.However,these high CFRDs are located in the meizoseismal area and have a high fortification intensity(not less than 8 degrees).The dam will operate for a long time(even more than 100 years),so the probability of encountering a strong earthquake and damage during the service period is high.Moreover,high dams have large investments and are responsible for power generation,flood control,irrigation and other important tasks.Once the dam failure,it will not only impact on the regional economic development,but also cause incalculable secondary disaster to downstream regions,due to the sudden release of a huge amount of reservoir water.Therefore,it is very important to carry out seismic research on high CFRDs and accurately evaluate their safety during the operation.CFRD is a complex cross-scale system with obvious interaction.The size of local key components in anti-seepage structures is very small(the thickness of slab and anti-seepage walls is only 0.3m),which is thousands of times different from the overall scale of the dam(the length of the foundation for the 300m-high dam is up to kilometer level).Thus,it is a great challenge for efficient analysis of essential structure failure and overall response of the dam.However,the current 3D analysis model of CFRD is mainly based on the simplified coarse mesh,which is difficult to accurately capture the dynamic response of impervious structures and assess the safety of high CFRD.Moreover,the concrete is a kind of quasi-brittle material,which may induce local damage during strong earthquakes.The current linear elastic models cannot describe the material characteristics of stiffness degradation and strain softening during the failure process,so it is difficult to evaluate the seismic performance of the slab reasonably.In addition,the traditional finite element method of classical continuum mechanics based on the assumption of small deformation is a problem to accurately reproduce the failure process,which is the large deformations and strong discontinuous local failure in the dam crest zone(such as looseness,collapse,slip and rolling of rockfills,slip of wave walls,a separation between slab and cushion).Therefore,it is necessary to further develop and improve the high CFRD numerical analysis method.To tackle these problems,the non-matching nodes analysis method between soil and structure is first proposed in this paper,which provides theoretical and technical support for the fine analysis of slab seismic damage and cracking.Then,the plastic damage model and cohesive zone model of concrete are introduced and developed,and the refined damage and cracking evolution analysis technique of the slab is presented to investigate the seismic failure mechanism,failure mode and evolution law.According to this,the slab anti-seismic measures are proposed and the effect is verified and quantified.Finally,the dynamic failure analysis program for CFRD based on DEM-FEM is independently developed to simulate the dynamic analysis of the CFRD under earthquakes.The initial seismic failure mode and evolution law of the dam crest zone are reproduced visually,and the effectiveness of anti-seismic measures verified and quantitatively evaluated.The main contents and conclusions of this paper are as follows:(1)The Guyan reduction method is applied to construct a non-matching nodes interface element for the meshes transition between soil and structure based on the contact theory,which realizes the analysis of the interaction between soil and structure with non-matching nodes.This method can obviously reduce the number of elements,improve the calculation efficiency on the basis of ensuring accuracy,and provide the theoretical and technical support for the fine analysis of CFRD.(2)A concrete plastic damage model that can reflect the steel fiber characteristics is developed and programmed to simulate the concrete properties with different steel fiber content.Combined with the generalized plastic model of rockfill and interface and the non-matching nodes analysis method,the seismic damage evolution of the concrete(reinforced concrete and steel fiber reinforced concrete)slab is finely analyzed.Then,a new slab anti-seismic measure of local replacement with steel fiber reinforced concrete is offered,and the effect is verified and quantified by practical projects.(3)The application of the concrete cohesive zone model is extended to the CFRD,and then a fined elasto-plastic 3D crack analysis method for slab under the explicit framework is established and used to analyze the 3D seismic cracking of the CFRD.It reveals the seismic failure mechanism and law of the slab,clarifies the action mechanism of reinforcement.This technique can locate the seismically vulnerable areas of the slab accurately.Furthermore,an intuitive and quantitative slab seismic assessment method is proposed,which overcomes the limitations of traditional linear elastic analysis methods based on strength criterion.(4)A CPU multi-core parallel and GPU accelerated 2D polygon discrete element analysis program is developed independently.Combined with the designed call and information interaction interface,the program is packaged as a DEM class and integrated into the finite element platform GEODYNA,which establishes a dynamic failure program for CFRD based on DEM-FEM.Therefore,an efficient and multi-region interface coupling analysis within the same computing framework is realized.(5)This paper first carries out the failure analysis of CFRD under earthquake based on DEM-FEM,and reproduces the initial failure mode and evolution law of the dam crest zone visually.Besides,the influences of the wave wall type are discussed,and the effects of antiseismic measures are verified and quantified.It solves the problem that the traditional dynamic analysis method based on continuum mechanics is difficult to describe the large deformation and discontinuous characteristics of the dam crest zone under earthquakes. |
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