Study On Deformation Of High Concrete-faced Rockfill Dam In Narrow Valleies And Micro-mechanics Of Rockfills

Based on the combined finite-discrete element method,a non-thickness interface element and a cohesive model are introduced into the combined finite and discrete element method to simulate the breakage of irregularly shaped particles.The uniaxial compression test is carried out for the crushable granular materials considering the different factors,such as initial density,particle strength,and material heterogeneity.I investigate the compression hardening characteristics of the sample and the evolutions of the normal compression curve(NCL)and the particle breakage.The macroscopic mechanical properties of the numerical triaxial tests for crushable granular materials,with different confining pressures and breakage strengths,match well with those in laboratory tests,which reproduces the typical mechanical properties of the crushable granular materials and indicates that the fundamental mechanisms have been reasonably considered in the current numerical simulation framework.Comparing the micro-mechanical properties of non-crushable and crushable particles in assemblies,we find that due to particle breakage,the formation and development of shear band,as well as the dilatancy behavior,are restrained.The relationship between the energy dissipation mechanism and the macroscopic mechanical response is studied.I find that the external work of granular materials is mainly dissipated through intergranular friction and particle breakage,and the mesostructure is changed by increasing the additional freedom of particle motion which further inhibits the accumulation of strain energy while promotes friction dissipation.Taking the cushion material and transition material of Gushui rockfill dam as the research object,the numerical sample was prepared to carry out the confined uniaxial compression numerical tests.From a microscopic point of view,I investigate the influence of the thickness of cushion and transition materials on the macroscopic mechanical properties and the evolution of fabrics.Particles on both sides move down relatively slower than the intermediate particles which are at the same height.More interesting is that the difference is more intensive with the thickness of sample increasing.Meanwhile,the force chains distributing in the bottom of the sample are finer and more dispersed distribution,and the contact force distributions between particles become more uniform.The nonuniformity coefficient decrease and tend to be stable.The thickness corresponding to the convergence of the nonuniformity coefficient is identified as the thickness of the cushion transition layer.The minimum thickness of the cushion layer and transition layer of Gushui rockfill dam is suggested.With the maximum particle size decreasing,the coordination number and distribution range of contact forces between particles show a tendency to decrease and converge.When reduced to a certain value,the nonuniformity coefficients of contact normal,normal contact force and tangential contact force tend to be stable,which is considered to be a reasonable value of the maximum particle size for the cushion material.The solid panel unit is built on the top of the numerical sample of the cushion material.The influence of the thickness of the cushion layer on the panel stress and the mechanism of nonuniformity force transmission are investigated by the confined uniaxial numerical compression test.With the increasing thickness of the cushion layer,the overall distribution of the Mises stress,the first principal stress,and the third principal stress tends to be homogenous,and the stress decrease,as well as the stress distribution,is improved;The influence degrees indicate decreasing tend along through-thickness direction and the contact area between the panel and the cushion layer,and the decreasing amplitude converges with the increase of the thickness of the cushion layer.At the same time,the peak stress and its distribution range of the contact region between the panel and the cushion layer are gradually decreased.Stress distribution tends to be stable when the thickness is greater than a certain value,which is identified as the minimum thickness of the cushion layer,at which the stress state of the panel is optimization.The stress deformation evolution of the Houziyan concrete-faced rockfill dam is investigated based on the three-dimensional finite element model.Duncan EB model is chosen as the constitutive model rockfill materials.Two sets of EB model parameters,taking from laboratory tests and numerical tests,are used to analyze and compare stress deformation evolution of typical cross-session and concrete face.Compared to the results based laboratory parameters,the results based numerical parameters show that the upstream displacement increase slightly but the downstream displacement decrease apparently,and the vertical displacement increase largely.Moreover,the third principal stress decreases slightly and the first principal stress decrease.However,the stress and displacement of the concrete face based on laboratory parameters and those based on numerical parameters have little difference.The deformation of the ultra-high concrete faced rockfill dam in the narrow valley was further investigated and discussed.The influence of river valley shape on the deformation of the Yellow River Maerdanggao concreted faced rockfill dam,and the deformation evolution of Houziyan concrete-faced rockfill dam during the construction and operation period are analyzed.Safe operation of ultra-high concrete-faced rockfill dams and dams with the special geological condition,such as marrow river valleys and deep foundation pits,are further discussed,and suggestions for revision of the specifications of concrete faced rockfill dam are presented.