| Deep alluvium is widely distributed in rivers in Southwest my country.It has the characteristics of poor particle size distribution,looseness,strong Compressibility and strong permeability.More and more concrete faced rockfill dams(CFRDs)are facing the challenge of unfavorable geological conditions such as deep alluvium foundation.Under the action of dam weight and reservoir water pressure,the alluvium will have a significant impact on the mechanical properties of the rockfill dam above it.It may cause problems such as dam excessive unevenness,long-term deformation,and face slab cracking.Especially during the impoundment period,the alluvium foundation and some dam are located below the seepage free surface,and there is an obvious seepage stress coupling effect between the rockfill and the foundation,which will futher affect the stress deformation behavior of the foundation and dam.Deformation(especially long-term deformation)analysis and control is one of the key technical issues faced by the construction of CFRDs on deep alluvium.Based on the quantitative analysis of the influence of alluvium foundation on the stress and deformation of CFRD,this paper proposes a seepage-creep coupling analysis method for CFRD on alluvium.The long-term deformation mechanism and evolution process of alluvium CFRD under the seepage-creep coupling effect are revealed.Furthermore,the influence of spatial variability of material parameters of alluvium foundation on long-term deformation is discussed.The main research contents and conclusions are as follows:(1)This paper defines 4 dynamic parameters describing the distribution of the alluvium foundation,the alluvium relative thickness coefficient ζ,the steepness coefficient of both sides of the valley δ,the asymmetry coefficient in the direction across the river γ,and uneven distribution coefficient in the direction along the river η.The influence of an alluvium foundation distribution on CFRD mechanical properties is quantitatively analyzed according to the numerical calculations and measured data from case histories.The results show that the stress and deformation of the dam will increase with the increase of ζ;When δ>1 and γ>1.5,the shear stress region of the dam significantly increases,and both sides and bottom of the slab bear large tensile stresses;When η>1,the dam produces significant uneven settlement.(2)The Drucker-Prager(D-P)plastic and time-hardening creep models are used to describe the instantaneous and creep deformations of rockfill and alluvium materials.BP neural network method is adopted to inversion the material creep model parameters.The dam and foundation seepage process is described using Signorini’s type variational inequality method.A seepage-creep coupling analysis method for CFRDs on alluvium is proposed on the basis of momentum conservation principle and the Kozeny-Carman equation.(3)Based on the seepage-creep coupling calculation method,the seepage-creep coupling analysis is carried out for the CFRDs on the bedrock and alluvium respectively.Comparetive and analysis the differences between the bedrock and the alluvium CFRDs under the seepage-creep coupling effect.The CFRD deformation mechanism and evolution process on alluvium under the seepage-creep coupling effect are deeply studied.The results show that the CFRD deformation behaviour on the alluvium foundation showed that the rockfill material and the alluvium instantaneous deformation is the main source of dam deformation.Creep is the main source of time-dependent deformation.The seepage-creep coupling effect causes large long-term deformation increments.(4)Based on the orthogonal test method,the sensitivity analysis of seepage-creep coupling model parameters to the dam settlement was carried out.The main influencing parameters affecting the long-term deformation of the dam are clarified.Combining the random field theory and the Cholesky decomposition method,a long-term deformation calculation method for alluvium CFRDs considering the spatial variability of the alluvium foundation material main parameters is established.Considering the alluvium foundation spatial variability,the influence of the alluvium foundation material parameters uncertainty on the stress and deformation of CFRDs is studied.The results show that the probability of exceeding the standard is 69.3%,which indicates that the spatial variability of alluvium foundation material may lead to the increase of dam settlement deformation.Considering the spatial variability of the alluvium foundation material,the settlement deformation and downstream horizontal displacement of the dam are greatly affected,which is not conducive to the stability and safety of the dam.It is necessary to consider the spatial difference of foundation materials in the study of long-term deformation of alluvium rockfill dam. |
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