Study On Constitutive Relations Of Dam Rockfill Considering The Effect Of Stress Path

Rockfill,as a common construction material in civil engineering,is widely used in the earth-rock dam engineering for its advantages of high strength,good compactibility,low cost and stable properties.With the increasing of design height in earth-rock dam,the stress state of rockfill becomes more complex,and the stress-strain relations of rockfill have already become one of the basic properties that must be deeply understood in the engineering design. At present the laboratory tests are usually conducted in triaxial shear state with constant confining pressure until the samples reach the failure state,the stress path of which is quite different from that of rockfill during dam construction and reservoir filling,and the results in the stress-strain analysis of dam body using the calculating constitutive model proposed by triaxial test results have differences with the measured data in some degree.The main reason of the problem is that the constitutive model adopted can not fully take the effect of stress path into account.Based on the above problems,the paper carries out the study on constitutive relations of dam rockfill considering the effect of stress path.The main work is as follows:(1) The engineering characteristics of coarse grained soil are studied.Based on the latest research on stress path summarized,the necessity of studying on the stress-path constitutive model of rockfill is to be considered.For simulating the actual stress path of dam rockfill, drained triaxial tests under two types of stress path are introduced,which are the stress paths of constant stres ratio during dam construction and the transitional stress paths upon reservoir filling.According to the measured stress-strain relation curves,the stress and deformation characteristics of rockfill under different forms of stress path are analyzed in detail.(2) Employing the method of decoupling analysis on strain variable,the coupling effects of mean principal stress p and shear stress q are taken into account.On the premise of considering practical application,the incrementally nonlinear models of rockfill under the stress paths of constant stress ratio including four modulus and three modulus are proposed respectively.The two proposed models are suitable for describing the stress-strain relations of rockfill under the paths of constant stress ratio.(3) Based on the stress-path test results of rockfill,the applicability of classical Duncan-Chang model in stress-path analysis is discussed,and a new stress-path constitutive model is proposed.According to the deformation regularity of rockfill under different stress paths,the stress paths are divided into several parts and the constitutive compliance matrixes in each stress-path partition are presented.The proposed model is simple and can fully reflect the effect of stress path.(4) Referring to the Gudehus-Bauer hypoplastic constitutive model,the model is improved appropriately to describe the stress-strain relations of rockfill under complex stress paths.The mutation particle swarm optimization algorithm is employed to determine the constitutive parameters and it is proved to present good performance.For considering the effect of stress path,the relations between the constitutive parameters in Gudehus-Bauer model and instantaneous stress path are analyzed and the stress-path factor is integrated into the hypoplastic constitutive model.The calculation results show that the improved Gudehus-Bauer hypoplastic model can well predict the main mechanical properties of rockfill, which is suitable for the stress-strain analysis on rockfill dam.