Effect Of Loading History On The Cyclic Residual Deformation Behavior Of Rockfill Material

Earth and rockfill dams are widely applied for their advantages of simple structure,low cost and fast construction speed.With the rapid development of water conservancy and hydropower in China,dams with a height of more than 300m are builted,most of which are built in the west.The magnitude of earthquakes is particularly important for the seismic study of earth and rockfill dams.Rockfill is the most important material for earth and rockfill dams.Triaxial test is currently the most widely used method to measure the deformation characteristics of rockfill.However,there are some problems with traditional measurement methods,such as the effect of sample membrane embedding and the existence of water reservoirs inside the sample Etc.These problems will cause the measurement results to deviate from the actual values.The local measurement technology is an effective way to solve these problems,but the method of measuring small strains applied to circular samples for local measurement is less studied.How to consider the effect of early vibration on the residual deformation of the sample.In this paper,the above problems are studied,and the local displacement sensor（LDT）is used to collect the axial and radial deformation of the sample in real time to exclude the effects of end contact and end constraints.（1）In order to more accurately analyze the characteristics of the rockfill material in the stage of small strain deformation,this paper applies the small strain measurement method designed by ourselves to the circular sample.Test with materials with known Poisson’s ratio,measure the axial radial strain,calculate the Poisson’s ratio for comparison,compare the measurement results of the round and square specimens under the same working conditions,the axial strain and diameter of the two The direction strain can coincide in the ε₁-N and ε₃-N systems,indicating that the design is reliable.（2）The local deformation method is used to analyze the permanent deformation test to study the residual deformation characteristics of the specimen under different strain amplitudes.Based on the analysis of Shenzhujiang model and Dagong model,the Cdr-γ_d obtained by Shenzhujiang residual deformation model and the Asr-γ_d obtained by Dagong model both show an increase in the amplitude of the following shear strain.The maximum dynamic stress in this paper deviates from the test point by a straight line relationship.（3）The same sample is subjected to vibrations of different amplitudes,and the change law of residual strain is analyzed.Different stress amplitudes produce different growth rates of residual strain.The growth rate of residual strain of the sample has been decreasing.It can be used in double logarithmic coordinates.A straight line to describe.The existing model fits the residual strain of the sample with previous stress history,which cannot accurately reflect the whole process curve of residual deformation.Different previous stress history,vibration of the same dynamic stress amplitude,there is a point where the residual strain rate is the same,after which point the deformation rate of the sample basically coincides.Consider the effect of early vibration and propose a fitting formula.（4）The impact of the early stage vibration of the rockfill material on the dynamic modulus and damping ratio has verified that the change of the test void ratio is one of the factors affecting the dynamic modulus,and the deformation resistance of the sample subjected to the early stage vibration is improved.