Study On Creep Characteristics And Creep Model Of Reconstituted Silty Clay

Soil’s behavior has been proved to be time-dependent which may cause serious post-construction settlement of and even damage to buildings in soils.Silty clay is a typical ground soil in the middle and lower reaches of Yangtze River,the area of rapid economic development where all kinds of constructions are being carried out.Hence,the understanding of the creep behavior of silty clay under loadings is vital to the design and maintenance of structures on it.In this research,both laboratory tests and simulations by discrete element method were carried out on the creep characteristics of silty clay in order to establish an applicable creep model.The main contents and results of this research are as follows.1.Isotropical compression tests were carried out in triaxial apparatus on reconstituted silty clay specimens with different loading steps.The deformation characteristics of the silty clay under different stress levels and with different loading steps were compared.It is found that,the higher the stress level is,the more creep deformation develops.But,for the same compression stress level,the preloading steps have little effect on the final volumetric strain development,i.e.the same hydraulic pressure with different loading steps leads to the same volumetric strain.2.Triaxial shear creep tests were carried out on reconstituted silty clay with different loading steps.The results show that,the higher the shear stress level is,the more deviatoric creep develops,and the deviatoric strain-time curves of the silty clay are obvious nonlinear.It is also found that the preloading steps have clear effect on the final deviatioric strain development of the specimen.3.The division of primary and secondary consolidation stages of silty clay under different loading conditions was tried by both “Cassagrande” method and pore pressure dissipation method.The results show that the tEOP determined by the former is smaller than that determined by the latter.For the isotropical compression creep test,the degree of pore pressure dissipation corresponding to the tEOP determined by the “Cassagrande” method is about 90%.For the triaxial shear creep test,the degree of pore pressure dissipation corresponding to the tEOP determined by the “Cassagrande” method is about 80%.4.PFC2 D was applied to simulate the laboratory isotropical compression test and triaxial shear test on the reconstituted silty clay.The variations of the mesoscopic structural parameters(pore ratio,coordination number and the distribution of the normal/shear contact force)in the sample are analyzed statistically.And the creep evolution mechanism of the specimen is revealed from the microscopic point of view.5.Based on the results of experiments and numerical simulations,a hyperbolic function model is suggested to describe the creep behavior of reconstituted silty clay.The values of the model parameters were discussed according to the test results and simulation results.It is found that the model parameters are related to the stress level and the initial void ratio of the sample.The model parameters of the hyperbolic model were suggested for silty clay under isotropical compression and triaxial shear,respectively.