Influence of Freeze-thaw Cycling on Mechanical Properties of Silty Clay and Ducan-Chang Constitutive Model
(2.Transportation Industry Laboratory of Highway Construction and Maintenance Technology in Permafrost Regions—Qinghai Research Observation Base, Qinghai Research Institute of Transportation, Xining, Qinghai, China 810000)
(3.School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, Hebei, China 050043)
【Abstract】In order to describe the change rule of the undrained shear behavior of compacted clay under the freeze-thaw cycling, an improved constitutive model which reflected the influence of the freeze-thaw cycling based on the traditional Duncan-Chang model was put forward. A set of freeze-thaw cycling tests were conducted on samples which were made of silty clay from the Qinghai-Tibet Plateau, and unconsolidated undrained triaxial tests were subsequently carried out on the freeze-thaw expansive samples. Besides, the change rule of the parameters of Duncan-Chang constitutive model with the number of freeze-thaw cycles and its corresponding regression relation were determined by stress-strain relations. The stress-strain relations were obtained by dint of triaxial compression tests, on the basis of Duncan-Chang hyperbolic model. Finally, based on the functions of model parameters, the improved Duncan-Chang constitutive model taking the number of freeze-thaw cycles as influence factors was established, whilst a corresponding calculation program for the improved Duncan-Chang constitutive model was drawn up. The results showed that the stress-strain curves of samples with silty clay are curves of strain hardening type. The failure strength decreased with the increases of the number of freeze-thaw cycles, and the deterioration effect of the freeze-thaw cycling gradually decreased with the increase of the confining pressure. Among the Duncan-Chang model parameters, the shear strength index, initial tangent modulus, ultimate deviatoric stress, and K all kept decreasing with the increasing number of freeze-thaw cycles, and all parameters can be fitted by the Logistic function. The failure ratio kept increasing with the increasing number of freeze-thaw cycles, and can be fitted by the ExpAssoc function. The n decreased at first and then increased with the increase of freeze-thaw cycles, and it can be fitted by cubic polynomial function. The calculated stress-strain curves were identical with measured ones, so this improved model was appropriate to describe the variation characteristics of silty clay deformation and mechanical properties under different number of freeze-thaw cycles.
【Keywords】 road engineering; silty clay; triaxial test; freeze-thaw cycling; undrained shear behavior; improved Duncan-Chang constitutive model;
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