EXPERIMENTAL STUDY ON YIELDING AND STRENGTH PROPERIES OF SILTY SAND UNDER FREEZING-THAWING CYCLES
CHANG Dan1,LIU Jiankun1,LI Xu1,2
(1. School of Civil Engineering,Beijing Jiaotong University,Beijing 100044,China;2. Transportation industry laboratory of Highway Construction and Maintenance Technology in Permafrost Regions-Qinghai Research Observation Base,Qinghai Research Institute of Transportation,Xining,Qinghai 810000,China)
Abstract:In order to study the influence of freezing-thawing cycles on the yielding and strength properties of silty sand from Qinghai—Tibet,the consolidated drained triaxial shear tests under different confining pressures and freezing-thawing cycles were conducted. The freezing temperature was chosen to be -5 ℃ during freezing- thawing cycles. It was found that the silty sand exhibited shear contraction and strain hardening during shearing. The types of volumetric curves and stress-strain curves were not changed after freezing-thawing cycles. The volumetric yield surface of unfrozen silty sand was expressed with an elliptic curve,while the yield surface for shearing was represented with a linear function passing the origin. The shapes of both volumetric yield surface and shear yield surface were not changed after freezing-thawing cycles. Both the volumetric yield function and the shear yield function were expressed as the power function of the plastic strain and numbers of freezing-thawing cycles. The shear strength of silty sand increased with the increasing of the normal stress,but decreased and then rised with increasing the number of freezing-thawing cycles. The cohesion of the silty sand was changed from 4.82 kPa to 2.07 kPa and the angle of internal friction was varied from 27.11°to 22.93°after freezing-thawing cycles. The linear Mohr-Coulomb criterion was adopted to describe the strength properties according to the strength variation of silty sand to the normal stress under freezing-thawing cycles.
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