In-situ dynamic shear modulus and decay characteristics of silty clay under cyclic freezing-thawing
CHEN Shufeng1, 2, KONG Lingwei1, 2, LI Jingjing1, 2
1.State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China;
2.Shaanxi Key Laboratory of Safety and Durability of Concrete Structures,Xijing University,Xi’an 710123，China;
3.University of Chinese Academy of Sciences,Beijing 100049,China
Abstract：According to the actual soil state of geotechnical structures in deep seasonally frozen region,systematic in-situ seismic dilatometer tests and laboratory resonant column tests were conducted.The in-situ G-γ decay characteristics of silty clay were investigated based on the in-situ maximum shear modulus and laboratory decay characteristics.The results show that freezing and thawing cycles exert great impacts on the G-γ decay characteristics of silty clay.The maximum dynamic shear modulus Gmax drops from 97.9 MPa to 53.6 MPa over successive freezing-thawing cycles.The maximum attenuation occurs in the prophase of cyclic freezing-thawing process.After several freeze-thaw cycles,the normalized Gmax-γ curves shift upwards.The G/Gmax-value of the specimens subjected to freezing and thawing cycles is relatively higher,which indicates that cyclic freezing and thawing can relieve the shear modulus decay.On the other hand,the in-situ dynamic shear modulus G0 by in-situ SDMT was greater than the Gmax from laboratory RCT.This is due to the soil disturbance during sampling and transportation,and suggests the necessity of in-situ tests.G0 decreases with freezing and thawing cycles.Moreover,the influence of freezing and thawing decreases with shear strain and is negligible when the shear strain exceeds the working strain γDMT.Rational selection of the value of soil modulus with the consideration of actual strain level and freezing-thawing is the key for the engineering design in deep seasonal frozen area.
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