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Abstract The three-parameter viscoelastic constitutive model is applied to describe the creep properties of geogrids at low stress levels. Combining with the creep tests results of geogrids，the model parameters are obtained by using the utmost optimization method. It has been proved that the three-parameter viscoelastic model of geogrids can relatively accurately reflect the two-stage attenuation creep properties of geogrids at low stress levels. Then，one constitutive model of reinforced soil considering viscoelasticity of geogrids is suggested. The stress and strain formulas of reinforced soil when soil is in the elastic and plastic stages are obtained. The study results show that stress of geogrids is not only associated with the external forces that reinforced soil bears，the properties of geogrids and soil，but also with the reinforcement layer spacing and working time. When soil enters into the plastic state，geogrid mainly displays creep properties with its stress changeless，which leads to the increase of strain of reinforced soil with time. As time goes by，geogrid displays stress relaxations；and its stress as well as the stress of soil would decrease. The stress relaxation values of geogrids placed in soil are smaller than that placed in air. Moreover，the stiffness coefficients E2，viscosity coefficient of geogirds and the internal friction angle of soil affect the time required for the reinforced soil arriving at plastic state which is called Tp most.
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Received: 26 November 2010
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2011, Vol. 30 
