Time and strain-rate effects on viscous stress-strain behavior of plasticine material

A plasticine material exhibits the characterized viscous stress-strain behavior with some similarity to the behavior of clayey soils. This paper presents a series of experimental tests, which include oedometer tests, isotropic creep tests, and triaxial multistrain rate compression tests, on a plasticine material. The test study focuses on effects of time and strain rate on viscous stress-strain behavior of the plasticine material under one-dimensional (1D) straining, isotropic stressing, and triaxial compression conditions. Values of compression index (Ccε), rebounding index (Crε), and creep coefficient (Cαε) are obtained from the 1D straining and 1D stressing test data. The plasticine material has no primary consolidation period, and creep occurs from the beginning. Values of Ccε, Crε, and Cαεare smaller than those of the soft clays. The triaxial multistrain rate compression test data show that the stress-strain behavior of the plasticine depends on the strain rates and the confining pressures. A parameter of ρ0.01 is adopted to evaluate the strain-rate effects. The strain-rate effects on the stress-strain behavior of the plasticine material are obvious and significant. The values of ρ0.01 are larger than those of clays. Both friction angle and cohesion of the plasticine increase with strain rate. This is different from the friction angle and cohesion at the critical state for all soils. The friction angle of the plasticine is from 2.57° at a strain rate of 0.01%/min to 3.21° at a strain rate of 1%/min, which is much smaller than that of all clays. With the help of a scanning electron microscope, the microstructures of this plasticine material before and after oedometer and isotropic creep tests are visualized and compared. The compression of the plasticine material is mainly due to the irrecoverable porosity decrease of the material and the structural compression.