This paper is concerned with a new concept of modeling the ,,,train softening behavior of diatomaceous soft rocks based on the laboratory investigation. An approximate solution was described for a stress-strain-time relation taking into account strain softening phenomenon. The treatment of the post-peak behavior in the calculation is discussed and comparisons of the experimental observations of normally consolidated specimens with results of numerically simulated undrained triaxial tests are given. The strain rate effect and strain softening behaviors are controlled by the time dependent stress strain relation.
A series of experimental tests were conducted to analyze the change of dielectric constant with varied particle composition and moisture content, and the experimental data were compared with several commonly used dielectric constant models. Results show that both the empirical models and the volumetric mixing models are more applicable to sandy soils and will overestimate the dielectric constant of cohesive soils due to the neglect of the effect of bound water. Actually there are a large number of strong and weak bound water in cohesive soils and the dielectric constant of bound water is much smaller than that of free water. To describe the effect of mesoscopic particle composition and bound water, a new logarithmic dielectric constant model is put forward. The application of this model is verified by others' experimental data and the calculation of dielectric constant of cohesive soils can be more accurate with this model. The moisture condition of soils can be judged roughly according to the ratio of the increment of dielectric constant and volumetric water content.
This paper aims to study dynamic properties of loess. This study is helpful to the subject on how to avoid or decrease the seismic disasters on loess ground. Dynamic triaxial tests are carried out with saturated remoulded soil samples taken form loess sites in Xi'an, China. Dynamic stress and strain relationship as well as the rule of the accumulated residual strain are obtained from the test results. Linear relationship between accumulated residual strain and vibration circle under constant amplitude circular loading is presented. A hypothesis about the accumulated residual strain is proposed. 1D dynamic constitutive relationship model which can well describe the real relationship between dynamic stress and strain under irregular dynamic loading is established. Numerical program with this model is developed and an example is tested. Numerical results of hysteresis loop, accumulated residual strain, amplitude of dynamic stress and damping ratio show good agreement with test results. It is indicated that the hypothesis of accumulated residual strain and the 1D dynamic constitutive relationship model can accurately simulate the dynamic triaxial tests of saturated remoulded loess.
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