دانلود رایگان مقاله انگلیسی شبیه سازی روانگرایی خاک غیر اشباع با استفاده از مدل خاک در حالت بحران - وایلی 2017

SUMMARY

Several researchers have reported that the mean effective stress of unsaturated soils having a relatively high degree of saturation gradually decreases under fully undrained cyclic loading conditions, and such soils can be finally liquefied like saturated soils. This paper describes a series of simulations of fully undrained cyclic loading on unsaturated soils, conducted using an elastoplastic model for unsaturated soils. This model is a critical state soil model formulated using effective stress tensor for unsaturated soils, which incorporates the following concepts: (a) the volumetric movement of the state boundary surface containing the critical state line owing to the variation in the degree of saturation; (b) the soil water characteristic curve considering the effects of specific volume and hydraulic hysteresis; and (c) the subloading surface concept for considering the effect of density. Void air is assumed to be an ideal gas obeying Boyle’s law. The proposed model is validated through comparisons with past results. The simulation results show that the proposed model properly describes the fully undrained cyclic behavior of unsaturated soils, such as liquefaction, compression, and an increase in the degree of saturation. Finally, the effects of the degree of saturation, void ratio, and confining pressure on the cyclic strength of unsaturated soils are described by the simulation results. The liquefaction resistance of unsaturated soils increases as the degree of saturation and the void ratio decrease, and as the confining pressure increases. Furthermore, the degree of saturation has a greater effect on the liquefaction resistance than the confining pressure and void ratio.

3. SIMULATIONS

All the analyses were performed using the parameters of Tsukidate volcanic sand (non-plastic sand), which has a specific gravity of 2.478 [9] (Tables I and II). In the simulation of the cyclic triaxial tests for the calibration of the model parameters and validation of the model, three types of initial shearing states were considered (Table III). Saturated soil was used in case c-1, while unsaturated soils having different degrees of saturation were considered under varying pore air pressure in cases c-2 and c-3. Then, cyclic shearing, for which the axial strain amplitude was increased every 10 cycles as shown in Figure 3, was applied to the specimens under the fully undrained conditions at a constant confining pressure.

3.1. Fully undrained simulation

The fully undrained condition, that is, unexhausted air and undrained water, is the condition where air and water are unable to drain out of the soil. In other words, the mass of water and air are constant. So as to simulate the unexhausted air condition, we assumed that air is an ideal gas, and the temperature is constant. Therefore, Boyle’s law, which states that the absolute pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature, can be used as where ua is the pore air pressure and Va is the volume of pore air. As the volume of soil particles, Vs, is constant, we obtain A classical equation for solving problems involving three-phrase relationships (solid, water, and air) can be used to satisfy the undrained water condition as where w, e, and Gs are the water content, void ratio, and specific gravity of the soil particles, respectively. As Gs is constant, we get For the detailed procedure of the simulation, please refer to the Appendix A.