Cyclic and Monotonic Behavior of Non-plastic Silts with the Presence of Initial Static Shear Stress Using Strain Energy Approach: A Case Study for a Tailings Dam

Mining Exploration, excavation, and construction are considered as mining activities which are recently growing dramatically. Therefore, utilizing the mining wastes with the least environmental damage is a significant concern. Tailings dams are one of the conventional solutions that store the extracted hazardous substances safely for water resources management and environmental protection. This reseach deals with the effects of monotonic and seismic loadings on silt-sized copper wastes existed in a tailings dam at Northwest Iran as a case study. Various values of initial static shear stress are performed using an automated cyclic triaxial system. Monotonic undrained compressive tests were performed with a relatively constant density and considering three values of ۵۰, ۱۰۰, and ۱۵۰ kPa for mean effective stress. Depending on the first density of samples, applying a mean effective confining pressure of ۱۰۰ kPa, increased the initial densities by ۲۵ to ۳۰% as compared to the initial condition.Moreover, the effect of initial shear stress ratio with three values of ۰, ۰.۲, and ۰.۴ was evaluated. No peak point was observed for samples under α = ۰, whereas, samples with α = ۰.۴ encountered a peak point before reaching to the phase transformation point. The results of cyclic experiments were used to evaluate capacity energy and residual pore pressure based on the strain energy approach. Cyclic tests on the samples were performed considering the shear amplitude of ۰.۷۵% and frequency of ۰.۳ Hz. It is shown that the most energy dissipation occurs at the first cycle possessing the highest stiffness. For α = ۰, energy density increased from ۴۷۴ J/m۳ to ۱۱۴۷.۴ J/m۳; however, a more intense increase was measured from ۶۸۲ J/m۳ to ۵۸۳۹ J/m۳ when α = ۰.۴. It is also found that applying initial shear stress has a pretty considerable influence on monotonic strength and the liquefaction resistance of silts. The increase of α from ۰ to ۰.۴ yielded a linear increase in the shear strength of samples in the range of ۲۰ kPa to ۷۰ kPa. The results of this paper were then validated accurately through some previous studies.

کلیدواژه ها:

Triaxial ، static shear stress ratio ، Liquefaction ، Strain Energy ، non-plastic silt