توصيفگر ها :
روش عددي , پايداري ديناميكي , سد باطله , تأثيرات محلي , روانگرايي , اختلاف سختي , مدل رفتاري فين - بايرن
چكيده انگليسي :
Abstract: The stability of tailings dams under static and dynamic loads has been always a great concern to geotechnicians and mining engineers. Despite the static analyses, the dynamic stability analysis of these structures, where the liquefaction is the greatest concern, has been studied in a limited and general way. In this study, the dynamic stability of this type of dam is investigated, using the finite difference method under the Finn-Byrne nonlinear elastoplastic constitutive model. The results are compared with those from an empirical method. For this purpose, the Esphordi tailings dam, which was constructed in earthquake-prone areas, has been selected as a case study. In general, first, the dynamic stability of tailings dams is investigated by examining potential landslides and liquefaction phenomena. Then site effects such as elastic modulus, Poisson ratio, and normalized amount of standard penetration test, (N1)60, have been investigated. on the overall dynamic stability of the dam. The results show that, with increasing (N1)60 in both numerical and empirical methods, the safety factor against liquefaction increases. Also, with the increase of the elastic modulus in the dam body and reducing the stiffness contrast between the foundation and the dam body to 5 over 1, the maximum horizontal and vertical displacements as well as the maximum liquefaction coefficient in the dam body have increased by 2.3, 3.5, and 2 times, respectively. It was also concluded that the displacements and liquefaction of the dam body are completely dependent on their Poisson’s ratio. Where increasing the Poisson’s ratio from 0.25 to 0.4, the maximum horizontal displacement, maximum subsidence, and the maximum liquefaction coefficient in the dam body have raised 2.4, 2.3, and 1.75, respectively. The Poisson’s ratio of tailings had a significant effect on the liquefaction of the dam body. In which, increasing the Poisson’s ratio from 0.25 to 0.4, the maximum liquefaction coefficients were increased 1.75 times. The variation of tailings dam elastic modulus did not have a significant effect on the displacements and subsidence, however, its increase from 2 to 10 MPa the liquefaction coefficient is doubled, which may cause a serious threat to the stability of the dam. As the results show, that the liquefaction phenomenon has a great impact on the stability of tailings dams which is related to the wave characteristics. Therefore, the effect of seismic wave parameters was investigated on this phenomenon. It was found that the frequency and in particular, the power amplitude of earthquakes has a significant effect on the dynamic stability of tailings dams. Whereat very low frequencies (<2 Hz), the power amplitude increased and this phenomenon appeared as an increase in liquefaction coefficient. At low frequencies (2 to 5 Hz), the amount of liquefaction coefficient did not change significantly, but these changes were accompanied by the expansion of the excess pore pressure region. At high frequency (10 Hz), due to the increase in damping ratio, the liquefaction coefficient decreased significantly. The results showed that for real earthquakes, the liquefaction occurrence cannot be predicted based on a single property of the wave. However, the coupled effect of the wave parameters such as maximum ground acceleration, magnitude, duration, frequency, or power amplitude as a set of interrelated systems plays a role in the possibility of liquefaction occurrence in the tailings dam. Therefore, due to the incapability of the empirical methods for considering all these parameters, numerical methods should be implemented to analyze the liquefaction hazard in these types of structures.
