Cyclic and monotonic undrained response of unsaturated filtered copper tailings

This article studies the undrained behavior of filtered copper tailings in unsaturated conditions under monotonic and cyclic loading at controlled matric suction. Two dry densities with the same water content were used. The material behavior was studied in terms of the increase of saturation, the evolution of suction, and volumetric strain during the transition from unsaturated to saturated conditions. The results show that, during the shearing, suction decreases and the degree of saturation increases, regardless of the type of load applied (cyclic or monotonic). This effect is related to the volume reduction of the air phase during the transition to a fully saturated condition. In terms of undrained shear strength, the evolution of the material is studied in terms of the phase transformation line, comparing its location in saturated and unsaturated cases. Regarding the cyclic strength ratio, the unsaturated condition shows a higher value than the saturated case by about 26% and 58% for the high and low densities, respectively. However, when the volumetric strain is higher than 3% or the double amplitude axial strain exceeds 2%, a cyclic strain localization takes place, leading to an extension failure over the sample.