Effect of non-plastic fines on the undrained response of a tailings sand under high pressures

Abstract

Tailings dams have a critical role in mining operations and nowadays are reaching heights of as much as 250 m in Chile, inducing stresses beyond those seen in standard geotechnical engineering practice. Adding the constant risk of liquefaction in a seismic country, understanding tailings sands behaviour under these conditions is vital for developing improved and safer designs. This work presents the analysis of 56 undrained triaxial tests to address the effect of the fines content and stress level on the monotonic undrained behaviour of a tailings sand. Sand remoulded specimens were prepared with fines contents of 1% and 20% by dry weight of sand, covering the range of fines content allowed by Chilean normative, and initial effective confinement from 0.2 to 5 MPa. The results suggest that the variation in fines content has significant effects on the ultimate undrained shear resistance and the steady-state of the soil, and little effect on the internal friction angle and deformation modulus. On the other hand, large confining stresses decrease the friction angle, suppress the dilatancy, curve the failure envelope, and induce particle abrasion. The results are also  compared with those obtained for drained and compression tests on the same tailings sand.