GCL-LLDPE geomembrane interface friction angle evaluation and stability analysis of a valley fill leach pad project

¹ MSc Candidate in Seismic and Geotechnical Engineering, University of Chile.
² Chair, IGS Chile. CEO, Axios Engineering SpA, Chile.

^* Daniel Zúñiga: daniel.zuniga@ug.uchile.cl

Abstract

The Los Chancas mining project, initiated in 1998, is a copper mine focused on extracting copper sulfides and oxides. In 2020, a mine plan update required a review of the constructability design and an evaluation of the Permanent Leach Pad and Filtered Waste/Rock Dump's physical stability. This paper presents results from an evaluation study regarding friction angles at the liner interface and stability analysis in the VLF pad. Previously, an internal friction angle of 23° was established for the basal liner interface (LLDPE-GCL) to meet stability requirements. However, due to the high required friction angle, the pad design was updated with lower slopes. The study evaluated various GCL materials from two suppliers using direct shear tests, revealing that the GCL from the second supplier achieved a high friction angle of 22.3° at the interface. Stability analysis considered two critical sections, examining three types of failure under both static and pseudo-static conditions. Results showed a need for a minimum friction angle of 16° in static conditions and 20.5° in pseudo-static conditions to ensure compliance. These results suggest the potential use of high strength geosynthetic materials in the studied areas, with a preference for the GCL material offering the highest friction angle.