Abstract
Velardeña, a polymetallic mine in Durango, Mexico, produces zinc, lead, and copper, and has two operational upstream-constructed Tailings Storage Facilities (TSFs). In 2020, Cone Penetration Tests (CPTu) with pore pressure dissipation measurements (PPD) and parallel sonic boreholes were conducted to assess hydraulically deposited tailings and develop a geotechnical model for stability analysis to support additional upstream raise designs. In 2022, after implementing two more upstream raises, a new CPTu site investigation aimed to validate and update the geotechnical model for further raises. Parallel borings along with geophysical surveys aimed to assess compressional and shear wave velocities (Vp and Vs), were performed at similar locations as in 2020.
This paper presents the results of both site investigations, where aging and overall geotechnical conditions improvement were expected after two years. Up to double the improvement in CPTu parameters such as tip resistance (qc), sleeve friction (fs), and pore water pressure (u) was observed. However, this increase could be partly attributed to partial saturation and associated suction. Low pore pressure ratio (Bq) with increased qc and fs suggested potential lower moisture content. Shear wave velocity values allowed for microstructure assessment using Robertson (2016) to confirm the link between increased CPTu parameters and material aging.
The assessment of phreatic conditions in tailings indicated drier environment, as observed through the continuous profile of pore water pressure (u) obtained using CPTu soundings and PPD tests at specific depths, even amid active deposition cycles between tailings storage facilities.
