Effect of Weathering on the Gravitational Stability of Questa Rock Piles

The Questa Rock Pile Weathering and Stability Project (QRPWASP) is a scientific research project whose purpose was to determine how and to what extent weathering affects the gravitational stability of the Questa mine-rock piles in 100 and 1000 years. The project studied a theoretical composite rock pile taking characteristics from several on site, and was not a site-specific engineering or regulatory analysis of a specific rock pile. Gravitational stability refers to the static stability evaluated along circular (and other-shaped) failure surfaces.

The Questa molybdenum mine (Chevron Mining Inc., formerly Molycorp, Inc.) is located in the Sangre de Cristo Mountains in north-central New Mexico and is on southward facing slopes at elevations of approximately 2290 to 3280 m. During the period of open-pit mining (1969-1982), approximately 317.5 million metric tons of overburden rock was removed and deposited onto mountain slopes and into tributary valleys, forming nine rock piles surrounding the Questa open pit.

SoilVision Systems Ltd. was entrusted with the numerical modeling of the hydrological and slope stability aspects of the waste rock pile. The research aspect of the project required the furthering of current state-of-practice in order to employ new technologies for the analysis of rock piles. The project required the inclusion of unsaturated aspects of slope stability analysis and therefore a corresponding calibrated hydrological model in order to accurately describe the distribution of pore-water pressures in the rock pile.

Questa molybdenum mine, New Mexico

Example saturation levels at the base of the waste rock

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