MONITORING SOIL MOISTURE IN AN EXPERIMENTAL WASTE ROCK PILE USING ACTIVE FIBER OPTIC DISTRIBUTED TEMPERATURE SENSING

A major challenge in mine site reclamation is the long term management of waste rock piles. Waste rock piles consist of coarse grained heterogeneous material and their construction and design influences the internal movement of fluids which may promote the production of contaminated leachate. New waste rock pile designs have been developed to incorporate inclined covers made of fine grained, non-reactive waste rock. Numerical simulations show these improved designs create a capillary barrier effect which directs water away from the pile interior. We present results using active fiber optic distributed temperature sensing (FO-DTS), for the first time, to observe the internal hydrology of a waste rock pile. Recent FO-DTS advances have shown that soil moisture conditions can be measured by heating the metal sheath that shield fiber optic cables. Results are presented for two experimental systems:

1) The experimental waste rock pile, which is 60 m long, 32 m wide, and covered with 0.25 m of non-reactive crushed waste rock and 0.75 m of sand. Five hundred meters of fiber optic cable is laid in a grid pattern at three levels within the pile.

2) A laboratory waste rock column (0.80 m diameter) with 0.45 m of non-reactive crushed waste rock overlain by 0.20 m of fine sand. The fiber optic cable is curved to 3 helixes within the cylindrical column.

The FO-DTS system has a spatial resolution of 0.50 m, a temporal resolution of 20 seconds, and resolves soil moisture once every hour. Volumetric water content is calculated during heat cycles that lasts 900 seconds at 10 and 15 W/m in the waste rock pile and column respectively. Results from the waste rock column suggest that the cover creates a capillary barrier that limits downward water infiltration. This study will ultimately help guide future mine waste storage design initiatives, leading to improved environmental response in reclamation stage mining.