MONITORING THE HYDROLOGY OF AN EXPERIMENTAL WASTE ROCK PILE USING FIBER-OPTIC DISTRIBUTED TEMPERATURE SENSING

One of the major challenges in mine engineering and operation is the construction and long-term maintenance of waste rock piles (i.e. the onsite storage of geologic material that is extracted but not processed). Waste rock piles consist of heterogeneous coarse-grained material, and their design influences the movement of water and vapor, which may promote the production of acid mine drainage or contaminated neutral drainage. New waste rock pile designs have been developed that incorporate inclined fine-grained layers. Theoretical numerical simulations show that this improved design can create a capillary barrier effect which sheds water as opposed to allowing it to infiltrate the pile. To test this new design, a full-scale, instrumented waste rock pile was constructed at the Tio Mine (Rio Tinto, Fer et Titane), located ~950 km north-east of Quebec City. Fiber-optic distributed temperature sensing (FO-DTS) is one of the key tools used to observe the internal hydrology of this unique experimental test site.

The experimental waste rock pile is 60 m long (with an additional 5.3 m toe) and is 32 m wide. The pile has a maximum and minimum thickness of 7 m and 4 m respectively, for a surface inclination of 5%. The coarse grained waste rock is covered by a 1 m thick compacted finer-grained layer: 75 cm of sand over 25 cm of non-reactive crushed waste rock. The pile is underlain by six lysimeters that capture water that flows through the pile. At three layers (at the base, just below the cover, and in the cover) there is approximately 500 m of fiber-optic cable laid in a grid pattern per layer. The system utilizes ‘hot’ FO-DTS, whereby the cable is doubled (i.e. the cable runs parallel to itself) and half of the cable can be heated and the thermal response of the unheated cable is used to evaluate moisture content and fluxes. The system has a horizontal spatial resolution of 0.5 m and temporal resolution of 20-40 seconds. The experimental pile will be briefly described, and initial FO-DTS results from in-situ measurements will be presented. The presentation will illustrate how temperature is used to sense the internal hydrology of the pile, including comparisons to moisture sensors and lysimeter fluxes. Additionally, results will be presented from an artificial infiltration tests that tests the pile’s ability to inhibit infiltration.