Measurement of Wind‐Induced Pressure Gradients in a Waste Rock Pile

Abstract

An automated data logging system designed to measure gas pressures within a 15‐m‐high waste rock test pile was installed at a diamond mine site in the Northwest Territories, Canada. Data collected from 12 Aug. 2007 to 15 Oct. 2007 shows distinct gas pressure gradients within the waste rock pile. The magnitude of the gradients within the pile shows a clear response to wind speed external to the pile. The direction of the gradients shows a response to the wind direction. The results demonstrate the ability to measure wind‐induced gas pressure gradients within a waste rock pile or other similar porous structures. The general pattern of the observed gradients is inconsistent with the results of numerical modeling assuming homogeneous permeability within the pile. This inconsistency suggests that heterogeneity within the pile and an irregular landscape surrounding the pile affect the way in which the wind flows around and air flows through the rock pile. Calculations of O2 fluxes using the observed gradients show that wind‐induced air flow through the pile has the potential to be a significant mechanism of O2 transport, similar in magnitude to other mechanism such as diffusion and convection. These results suggest that wind‐driven advection may be an important process in waste rock piles where the supply of oxygen limits the overall rate of sulfide oxidation.