The utility of aggregate processing fines in the rehabilitation of dolomite quarries

Abstract

It is economically and environmentally desirable to use aggregate processing fines (pond fines), a by-product of dolomite crushing/washing operations, in the rehabilitation plans of the aggregate quarry where they are produced. A study was undertaken to determine if the physical and mechanical properties of these dominantly silt-sized materials also made them suitable as embankment material from a geotechnical perspective. The after-use proposed for the dolomite quarry investigated in this study (Ontario, Canada) was to be a naturalized area surrounding a large water reservoir, and pond fines were being used to construct sloped embankments at the base of the vertical perimeter quarry walls for this purpose. The specific objectives were (1) to measure and analyse the physical and mechanical properties of the pond fines that are relevant to their usage in site rehabilitation (earthen embankment), and (2) to predict the long-term stability of the embankments given current emplacement practices and a scenario of partial submergence by a reservoir. Shear strength, measured by direct shear and drop cone penetrometer methods, increased with higher clay-sized particle content and higher dry bulk density, with lower sand content, and it peaked at soil water contents (4–9 per cent kg kg−1) well below the measured field capacity of about 16 per cent kg kg−1. Factors of safety calculated for slope stability (modified Bishop method of analysis) decreased with decreasing shear strength (cohesion, angle of shearing resistance), with increasing slope gradient, and with the introduction of a water table. Nevertheless, the factors of safety were acceptably high for all scenarios tested (≥1·8), including scenarios using the maximum measured slope gradient of 37 per cent. Increasing the dry bulk density by 0·1 g cm−3 over the mean density measured in situ (i.e. to about 87 per cent of the Standard Proctor maximum dry density) did not improve the calculated factors of safety for slope stability enough to warrant increased mechanical compaction of the pond fines during embankment construction. Copyright © 2000 John Wiley & Sons, Ltd.