Environmental factors affecting geotextile filter design in coal refuse impoundments

Abstract

The US Mine Safety and Health Administration (MSHA) issued the Second Edition of Engineering and Design Manual for Coal Refuse Disposal Facilities prepared by D'Appolonia in 2009. This second edition provides design guidance on the use of nonwoven geotextiles for drainage applications when replacing graded granular filters in coal waste impoundments. Coal refuse is susceptible to slaking that produces an increase in fine particles which may lead to geotextile clogging. This article presents the results of research which investigated the effects of slaking on the hydraulic conductivity of permeated refuse specimens in order to identify parameters influencing the design criterion for selecting candidate nonwoven geotextiles for drainage applications. Permeability tests were performed on refuse–geotextile samples at different compaction energies and varying moisture contents, followed by post-grain size distribution (GSD) tests. Conclusions indicate that (i) the k soil of the acid-permeated refuse samples is one order of magnitude higher than the k soil of the water-permeated refuse samples and was attributed to fine particle aggregation. Any potential increase in the k soil due to continued particle aggregation may approach a failure criterion where the soil permeability is too high. The long-term effects of low-pH groundwater may cause an increase in refuse permeability, leading to criterion failure due to particle aggregation; (ii) comparisons of the coarse coal GSDs for the pre- and post-compacted, water-permeated specimens showed an increase in the production of particle fines due to slaking at critical indices.