Nonwoven Geotextile Filtration Performance with Coal Refuse

The project involved bench scale testing investigating geotextile filter clogging by fine particle intrusion and fabric blinding from coarse and fine coal refuse with nonwoven geotextile filter fabric. The research explored the fine particle distribution through the refuse material and interfacial contact with the geotextile. The coal refuse was obtained from an active mining and coal waste impoundment operation located in Boone County, WV. The research involved testing of non-woven geotextiles with coarse and fine coal refuse under standard and reduced compaction energies in order to simulate field performance of the fabric to the effects of loose compaction conditions, such as direct end dumping, compared with a maximum compaction effort, standard Proctor, occurring in field conditions.;Conclusions of the research identified several key findings. During the compaction of the rigid wall permeameter samples the refuse experiences crushing and slaking effects which for a coarse grained refuse will produce an increase in the percentage of fines. This effect occurs at compaction energies ranging from optimum to reduced (13,288 to 1,417 ft-lb/ft3). The percentage of fines produced appeared to be a consistent percentage increase of approximately 32%. The characteristics of the grain size shift can result in filtration concerns when evaluating the D15 criteria used in the clogging evaluations.;Graphs of the hydraulic conductivity versus time indicated that there was no stable filter developed within the coarse coal refuse specimens. The GSE Lining Corporation\u27s NW 6 nonwoven geotextile was selected as the worst case filter for comparison of the soil-geotextile system because it has the largest Apparent Opening Size (AOS) of 0.212 mm. Results indicated that for both the initial (non-compacted) and the compacted refuse at all compaction density ranges that the Retention and Permeability Criteria were met (passed) both the MSHA and Giroud design criteria. The corresponding results of the Clogging criteria indicated that the refuse failed under non-critical conditions.;Blends of fine and coarse coal refuse were developed in the laboratory which provided for a uniformly graded grain size distribution. This distribution was at 80% coarse to 20% fines (80/20) and at 60% coarse to 40% fines (60/40) which passed the No. 100 sieve. Results of the post compaction grain size distributions for the blended refuse samples identified that the crushed particles formed aggregates and produced a shift in the shape of the curve which resembled more of a coarse refuse material. The aggregation of the fine particles was consistent across all tested samples and exhibited similar ranges of increases to the D85, D60, D15 and D10 particle sizes.;A series of rigid wall permeability tests were conducted on Coarse Coal Refuse and Blended 80/20 and 60/40 refuse samples using a strong pH2, sulfuric acid. Results of the Coarse Coal Refuse and the Blended 80/20 and 60/40 mix, the hydraulic conductivity versus time showed a one-order of magnitude decrease when compared to the water permeated samples at similar testing parameters. For the acid permeated Coarse Coal and 80/20 Blended samples the post grain size distribution indicated that the acid does not alter the Retention, Permeability, or Clogging criteria. For the 60/40 Blended samples the post grain size analysis indicated that specimen passed the Clogging criteria.;The following recommendations are presented for the use of nonwoven geotextiles in non-critical conditions. Post grain size distribution tests should be performed on specimens at the optimum compaction level to observe changes in D 85 for meeting the Retention Criteria requirements. This will take the particle crushing and slaking effects into consideration. It should be noted that the continued or repetitive compaction of the CCR material may reduce the particle diameter to less than the geotextile\u27s Apparent Opening Size (AOS) which then renders potential failure in achieving the Retention Criteria. (Abstract shortened by UMI.)