Laboratory Experimentation and Numerical Modeling to Enhance Drainage in Geotextile Tubes

Laboratory Experimentation and Numerical Modeling to Enhance Drainage in Geotextile Tubes Jonah G. Tyson Geotextile fabrics are commonly used in the dewatering and filtration of high-water content geomaterials. Acid Mine Drainage (AMD) sludge is a geomaterial and has increasing production volumes in West Virginia. The WVDEP has large sludge storage sites for dewatering and long-term disposal. Currently the AMD is treated then transferred by pumping the material into geobags for long-term disposal in tubular shape geotextile bags that dewater the sludge. The current design of the geobags limit the pathways for the water to filter out due to the quality of the material. This research investigates the geotextile fabrics currently used and explores options to insert internal lateral drains to shorten drainage paths and accelerate dewatering. AMD sludge was collected from the field to determine the current geotextile filtration and dewatering efficiencies with and without polymer additives. Analysis of column filtration tests concluded that a nonwoven geotextile exhibited the highest filtration efficiency (>91%) and a relatively efficient drainage hydraulic conductivity (1.5x10-3 cm/s) for all permutations tested. The influence of polymer dosing on the AMD sludge indicated that for the no-polymer dose condition and a woven geotextile, the sludge hydraulic conductivity stabilized at 3x10-4 cm/s after approximately 50 hrs but had a filtration efficiency of 75 % particle retention. In contrast, the 20 ppm cation polymer dosed sludge exhibited a hydraulic conductivity at 3x10-5 cm/s within 150 hrs and a filtration efficiency of 91%. The polymer dosed sludge is preferred for minimizing solids pass through for environmental permit compliance. Field in situ moisture and total solids percentage testing was performed on several AMD sludge filled geobags. Results indicated that dewatering trends are not consistent between bags and there was no clear placement location or position for installing internal lateral drains to enhance drainage.