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Construction, closure & capping of geosynthetic lined slurry pond at Vishakhaptnam-India-15 year experience

Design and development of slurry pond having in adequate space and having soft soil at the base was a big challenge for the Hindustan Zinc-Vishakhapatnam in 1999. Further, because of limited space, capacity enhancement and optimization could only be done with steepening the slope. The construction of steep slope of 1:1 of dyke height of 9 m means, you need extremely strong soil material and reinforcement geosynthetics interspersed at designed depths to arrest the failure of the slopes. In addition to this, the double lining system with HDPE Liner of 2.0 mm thickness and Non-Woven Geotextile laying and anchoring had to be designed in such a way so that, the inner pressure of slurry during operational period would not pull it out of the anchor trench. The effluent management system at the bed was also designed to evacuate the water through the slope riser. After 10 years of operation, the site had to be closed as per the environmental guidelines and the challenge was to create a cover on a slurry bed. As the sludge surface is soft and having no strength to withstand the fill material, liner and cover vegetative soil, and special techniques were deployed to strengthen the strength of the underlying sludge. This was be done using high strength geotextiles and filling the same with fill material. Once the stabilization process was over, the lining system was constructed in such a manner to promote surface water runoff without causing ponding or severe erosion of the final cover. The slope or grade of the land and the length strongly affects soil erosion of the slope. Final slopes of filled portions of the landfill site was constructed with 3-5% percent in grade. Terraces, waterways, diversions will be constructed for smooth transportation of the rainwater precipitation This case study deals with the 15 years of experience in design, construction, operation and closure of the slurry pond in HZL-Vishakhapatnam.