The capping of sludge and other weak deposits

Arising from many different industrial and commercial processes, sludge and other weak deposits are often placed into on-site lagoons. There normally comes a time, commonly when a lagoon has reached its capacity, when these deposits have to be closed. The practice of closing, or capping over the weak deposits, has been made possible by the application of geosynthetic products generally and geogrids in particular.

At the commencement of the capping operation, often the biggest problem is the difficulty in gaining safe access onto the weak deposits for construction personnel, followed by the ability of the working platform to safely support the weight of the earthmoving plant. Finally integrity and robustness of the capping has to be provided for the long term utilisation of the surface.

This capping of tailing lagoons, sludge lagoons, dock silts and dredged deposits has been one of a developing methodology over a number of years, and the successful use of Tensar biaxial geogrids on a number of challenging projects has provided the opportunity to identify the main components of an appropriate technique.

The projects described in this paper illustrate important design and construction issues associated with the safe and ecologically acceptable capping of sludge and weak deposits. Emphasis is placed on the use of geogrids as part of a bespoke practical approach to each problem.