Proceedings - Fifth International Conference & Exhibition on Piling and Deep Foundations, 1994, Bruges, Belgium, (DFI)
A new method of installing synthetic liners in deep diaphragm walls for the vertical enclosure of contaminated sites
K. Krubasik & F. Hupert
Encloeure of contaminated ground with vertical sealing walls is an often used technique of ground pollution management. The sealing wall is a diaphragm wall filled with bentonite-cemenet slurry rich in solids to achieve low hydraulic conductivities. Since permeability characteristics of sealing walls may deteriorate with time, particularly if they are subject to attack by aggressive leachates, efforst have been made to develop systems which retain their properties over long periods of time. One such system is the incorporation of synthetic liners (HDPE) into the slurry wall. Up until now sheets of liner were fastened onto a steel frame and lowered by crane into the slurry wall. Problems were posed by the design of the interlocks between sheet partitions and the actual placement of the frame, with the sheet offering large wind resistance. This restricted frame length and therefore wall depth to ca. 18 m and often made installation even in only slight winds impossible. These problems have been solved with a new technique for installing synthetic liners into sealing walls. The custom-tailored sheet, 5.0 m wide and equipped on both sides with interlocks for neighbouring sheets, is rolled onto a drum. The drum is mounted on a mobile crawler unit which can be positioned exactly on the point of placement. The diameter of the drum is large enough to avoid permanent deformation of the locks. The interlock is threaded into the lock of the neighbouring sheet partition already in place. A crane-held guiding frame is connected to the footing edge of the liner. As the frame is lowered into the slurry-filled excavation it unrolls the liner from the drum and introduces it into its correct position. If necessary, extension sections can be mounted during the lowering process onto the guiding frame. The depth of a sealing wall with synthetic liner is therefore only restricted by the size and power of the crane which has to lift the frame out after placement of the liner. So far synthetic liners have been installed with this technique up to a depth of 35 m. Interlocks between neighboring sections of liners form hollow tubes which can be pumped dry after placement, controlled by camera and welded and/or filled with an appropriate sealing material.
|article #792; publication #36 (IC-1994)|