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The Use Of Cut-Off Walls At Waste Disposal Sites In West Germany

Abstract:


A method for the securing of predominantly large old storages consists of their encapsulation with diaphragm walls. Such vertical locking is especially well suited when under the storage natural, low-permeation soil layers are found, into which the diaphragm walls are embedded. These diaphragm walls are, as a rule, produced in the versatile and low-cost cut-off wall procedure.

The sealing wall masses used there must also be resistant to attack by seepage waters from the old storages. The composition and features of mineral sealing wall masses are determined for each individual case in laboratory experiments. In the course of a quality supervision, these features are tested on the building site. In the course of this paper, the results of research work on the chemical resistance of sealing wall masses and the results of suitability and qualification tests referring to building-sites are shown.

In the self-hardening wall procedure, the slot is removed section by section with the special tools of the cut-off wall construction (grab, chisel). The vertical earth walls are supported during the removal of the soil by a bentonite-cement suspension (sealing wall mass). This sealing wall mass remains in the cut-off wall after the completion of the soil removal and slowly harden due to the cement.

With wall depths of up to 12 m, diaphragm walls can be produced continually in, the self-hardening method. The gradual soil removal is replaced by the continuous removal with an excavator. This results in a jointless wall which is especially economical due to the great progress in building. Cross-sectional weaknesses at the intersection of slices, as are possible in the removal with cut-off wall grabs, do not come about, as there are no individual slices.

Experiments followed, adding fillers such as rock flour, clay flour or fly fuel ash. After successful laboratory experiments, the first calcium-bentonite mixture was tried out on a building-site in 1980. The problems of the encapsulation of old storages with diaphragm walls has led within the past few years to the development of sealing wall masses containing more and more solid matter, which can be used in the self-hardening wall method.

Authors:

Hermanns, Rita and Meseck, Holger

Index Terms:

Clay; ClayGroup; remediation; encapsulation; contaminated sites; slurry walls; barriers; Ton; Einkapselung; Barrieren; Altlasten; Sickerung; Sanierung; Meseck, Holger

Further Information:

Date published: 1988