by John H Dixon, Netlon and Kent von Maubeugez, Naue-Fasertechnik.
This paper was first published in the GE’s December 1992 issue.
A common requirement for the base and side seals of new landfills is now a composite lining consisting of a low permeability, chemically inert geomembrane directly overlying a low permeability clay layer (Council Directive 1991).These two components are complementary; the geomembrane being chemically resistant to test liquids and leachates and the clay layer able to absorb chlorinated hydrocarbons which could migrate through the geomembrane.
German landfill design has influenced the European approach. The German minimum requirements for domestic landfill wastes are recorded in LAGA-Merkblatt (1990) and TA-Siedlungsfall (1991).
A composite lining is required in Germany including a high density polyethylene geomembrane and in addition the leachate head on the lining must be controlled by a drainage layer. This layer consists of a continuous blanket of granular inaterial with an interconnected pipe collection system. To minimise biochemical clogging, this granular material must be coarse (16mm-32mm particle size) and (10% calcium carbonate by weight. A protection layer is essential between this coarse drainage layer and the geomembrane to avoid mechanical damage to the liner. Sand protection layers are considered undesirable (von Maubeuge 5 Dixon 1992)and geosynthetic protection layers are favoured.
The general German philosophy on protection layers is that they must withstand all chemical, biological and mechanical stresses and last ‘a day longer’han the geomembrane —the geomembrane can only be as good as the protection layer allows. For this reason the protection layer is also manufactured from HDPE.