The properties of Lias Clay for landfill liners

The design and specification of a landfill clay liner require compromises to be made between the requirements of low hydraulic conductivity (permeability), adequate shear strength, sufficient interface shear strength (when the clay is used in a composite liner), minimal shrinkage during service, and sufficient ductility to accommodate tensile and shear strains, which may increase permeability. This paper focuses mainly on the first three requirements. The results of construction quality assurance (CQA) from four landfill sites and the results of ground investigations from two landfill site extensions are reported. Proposals are made for a methodology to derive a specification, and for assessing the results of CQA tests. Undrained and effective stress strength parameters are presented for recompacted Lias Clay. The interface shear strength of clay against a geomembrane or geotextile is shown to be dependent upon the density and moisture content of the clay and normal pressure.