Consolidation behaviour of double-porosity clay using flexible wail permeameter

Restoration of a site that has previously been prepared using dredged clay is a serious geotechnical challenge. Much of these clays exists as lumps suspended in slurry. These double-porosity soils consolidate due to the expulsion of water from the voids within each lump and the voids between the lumps. Due to this complex nature, the conventional theory of consolidation is not applicable to them. This study discusses the laboratory consolidation test results of double porosity samples. The tests were conducted on 10-30 mm clay lumps. The size, initial packing and the stiffness of the lumps were the variables. At low confining pressure the 30 mm lumpy samples experienced a significantly higher deformation than the 10 mm lumpy samples. In all the tests, the lumps and slurry merged to close the inter-lump voids as confining pressure neared or reached the pre-consolidation lump pressure. This paper also discusses the use of a simple constitutive relationship to model the behaviour of double-porosity fill. It uses the structured clay framework to describe the volumetric strain in the double-porosity samples by using two parameters, in addition to those required in the critical state soil mechanics. A parametric study demonstrated the capabilities of this model.