Modelling of lumpy clay fills

MODELLING OF LUMPY CLAY FILLS Jan Najser Abstract An extensive open cast mining of brown coal has been taking place in NW Bohemia since 1940's. During the mining process, overburden clay is placed in the form of irregularly shaped lumps of typical dimensions up to 500 mm into large spoil heaps. The total thickness of the lumpy clay landfills is usually 20-50 m. Their material has a double porosity structure: the porosity of intact clay (intragranular porosity) and the voids between clay lumps (intergranular porosity). The total porosity of the fresh fill can be up to 70%. This soil presents special challenges for geotechnical design, primarily because of its high and non-uniform settlement. Further, the progressive tranformation from the "granular" to "fine-grained" material makes the lumpy clay difficult to characterise and model. The aim of the presented thesis is to describe the behaviour of the landfill and the change of its structure by means of field measurements, the centrifuge and numerical modelling. During site investigation for a motorway over a 20-30 years old landfill, two trial embankments were built and monitored over the period of 3 and 6 years respectively. The subsoil of the embankments was instrumented by hydrostatic levelling profiles, pore pressure transducers and depth reference points..