Soft Clay Stabilisation by Mandrel Driven Geosynthetic Vertical Drains

Geosynthetic (prefabricated) vertical band drains are now considered as one of the most cost effective ground improvement technics in many parts of the world, where construction on soft compressible clays is inevitable. However, smear effects caused by PVD installation (eg. mandrel based), drain clogging, drain kinking and well resistance of long drains retard the excess pore pressure dissipation making these drains often less effective in the field, contrary to expectations. Consequently, the rate of settlement of the stabilised soft clay becomes significantly less than what is expected from ideal drains. This paper addresses comprehensively, the numerical modelling aspects of PVD, and the interpretation of field data taken from several case studies, which elucidate the drain performance under various boundary conditions. Theoretical and finite element modelling details are described based on various research studies, mainly through the authors’ own experience. In particular, the experimental data obtained from large-scale consolidation tests are highlighted and interpreted.