Long-Term Settlement (Creeping) of Soft Soils, and Ground Improvement

Abstract

This keynote paper focuses on the long-term settlement (creeping) of highly compressible soils, considering also soft sludge. Long-term oedometer tests lasted up to 42 years and were performed on silty sand, (organic) clayey silt, peat and (pre-treated) sewage sludge. Secondary consolidation (creep) could be observed in all cases, lasting over many years and occurring widely linear with the logarithm of time. However, temporary acceleration may also be observed, indicating a discontinuous nature of internal deformations due to accelerated rearrangement in the fabric – mainly in very soft soils with peaty components. This long-term phase is followed by tertiary creeping with a long lasting fading out period. In both phases microcrystalline sliding occurs.