Long-term settlement observations of a bridge foundation on clay of very high plasticity

摘要

Four bridge piers, all of which are resting on preconsolidated clay of very high plasticity, have, since erection, had a measured settlement of between 0.25m and 0.65m. This paper presents the settlement observations carried out over a period of more than 75 years. The settlements progress in a nearly linear manner when plotted against log time. Together with the observed fast progress of the settlement, considering the extremely small permeability of the clay, this strongly suggests that primary consolidation cannot be the primary cause of the observed settlements. Therefore, other causes must be found to explain the observed behaviour. Some form of creep seems obvious. Perspective calculations strongly suggest that the observed behaviour is primarily caused by plastic deformation, developed as a result of applied loads approaching the bearing capacity of the clay (too little safety against bearing capacity failure). The piers with the smallest bearing capacity reserve have the greatest settlements, and the slope of the seabed plays a crucial role.