Database for retaining wall and ground movements due to deep excavations

A database of some 300 case histories of wall and ground movements due to deep excavations worldwide is presented. Although recognizing the weakness in the approach, a large database is used to examine general trends and patterns. For still soil sites, movements are generally less than those suggested in the well-known relationships proposed by Clough and his coworkers. However, for walls that retain a significant thickness of soft material but have a high factor of safety against basal heave, movements are similar to those calculated using the Clough charts. In these cases, when soft ground is actually present at dredge level, the Clough charts will underpredict movement and need to be used with care. For the above cases there is no discernible difference in the performance of propped or anchored systems but there is some evidence to suggest top-down systems perform better. In cases where there is a low factor of safety against excavation base heave, large movements can occur, but the Clough charts will give reasonable preliminary estimates of the likely movement in such cases. Cantilever walls have shown displacements that are often independent of the system stiffness. There is evidence to suggest that, in the case of cantilever walls and for all walls in stiff soils worldwide, design practice is conservative. Finally, the inclusion of a cantilever stage at the beginning of a construction sequence seems to be the main cause of unusually large movements.