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 d eep excavations worldwide is presented. Although recognizing the weakness i n the approach, a large database is used to examine general trends and patt erns. For still soil sites, movements are generally less than those suggest ed in the well-known relationships proposed by Clough and his coworkers. Ho wever, for walls that retain a significant thickness of soft material but h ave a high factor of safety against basal heave, movements are similar to t hose calculated using the Clough charts. In these cases, when soft ground i s actually present at dredge level, the Clough charts will underpredict mov ement and need to be used with care. For the above cases there is no discer nible difference in the performance of propped or anchored systems but ther e is some evidence to suggest top-down systems perform better. In cases whe re there is a low factor of safety against excavation base heave, large mov ements can occur, but the Clough charts will give reasonable preliminary es timates of the likely movement in such cases. Cantilever walls have shown d isplacements that are often independent of the system stiffness. There is e vidence to suggest that, in the case of cantilever walls and for all walls in stiff soils worldwide, design practice is conservative. Finally, the inc lusion of a cantilever stage at the beginning of a construction sequence se ems to be the main cause of unusually large movements.