Effect of Building Stiffness on Excavation-Induced Displacements

Mohammed El-Shafie, Cambridge University
Geotechnical Engineering Group


In urban areas construction of excavations can induce ground movements which may distort and, in severe cases, damage overlying buildings and services. Recently, a new approach, based on the relative stiffness of a building and the underlying soil, has been proposed (Potts and Addenbrooks (1997) & Franzius (2004)) to account for the effect of a building stiffness when predicting its deformation and potential damage. The primary objective of this research is to investigate the effect of building stiffness on excavation-induced displacements by comparing building movement to greenfield movement and hence assessing the relative building/soil stiffness method. Furthermore, it is aimed to understand the mechanisms which influence this excavation-soil-building interaction problem. .

This has been achieved by performing two parametric studies (using two independent approaches) that investigate the influence of relative building/soil stiffness parameters (as defined by Potts and Addenbrooke, 1997) on excavation-induced displacements. The excavations covered in this research are in dry sand retained by a cantilever retaining wall. Firstly, a series of numerical analyses simulating excavation construction in greenfield conditions, and beneath beams (representing buildings) of varying stiffness, were undertaken to assess the differences between greenfield ground movements and those modified by the building (this section is summarised from Elshafie, 2004).

Secondly, a centrifuge model, which adopted a new technique for simulating the excavation process in-flight, has been developed to investigate the interaction between the soil and model buildings (micro-concrete blocks of different properties). The effect of building stiffness, building weight, the nature of the building-soil contact and the introduction of spread footings on the behaviour of the both the building and the soil has been investigated in the centrifuge. The outcome that has been obtained from the centrifuge modelling studies, combined with the numerical analyses results, has lead to an improved understanding of the excavation-soil-building interaction problem.