Deformations and damage to buildings adjacent to deep excavations in soft soils

Deformations and damage to buildings adjacent to deep excavations in soft soils

Korff, M.

2009-11-26

The objective of this study is to gain insight into mechanisms of soil-structure interaction for buildings adjacent to deep excavations and to find a reliable method to design and monitor deep excavations in urban areas with soft soil conditions. The research focuses on typical Dutch conditions. The main questions are: How can we predict the behaviour of one or more a deep excavation will be constructed? What kind of modelling and/or measurements can be used to predict this effect? This report describes the literature reviewed for this topic and several case studies related to the topic from literature. General damage assessment procedures are also given. Assessing the response of buildings to excavation-induced deformations involves a combination of geotechnical and structural aspects, such as green field displacements (2D/3D, caused by deep excavations), building behaviour, soil -foundation -building interaction, monitoring techniques and modelling techniques. Each of these topics is described in this study. Some of the conclusions from this literature survey are: - Several, mostly empirical, relationships are available to predict green field displacements, which do not always show improvement in the amount of settlement found behind the wall over the years, especially if soft clays are present. One should expect for a deep excavation in soft clay to find a wall deflection of about 0.5 -1.0% of the retaining height (for an average system stiffness and sufficient basal stability) and a settlement behind the wall of 1%H maximum. Margins of 50%-100% should be expected. Diaphragm walls with stiff supports tend to the lower bound of these numbers or can even perform at 0.2%H if installation and other effects are strictly controlled. - Damage to buildings can be assessed by several damage criteria. The use of relative rotation and deflection ratio are both widespread, but also widely discussed. It is important to be extremely clear on how rigid body rotation and overall translation have been incorporated in the calculation. - Rigid body rotation or building tilt, is a very important parameter when discussing excavation induced damage. Real rigid body rotation should be assessed in three dimensions and it should always be made clear exactly if and in what way tilt is considered. - Soil-foundation-structure interaction should be taken into account when damage is assessed. The amount of displacement transferred to the building depends on the stiffness of the building in axial and bending modes and the interface between soil and foundation and between foundation and building. Three different case studies are presented for the insight they provide in the soil-structure interaction caused by deep excavations, tunnelling or subsidence. Both ground deformations and building deformations have been collected. These cases show aspects of the relationship between deformation of the building and damage occurring.

Deep excavation
building
damage
Deformations
soft soils
soil
F531
CT01.10
Beheerst Boren
Gedrag bouwputten - NZL II
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(c) 2009 Korff, M.