Construction Technology 1

House construction, fourth edition

by Mike Riley and Alison Cotgrave

Chapter 4 case study 1: Foundations, ground consolidation and preparation

The site selected here is close to the industrial zone of a major city. The site has been built on in the past, but has since been cleared. This is known as a ‘brown field site’. The ground here consists of areas of fill where demolition has occurred. This has poor loadbearing capacity and is in need of consolidation. The consolidation is effected by driving aggregate into holes formed by a displacement driver. The action of forcing the extra volume into the ground increases its density and hence its strength. On the same site, areas of rock must be excavated using mechanical plant to allow for the provision of drainage below ground.

Preparing for foundations

The excavation of foundation trenches is far less exact than the design drawings of a typical scheme would indicate. Here we see the excavations on a site awaiting the placement of concrete. Note that they are unsupported in the example to the left. This is due to the nature of the soil, which is termed ‘cohesive’. The example on the right is a different type of foundation, known as a raft. The foundation and ground floor slab are combined and the edges are reinforced to ensure the rigidity of the raft.