Engineering and Construction

The allowable settlement is defined as the acceptable amount of settlement and it usually includes a factor of safety. In many cases the structural engineer or architect will determine the allowable settlement of the proposed structure. At the start of a project, the structural engineer or architect should be consulted about the anticipated loading conditions, allowable settlement of the structure, and preliminary thoughts on the type of foundation.

If this information is unavailable, then the geotechnical engineer will have to estimate the allowable settlement of the structure in order to determine an appropriate type of foundation. There is a considerable amount of data available on the allowable settlement of structures (e.g., Leonards, 1962; ASCE, 1964; Feld, 1965; Peck et al., 1974; Bromhead, 1984; Wahls, 1994). For example, it has been stated that the allowable differential and total settlement should depend on the flexibility and complexity of the structure including the construction materials and type of connections (Winterkorn and Fang, 1975). Brief discussions of other studies are as follows:

Coduto (1994). Coduto (1994) states that the allowable settlement depends on many factors, including the following:

1. The type of construction. For example, wood-frame buildings with wood siding would be much more tolerant than unreinforced brick buildings.

2. The use of the structure. Even small cracks in a house might be considered unacceptable, where- as much larger cracks in an industrial building might not even be noticed.

3. The presence of sensitive finishes. Tile or other sensitive finishes are much less tolerant of movements.

4. The rigidity of the structure. If a footing beneath part of a very rigid structure settles more than the others, the structure will transfer some of the load away from the footing. However, footings beneath flexible structures must settle much more before any significant load transfer occurs.

Therefore, a rigid structure will have less differential settlement than a flexible one. Coduto (1994) also states that the allowable settlement for most structures, especially buildings, will be governed by aesthetic and serviceability requirements, not structural requirements. Unsightly