As with tunnels, the location of bridges may be predetermined by the location of the routeways of which they form part. Consequently, this means that the ground conditions beneath bridge locations must be adequately investigated. This is especially the case when a bridge has to cross a river (Nichol and Wilson, 2002). The geology beneath a river should be correlated with the geology on both banks, and drilling beneath the river should go deep enough to determine the solid rock in place. The geological conditions may be complicated by the presence of a buried channel beneath a river. Buried channels generally originated during the Pleistocene epoch when valleys were deepened by glacial action, and sea levels were at lower positions. Subsequently, these channels were occupied by various types of sediments, which may include peat. The data obtained from a site investigation should enable the bridge, piers and abutments to be designed satisfactorily.

The ground beneath bridge piers has to support not only the dead load of the bridge but also the live load of the traffic that the bridge will carry, in addition to accommodating the horizontal thrust of the river water when bridges cross rivers. The choice of foundations usually is influenced by a number of factors. For example, the existence of sound rock near the surface allows spread foundations to be used without the need for widespread piling, whereas piled foundations are adopted for flood plains and rivers where alluvial deposits overlie bedrock (Kitchener and...