Bored Piles - Characteristics.

The bored pile is usually formed by using a simple cable percussion rig. The soil is removed by shell and auger and the hole filled with in situ reinforced concrete as required (see Fig. 9.36).

For filled sites or soft clay sites overlying stiff clay or rock, small to medium bored piles often prove to be economic.

The relatively small on-site cost of bored piles means that smaller sites can be piled more economically than they can using a driven piling system. The bored pile is not usually economic in granular soils where removal and disturbance of surrounding ground can cause excessive removal of soil and induce settlement in the surrounding area. During  piling operations the hole can be lined with a casing which can be driven ahead of the bore to overcome difficulties caused by groundwater and soft sub-soil but sometimes difficulties of withdrawing the casing after casting can prove expensive.

Fig. 9.36 Bored pile.