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.