Where the underlying ground conditions are loose or weak, up to 20m from the surface, a temporary or permanent casing can be used so that the pile can be bored without collapsing the ground.
In some instances, the ground is unstable throughout the length of the pile, either through groundwater ingress or deeper loose ground. This necessitates either full depth casing or drilling fluid, typically polymer or bentonite.
The advantages of RBP over CFA piling are the achievable enhanced pile capacities. Therefore, by using casing, an open hole can be formed in larger diameters to great depths. This enables augering or coring to form sockets into deep and competent strata; installing long, multi sectioned and/or complex reinforcement cages; or complex pile instrumentation and load cells to determine the maximum load capacity or validating design assumptions.
RBPs deeper than 60m are common and recent trends have seen piles that are over 70m deep.