Driving timber piles into rock can be problematic. There is usually no option but to displacement drive the pile into a pre-bored rock socket. The challenge then encountered is keeping the rock socket sufficiently clean, so the pile doesn’t refuse too early during installation.
A known construction technique is to allow debris in the rock socket to escape during driving. This is achieved by cutting a channel up the side of the pile (refer to photo – courtesy of Dave Mitchell). In some cases, jetting is required to assist cleaning of the socket during installation. Jetting is the practice of underwater high-pressure water-blasting to loosen or liquify soil material.
In earlier times, cast-iron driving shoes were fitted to the toe of piles when hard driving conditions were expected (refer to sketches). The cast iron shoe was fixed to the timber pile with wrought-iron straps. It added weight and strength to the pile toe. Modern piling techniques have, in most cases, eliminated the need for these shoes.