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Bachy Soletanche's displacement piling technique relies on imparting high torque rotary energy directly down to the drill bit - here a large conical screw. This requires the firm's highest powered rig - a Casagrande C90 that provides 55tm torque through an HT55 rotary head - to be modified so that a strengthened kelly bar can be passed through the rig's rotary drive and be powered directly by a sleeve in the centre of the casing adapter.