Abstract: An expansible mandrel for use in driving or withdrawing tubular piles has lengthwise sections which are subjected to expanding forces in a plurality of zones spaced lengthwise of the interior of the mandrel to establish their pile-gripping relationship. The pile-entering relationship of the sections is re-established by a series of transversely spaced pairs of assemblies spaced lengthwise of the mandrel with each pair between adjacent zones. Each assembly includes, in the disclosed embodiment, two coil springs each of which is confined in a tube. The tubes are spaced apart lengthwise of and are secured to one mandrel section. The proximate ends of the tubes back the springs.

Abstract: Expandable tubular mandrels have lengthwise sections the upper ends of which are joined by a head. Hydraulically operated piston-cylinder units within the mandrel are spaced apart lengthwise of the sections and connected to the mandrel in a manner such that the axis of each unit extends lengthwise of the mandrel and expanding and contracting forces are applied to the mandrel sections when the units are operated to vary their overall length, to effect mandrel expansion when their overall lengths are changed in one direction and mandrel retraction when changed in the opposite direction.