ABSTRACT
The versatility of the downhole hammer (DTH) has been well illustrated by the diversity of its applications. Conventional hammers are now available in larger sizes, making it possible to drill holes up to 36 inches in diameter using direct flushing methods. The technique now widely practised uses a downhole hammer in which the bit cutting system has been developed to underream the pile. When the rock head has been reached and drilled to the required depth, the DTH hammer with the specially developed underreaming bit working on an eccentric principle. Pile driving by percussive means is therefore eliminated, providing a substantial reduction in noise levels during the drilling process, a most important point in urban areas. At the same time the new DTH technique provides a more precise method for both locating and founding piles than can be achieved in driving from the surface.
