A steerable earth boring device comprises a compaction auger rotatably mounted to a housing at one end of the auger such that the compaction auger is substantially externally exposed. A steering tip is pivotably disposed at the other end of the compaction auger for providing steering control for the...http://www.google.es/patents/US4974688?utm_source=gb-gplus-sharePatente US4974688 - Steerable earth boring device
