A method and apparatus is disclosed for installing a large diameter pipe--in the range of 30 inches diameter--for spanning an obstacle, such as a river, along an invert arcuate underground path. An inclined drill rig, having a mud supply system and power pod, includes an angularly inclined ramp and driven...http://www.google.co.uk/patents/US4221503?utm_source=gb-gplus-sharePatent US4221503 - Drilling method and apparatus for large diameter pipe
