Title: Drilling method and apparatus for large diameter pipe

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Abstract: 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 car for crowding, without rotation, a pipe either pre-bent to a preselected and constant radius of curvature or a straight pipe into the ground. The pipe at its head includes an articulated drill head, which by appropriate articulation, assures placement of the pipe along a radius of curvature equal to the pre-bent radius of curvature of the pipe. The articulated drilling head includes a hydraulic system for articulating and driving the cutting head and pumping mud and tailing from the pipe path. Two discrete mud systems are used. The first mud system is utilized to entrain and carry away cuttings. The second mud system is combined with a flared skirt about the point of drill head articulation to provide a clean and high lubricity annulus of mud about the advancing drill string. The density of the first mud system can be used to vary the drill string mass, while the density of this second mud system can be used to vary the density of the fluid in which the drill string is buoyantly supported.


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