Cutting head

Abstract

A method for forming substantially lateral boreholes from within an existing elongated shaft includes positioning a drilling unit within the existing shaft, bracing the drilling unit against a wall surrounding the existing shaft to transmit forces between the drilling unit and the medium surrounding the wall, and applying a drilling force from the drilling unit to cut through the wall of the existing shaft and form the substantially lateral borehole in the surrounding medium. A preferred apparatus for practicing the method includes an extendable insert ram within the drilling unit for extending a drill bit from the drilling unit and applying a drilling force to the drill bit to cut through the wall of the existing shaft. A supply of modular drill string elements are cyclically inserted between the insert ram and the drill bit so that repeated extensions of the insert ram further extends the drill bit into the surrounding medium to increase the length of the lateral borehole. The insert ram may also be used to engage and retract the module drill string elements from the borehole once the borehole has been completed. The drilling unit also includes a supply of modular liner elements which the insert ram may insert into the lateral borehole to line the borehole after the drill string elements have been withdrawn from the borehole.