Patent ID: 6839989

Claim:
Apparatus for drilling trenches in the ground, the apparatus comprising a frame and a drilling assembly having a horizontal support plate connected to the bottom end of the frame, said plate supporting drilling tools disposed-beneath said plate, said trench being filled with a drilling mud, the apparatus being characterized in that the periphery of said plate has resilient sealing means for co-operating with the walls of the trench so as to provide at least partial sealing between said plate and the walls of the trench, and means for adjusting drilling mud flow rates from the portion of the trench situated above said plate to the portion of the trench situated beneath said plate, and also in the opposite direction, so that the pressure of the drilling mud beneath said plate is well below the hydrostatic pressure exerted by the column of drilling mud in the trench above said plate, and so that the flow of drilling mud extracted from the portion of the trench beneath said plate is sufficient to extract the drilling spoil that results from the drilling action of said drilling tools.