Abstract: Pipe sections are forced through the ground, separating from the mass of the ground its part received in these pipe sections. This part of the ground is evacuated with the sections. As the pipe sections are evacuated, a stationary pipe is layed. The pipe sections are forced into the ground by a main hydraulic power unit and an intermediate hydraulic power unit positioned between the pipe sections having each a cavity communicating with a hydraulic system and intended to exert pressure on the end of the preceding pipe section. This cavity is defined by two rings rigidly secured at the preceding section. The front end of the succeeding section having an annular sealing element is inserted in a clearance between the rings.

Abstract: A hydraulic jack includes a body (1) with front (2) and rear (3) covers and a rod (4) moving relative to said body (1) and having at least one projection made therein and mounting an additional member (7) and at least two grooves which form the respective projection (8) and of which each accomodates piston semi-rings (6) installed therein by pairs, the rod (4) portion having the projections (8) and the grooves forming a piston unit (5).