Trenchless laying of underground pipes

Claim 1

A method of laying a length of underground pipe in situ, which comprises forming a generally horizontal underground tunnel by forcing the mole of a mole plough through the ground, towing an expander behind the advancing mole to expand the cross section of the underground tunnel, and towing a length of pipe behind the expander along the expanded tunnel into its required final position, the pipe being of smaller cross section than the expander so that an annular-section clearance is defined between the exterior of the pipe length and the interior surface of the expander tunnel, and simultaneously extruding a thixotropic slurry of Bentonite and water under positive pressure through an extrusion orifice in the advancing expander and into the said annular clearance around the advancing pipe length to fill the said clearance with an annular layer of said thixotropic slurry through which the pipe length advances behind the expander as said tunnel is progressively formed and expanded, the slurry being pumped to the extrusion orifice by means of a positivedisplacement pump from a reservoir above ground through a duct extending down to the expander.

Claim 2

A method of laying a length of underground pipe in situ, which comprises forming a generally horizontal underground tunnel by forcing the mole of a mole plough through the ground, towing an expander behind the advancing mole to expand the cross section of the underground tunnel, and towing a length of pipe behind the expander along the expanded tunnel into its required final position, the pipe being of smaller cross section than the expander so that an annular-section clearance is defined between the exterior of the pipe length and the interior surface of the expander tunnel, and simultaneously extruding a thixotropic slurry of Bentonite and water under positive pressure through an extrusion orifice in the advancing expander and into the said annular clearance around the advancing pipe length to fill the said clearance with an annular layer of said thixotropic slurry through which the pipe length advances behind the expander as said tunnel is progressively formed and expanded, the slurry being pumped to the extrusion orifice by means of a positivedisplacement pump from a reservoir above ground through a duct extending down to the expander.

Claim 5

A method of laying lengths of underground pipe by forming an underground tunnel by means of a mole plough, and drawing a length of pipe into the tunnel into its required final position, characterized in that a liquid slurry is injected into the tunnel formed by the mole before the pipe length is drawn into the tunnel, the slurry serving to lubricate the pipe during its travel along the tunnel, the principal ingredient of the slurry being Bentonite, the slurry comprising a mixture of Bentonite and soil in water, forming a gel having thixotropic properties, and in which a mixture of Bentonite and water is delivered separately into the tunnel by a positive displacement pump and is there mixed in place with the soil of the tunnel wall by means of an underground mechanical mixer towed behind the mole.

Claim 6

A method of laying lengths of underground pipe by forming an underground tunnel by means of a mole plough, and drawing a length of pipe into the tunnel into its required final position, characterized in that a liquid slurry is injected into the tunnel formed by the mole before the pipe length is drawn into the tunnel, the slurry serving to lubricate the pipe during its travel along the tunnel, the principal ingredient of the slurry being Bentonite, the slurry comprising a mixture of Bentonite and soil in water, forming a gel having thixotropic properties, and in which a mixture of Bentonite and water is delivered separately into the tunnel by a positive displacement pump and is there mixed in place with the soil of the tunnel wall by means of an underground mechanical mixer towed behind the mole.

Claim 7

A method of laying a length of underground pipe in situ which comprises forming a generally horizontal underground tunnel of appreciably greater cross-sectional area than the pipe to be laid therein by forcing the mole of a mole plough through the ground, whilst simultaneously extruding a thixotropic slurry of Bentonite and water under positive pressure into the tunnel through an extrusion orifice at the rear of the advancing mole to fill the tunnel completely with pressurized slurry as the tunnel is progressively formed behind the advancing mole, and, subsequently, drawing a length of pipe by means of a cable and winch along the length of the preformed tunnel and through the filling of slurry therein into the required final position of the pipe length, the pipe length being drawn lengthwise through the filling of slurry which forms an annular layer of slurry surrounding the pipe length and separating it from the wall of the tunnel as the pipe length advances.

Claim 8

A method of laying a length of underground pipe in situ which comprises forming a generally horizontal underground tunnel of appreciably greater cross-sectional area than the pipe to be laid therein by forcing the mole of a mole plough through the ground, whilst simultaneously extruding a thixotropic slurry of Bentonite and water under positive pressure into the tunnel through an extrusion orifice at the rear of the advancing mole to fill the tunnel completely with pressurized slurry as the tunnel is progressively formed behind the advancing mole, and, subsequently, drawing a length of pipe by means of a cable and winch along the length of the preformed tunnel and through the filling of slurry therein into the required final position of the pipe length, the pipe length being drawn lengthwise through the filling of slurry which forms an annular layer of slurry surrounding the pipe length and separating it from the wall of the tunnel as the pipe length advances.