Method and apparatus for trenchless extraction of pipe
Apparatus for trenchless extraction of pipe includes a housing rigidly connectable to a pipe to be extracted, a tension helmet disposed over an end of the housing, the tension helmet connected by tensile elements to a hydraulic impact hammer supported by the housing, and resilient shock absorber disposed between the tension helmet and the housing. The hammer is operated to impact a striker plate on the housing, which drives the pipe to be extracted forward and thereby creating a gap between the striker plate and the hammer and compress the shock absorber. The shock absorber then resiliently expands, thereby pushing the tension helmet forward and bringing the hammer back into alignment with the striker plate.
1 . A horizontal pipe extraction apparatus comprising:
a housing, said housing having a first end and a second end opposite said first end, said second end fixable to a pipe to be extracted;
a striker plate disposed on said first end of said housing;
a percussive hammer supported by said housing in alignment with said striker plate, said hammer longitudinally displaceable relative to said housing;
a tension helmet disposed over said first end for slidable displacement relative to said housing;
one or more tensile elements connecting said hammer to said tension helmet; and
a resilient shock absorber disposed between and connected to said tension helmet and said first end;
wherein said one or more tensile elements urge said hammer against said striker plate when said shock absorber is in a rest configuration.
2 . The pipe extraction apparatus of claim 1 wherein said shock absorber is a pneumatic shock absorber.
3 . The pipe extraction apparatus of claim 1 wherein said one or more tensile elements are cables connecting said hammer to said tension helmet.
4 . A method of trenchless extraction of horizontal pipe, said method comprising:
providing a pipe extraction apparatus, said pipe extraction apparatus comprising:
a percussive hammer supported by a housing in alignment with a striker plate, said striker plate mounted to said housing, said hammer longitudinally displaceable relative to said housing;
a tension helmet disposed over said striker plate and connected to said hammer by one or more tensile elements; and
a shock absorber disposed between said striker plate and said tension helmet; mounting said pipe extraction apparatus to an exposed end of a pipe to be extracted from a surrounding substrate; and
operating said hammer to strike said striker plate repeatedly in a direction away from said surrounding substrate, thereby displacing said pipe out of said surrounding substrate incrementally, said shock absorber urging said tension helmet away from said striker plate after each successive strike, said one or more tensile elements thereby urging said hammer toward said striker plate after each successive strike.