Patent ID: 6536143
Filing Date: 2003-03-25
Classification: E02F

Abstract:
A method for digging a trench in a hard earth formation, comprising the steps of:positioning a multiple-chain trenching head assembly in the earth formation at a desired trench depth below a ground surface, the trenching head assembly comprising a frame having a proximal end adapted for operably connecting to a prime mover positioned on the ground surface and thereby enabling positioning of the trenching head within the trench below the ground surface, a set of primary sprockets, the set comprising at least one proximal primary sprocket rotatably mounted on the frame and at least one distal primary sprocket rotatably mounted on the frame at a distal end thereof, at least one of the frame and the set of primary sprockets defining a primary chain path, a primary chain engaged with and circulating around the set of primary sprockets and comprising a plurality of pivotably connected links and a plurality of cutting tools substantially rigidly mounted thereon for disintegrating the earth formation, a set of secondary sprockets, the set comprising at least one proximal secondary sprocket rotatably mounted on the frame and at least one distal secondary sprocket rotatably mounted on the frame at the distal end thereof, at least one of the frame and the set of secondary sprockets defining a secondary chain path, and a secondary chain engaged with and circulating around the set of secondary sprockets and comprising a plurality of pivotably connected links and a plurality of cutting tools substantially rigidly mounted thereon for disintegrating the earth formation; driving the primary chain at a primary chain linear drive speed in a forward chain direction along the primary chain path, thereby disintegrating material at a leading edge of the trench and conveying disintegrated material upward and out of the trench; driving the secondary chain at a secondary chain linear drive speed along the secondary chain path, thereby disintegrating material from the leading edge of the trench; and moving the trenching head assembly in a forward trench-digging direction, at least one of the frame, the set of primary sprockets, and the set of secondary sprockets being adapted so that at least a portion of the secondary chain path extends farther toward the leading edge of the trench than the primary chain path, so that disintegration of material by the secondary chain produces a relief slot in the leading edge of the trench.