To increase downwards acting vertical force to two driving heads installed to a boring tool.
In the boring tool with two driving heads 28, 30 which are used to sink a boring pipe string 54 and a borer string 76, controllable coupling mechanisms 84-112 are fitted between both driving heads 28, 30. Devices 158, 162 applying additional downward acting vertical force to the lower driving head 28 are installed for the driving head 28. When both driving heads are coupled, the upper driving head is also subjected to downwards acting vertical force similarly. In order to free the top end of the boring pipe string 54, the coupling mechanisms 84-112 can be released so that the upper driving head 30 can be fully raised, whilst the lower driving head 28 remains in position adjacent to the ground.
KEHRBERGER ACHIM DIPL ING (DE)
SCHEID WINFRIED (DE)
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