可能是世界上最深的坑道钻孔已经在南非Free Stare Geduld矿第一号矿井由Boart钻探组完成。该钻孔系使用改装后的长年44型地表钻机和BW铝制钻杆,最终孔深5880英尺。钻孔开孔时与水平面20°夹角(水平面之下),终孔时在水平面下5°,呈倾斜状态。1978年开孔时使用BX钢钻杆,钻杆提升利用木结构构件,立根长度达39英尺。当孔深4550英尺时,由于钻杆重量和钻孔倾斜的缘故,使钻杆提升和下放成了问 Probably the world’s deepest tunnel borehole has been completed by the Boart drilling team at No. 1 Free Stare Geduld Mine in South Africa. The drilling system uses a modified Long Year 44 surface drill and BW aluminum drill pipe, the final hole depth of 5880 feet. Hole drilling hole with the horizontal angle of 20 ° (below the horizontal plane), the final hole in the horizontal plane 5 °, was inclined state. BX steel drill pipe was used for opening the hole in 1978. The drill pipe was raised to utilize wooden structural members, and the root length was 39 feet. When the hole depth is 4550 feet, the drill pipe is raised and lowered due to the weight of the drill pipe and the inclination of the drill hole