Abstract: Apparatus including a rotary drilling cutter and a spoil removal conduit for the digging of a deep trench, characterized in that the spoil removal conduit is gradually adjustable in length during excavation and comprises: (a) a first conduit section, arranged proximate to said rotary cutter, and comprised of associated slidingly adjustable rigid male and female telescopic tube elements; (b) a second conduit section comprising a flexible tube having two ends, said flexible tube being connected to said first conduit section by one of its ends, its other end being disposed in the vicinity of the ground at a predetermined spoil discharge point, (c) a pulley supporting said flexible tube between said two ends; (d) lifting gear for suspending said pulley; and (e) a first cable associated with said lifting gear for supporting said pulley at selected adjustable heights.