By late summer, the decision had been taken to build a broad tunnel, high and wide, and the company advertised for tunnellers in September. The tunnel would be long and below ground at its deepest point. It was expected to take four years to complete, beginning in early 1784. To speed the work, 26 shafts were sunk for many simultaneous workfaces, the deepest of which was . Small tunnels, known as headings, were dug in two different directions from the base of each shaft and the spoil lifted up the shaft and dumped in Spoil tips above the route of the canal. A small temporary railway was later installed to take workers into the tunnel and remove waste materials. The use of explosives to expand the headings to the full size of the tunnel meant that acrid smoke and foul air built up. Chimneys were built in the shafts, with fires at their base to try to remove the foul air. The construction contract was awarded to Charles Jones, who managed to build about one third of it, but then had financial difficulties, and so other contractors were engaged to work on smaller sections.