DESIGN AND OPERATION OF AN UNDERWATER PIPELINE TRENCHING PLOUGH

An underwater trench 1·5 m deep was required for a pipeline shore crossing in the Canadian Arctic. At the site the sea bottom is soft mud, and the trench would be close to its limit of stability. It was decided to excavate the trench with a large plough, built to a new design which would avoid the difficulties that had been encountered with earlier trenching ploughs. The design uses the principle of the long-beam forestry plough, which gives accurate control of trench depth, and the mechanics of a plough of this type are described. Dimensional analysis was used to develop the similarity conditions that have to be obeyed in model tests of a plough in clay, and the results were used in an extensive programme of model testing, which checked the operation of the plough and was used to refine the design. The full-scale plough was then fabricated, tested in a river delta, and transported to the Arctic, where it successfully excavated the required trench. Une tranchee sousmarine, d'une profondeur de 1,50 m, etai...