Mécanisation des travaux de drainage souterrain

The mechanisation of underground drainage work

Docteur-Ingénieur, Ingénieur du Génie rural, des Eaux et des Forêts.

Résumé

Farm drainage development is very slow in France and costs are generally high. This is due to the fact that productivity in this type of work has remained practically static for years. Mechanisation of this work, with wlüch a start was made ten years ago, is therefore an economic necessity. It is also a social one. Drainage works today are mainly carried out with trenchers adjustable for depth and with a visu al lining-up device and a drain-laying system. Working rates depend on the power output of the equipment and range from 100 to 300 metres hourly, with daily capacities of about 1 000 metres hourly. An economic study shows that both these rates and the number of hours of annual use of the machine must be increased appreciably if its cost is to be reduced. This involves problems associated with the structure of the network, however, and it is readily shown that a fast-working machine is only an attractive proposition where the drain alignments are of sufIicient length to ensure that inoperative times are reduced to a minimum. Optimum rates for 200-300 metre alignments are between 800 and 1 500 metres hourly. Such rates are beyond the scope of trenchers, however, but they are no problem for fixed burrowing tool machines derived from the mole plough, which are also capable of laying the drains mueh faster, especially where flexible plastic drain pipes are used. This type of equipment requires a very high propulsive force, i.e. about 10 tons for continuous operation with the possibility of reaching 20 tons, for whieh a power output ranging from SO to 120 kW is neeessary between working rates of 800 and 1 200 metres hourly. These machines must be craftsman-built and of robust construction, especially where their transmissions are eoncerned. Moreover, visual lining-up by the operator is only just adequate at these high rates, and it is preferable to have some form of automatic guiding system. Systems based on a highly collimated light rayas a datum line have been tried. They should be satisfactory whilst enabling a check to be kept on the operation by a strip chart recorcling of drain laying depth and quality. These are powerful, fakly sophisticated machines, and as such they are expensive. They will enable considerable savings to be achieved, but only on well-organised sites and where used to lay specially designed networks. On ordinary sites and for drainage plans designed for the usual factors, slower less expensive trenchers still remain the most economic form of equipment if used properly.