Pulling instead of digging
Drainage systems are once again being installed using tile ploughs. During the 1970’s a deep plough, with a torpedo-shaped tip, attached to a narrow blade was pulled behind a bulldozer through the soil. This was a predecessor of the trenchless plough. The main disadvantage of this system was that the soil was pressed together sideways, exactly where it needed to be permeable. It was also quite difficult to install at exactly the right depth. The reason for this was that the blade plough was too far behind the tilting point of the bulldozer or tractor. If the height of the bulldozer changed slightly due to the unevenness of the ground, this had a great effect on the depth of the plough. When the vertical blade changed to a V-shape, the problem remained. Even at a minimal depth of drains below the surface, for example 80 cm, a considerable distance is needed behind the tractor or bulldozer to lift the plough above the ground for transportation. The bulldozer or tractor should be driven at low speed when a V-shaped blade is used.
Slanting instead of vertical
When the vertical blade is positioned at a slanting angle, the sideways compaction of soil will no longer occur. However, a sideways pressure will occur which has to be absorbed by the tractor. The problem of the distance to the tilting point remains and a great deal of attention is required to prevent height differences in a single length of field drain.
Weight and friction
Trenchless ploughing requires a lot of pulling power. Two factors need to be taken into account when installing drainage using heavy machinery: pressure and friction area. By using more wheels or even caterpillar tracks, the pressure on the ground caused by a machine can be reduced. However, if pulling power is required a large friction area is needed. A small amount of pressure means that a large surface area is required. On sandy, clay and peaty soil with a clay cover, this might easily lead to skidding due to a lack of grip.