In an ISTT meeting held on 15 September 2005, a decision was taken to accept ‘Ploughing’ technology, also known as Cable Plough or Mole Plough technology, as a trenchless technique. This will allow ploughing to run alongside the established techniques such as microtunnelling, horizontal directional drilling and pipeline renovation systems, as a full member of the trenchless technology family.
In making this decision, the ISTT considered that ploughing met all the key benefits of a trenchless system, in that it reduces environmental impact and disruption, minimises the need for excavation and, once completed, leaves little evidence that the insertion of a pipe or cable has occurred at all. The ISTT felt the brief excavation of a trench is only for a very short time, since it is closed immediately after the pipe or cable has been laid, and the process does not involve any of the usual activities involved in ‘open cut’ such as spoil removal, shoring, placement of bedding materials, etc.
WHAT IS PLOUGHING?
Ploughing is exactly what it says it is. The system uses a specially designed ploughshare, blade or lamella (you can choose which term you prefer as they basically are the same thing) which is pulled through the ground using a strong wire cable attached to a towing unit or a wheeled/tracked towing unit. The blade runs through the ground at a pre-set depth to create a furrow, exactly as it is done in farming. The main difference to farming practices is that utility installations need only a single furrow (trench), rather than many in a row, and to a far greater depth than is need for agriculture. The cable or pipe is laid automatically immediately behind the ploughing blade before the trench has time to collapse or fill with soil. Filling the furrow is not left to chance; a second blade on the plough is used to return the material, opened out of the furrow by the first blade, to its original position so closing the excavation.
This description is of course something of a simplification. Various options allow the system to be used to install trench bedding material if required and the design of the system normally allows the weight of the ploughing unit to be utilised to compact the base of the ‘trench’ as the furrow is opened. The product, be it cable or pipe, is normally supplied via reels which are moved along the route of the installation connected to the ploughing unit so that the product can be fed directly into the ground through a feed mechanism on the plough body.
The technique is not generally as applicable to the tight urban spaces often associated with trenchless techniques and it is more suited to open, cross-country situations. However, where grass or open soil verges of some length exist in urban areas it can be very suitable provided that other services are not likely to be disturbed by the plough.
The main advantage of this is that great distances can be achieved in a single working shift with up to 5,000 m being completed in a single day in the right circumstances. This is well in excess of the tens of metres per day achieved using more traditional open cut techniques and even outstrips significantly the often 100s of metres per day of the more recognised trenchless systems like HDD.