The technique is particularly suitable for sparsely populated rural areas where long pipelines with few connections are required.
An all-terrain traction unit pulls the plough with a cable winch, with bumpy terrains levelled by universally adjustable extensions and hydraulically adjustable rubber tyres. At the starting point of the bore path the plough lamella is placed in the starting pit at a level with the installation depth.
Being pulled by the rope, the plough lamella displaces the soil in the pipeline zone, settling the ditch bottom with its own high weight, creating a hollow space for pipeline installation. By means of an automatic sanding cart attached to the plough, the hollow space can be filled with sand.
Then the pipe is installed on the bottom of the ditch at the desired depth free of any mechanical stress. The pipe and cable plough installs PE and PE-X pipes of diameters up to 255 mm.
Small, flat waters can be crossed using this technique and pipes can easily be installed in embankments. Using the technique to install pipes below ground water level has proved to be very economic and environmentally friendly.
The terrain around the project area should not be fortified and should be free of larger obstacles. Prior to the installation the exact position of crossing lines and the prevailing soil conditions have to be investigated.
Case study – water pipeline installation in Germany
Tracto-Technik GmbH and Georg F̦ckersperger GmbH have established an alliance for trenchless and cable ploughing projects, known as “÷Drill’n’Plough’. Tracto-Technik provides steerable boring units for trenchless pipe installations while Georg F̦ckersperger provides cable and pipe ploughs. The systems complement each other extremely well “Ó steerable boring units are usually preferred for solid surfaces and under-crossings, while the cable and pipe ploughs are advantageous in open, rural terrains.
Nordstrandischmoor is a small North Sea island in Germany’s mud-flats, with 18 inhabitants. A small passage leading through a dam connects the island to the mainland 5 km away. The job that needed to be completed involved the installation of a 225 x 17.3 mm drinking water pipe over a length of 5.2 km.
The tide determined the execution of the project, as work was only possible at low tide. First, the pipe was installed at a depth of 1.5 m over approximately 400 m applying the plough method. A cable and plough unit was used from F̦ckersperger, who developed, constructed and successfully applied the first hydraulically adjustable plough. With this technique up to 24 cables or pipes of up to 355 mm diameter can be installed simultaneously.
The installation unit consists of a winching unit suitable for various terrains and the cable plough. Lowering the plough plate into the starting pit produces the penetration required for the hollow space for the installation. The pipe itself is fed in via the installation shaft and pulled in parallel to the plough route.
For this application the unit had to be adapted to meet the prevailing conditions in the mud-flats. The winching unit was equipped with an undercarriage with rubber tracks. The undercarriage of the pipe and cable plough, with its four all-round hydraulically adjustable extensions with runners, was adapted to overcome the uneven surfaces and keep the soil load to a minimum.
Even though this conversion work took several weeks, installation of 4 km of the drinking water pipe itself only took eight working days – however, having almost reached the target the ground conditions suddenly became softer with less load bearing capacity for the vehicles, which slowly sank despite all precautions.
Retrieving the cable and plough unit and the vehicle before floods set in was a dramatic act. Due to the very soft ground conditions the plough could not be used any more, and ultimately it was decided that the last 400 m would be installed by HDD.
The first pilot bore over 200 m was completed without any problems. The bore was carried out in the direction of the pipe installed by the plough, which had emerged from the mud-flats and was visible from the shore. A Grundodrill 12G, which was standing on a pontoon, was used.
To facilitate steering of the bore head submerged in the soft ground, it was equipped with wider steering plates so that it could be steered more easily. The pipe string was ready for installation.
The 12 m pipe lengths were welded together with an automatic butt fusion machine to a total length of 200 m. The undercarriage pulled the pipe length into the mud-flats. Over half of the pipe length had to be separated, as the vehicle became stuck in the mud-flats (due to the load). The drilling crew quickly removed the bore head from the drill rods and attached a 355 mm backreamer to the pipe string. Meanwhile the automatic butt fusion machine was driven into the mud-flats and during a break the welders successfully welded the two pipe lengths together. The operation went to plan without any unforeseeable interruptions.
The connection of the pipe ends at a depth of 1.5 m was a real challenge. The line was cut free over a length of 25 m and 3 – 4 m width at 1.8 m depth. The team was able to connect both pipe ends without any problems during low tide.
A specially-hired amphibian type vehicle, which could carry a load of 14 tonnes and be used either as a driving or floating vehicle, was used in the installation. If it becomes stuck, operators only have to wait for the tide for it to move again. This was much more flexible and cost-saving and proved to be the best decision. A pontoon was used for the planned bores.
The particular conditions in the mud-flats made this project a real challenge. Adapting the different construction phases to the tide and the struggle with the elements meant high performance standards were set for the construction company (Paasch).
The water supply board took care of all required licenses, while rangers from the national park were on hand to check that all provisions were met and all actions were documented in great detail. Any damage to the surface had to be levelled out, and every movement of the amphibian vehicle had to be authorised. A GPS detection system was used to ensure that the pipeline was constantly surveyed in case of any damage.