German contractor Paasch Rohrleitungsbau has successfully completed a complex horizontal directional drilling (HDD) project using TRACTO-TECHNIK’s GRUNDODRILL.
The HDD project took place in Europe’s Elbe River and involved scheduling operations around the tide, underwater works and varying geology. In order to install two new tide gauges, the contractor used the TRACTO-TECHNIK GRUNDODRILL 15N, three professional divers and a bomb disposal team.
With a catchment area of 148,300 km2, the Elbe River is the fourth largest river in Central Europe. It runs 1,094 km from the Riesengebirge mountain range in the Czech Republic to the North Sea in Cuxhaven, not including tributaries, and is one of the main transport routes for inland shipping in Europe.
The river is difficult to navigate in some places, like the intertidal zone near the estuary in the Lower Elbe River. In order to predict the tides, water levels are measured by a network of tide gauges installed approximately every 10 km along the shipping passage in sight of the river bank.
With up to 80,000 ships moving through each year, two new gauges were required to be installed between Hamburg and Cuxhaven. The first was to be installed near the island of Krautsand, which sits on the bank of the Lower Elbe River, while the other needed to be installed 10 km away, at the Grauerort Fortress, before being linked in with the data network.
As Krautsand is a popular holiday destination and swimming resort thanks to its idyllic location in the green Kehding region, the operation could have proven quite difficult. This was not the case for experienced pipeline and plant construction specialist Paasch, which took to the task with the GRUNDODRILL 15N.
Installing technology that measures up
The existing reference levels have aged immensely in technical and structural terms, so the Hamburg Waterways and Shipping Office (WSA) – responsible for this particular stretch of the Elbe River – arranged for new measuring stations containing state-of-the-art technology to be installed right alongside the existing reference levels.
The worksite was located in a sensitive and partially protected area that the authorities knew could not be passed using the open cut construction. In order to manage this, the WSA issued a tender for the project that expressly demanded the application of a trenchless installation method.
Based on its previous experience and history of planning and implementing complex projects, Damendorf-based company Paasch was awarded the contract for the HDD project, including all underwater connection jobs.
The project required the installation of two cable protection pipes – more than 234 m at Grauerort and 180 m at Krautsand – with an outside diameter (OD) 110 x 10 mm each from the beach to the foundations of the tide gauges at the bottom of the riverbed. This HDD operation posed a challenge in logistics and planning; all works at the tide gauges required to be take place underwater.
One week was allowed for each of the installations and each job had to be carefully planned around the tide, creating a number of restrictions for the project.
The transport ship carrying the pipe bundles, drum carrier and other materials could only dock at the port in Krautsand when the tide was high; similarly, work boat Heros I, bearing materials and equipment, also depended on a high watermark.
To help manage the underwater pipework, Paasch contracted three professional industrial divers from underwater construction specialist Heros GmbH.
Handle with care
Work at the Grauerort Fortress, which was formerly used as an ammunition depot for sea mines until the end of WWII, was carefully planned and supervised by the WSA. To manage the possibility that the surrounding area was still contaminated by mines, a bomb disposal team evaluated the site around the bore path before work could start.
When it was clear that there was no threat of an explosion by forgotten mines, the drilling team arrived to prepare the site and establish the head access holes.
Tackling the first drill
The work boat with the diver crew moved in the next day and the pilot bore for installing the two protective high density polyethylene pipes could start.
Halfway through drilling, the bore head came across an unknown obstacle; this turned out to be the remains of an unmapped old building structure. The brickwork was impenetrable and there was no alternative but to bypass the obstacle by redirecting the bore path and drilling underneath.
A medium drill head was used to carry out the task; to prevent the drill head from drifting off course in the tidal current, a diver fastened it to the crane cable of the ship. The next morning, a diver went down to replace the drill head with a backreamer and attach the pipe bundle that had been prepared on the ship beforehand.
In order to move the pipe coils in the right pulling-in direction and keep them there, the work boat had to change position several times. The captain navigated with extreme care to prevent injury of the crew above and beneath the water, and to ensure that the pipe string did not tear off.
Finally, the still empty – and therefore lightweight – pipes were weighed down with concrete half shells as a protection against the current. Thanks to these measures, drilling over of a distance of 234 m for the first tide gauge was completed within the stipulated period of time.
Drilling where people go swimming
The team set up the site at Krautsand over the weekend, for work to start the following Monday. The location was different to the almost deserted Grauerort; many holidaymakers were at the beach at Krautsand.
To avoid disturbing beachgoers, the GRUNDODRILL 15N was positioned beneath the trees slightly above the beach. The truck containing the mixing system was parked at the car park on the other side, so that only the hose running to the drill rig gave a hint of the drilling operation.
When the pilot bore started the next day, the holidaymakers barely noticed, with a few visitors becoming curious only when the work boat was fastened to the mole.
Locating was carried out from a rubber dinghy, which was also used to transport people and material to the work boat. The 180 m pilot bore to the tide gauge was finished in one day and the drill head was attached to the ship like before.
The challenge was then to complete the underwater work to the tight schedule set by the tide. To achieve this, team went straight back to the port to load the stored pipe material into the work boat once the pilot bore was completed and pipe pulling was scheduled for the next morning.
After the divers were deployed, great caution was necessary when navigating the work boat. A high number of large cargo ships moving through the channel caused waves, creating difficulty for both those working under water as well as those confined up on deck.
The crew from Paasch and the divers used their experience and, keeping calm, were able to install the two pipes within one day; however, the WSA was concerned that the new protective pipes might be damaged by ship anchors.
For further protection, the Paasch project manager suggested installing a smaller OD 50 mm ductwork into the OD 100 mm pipe the following day and the data cables were subsequently pulled into these pipes with the aid of the divers.
A successful connection
Both tide gauges are now connected to the power grid and data network onshore, reliably transmitting the water level values in Grauerort and Krautsand. Operations took place without disturbing the holidaymakers or interfering with the protected landscape.
The specialists from Paasch have proven their competence in planning and implementing complex HDD projects, illustrating that even such logistically elaborate undertakings can be realised in an efficient way by means of HDD technology. The WSA was delighted with the outcome.
This article was featured in the Summer edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device click here.
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