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Construction of a seawater withdrawal point with the GRUNDODRILL 28Nplus

22.10.20 - Grömitz, the "Baltic Sea spa on the sunny side", with its mild climate, wide range of cultural activities and numerous leisure and sports facilities, invites around 260,000 overnight guests and around 550,000 day trippers to spend carefree holidays there every year. It is situated on the north-western boundary of Lübeck Bay, which has been a seaside resort since 1813 and is not only the third most important holiday resort in the region, but also the most important in this region on the Baltic coast. The 8 km stretching Baltic Sea beach with romantic dune landscapes, two bird sanctuaries, natural beach sections, as well as a 3.5 km long spa and beach promenade with spa gardens and a 398 m long pier ensures relaxing, beautiful and simply carefree (family) school holidays and vacations.
As a special highlight on the spa promenade, the funtime swimming pool “Grömitzer Welle” enjoys great popularity with young and old. A water park covering 1,000 m² and 600 m² sauna world, the seawater pool offers plenty of space for fun and games, relaxation and recreation - often with a direct sea view. All the pools and water attractions are operated with pure seawater, which depending on each application, are warmed up to temperatures between 27°C and 33°C. In total approx.1,1 million litres of water are transported inside the “Grömitzer Welle”.

Only minimally invasive

In order to remain true to the motto of the water park, “Experience the sea and enjoy more”, a new seawater withdrawal point had to be built at the beginning of Spring 2020, which involved an almost 400 m length transport pipeline in the Baltic Sea. The Grömitz Tourism Service, who operate the pool, commissioned the engineering office Wald and Kunath with the planning of this construction task. They had to consider in detail that within the framework of the invitation to tender and the local construction supervision, it was vital to ensure compliance with the requirements of nature conservation.

It was therefore fairly clear from the outset, that this task should be minimally invasive: preserving, nature-conscious and as non-destructive as possible! Especially the areas, such as the dune landscapes, the natural beach sections, the bird paradises and the spa and beach promenade react very sensitively to gross interventions that leave deep traces and cause noise emissions, CO2 and dust particles. Those responsible therefore decided very quickly that the construction of the transport pipeline from the extraction point to the connection point, in the existing pipeline, on the beach at the “Grömitzer Welle” simply had to be done using the underground HDD bore method. Fast, economical and environmentally friendly – simply minimally invasive.

Sought and found

After a restricted invitation to tender for this special construction task, the special civil engineering company Paasch was awarded the contract for this project. The company is an “old hand” in the underground pipe installation field and offers all pre-requisites for implementing this type of construction project à la Grömitz: suitable equipment, longstanding experience, extensive knowhow, assured routine and sophisticated logistics. The Paasch crew has already solved many a tricky task of this kind in the past - with bore paths above and under water, in the Wadden Sea and in nature reserves and with the corresponding, demanding underwater work, as was also required here.

Pro-Crew, Pro-Equipment

For the assembly of the new seawater withdrawal point at 3,80 m water depth and the installation of the approximately 400 m length transport  pipeline with the HDD method, it was now essential to set up the jobsite with all the necessary equipment. For this purpose, the team excavated a starting pit on the beach, directly in front of the “Grömitzer Welle” and installed the HDD bore rig GRUNDODRILL 28Nplus in a fenced-off area. A workboat with pontoon float was placed in position for the various underwater tasks close to the target position in the Baltic Sea and the boat was sent floating on the water to carry out measuring and directional checks, during the bore process. Paasch construction manager, Guido Röhlich explained the reason for their choice of bore rig: “Due to the length of the bore of around 400 m, we decided to use a HDD bore rig from the 28-ton-class from TRACTO-TECHNIK, which has pushing and pulling forces of 28 t. This way we can overcome obstacles even if the bore path gets tight.” And these were definitely to be expected in the sandy sea bed with numerous large stones.
 
Even the choice of the bore tools and the composition of the drilling fluid were determined in advance: For the pilot bore a Hard Drill Head Type 1 for TD 82 – Diameter 130 mm was chosen, for the drilling fluid a specially prepared mixture from Phrikolat Drilling Specialities GmbH, which was precisely adapted to the requirements for this construction project. They have been a partner, providing professional advice for Paasch-Projects with regard to drilling fluid, for many years. To expand the bore a stepped reamer with 320 mm diameter was provided. A DigiTrak Falcon F5 Directional Drilling System was applied as a precise detection technology on the water surface. Last not least, the pipe length to be pulled in (HDPE OD 160 SDR 11) was partially suspended from the crane, while also partially floating on the water.  
 

A bee-line from the beach into the Baltic Sea

And off they go: The pilot bore with a diameter of 130 mm started from the beach in the direction of the Baltic Sea with no problems whatsoever in the fine sand. The signal from the sonde, integrated inside the bore head was calibrated every 3 m when loading each drill rod, in order to determine the height, inclination, rolling process etc, so that the direction of the bore path was also maintained. Along the bore path on the water, the colleagues stretched a rope and drove the detection system back and forth with the boat in order to check and make any necessary alterations. As the sea was calm, this was all carried out with no problems whatsoever.  
 
Over the first bore metres, it proved necessary on several occasions to pull the bore back, due to the positions of large pieces of rock and adapt the bore tool accordingly. The bore team reacted professionally and fast and, in no time, they were able to carry on. The GRUNDODRILL 28Nplus then worked like clockwork: at 2,50 m below the top edge of the seabed the pilot bore progressed with a torque of between 2.000 and 4.000 Nm and an average push/pull force of up to 70 kN metre by metre; the average drilling fluid consumption was about 200 l/min. Here, it paid off to apply this HDD bore system with the TD 82 drill rods, as both the drilling fluid quantity and the fluid pressure was constantly guaranteed during this long bore. 
 

Under Water: Arrive, Expand, Install

After reaching the target pit (under water in the Baltic Sea) after precisely 396 m and about 11 hours, spread out over two half-days, the divers were now in demand. It was their task to retrieve the bore head and exchange it against the stepped reamer Ø 320 mm to extend the bore hole, as well as attaching the product pipe HDPE OD 160 mm to be simultaneously pulled into the bore path. With professional preparations, technical expertise and great skill, the diving team carried out the numerous tasks required and gave the signal for the pipe pulling to begin. With a pulling force of 50 kN this and the simultaneous “dismantling” of the 3 m length drill rods were achieved over 396 m in approximately 15 hours (at 26,4 m/h).
 
By the way, the divers also installed the stainless steel seawater extraction point, which is equipped with a sieve and pig trap at a depth of 3,80 m, which finally feeds the new pipeline for the “Grömitzer Welle”.
 

Well done – to all of them

The divers and crew of the work ship, the Paasch bore crew and last not least the GRUNDODRILL 28 Nplus – all proved themselves, once again, to be truly top performers. The pure pilot bore and pipe installation had been completed in only 3 days – an unbeatable time, especially compared to the open trenching method. Unfortunately, due to a bad weather interlude, work had to be interrupted in-between for one day: high waves prevented the positioning of the working pontoon in the target area in the Baltic Sea.
 
Not only the parties involved in the construction could be satisfied, but also the Tourism Service Grömitz, which thanks to the economically convincing trenchless solution, was able to obtain a new seawater extraction point with supply line for the “Grömitzer Welle” within a very short time. The locals and the holiday guests of the adventure pool can continue to enjoy the fresh seawater in-house and – extremely important – the natural surroundings remained unscathed! Dune landscapes, natural beach sections, bird paradises, as well as spa and beach promenades were all preserved and therefore, as a matter of fact, did not notice anything at all.
 
Managing Director Martin Paasch did not want to miss the opportunity to add a few concluding words: “True to our motto: ‘We solve it!’ we were once again able to prove our competence with our excellent, motivated employees. I am proud of our employees, without their commitment, expertise and team spirit we could never have managed such a project. The powerful GRUNDODRILL 28Nplus has reliably played its part.”
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