Microtunneling – a trenchless method
The landfall will be constructed with the trenchless microtunneling method. It has been selected as the preferred solution, taking into account such technical aspects as the pipeline diameter and geotechnical parameters of the soil, to protect the coastal environment and minimise impact on the nearshore area and the beach . Tunnel Boring Machine (TBM) with fully rotary cutting shield will be used to drill the opening. As the boring progresses (starting from the launch shaft), sections of concrete pipe will be pushed into the opening to form a permanent tunnel casing. The method is called “pipe jacking”.
Taking into account the pipeline diameter (36”) and the conditions in the construction area, the tunnel with the minimum internal diameter of 2 000 mm (external diameter of 2 500 mm) has been designed. For instance, for the landfall in Niechorze-Pogorzelica, the seabed survey allowed selecting the location of the tunnel exit pit 400 m from the shoreline while the launch shaft will be located 200 m inland, which gives the total tunnel length of ca. 600 m. Such locations of the tunnel launch shaft and exit pit, as well as the method selected for the execution of this part of the investment, preclude interference with the particularly sensitive beach and cliff landscapes and will leave the dunes and cliffs untouched.
The landfall tunnel diameter is the same in Poland and Denmark. The landfall design for Faxe South covers the construction of a 1 000 m long tunnel. It will extend from the launch shaft location 400 m inland to the tunnel exit 600 m away from the shoreline.
Tunnel boring will be performed from the launch shaft, under the shoreline and seabed, to the tunnel end below the seabed. At the end of the tunnel (underwater), the TBM will be uncovered and lifted to the special crane vessel (or with a crane on a barge) and transported to the port. The pipeline will then be pulled through this tunnel and thus enter the land.
It will be done using an anchored shallow water lay barge. The pipeline will be welded on board of this barge and then it will be pulled to the shore with a winch anchored at the onshore construction site.
Steel cable of applicable diameter and strength will be used to pull the pipeline. The cable will then be extracted by a tugboat through the tunnel from the landside to the pick-up area at sea where it will be loaded on the shallow water lay barge.
The investment completion and the beginning of gas transmission is planned for October 2022.