The Wind Park Friesland (WPF) project is a new wind farm built on Ijsselmeer; a manmade lake which borders the 30km long Afsluitdijk sea defence dam in Holland.
The package of works, to deliver 55km of turnkey power distribution, was awarded to VolkerTrenchless Solutions in 2018. The works were split into two contracts to be delivered simultaneously, with a staggered start date of the Tennet Marnezijl Oudehaske (TMO) end.
The scope of works comprised 43 Horizontal Directional Drilling (HDD) crossings along a 55km linear route, with the offshore cables landing halfway along the Afsluitdike. The cables passed through the open cut and HDD ducting for 5km to the shore, and then travelled 50km along the A7 motorway to a new substation.
The ground conditions varied from glacial till, stiff clay and silt. The team encountered unexpected ground conditions within the dyke, causing the 250t drilling rig to get stuck during the bore enlarging phase of the works. To overcome this, the team mobilised a larger 450t drilling rig from our fleet to free the stuck tooling, which then continued to drill through very old hard wood timbers and boulders from the ice age that were buried under the dyke.
The project was initially designed by the client and it was assumed that no soil improvement was required over the entire cable route. However, in the final engineering calculations this proved to have a substantial load limiting effect on the HV cables. A redesign of the works was required which included having to remove 60,000m3 of soil import new material in addition to upgrading the cable core diameter to improve the system performance. Our in-house team led the engineering of this process, with minimal assistance from external parties, minimising the impact to the project, stakeholders and client.
Due to the substantial increase of traffic movements required because of the soil improvement process, the traffic measurement measures as originally anticipated were unsuitable. Our team worked closely with key stakeholders, including the road authority, to design a new traffic system in just one week. Due to the quality of the plans developed in collaboration with the road authority, the permits were granted in only half the application time normally required, enabling us to continue to deliver the works to the original programme.
As a major part of the work took place on the Afsluitdijk which is one of the prime coastal defences in The Netherlands. Usually, no substantial digging or drilling is allowed here during the storm season between October and March. To enable the works to be executed in this restricted season, VolkerTrenchless Solutions provided Rijkswaterstaat (dyke and road authority) with high quality plans and procedures which included provided a 24/7 emergency assistance service during the works for Rijkswaterstaat. This service which was utilised for issues with traffic management following vehicle incidents. By providing this effective stakeholder management, VolkerTrenchless Solutions halved the programme duration and completed the entire works within a 12-month period.