Netherlands' most challenging well drilling project

Bronbemaling.com has been asked by contractor combination Westlandse Entree to play a crucial role in the realization of the flyover junction of the N211 Wippolderlaan with the N222 in Wateringen. The project has had a long and intensive preparation, mainly because the drainage conditions are exceptionally challenging. Experts speak of the most challenging well drainage project in the Netherlands.

On the one hand, phreatic dewatering is necessary for the construction of the sunken location of the N211 at the level of the flyover junction, and on the other hand, tension dewatering is necessary to prevent the bottom of the construction pit from eroding, explains Han Boonman, project manager for execution at Bronbemaling.com. “An additional complication here is that the pumped up water cannot be discharged into the surrounding ditches and must therefore be completely returned to the soil.”

Extensive trial drainage

The construction pit measures 600 meters by 25 meters. The excavation has a total length of about 40 meters, divided into two 20-meter-long ditches. “The deepest point of the construction is about 7 meters below ground level, while the surrounding area is around 3 meters below NAP,” says Boonman. “Early in the project it became clear that standard solutions would not suffice here. It was therefore decided to carry out extensive test drainage.” During this test pumping, it turned out that the groundwater head was considerably higher than previously assumed. “An alternative by, for example, making a sheet pile pit and applying underwater concrete is therefore impossible. This would require sheet pile walls that would protrude far above ground level. This is technically impractical and also carries the necessary risks. So the conclusion was clear: only drainage offered a solution, but with a very robust system of return drainage.”

230 sources

The final concept consists of deep-well wells in the construction pit that pump and discharge water to a two-tier return drainage system, explains Marc de Leeuw, N211 project manager at Bronbemaling.com. “Approximately 30 abstraction wells will be deployed for the tension dewatering to prevent bursting of the basin. The extracted water, at peak times about 825 m3 per hour, is returned to the soil/deeper sand layers via about 200 return wells due to the high chloride content in the groundwater.” The drainage within the sheet pile pit consists of a combination of vertical filters and horizontal drainage. “We are also providing some drainage work outside the sunken pit. All drainage work is expected to be completed by the end of 2027.”

Groundwater Management

What sets this project apart, according to both gentlemen, is primarily the scale and complexity of groundwater management. “It is not the drilling of the wells that is the biggest challenge, but rather the integral management of the system within a busy infrastructure project,” Boonman assures us. “We are among a very limited group of drainage companies in the Netherlands that can handle projects of this magnitude.” With this project, Bronbemaling.com strengthens its position in the Southwest Netherlands, a region that the company sees as an important growth market. “We have been active in this region for years on major projects such as the A24 Blankenburg connection, the Princess Amaliahaven and the hydrogen power plant in the Botlek area, and will soon open our own branch here,” De Leeuw reveals in conclusion.