Within the framework of the Dutch "Room for the River" programme, modifications are being made to various waterways at more than 30 locations in the Netherlands.
One of those waterways is the River Waal. The water of the River Waal has to flow through a relatively small winter bed at the bend between Nijmegen and Lent. Here, the winter bed is only 350 m wide, while the average width elsewhere is 1 km. Due to this bottleneck, the water impounds, which is not beneficial to the discharge of the water through the Waal. To facilitate a higher river discharge, the river has to be given more room at this location.
On the instructions of Rijkswaterstaat, a by-pass channel is being constructed by Bouwteam iLent. This project is part of the "Room for the River" programme and is called "Room for the River Waal".
Due to the construction of the side channel, the dyke is also being moved to the North. This water barrier is intended to hold back water not only aboveground but also below ground level. A cut-off wall is therefore being constructed up to approximately 20 m below ground level. This barrier consists of a composite slurry wall: a 1.5 km long cement-bentonite trench wall with HDPE-lining.
Before the lining can be placed, a trench has to be excavated in the soil. This will be done with a duty crawler crane with a rope suspended wall grab. This grab is roughly 10 m high and weighs 15 tons. The grab excavates the soil and the removed soil is immediately replaced with cement bentonite. Due to the high specific weight of the mixture, the trench remains stable and doesn't collapse. Depending on the cement content, the mixture remains liquid from a certain time, leaving enough time for the lining to be lowered in the trench.
The lining sections of roughly 2.5 m in width have built-in locks, so they form a continuous wall. Together with the cement bentonite, which hardens in time, this produces an underground water barrier.
The groundwater barrier also crosses the route of the rail bridge. Under the rail bridge, instead of a cement bentonite wall with lining, a diaphragm wall will be installed that connects on both sides to the composite slurry. Due to the limited working height, adapted equipment will be used for installing the diaphragm wall. This equipment is the same as that is used for reinforcing the rail bridge pillars. Due to the installation of the by-pass channel, these pillars must been reinforced to avoid scouring of the foundation.
Once the lining has been applied and the cement bentonite has hardened, Bouwcombinatie i-Lent will, for approximately 1 kilometer, construct a concrete L wall, into which the top of the lining will be concreted and, for roughly 500 m, the composite slurry wall with HDPE lining will be incorporated in a traditional dyke.
