Room for the Lek
One of the sub-programmes within the Room for the River programme is the Room for the Lek programme. This will make the River Lek save and suitable for shipping for the next 50 years. The river will be given more room by creating gullies, lowering a dam and relocating a quaywall. The riverbanks allong the river will also be improved.
One of the riverbanks we have been working on is the ringdam near the historic town of Vianen. The stability of a 250 metre part of the Lekdijk near Vianen fails to comply with the safety requirements for the future. The riverbank is high enough, but a study has shown that, in the event of extremely high level of the river, the stability of the embankment may be insufficient.
For this section, the authority Waterschap Rivierenland did not choose for reinforcement with the traditional method of adding a revetment to the interior of the embankment, but to use the innovative technique of soil nailing. Main reason for this alternative is the presence of the archaeologically valuable site of the former Batenstein Castle that is situated at the inside of the embankment.
The Vianen Riverbank Nailing project consists of installing 273 soilnails at a slight angle through the toe of the embankment up to a depth of roughly 18 metres. The nails are installed at three different levels. The distance between the nails is 2.75 m. The soilnails consist of a nail element with a grout shell and a diameter of 150 mm.
Possible rises in groundwater pressure or levels were continuously monitored during nailing.
With the soil nailing technique, the embankment is reinforced by inserting a number of nails into the toe of the embankment. The nails hold the outer part of the bank or levee, which has a tendency to shift in an ultimate loading situation, to the part that remains stable. The elements also reinforce the earth body in the same way as rebar does for concrete, so the bank becomes stronger and the parts are less likely to shift.
The nails are installed by drilling without vibration or noise. The space needed to insert the nails is also small. Consequently, the technique of soil nailing is especially suitable for reinforcing and improving embankments in urban areas or in areas where vibrations and noise are not an option.
Since 2005, Boskalis Nederland and Volker Staal en Funderingen together have been developing the soil nailing technique in the 'Consortium Dijkvernageling'. The consortium is being supported in the development of this technique at an engineering level by a joint venture of the companies Witteveen & Bos and Sweco.