In February 2025, Rijkswaterstaat conducted a pilot joint injection in the Roertunnel (A73). This trial investigated whether joint injections can reduce the nuisance of noise and vibrations for local residents.
Measurements show that the gel injection results in a noise reduction of 3 to 4 dB. The gel injection helps a little, but the reduction is too small to provide a noticeable improvement. Follow-up steps have been taken, such as measuring effects over a longer period and developing a plan for a new trial measure: a soil injection under the tunnel joints.
The execution of the injection trial was successful, allowing the direct effect of the measure to be determined. Among other things, the environmental factors before and after the execution of the injection trial were comparable. Measurements show that the gel injection results in a noise reduction of 3 to 4 dB. A measure only provides a noticeable effect if it results in a decrease of at least 10 dB. For comparison, the difference in noise levels between summer and winter conditions in the Roertunnel is in the order of 10 to 12 dB.
Effect of gel injection in different seasons
During the summer, the tunnel elements expand, and the acrylic gel used in the injection is compressed in the joint. Acrylic gel has the property that it can be compressed well and remains flexible. In the following winter period of 2025 - 2026, the gel will expand again, and a repeat measurement must first be conducted to determine whether the effect of the gel injection is maintained. It will be investigated whether the noise reduction of 3 - 4 dB remains constant in 2025 and subsequent years.
Soil injection under tunnel joints
At the end of June 2025, we held another expert meeting to discuss possible follow-up steps. The most promising measure is a soil injection under one or more tunnel joints. It is possible that this could reduce the vertical movements of the tunnel sections. This could also lead to a reduction in noise and vibration nuisance.
New experiment
This is also an experimental measure where it cannot be determined in advance what the effect of the measure will be. Rijkswaterstaat has commissioned Nebest to develop a plan for this.
Councilor Vincent Zwijnenberg (Infrastructure and Mobility): ‘I am satisfied with Rijkswaterstaats persistent attitude. They are doing everything possible and applying the latest techniques to reduce the nuisance for local residents. The ministers visit has not been in vain.’