Monitoring the second Heinenoord Tunnel

Samenvatting

This is the final report of Commission KI00, part of the COB

Programme. During the period 1994-1999, K100 organised

an extensive programme in order to monitor the construction

of the first bored tunnel in the Netherlands: the Second

Heinenoord Tunnel. The fact that the face of the tunnel was

stabilised with slurry was unique to this project.

Monitoring the process produced a valuable set of measurement data available for further analyses. Measurements were preceded by and compared with predictions to gain a clear picture of modelling in the tunnelling process. In this way tunnel lining construction could be established, especially for the comparatively soft soils characterising the Netherlands.

In addition, detailed insight was obtained by conducting a

comprehensive evaluation of the measurements. This improved understanding of thrust forces, the influence of the boring process on the surrounding area, and the forces on the tunnel lining can make a positive contribution to future tunnel projects.

The Second Heinenoord Tunnel crosses under the river Oude

Maas at a relatively shallow depth. The monitoring project

showed that in order to prevent face instability for such tunnels, the margin between the maximum and minimum allowable face pressures is small. Forces within the TBM also were measured and evaluated in order to optimise the design of TBMs in general. Slurry pressure at the face and friction along the TBM proved to be the most important components of the thrust force.

Available numerical and analytical models largely overestimated settlements in the surrounding area caused by the tunnelling process. The governing factor for settlements occurring was the grouted annulus behaviour around the tunnel. Accordingly, this factor should be incorporated in future

design models.

Stacked segments to construct the tunnel rings created large

forces in the segmented tunnel lining. It was found that half

of the final internal lining force was already present prior to

being loaded with external grout or earth pressures. This was

a surprising result. However, further research is needed to

facilitate the modelling of the complex load distribution

around segmented tunnels in general, and of the forces resulting from stacking tunnel segments in particular.