Keeping the Nice Sea Outfall Straight and True
The construction of a new sewage tunnel in Nice, France required a sea outfall to be installed using a tunnelling procedure. Using microtunnelling the sea outfall was designed as a 482 m long installation running along a straight route, holing out on the seabed some 450 m from the shoreline.
The 1,600 mm diameter pipeline was installed with a Herrenknecht AVN1600 using concrete pipes with a wall thickness of 280 mm. A VMT SLS-Microtunnelling LT navigation system provided the guidance necessary to keep the bore on the required line and level.
The first 115 m of the straight drive was completed using a laser guidance system already owned by the contractor. Beyond this, however, there was a requirement for a more sophisticated system to ensure the successful completion and accuracy of the drive to its terminus some 400 m further out under the sea. Therefore it was decided to introduce the VMT SLS-Microtunnelling LT system.
The contractor, Ludwig Pfeiffer, commented that the selection of the VMT navigation system was an easy one given that the company had worked with VMT on many occasions previously with excellent results. For the Nice project the contractor purchased a brand new SLS-Microtunnelling LT system to utilise.
For the recovery of the machine, a module was installed to remotely disconnect electrical and data cables as well as the slurry line. Then thanks to the previously installed lifting eyes on its upper side, the TBM can be lifted with the support of a dedicated team for the underwater operations. The installation was completed in just 50 days.