TUNNEL TECH

Traditional cross passage excavation is usually characterized by many operational issues, which can come from bringing in excavators, excavator-mounted hammer heads, or Drill&Blast equipment. One possible solution for the cross passage challenge relies on existing methods and technologies, applied in a different way. In SYSTRA SWS we like to call it Smart Cross Passage.

This innovative approach to CP excavation makes use of a small scale TBM, moved along the track and oriented sideways to drill through the tunnel wall. A standard segmental lining with sealing gaskets is installed during excavation, providing a complete water tightness. After CP completion the TBM is then pulled back and moved forward to repeat the process.

In current design practice, remarkable overstressing in the final lining is expected when the surrounding rock mass presents either poor mechanical parameters or particularly high cover. When mechanized excavation with shield TBM is selected, one possible countermeasure for this problem can be the implementation of a compressible filling for the annular gap.

During Brenner Base Tunnel conception SYSTRA SWS, in collaboration with the Politecnico of Milan, investigated the advantages associated with the application of expanded clay. Due to its mechanical properties, in fact, this material provides an effective support during segment erection, keeping under control long term rock mass pressures.

Thanks to its research activity in this field, in 2012, SWS won the recognition for the best technical innovation of the year at ITA AITES International Tunnelling Awards.

The present market trend in tunnel construction industry promotes the implementation of steel fibres as reinforcement of concrete segments, replacing the conventional use of rebars due to easier production and higher performance. Current Guidelines and design Standards allow using different methods for analysing FRC segments, ranging from simplified equations to advanced FE models.

Considering the economical and technical advantages of this technology, SWS invested in developing a strong competence in designing fibre reinforced components, even establishing partnerships and collaborations with other companies, universities and research institutes.

In the past 20 years the FEM has proven to be a powerful method for estimating deformation, stability and groundwater flow in geotechnical structures. Much has been achieved in terms of advanced models for soil behaviour, 3D modelling and meshing, realistic simulation of soil-structure interaction and construction stages, robust numerical procedures, parallel processing and visualization of results.

Recognising the advantages of numerical simulation, SYSTRA SWS invested time and resources in developing state-of-art modelling and simulation skills, being able to use all the most advanced software packages currently available on the market (like Plaxis, Flac 3D, RS2 …).

Fire safety is currently one of the emerging challenges in tunnel engineering, considering that the fire scenario needs to be analysed using a rigorous scientific approach in order to overtake common limitations coming from simple prescriptive codes.

Considering the big benefits coming from Performance Based Design (PBD), SYSTRA SWS provides advanced engineering services aimed at investigating the behaviour of the system in terms of structural performance, detailed analysis of the fire zone (visibility, temperature distribution, smoke…) and simulation of the evacuation process (self-rescue or assisted evacuation). Due to its reliability, FDS CFD code has been selected to perform these simulations, taking advantage of enhanced post processing provided by Smokeview and Evac.