High potential for damage, relatively high pore pressures and limited pre-construction accessibility are all features of subaqueous tunnels. Potential hazards include high water inflows or even a complete flooding of the tunnel in the case of a connection opening up to the seabed. In subaqueous tunnels, very high pore pressures may occur at small depths of cover, i.e. often in combination with a low shear strength ground, resulting in particularly adverse effects in terms of stability and deformations of the opening. This lecture illustrates some of the geomechanical issues relating to subaqueous tunnels (face stability in fault zones, the limits of open mode TBM operation in weak sedimentary rocks and the effect of advance drainage in squeezing ground) with reference to five case studies – the Storebælt tunnel, the “Melen 7” Bosphorus tunnel, the Lake Mead Intake No 3 tunnel, the Zurich Cross Rail and the future Gibraltar Strait tunnel project.
At its meeting in Helsinki in 2011, International Tunnelling Association Working Group 5, identified the need for guidance on the provision of refuge chambers in tunnels under construction. A refuge chamber is a place of relative safety in a shaft or tunnel where tunnellers can be accommodated with access to basic life support services until rescued or it is safe for them to exit the tunnel.
Refuge chambers should be easily identifiable and readily accessible by tunnellers at risk and by the emergency services
This document will be reviewed and revised as necessary in the light of practical experience with the provision of refuge chambers in tunnel under construction.
This document is a guideline to the best practices on backfill grouting. It is intended to address the various considerations when applying backfill grout. It does not address the theory or details of applying, or mixtures of, the backfill grout itself, but does give reference for such theory and application.The document gives general guidelines: site and machine-specific guidelines should be developed based on this document as well as the project specifications.
Responding to an increasing demand of underground infrastructures monitoring of hydro-geotechnical and structural parameters during the construction of urban tunnels in soils and rock (except hard rock) is a field of activity which has seen impressive technological changes and progress in the past years. Monitoring has thus become an essential part of the overall risk management which normally is implemented for such type of construction works.
The document “An Engineering Methodology for Performance-Based Fire Safety Design of Underground Rail Systems” shall improve the safety design of underground mass rapid transit systems (MRTS). It shall fill a gap, as current safety requirements for rail tunnels and underground systems, compared to road tunnels, are less specific and lack international harmonization.
The focus of this document is on the methodology to be followed while analyzing the effectiveness of any safety measure of MRTS. The performance-based approach aims at integrating the different methods to achieve a safe tunnel design including standards and norms. As the topic is complex, the methodology at hand needs further refinement in the future and is considered as a first proposal only.
For hundreds of thousands of years, our natural domain has been a principally two-dimensional space : the surface of the ground.
Urged by necessity, curiosity, and even by temerity, we have always tried to escape from this space, either by widening it, which is only possible in a very restrictive sense, or by searching to utilize the third dimension, upwards or downwards. In these efforts, we have always encountered great difficulties that have been overcome thanks only to an astonishing tenacity.