LETTER TO THE EDITOR |
LETTER
From Dr Nick Barton, Nick Barton & Associates
I wonder if I am alone in thinking that the Jerusalem City planners/architects were rather optimistic in their stringent plans for the parking caverns beneath the motorway (city approach/exit) tunnels (T&TI, Sept 2021, p37). Unless there were serious concerns with water pressures and difficulties in pre-grouting at this scale, surely ‘tens of millions’ (in many currencies) could have been saved by: a) going say, 10m deeper to get better rock in the wide tunnel- and cavern arches and
b) having wider spacing between the tunnels/caverns, which in ‘my book’ is asking for trouble unless the rock
is little jointed. Bedded limestone/ dolomite also has sub-vertical jointing? I wonder how much extra unnecessary support and perhaps observations of cracking during construction there would have been.
In some countries, motorway tunnels are deliberately diverted to give bigger pillar widths. In relation to the benefit of horizontal stress in the stability of large arches, it is also certain that cavern A will ‘steal’ tangential stress potential from cavern B. And construction of B will cause added deformation to A. In case of pre-injection, the already achieved result may be compromised. So, where did the (assumed) extra ‘tens of millions in any currency’ come from? Or were designers well aware that they were asking for something expensive from the start?
LETTER
From Dr Roberto Schürch, Pini Group
Thank you for sharing the questions and comments with us. Basically Mr Barton is absolutely right in all his comments and we share the same opinions. However, theoretical thoughts must often face political decisions and practical limitations. In our case, the decision to create the
caverns was 100% political and driven by the desire to have no traffic interruptions at the surface (being a major entrance to the city). With respect to the spacing of caverns,
the distance was dictated by existing and future buildings in the area. No other layout would have been possible. As for “going 10m deeper”, creating
caverns at a greater depth would not have been possible because of the vertical road alignment (which concerns the entire road and not only our caverns). So, to summarise, a good designer
should be able to develop a project for the given boundary conditions and by following the requirements of the owner. This was the difficult part of the Shazar Caverns project – making feasible a project judged to be not feasible, thereby fulfilling the owner’s needs.
Have your say... Above: Cross-section of the caverns showing the traffic lanes above the parking decks
If you would like to add to this discussion or comment on any other aspect of this publication please email your letter to:
george.demetri@
tunnelsandtunnelling.com
8 | November 2021
shutterstock.com /Dmitriip
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