Good news for the Brits this month! A 35km long, 7.2m i.d. tunnel has been chosen as the preferred solution to the River Thames’ pollution woes by the Thames Tideway Strategic Study Steering Group.
Currently the decision as to whether it will happen or not is with the UK’s Environment Minister, but if it does, it means a raft of large diameter TBM works under London starting around 2007 – 2008 with roughly an eight year long construction period. Here’s the sticking point, it’s going to cost around US$2.8bn. The study group has assessed that much of this could be shouldered by rises in annual sewer bills of some 17%, graduated over the predicted eight-year construction period.
But knowing the UK’s reticent attitude toward bill increases, I can’t help but think this could prove an uphill struggle. So here’s the situation, we’ve got a west to east mega tunnel under London, the construction of which is justified following some pretty unpleasant pollution incidents in the Thames. Recent tunnelling projects under London (CTRL 2, North London Cable Tunnel) show that technologically it’s a goer. The main problem is cost.
Now consider Crossrail, part of which includes a multi-billion dollar, large diameter TBM driven rail tunnel under central London from west to east with construction hopefully starting in the next few years. Everybody wants it, and again, the technology and people skills are proven, its only sticking point is the cost!
Now let’s look to Malaysia where a large diameter stormwater tunnel was needed to rectify some pretty serious flooding problems in Kuala Lumpur. It was also decided that central Kuala Lumpur had some crippling traffic problems. The solution – build a large diameter stormwater tunnel with a central 4km-5km that doubles as a road tunnel, with the stormwater running in the invert under the carriageway. As a T&TI reader you’re probably familiar with the Stormwater Management And Road Tunnel (SMART) scheme, so I won’t go into detail. If you’re not, watch out for a T&TI special supplement next month dedicated entirely to this innovative project.
The project has effectively killed two birds with one stone, and saved millions in terms of cost. The question is, could this be possible under London? After all, the planned Crossrail tunnel runs very close to the planned central section of the sewer tunnel.
The Crossrail route is fixed by station locations, not a ‘moveable feast’. But the sewer tunnel route is more flexible. Would strategically placed CSO drop shaft connections be possible into a slightly larger diameter Crossrail, with the tunnel invert taking the flows under central London? Lots of questions to be answered, but for anywhere in the world considering tunnelling schemes it may be worth following the Malaysian attitude of lateral thinking. One project would be better than none!
Tris Thomas
