GUEST EDITORIAL | ALASTAIR SMITH, CHAIR, BRITISH TUNNELLING SOCIETY
Image of large diameter Thames Tideway ‘super-sewer’ built in London.
Image credit: Thames Tideway.
be a contractual argument and becomes, once again, an engineering problem to be solved. So should the Engineer be more involved in
contract set-up? I would suggest yes — and the recent successes show what that looks like in practice. Let me offer three propositions, none of them radical; they are simply the Tideway and Silvertown lessons written into every major scheme. First, no major tunnelling contract should have its
risk allocation, geotechnical baselines and contingency settled without a senior experienced tunnel engineer formally accountable for them, standing alongside — not behind — the commercial team; the GBR is a contract document and should be authored and owned as one.
REFERENCES ● 1
● 2
Second, we should restore an empowered
engineering role within NEC-based structures: a named professional with contractual standing, obliged to hold a fair balance on matters of tunnel engineering and ground risk and empowered to make decisions that keep the Works moving. Call it the Engineer; the word has an honourable history. Third, government should allow promoters to
seek consent on the basis of engineering parameters rather than prescriptions, so that detailed design can be developed with the people responsible for construction in the room, delivering the optimised outcomes and the improved certainty of cost and schedule that early involvement brings. All three, in the end, depend on one thing the best
Global Infrastructure Hub (G20), ‘The Channel Tunnel — case study: forecast cost of £4.8bn (1985 prices) against a final cost of £9.5bn (1994), an 80% overrun; opened May 1994, one year later than planned.
gihub.org
Statens Vegvesen (Norwegian Public Roads Administration, NPRA): the 24.51km- long E16 Lærdal Tunnel opened November 2000 at a construction cost of NOK 1.082bn (c. US$113m at the time). Restated to 2026 prices this is approximately £160m, derived both by indexing the krone cost on Norwegian CPI and converting at current rates, and by converting at 2000 rates and indexing on UK CPI.
● 3
Thames Tideway Tunnel — delivered broadly to budget through a dedicated infrastructure provider (Bazalgette Tunnel Ltd), an Alliance Model with painshare/ gainshare and early contractor involvement (ECI), and a Government Support Package acting as insurer of last resort for uninsurable events (Association for Project Management; Global Infrastructure Hub; Major Projects Association/ Emerald, Thames Tideway Tunnel: purpose, overview, delivery model and financing, 2025).
● 4
Silvertown Tunnel — Design-Build-Finance-Operate-Maintain (DBFOM) concession delivered by the RiverLinx consortium, carrying construction and long-term performance risk; opened 7 April 2025 (Transport for London).
recent schemes had and the worst lacked: a client with enough engineering capability of its own to insist on them. I sometimes think about my twenty-something self
stepping into the Channel Tunnel workings in 1988. The industry that built that project and others in that era took enormous risks and paid dearly for many of them — but it trusted engineers to run engineering. We have spent the decades since building systems to manage that trust: codes, contracts, assurance regimes, consent orders. Much of it was necessary. But process does not overcome the problem the ground will always present to tunnellers; only expertise and judgement can. The proof is already under London, delivered this decade to time and budget. If we want the next generation of major projects to be remembered for their engineering rather than their overruns, we must put tunnel engineers back where the decisions are made — in the contract, and at the very start of it.
12 | September 2026
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
