On 12 January 2004, Amec Capital Projects broke through its 3,295m long Little Marlow tunnel drive in Buckinghamshire, UK.
The project was undertaken for the client, Thames Water, as part of an upgrade for the High Wycombe Sewage Treatment Works. A Lovat 131 EPBM bored in closed mode for the entire length of the tunnel. Geology encountered was chalk of up to 15MPa with occasional bands of flint and there was no recorded settlement along the length of the drive at surface, said a spokesman for Thames Water.
Tunnel depth below surface varied from a maximum of 90m under Marlow Hill to just 10m at the reception shaft. A 2.85m i.d. bolted six-piece trapezoidal lining was installed as part of the work cycle. The shift pattern worked was two 12hr shifts Monday to Thursday, with two 8hr shifts on a Friday. Despite this, peak advance rates achieved were 260m in one week, 64m in a 24hr period and 34m in a single shift.
Overall the project was tendered on 13m per shift and the average advance achieved was between 12m and 13m. Andy Sefton, the Thames Water representative on site, told T&TI they were “very happy with the performance of the Lovat machine.”
The budget for tunnelling was US$28M and to date work has been carried out within budget.
Stuart Shurlock, Thames Water’s project manager, said: “The breakthrough at Little Marlow is a significant milestone towards major environmental improvements at High Wycombe and a significant increase in river quality for the whole area.”
