Low-volume-loss tunnelling for London ring main extension

Abstract

The Thames Water ring main extension is a 4·5 km long tunnel from Stoke Newington, in the London borough of Hackney, to New River Head in Finsbury, in the London borough of Islington. The 2·85 m i.d. tunnel was excavated by an earth pressure balance tunnel-boring machine (TBM) at depths between 40 and 60 m below the surface. Surface settlements along the route were measured by precise levelling, and were found to be small. It was therefore even more important to measure these settlements as accurately as possible, in order to provide informed estimates of subsurface movements induced in third-party underground structures much closer to the tunnel horizon. Because of the relatively large magnitude of the background movements measured, when compared with the small tunnel-induced settlements, it was necessary to adopt a rigorous statistical method to fit a Gaussian curve to the data. This exploited the analogy of the ‘error function' to define the Gaussian curve parameters i and Vl. In all, 13 tunnels were underpassed successfully by the TBM, all within the ‘conservative expected value' predictions, and without incident. The predictions and structural monitoring schemes undertaken for the High Speed 1 tunnels near Corsica Street and the Northern line tunnels near Angel station are described in the paper. It was found that the surface and subsurface trough width parameter K did not vary with depth as predicted: therefore a new relationship is proposed.

Greenfield tunnelling in sands: the effects of soil density and relative depth

“…It is worth noting that Jones (2010) showed that the Mair et al (1993) expression can overestimate the value of K for deep tunnels. Based on field data measurements, Jones proposed a logarithmic formula for the prediction of K which depends on the height above the tunnel z t À z rather than the relative depth z/z t .…”

Monitoring and Analysis of Ground Settlement Induced by Tunnelling with Slurry Pressure‐Balanced Tunnel Boring Machine

“…en, concrete segment lining is installed just rear of the shield skin plate as a permanent ground supporting structure, where simultaneous backfilling of pressurized grout is also conducted at the annulus gap around the segment lining to restrict excessive radial contraction of the excavated ground. According to the field observations in the literatures [2][3][4], ground settlement during shield TBM tunnelling develops in the following steps in accordance with the abovementioned ground supporting mechanisms: (1) before and during tunnel face excavation, (2) during passage of the shield skin plate, and (3) after installation of segmental lining and backfill grouting.…”

Editorial

“…Finally in this special issue Jones (2010) presents predictions for, and actual sub surface movement measurements of, underground structures adjacent to an extension to the Thames Water Ring main tunnel in North London. This case history indicated that the tunnelling settlement trough width parameter K did not vary with depth as predicted, leading to a new relationship being proposed…”