Settlement, rotation and distortion OfPiccadilly Line tunnels at Heathrow

This paper is based on monitoring results obtained during the construction of the new Heathrow Express tunnels in London, where at the Central Terminal Area (CTA), in London Clay, three large tunnels pass beneath the existing Piccadilly Line Tunnels with limited clearance. Extensive monitoring was undertaken in the existing tunnels including precise levelling and distortion checks. Aspects of the settlement have been reported in a previous paper ( Cooper and Chapman, 1998 ). The results have been analysed and curves showing settlement, rotation and distortion along the existing tunnels are presented in the present paper. The results are discussed and conclusions are presented. Analysis is presented of the asymmetry noticed in the settlement curves caused by driving a second tunnel alongside the initial tunnel. A comparison is made with relevant previously published work.