This thesis describes the results of a full-scale trial investigating the effects of tunnelling on piled foundations. The fieldwork took place during construction of the new Channel Tunnel Rail Link (CTRL) in the UK, in Contract 250 in Dagenham, Essex.
The contract involved the construction of 5.2km of twin 8.15m diameter bored tunnels using two Lovat Earth Pressure Balance (EPB) shields with tail-skin grouting. Well ahead of tunnel excavation four full-scale instrumented piles were installed above and at offsets from the two tunnels. The driven cast-in-situ piles (0.48m in diameter) were instrumented along their length with sets of strain gauges and inclinometer electrolevels, as well as load cells at their base. Two of the piles were end-bearing in the Terrace Gravels (8.5m long) and the other two were friction piles with their toes in London Clay (13m long). During tunnelling works the piles were loaded with kentledge to about half of their bearing capacities. The study also included comprehensive surface and subsurface instrumentation in the ground close to the piles.
Field measurements of the ‘greenfield’ ground response to tunnelling are presented and compared with the resulting pile response. The results indicate that zones of influence exist around a tunnel where piles are subjected to different degrees of settlement relative to ground settlements. The discussion also entails the load redistribution along the pile lengths as the tunnels approach and pass beneath them and the induced pile deflections and bending moments.
This thesis also describes the response of two piled structures to tunnelling, a three-storey steel-framed piled building and a reinforced concrete piled culvert that were located in close distance to the 'greenfield' instrumented site. The settlements of these structures due to tunnelling are presented and discussed in comparison with the 'greenfield' ground settlements.