The response of full-scale piles to tunnelling

Abstract

The construction of the new Channel Tunnel Rail Link (CTRL) in the UK provided a unique opportunity to monitor the response of full-scale piles to tunnelling-induced movements.This paper presents the results of a full-scale trial, which took place during the construction of CTRL Contract 250 in Dagenham, Essex, UK.Thecontractinvolvedtheconstructionof5.2kmoftwin8mdiameterboredtunnelsusingaLovatEarthPres- sureBalanceshieldwithtail-skingrouting.Wellaheadoftunnelexcavationfourinstrumenteddrivencast-in-situ reinforced concrete piles were installed above and at an offset from the two tunnels. All four piles were loaded usingkentledgetoloadsofupto50%oftheirultimatecarryingcapacity.Theintentionwastomaintaintheseloads during tunnelling which at the site of interest took place though London Clay.The study also included the instal- lation of several surface settlement monitoring stations to measure the profile of 'greenfield'ground surface dis- placement.Thispaperdiscussestheresultingchangesinthepilebaseloadandtheassociatedpilesettlementdueto tunnel construction.The comparison of ground and pile surface settlements due to tunnelling indicated that three zones of influence exist around a tunnel in which pile settlement can be correlated to 'greenfield'ground surface settlement.