The influence of bored piles on existing tunnels

• Main Author: Schroeder, Felix Christian
• Other Authors: Addenbrooke, Trevor ; Potts, Dave
• Published: Imperial College London 2003
• Subjects: 624.193
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397447

In the urban environment, deep foundations are often constructed in locations very close to existing tunnels. Many tunnels can often only tolerate minimal movements. Tunnel owners are concerned that the process of bored pile construction and/or the subsequent loading of the piles may cause intolerable movements or stress levels that might cause cracking of the tunnel linings. Over the last thirty years tunnel owners have developed restrictive guidelines based on their experience of the problem. This thesis investigates the influence of bored piles on existing tunnels using the finite element method and field measurements. In this thesis the finite element method was used to analyse the effects of bored pile construction and pile loading on existing tunnels in two separate analyses. The numerical results were supplemented with field measurement of the pile-tunnel interaction problem at a site in central London. It is shown that in order to adequately model the influence of bored pile construction on a nearby tunnel three dimensional analyses are required. Based on three dimensional analyses of the loading of rows of piles a plane strain approach is developed for the analyses of the influence of pile loading on existing tunnels. A general shell element for use in three dimensional finite element analyses has been developed from basic principles. The development, implementation and testing of this new element type in the Imperial College Finite Element Program (ICFEP) element library is presented and the element is then used to analyse the effects of a dry excavation of a pile bore in the close vicinity of an existing tunnel. The research presented in this thesis has led to a significantly improved understanding of the pile-tunnel interaction problem. It has been shown that there are many influential factors in the assessment of the influence of pile loading on nearby tunnels and that due to the number of influential factors it is not possible to produce simple design charts that are universally applicable. Therefore, it is concluded that universal guidelines based on just a single parameter, such as the specification of the minimum pile offset developed by the tunnel owners, are necessarily conservative with regards to pile loading and that job specific assessments of the influence of pile loading on adjacent tunnels may lead to economies in the design of building foundations.