Tunnelling-induced ground and building movement on the Jubilee Line Extension

Paul Dimmock, Cambridge University
Geotechnical Engineering Group

Abstract

This thesis investigates the nature of ground and building movement due to bored tunnelling at five sites along the Jubilee Line Extension (JLE). The primary objectives of the research are two-fold. The first is to link particular phases of the tunnel construction process to resulting ground movement. The second objective is to compare building movement to greenfield movement, and to assess the effectiveness of the Potts and Addenbrooke method (1997) for predicting the influence of building stiffness on green field ground movement.

The sites researched are Southwark Park, Moodkee Street, Keetons Estate, St. James's Park and Elizabeth House. Southwark Park, Moodkee Street and Keetons Estate were affected by an earth pressure balance machine tunnelling through the Lambeth Group and Thanet Sands. Southwark Park is a greenfield site monitored thoroughly for surface and sub-surface ground movement, whereas the monitoring at Moodkee Street and Keetons Estate was on the fašades of low-rise masonry structures. St. James's Park and Elizabeth House are on Contract 102 of the JLE where tunnelling was by open-face excavation in London Clay. At St. James's Park the tunnels were bored by open-face shield but at Elizabeth House the sprayed concrete lining technique was used. St. James's Park is a greenfield site monitored comprehensively for surface and sub-surface movement, pore pressure change and change in total stress. The monitoring at Elizabeth House, on the other hand, was of movement in the basement of a large reinforced concrete frame building, and of ground movement below the building foundations.

The nature of ground movement at Southwark Park and St. James's Park is compared to empirical, numerical and theoretical models. The thesis proposes new ways in which the magnitude of ground movement may be predicted, with an emphasis on the different stages of tunnel construction; a modified approach to the Load Factor Approach (Mair et al, 1981; Macklin, 1999) to estimating volume loss in London Clay is proposed. Also, based on the observed response of the masonry structures studied, guidelines are provided for the estimation of relative stiffness parameters for use in the Potts and Addenbrooke (1997) approach to estimating a structure's influence on tunnelling-induced ground movement. Some evidence of reducing building stiffness with progressive deformation is highlighted. The thesis also relates long-term ground movement, caused by the tunnel acting as a drain, to the observed reduction in pore pressure in the surrounding London Clay. Furthermore, the consolidation associated with the reduction in pore pressure is related to the change in lining load and the extent of lining deformation.