The influence of anisotropy on calculations of ground settlements above tunnels

Numerical analyses of ground movements above tunnels in soft ground using linear and isotropic stress strain models often give settlement troughs which are much wider than those observed in practice. Laboratory and in situ measurements of shear wave velocity in London Clay have revealed significant anisotropy in the shear modulus. Finite element analyses of the Heathrow Express trial tunnel have been carried out using a non-linear and anisotropic soil model and the calculated widths of the settlement troughs agree well with those observed in practice. The work demonstrates the significant influence of soil anisotropy on surface settlement troughs above tunnels.