The Effects of Relative Tunnel Depth and Volume Loss on Vertical Settlements above Tunnels in Dense Sands

Past studies have provided data on the variation of settlement distribution above relatively shallow tunnels in sands. There is, however, a lack of research that considers the case of relatively deep tunnels. This paper compares the results of a set of plane-strain centrifuge tests in dry dense sands. The cover-to-diameter ratio, C/D, of the tunnels ranged between 1.3 and 6.3, thereby including relatively shallow and deep tunnels. Ground movements are measured using an image-based measurement technique. Gaussian curves are fitted to the settlement data in order to evaluate the characteristics of the settlement profiles. An assessment of greenfield settlement trough shape, both at the surface and subsurface, is carried out. The effect that relative tunnel depth and volume loss has on the settlement trough shape is demonstrated and discussed. The results indicate a non-linear trend of settlement trough shape with C/D, which suggest a transition between shallow and deep tunnels within the investigated C/D range. To account for highlighted results, new relationships are proposed to estimate settlement trough shape parameters in dense sands.