Gravity Effects of Deformation Zones Induced by Tunnelling in Soft and Stiff Clays

We calculated gravity response of geotechnical models of deformation zones induced by tunnelling in two environments - soft clays and stiff clays. Approximately elliptic zones of deformation above the tunnels arise in both cases, but internal structures of the zones are different, and different are also theirs gravity effects. In soft clays, the deformation zone above the tunnel is actually zone of compaction and causes decrease of amplitude of gravity anomaly over the tunnel. In stiff clays a zone of dilatancy occurs next to the tunnel, but an overall gravity effect of deformation zone is insignificant and doesn’t affect the amplitude of gravity anomaly measured above the tunnel at the surface.