High-resolution tomographic imaging as a basis for geomechanical assessment prior to subsurface excavation

A 3D seismic tomographic data set for both P- and S-wave velocity models has been acquired in an urban setting to assist geomechanical modelling for subsurface excavation. The area poses challenging logistical constraints, but also offers possibilities for an advantageous non-conventional receiver-source geometry, which in turn required creative acquisition design approaches. High-precision geodetic surveys were also necessary to guarantee accuracy of the seismic models, given the small observation distances and high velocities in the hard rock lithology. The seismic velocity models were converted to elastic moduli for an assessment of the stability of the rock mass prior to the excavation.