Crosshole seismic tomography to assess rock mass foundation of dams - Alto Ceira II dam case study

Abstract

Crosshole seismic tomography is a widespread geophysical method to estimate the elastic properties of materials in the crosshole section, for a variety of applications, including engineering site characterisation and foundation treatment evaluation. This method was applied to Alto Ceira II dam in three phases: Phases 1 and 2 – before and after rock mass foundation treatment, and Phase 3 – after the reservoir first filling. The resulting time-lapse seismic tomographies allowed assessing the schist and greywacke rock mass foundation treatment, and the influence of the reservoir filling. This study demonstrated that the method can be used as a management tool to evaluate the rock mass behaviour along the dam’s construction phase and during its working lifetime.