In order to understand how the in-situ primary stress state has evolved with subsidence
and uplift in a granitic rock mass for anticipated of a radioactive waste repository
in Hungary, the authors investigated the applicability of seismic tomography as an
interpretive tool. Very high P wave velocity (Vp) values were obtained during the
tomographic scanning of the study area of the repository, and these were compared
with existing findings of in-situ and laboratory seismic measurements.Apart from seismic
tomographic survey, dynamic FEM numerical modelling, empirical calculations of residual
stresses, laboratory measurements of compression wave (ultrasonic) velocities on intact
rock cores, in-situ primary stress measurements as well as site geological model were
integrated to evaluate the use of seismic tomography for identifying possible in-situ
stress increases around the excavation.A detailed calibration modelling was carried
out based on the site seismic tomography measurements and during the large-scale modelling.
It was observed that the increasing Vp is directly related to simulated increasing
directional loadings on the rock mass. Using a measured wave raypath it was possible
to check the different in-situ stress parametrizations which resulted in the best
approximation to the measured Vp values.It was concluded that the rock mass under
investigation to extend the repository must have higher in-situ stress values than
the area of the constructed deposition chambers nearby. The results of this research
indicated that seismic tomography is a useful tool for determining relative stress
around and within the vicinity of underground excavation.
