Technical Report NTB 88-33

Site characterization and validationBorehole radar investigations, Stage 1

The borehole radar investigation program of the SCV­site has comprised single hole reflection measurements with centre frequencies of 22, 45, and 60 MHz. Crosshole tomographic measurements have been made between the boreholes W1-W2, N2-N3, N3-N4, and N2-N4. Crosshole reflection measurements have also been made between the same boreholes. The radar range obtained in the single hole reflection measurements was approximately 100 m for the lower frequency (22 MHz) and about 60 m for the centre frequency 45 MHz. In the crosshole measurements transmitter-receiver separations from 60 to 200 m have been used.


The radar investigations have given a three dimensional description of the structure at the SCV­site. A generalized model of the site has been produced which includes three major zones (RA, RB, and RH), four minor zones (RC, RD, RK, and RL), and a circular feature (RQ). These features are considered to be the most significant at the site. Smaller features than the ones included in the generalized model certainly exist but no additional features comparable to the three major zones are thought to exist. The results indicate that the zones are not homogeneous but rather that they are highly irregular containing parts of considerably increased fracturing and parts where their contrast to the background rock is quite small. The zones appear to be approximately planar at least at the scale of the site. At a smaller scale the zones can appear quite irregular.