Introduction

During the preliminary study concerning the construction of the Salonique subway 64 geotechnical boreholes have been constructed. A geotechnical well logging survey has been carried out to localize with accuracy the layers’ interfaces and to measure the shale content of each layer in the lithology column. 

Field works

In all logs, the natural gamma ray radiation of layers has been recorded.

The geophysical well logging system has been used for this purpose. Borehole data have been recorded in analog and digital form (resolution 12 bit). All natural gamma ray measurements have been carried out with a constant cable speed of 4 m/min, time of 5 sec and frequency of 100 Hz. The boreholes have one average depth of 30 m below the ground surface.

Data interpretation

 In all borehole records, the following interpretation has been applied:

• conversion in API units

• determination of the “clean shale” and “clean sand” lines

• calibration with the drillers log and reconstruction of the lithology column

• calculation of the “shale content” for each layer in the column

• synthetic interpretation of the well logs (cross-correlation of the logs to identify layers interfaces)

Conclusion