ABSTRACT
The rock mass is mainly made of siltstones which exhibit visual transfer from the completely weathered zone with yellow color through highly weathered, moderately weathered and slightly weathered deposits all the way to completely fresh rock mass colored gray and blue. With completely weathered siltstones, the rock mass is completely disintegrated, but the original structure of the rock mass has stayed intact (ISRM 1978). The layer of fresh siltstone rock has no visible weathering marks, except for color change on the main discontinuity surfaces. During decomposition of singular weathering zones of the flysch rock mass, along with visual check of the material from test drills, significant contribution came from results from geophysical measurements with surface seismic refraction methods and down-hole seismic method (Arbanas et al. 2007a).
