Support capacity of wedges along tunnels of Egnatia highway

Four tunnels along the under construction Egnatia highway, were studied in N. Greece (Polymylos and Vassilikos areas). The concept was to investigate the changes of the safety factors and the support ability of the wedges, regarding to their dimensions, taking also into account the spacing of the discontinuities. The safety factors of the wedges, as well as their ration before and after support, were correlated significantly with the weights and the volumes of the wedges, using powered regressions. According to these results the efficiency of the support ability of the shotcrete is very high in cases where the rock mass is cracked. There is no difference in safety factor between using only shotcrete and using shotcrete and rockbolts for supporting relatively small wedges. This ability decreases dramatically for bigger wedge volumes, over 20m³ and of weights in cases where these are over about 40tns. In these cases, the shotcrete presents low efficiency and bolting is the main support measure performed.