Issue 29

L. Contrafatto et alii, Frattura ed Integrità Strutturale, 29 (2014) 196-208; DOI: 10.3221/IGF-ESIS.29.17 198 limestone. The second numeric field identifies the diameter of the bar. The third numeric field identifies the embedment depth L of the bar. The last numeric field identifies the number of the sample for each series. Typically 3 samples in each series were tested. (a) (b) Figure 1 : Testing apparatus (a) and triangular reaction frame (b) . The failure mechanism of anchors in basalt and limestone was typically the yielding of the bar for an embedment length equal to five or ten times the diameter (see Fig. 2). (a) (b) Figure 2 : Typical failure mechanisms in the case L=10  Basalt test B-10-10-1 (a) and limestone test C-14-10-2 (b). Only for the length of anchor L=3  the breaking process exhibited the formation of a stone cone, eventually coupled with sliding at the rock/resin interface (see Fig. 3(a)). On the contrary, in the case of sandstone, for each diameter and anchor length the failure was accompanied by the formation of a stone cone (see Fig. 3(c)). (a) (b) (c) Figure 3 : Typical failure mechanisms in the case L=3  Basalt test B-10-3-2 (a) Limestone test C-14-3-2 (b) Sandstone test A-14-3-3(c)