Study of the systematic fully grouted rock bolts performance in tunnels considering installation condition of bolt head

A two-dimensional parametric numerical study is conducted to investigate some unknown aspects of the systematic fully grouted rock bolts performance in the stability of tunnels. The influence of the bolt head constraint conditions, i.e. a stiff steel plate on a smooth rigid basement or a rough basement (the rigid and flexible complexes, respectively) on the convergence confinement, development of the plastic band, and the maximum bolt force is studied in a tunnel located at a poor or good rock mass quality. As well, the difference of the tunnel convergence on the bolt head location and in the middle between the two bolts is the other investigated parameter. The results show that for a tunnel excavated in a poor rock mass quality at great depths (very squeezing condition), the difference of convergences must be considered, particularly for large openings in which the spacing of the bolts is not small.