Anchors or rockbolts are reinforcements (usually made of steel) which are inserted into the ground to increase its stiffness and strength. There are various sorts of reinforcement actions and the corresponding terminology is not uniform.
The following terminology is used in soil mechanics:
If the reinforcement bar is fixed only at its both ends, then it is called an ‘anchor’. Anchors can be pre-stressed or not, in the latter case they assume force only after some extension (e.g. due to convergence of the tunnel).
If the reinforcement bar is connected to the surrounding ground over its entire length, then it is called a ‘nail’ or ‘bolt’. The connection can be achieved with cement mortar (Fig. 15.1).