ABSTRACT
The response of competent unbolted roofs formed by rock layers of similar rigidity is usually evaluated with the assumption that the lower layers support their own unit weight only; i.e. they are not loaded by the overlying layers. However, it is acknowledged that if the layers may be made artificially thicker, e.g. by bolting, their response may be significantly improved. The friction angle between the layers is an important parameter in enabling the formation of such stronger layers. Its effect on the deflection, the strain and the distribution of the stress in the roof of an underground opening is investigated numerically.
