Borehole anchor

摘要

An anchor assembly or rockbolt for mounting in a borehole in a rock comprises an outer element which is secured proximal to the mouth of the borehole and an inner element which is secured well inside the borehole. The inner and outer elements are connected together in such a manner as to allow mutual limited shifting thereof without disconnection only on stressing of one of the elements relative to the other beyond a predetermined limit. To this end the outer element may be provided with a piston-like inner end that is slidable against a friction coating within a tubular inner element. It is also possible to form the inner and outer elements as separable tube sections interconnected by means of a central rod having a pair of pistons each received in a respective one of the sections and slidable therein on a tight friction lining thereof.