Dynamic rockbolt

A friction bolt comprising a first elongate tube having an internal diameter and defining a longitudinal split, the tube being radially expandable, the bolt having a first leading or distal end for insertion into a bore and a second or proximal end defining a head and further comprising a second elongate tube defining a longitudinal split and having an external diameter which is substantially the same as or larger than the internal diameter of the first tube located inside the first tube with its exterior in contact with the interior of the first tube and wherein the bolt comprises a slip and lock mechanism that allows the first or exterior and second or interior tubes to move relative to each other along the longitudinal axis of the friction bolt when a tensile force is applied to the bolt, but to lock together after the force is removed,

• wherein the slip and lock mechanism comprises formations or deformations on one or both of the first and second tubes which interlock the tubes together but which can disengage and allow the tubes to slide relative to one another under longitudinal tension.