Rock bolt with mechanical anchor

A rock bolt comprising

• a shaft having a first end region, a second end region and a center region joining the first end region and the second end region, and
• an anchoring device operative to retain the bolt when located in a drilled hole and comprising a mandrel mounted to, or integrally formed with, the shaft and at least one expansion element overlaying the mandrel,
• wherein each of the first end region and the second end region includes a first portion with a thread on an outer surface and a second portion without a thread on the outer surface, and the second unthreaded portion is axially outward of the first threaded portion,
• wherein at least one of the mandrel or the at least one expansion element is a movable member and is able to rotate relative to, and move axially along, the shaft, the at least one expansion element being arranged to be displaced radially outwardly on a predetermined relative movement between the mandrel and the at least one expansion element,
• wherein when disposed on the first threaded portion of the shaft, rotation of the movable member relative to the shaft causes axial movement of that member along the shaft, and when disposed on the second unthreaded portion of the shaft, the movable member is able to rotate relative to the outer surface of the shaft without being biased to move axially along the shaft.