Mechanical anchor for use in soft or highly fissured ground : Ground Engng, V11, N1, Jan 1978, P23–25

Abstract

In this article the author describes 40mm diameter mechanical anchors that have been designed specifically to function in the weaker rocks similar to the chalk encountered at Chinnor. The self-under-reaming reversed expanding (SURE) rock anchor has segments which expand over a cone in the reverse direction to a conventional anchor until locked between the cone and a cup. The radial force applied to the ground by the SURE anchor acts inwards, the rock is drawn into the path of the anchor and its ability to resist the load applied is enhanced. The SURE Anchor was designed for use in soft or high fissured ground where existing anchors may not develop adequate loads. The anchor was originally developed for chalk, however its use could be extended to other weak rocks as well as in artificial materials such as poor concrete. In very bad ground it is possible to distribute the load applied to the ground as does a resin anchor, by stacking anchors. Although the SURE anchor was designed with a nominal 40 mm retracted diameter, the design could be adapted to a greater diameter. A larger version can be designed to open to a proportionately greater span and withstand a 90kn load before failure of the steel. The cost of the SURE anchor is more than the conventional mechanism anchor, however the SURE anchor is designed to function in weak rock, alternative methods of suport in such circumstances, using concrete or steelwork would be more expensive.