Design and fabrication of cable bolt for excavation in a fractured rock

Abstract

In fractured rock masses, large excavations have an unsupported stand-up times less than the minimum time required to support the roof after the excavation. Therefore, the principal objective in the design of a support system is to help the rock mass to support itself. The use of rock bolts is a very flexible supporting method that can be combined with wire mesh, shotcrete and concrete lining. During past years a wide variety of dowels and bolt types were developed but most of them failed within a short period and the cost were high. Advantages of cable strand supports have been well documented and include flexibility, strength, and ease of installation. Main objective of this project is to design rock bolts using discarded wire ropes or cables at a low cost. A detailed designing methodology was carried out to fabricate this bolt. The bolt consists of nearly 1.6m long cable and 16 cm of anchored part and cable tightening part. Outer diameter of bolt is 33 mm and inner diameter is 12 mm and used cable diameter is 5mm. Field data illustrated the amount of load measurements that the bolt can carry is 5 kN. Suggestions were made to improve the design, which will enhance bolt performance. Field tests carried out at Bogala Lanka Graphite Ltd proved that cable bolts are effective in Sri Lankan conditions.