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ABSRACT
The growing use of friction rock bolts has raised theimportance of their design improvement, which, among other results, can result in ensuringtheir safer application in tunnels. At present, studies are underway at various scientific centers to increase the efficiency of rock bolts focusing on the properties of rock bolt performance in connection with elasticity and deformational characteristics of rocks, as well as perfection of rock bolt designs and methods of improving their working capacity, prevention of corrosion, etc
A proposed new design of a friction rock bolt consists of a metal tube and a bearing plate. A steel tube has a 3-4mm groove along the whole length. Before being placed into a borehole, a tube is filled with special expandable solution. During the hardening and expansion of solution, pressure (50-70MPa) develops on tube walls. Under pressure a tube opens around a groove allowing a close contact between tube and borehole surfaces, which leads to the operation of a rock bolt.
This paper describes results of computer modeling of stress condition of rocks around a rock bolt and tests conducted to establish the rock bolt capacity in different geological and technical conditions.
Keywords: Rock bolt, Expandable solution, Tunnel, Clampingforce
INTRODUCTION
Rock bolts started to be used for supporting tunnels in the 1920s. Their role in building shafts has become dominant in various countries, including the US, Australia, the UK and Canada, in the last 10-15 years. According to experts' estimates, about 250 million rock bolts are used each year for supporting tunnels in the shafts and mines in various countries. Experience shows that rock bolts are reliable for ensuring the stability of rock and have advantages over traditional means of support. Rock bolts are supplied in a variety of types [1,2,3] differing in terms of design and installation requirements. The most widely applied rock bolts can be grouped into three categories (table 1).
Mechanic rock bolt disadvantages include their low efficiency in soft rocks and low corrosion resistance. Epoxide rock bolts are also expensive and require longer setting time.
The last 10-15 years saw a particularly wide use of friction Split Set and Swellex tubular rock...