Stabilizing and stability control of a cave-prone area in the Tverrfjellet mine, Norway

In the Tverrfjellet Mine, mid Norway, serious stability problems have developed in connection with large open mining stopes. The problems may be related to high in situ horizontal rock stresses combined with unfavourable geometry. To stabilize the most critical area cable bolting has been used. Closely associated with the stabilizing measures is a caving warning system based upon eight borehole extensometers. Deformations in the rock mass in excess of 1 mm on any one of the extensometers will trigger red stop lights in vital haulageways passing through the threatened area. In the most critical area the deformation is continually monitored. About 1 ½ yr of operation have shown a steady decrease in deformation rate, indicating that the cable bolting works as planned. However, small deformations still take place, necessitating keeping the warning system operative until new by-pass haulageways are established.

The rock mechanics program in the mine also includes rock stress measurements and monitoring of stress change. A modified version of the doorstopper used for stress change monitoring has proved very promising.