Effect of rock jointing on the stability of underground workings of the Nurek hydroelectric station

Conclusions

• 1. For evaluating the stability of rocks in underground workings and predicting stability a differential consideration of the effect of geological factors and especially jointing is necessary.

• 2. It was established that the formation of falls in underground workings is due to the presence of a fall-hazardous model of joints. A rock block bounded by this model and located within the arch of the working is fall-hazardous. The shape and spatial arrangement of fall-hazardous blocks are predetermined by the joint systems developed in the rock mass. If the shape of the base of the fall-hazardous block is not isometric, then the orientation of the working influences the formation of the fall-hazardous model.

• 3. It was established that mineral filling of joints as a calcite coating does not have a strengthening effect on the rock. Falls are confined both to joints with and without calcite. The presence of a fall-hazardous model is determining. Joints with loose filling (clay gouge, rubble) not forming a fall-hazardous model do not participate in fall formation. In the absence of a fall-hazardous model the factor of the length and density of joints does not have an effect on fall formation.

• 4. A timely analysis of the rock mass around the tunnel by a geologist in the working under construction makes it possible to give recommendations on the use of temporary support and increases the safety and effectiveness of tunneling operations.