Abstract
This project examines the interaction of rock stress, fluid pressure and rock properties in initiating caving or strata collapse. The emphasis of the paper is on measurement. In the case of stress, it covers measurement through overcoring, hydrofracture, hydrojacking, borehole breakout and core ovality. Different rock types and stress situations require different methods and each of them has a place. The measurement of fluid pressure can also be undertaken in different ways. Some commonly used methods of testing and installing piezometers give false results. This is important as fluid pressure directly influences effective stress. The other factor in effective stress is how the fluid pressure acts within the rock mass – is it a poroelastic effect, or does it act within fractures? If so, how will the fractures change with mining? What is the changeover in behaviour from one case to the other and how does this impact on rock failure? Determining what might happen requires careful examination of core, geophysical logs and laboratory testing.