Critical Extensile Strain Theory
The minimum principal strain at peak load point is extension and its value is insensitive to such conditions as confining pressure, water contents, etc. although it is slightly affected by strain rate.
Critical extensile strain theory is a new criterion for brittle failure of rock. This theory states that the critical extensile srain, which is the extensile strain at peak load point, is insensitive to experimental conditions such as confining pressure, loading rate, water content and anisotropy.
It should be noted that strain is not a differential but total one (zero-balanced before the confining pressure was applied). An attempt to find a rigorous theoretical basis is carried out using molecular dynamics method.
Stability monitoring of underground caverns can be thought of as an application of this theory. Actually, stability of bolted roadways is evaluated from measured tensile strain value in British, Australian and Japanese coal mines.
Critical extensile strain is insensitive to the confining pressure.