Precursors for rock fracturing and failure—Part II: IRR T-Curve abnormalities

There are many precursors including the abnormality of infrared radiation (IRR) for rock fracturing. The temporal evolution of surface IRR from loaded rock is the combined effect of rock thermoelasticity, pore gas desorbing–escaping, fracture propagation and extension, rock friction, heat transfer and environmental radiation. Being the integral indicator of the surface IRR energy, the mean IRR temperature (AIRT) is selected as the quantitative index to study the temporal evolution of IRR from loaded rock and to identify the precursors for rock fracturing and failure. This paper introduces some typical AIRT curves of uniaxially loaded, compressively sheared and biaxially loaded rock samples. The temporal evolution features of the AIRT curves and three precursor messages, which are short dropping, fast rising and dropping-to-rising, for rock fracturing are analyzed. For theoretical interpretation, the mechanism of AIRT abnormality is studied by taking the actuator, the rock sample and the environment as an independent system in an energy balance state. The heat transfer, as well as the thermoelastic effect based on the sum of principal stresses, has a positive or negative effect on AIRT; the desorbing and escaping of pore gas, as well as the production of new fractures and the expansion of initial fissures, joints and new produced fractures, have a negative effect on AIRT, while the friction action between fractures and between grains has a positive effect on AIRT. It is concluded that the occurrence of precursors is at 77–94% rock strength, i.e., stress peak, and the compressively loaded rock and biaxially loaded rock have clear AIRT precursors for rock fracturing and failure.