ABSTRACT
An appearance of underground openings alters a stress field around them that sometimes provokes rock failure. Rock stress state is usually assessed at tunnel face or within boreholes using different types of electromechanical sensors that is laborious, expensive, and sometimes dangerous. Electromagnetic Radiation (EMR) caused by micro-fracturing is a non-destructive method of rock stress assessment. It is caused by the organized oscillation of charges on newly created surfaces in a frequency range kHz–MHz. Since the EMR in the MHz diapason appears much earlier than in the kHz range, it enables a short-term observation of failure transformation. The EMR parameters are related to the fracture length and width while its intensity is associated with rock elastic properties and stress state level. Despite of this comprehensive knowledge, quantitative unbiased criteria of stress assessment in the underground tunnels based on the EMR parameters are lacking yet. Here we consider several aspects related to the development of EMR quantitative criterion as follows: a. precalculation of the targeted EMR signal based on rock physical properties, b. regularity of the EMR attenuation based on the frequency of EMR signals, c. the symptoms of stress transformation from the steady to dangerous level.
