The results of stress measuring in quasi-plastic salt rocks and brittle sandstones are presented in article. Stresses were monitored in interchamber pillars using Goodman's hydraulic borehole jack. Acoustic-emission (AE) intensity was recorded as borehole walls were loaded. From in-situ experiment analysis data, Kaiser effect was found to express itself in various modes in quasi-plastic and brittle rocks. Thus, when a stress level determined by overlying rock weight is reached in salt rocks, AE activity increases drastically, followed by a smooth increase in intensity as borehole walls were loaded further. According to laboratory experiments, AE in salt rocks is due primarily to tension micro-fractures which nucleate at grain boundaries. Vertical stresses are distributed smoothly throughout pillar cross-section, bearing pressure areas being visible clearly. Kaiser effect expresses itself in sandstone as an isolated AE activity surge which is most likely due to accumulated elastic energy being transformed to irreversible shear strains at the existing relaxation surfaces. When moving away from pillar boundaries, dodging variation type of vertical stresses could be seen, without any pronounced bearing pressure areas which appears to be due to block-type structure of the massif.
When estimating stability of underground structure components, one of the main stages is study of stress distribution in the marginal massif. Since the 1970s, many published papers have dealt with development of experimental stress-measuring techniques [1]. Most of the methods use various ways of relief the massif and followed by converting strain to stresses, which often results in significant errors. Measuring techniques based on the Kaiser effect have been developed for stress determination in heterogeneous rocks. At present acoustic emission (AE) memory effect has been detected in most rocks also in cohesive and granular soils [2–4]. In the main, stress determination reports are devoted to laboratory experiments which were consisted in testing of rock samples taken from a massif.
