In situ stress reconstruction using rock memory

[Truncated abstract] Knowledge of in situ stress for underground construction or excavations is important. With an input of in situ stress magnitude/orientations, one can predict the potential failure, improve the efficiency of ground support and/or provide the parameters for numerical modelling/planning to make the design cost effective. In this thesis, two rock memory-based in situ stress measurement methods, the acoustic emission method and the Deformation rate analysis method, were studied. The acoustic emission method utilizes the Kaiser effect to recover the previously applied maximum stress, which is expected to be the in situ stress. The phenomenon that Kaiser has found and the usage of the Kaiser effect for the in situ stress measurement were reviewed, and a series of tests in aluminium, agate, sandstone, ultramafic and slate samples with different conditions in the sample end was performed. The result shows that the Kaiser effect method of the in situ stress determination has severe limitations. Firstly, the asperities/irregularities/residual material at the sample ends at low stress can manifest themselves as the Kaiser effect. This 'ghost' Kaiser effect created by the sample ends is not related to the rock memory and it is an artefact of the test preparation. A thin plastic sheet (TML strain gauge) plus silicone gel can be a buffer material to reduce the noise from end. A multichannel source location system could also be able to detect the origin of signal. Secondly, the process of crack generation/growth can create sufficient change in the stress path in the following loading cycle. Because the Kaiser effect is masked by the acoustic emission associated with the damage accumulation, the acoustic emission could start much earlier than the previous maximum stress. In order to prevent the damage accumulation from imitating the Kaiser effect and misleading the analysis, one should find the stress range in which the Kaiser effect can be detected, before using the Kaiser effect as a stress measurement method...