Due to local conditions (stress field, damage, pore space connectivity, ventilation, degree of saturation) rock parameters change with time. In particular, signals from disturbances caused by the borehole, such as identified BdZ, can be corrected for or, with wide enough separation between emitters and receivers, even neglected. Results from MSM closely sample the actual local in situ conditions. We consider the MSM to be a suitable tool to bridge in situ rock-mechanical results, results from laboratory testing, and results stemming from thermo- and hydro-mechanical modelling. The interdependence/applicability of the methodologies is given in Fig. In addition, we used a wide range of seismic monitoring tasks and targeted repetition of measurements to assess evolution of the rock mass with respect to seismic characteristics. The in situ investigations were conducted in single boreholes, between boreholes, non-destructively along and between drifts, and in combinations of these situations. ( 2017a), this issue) present an overview of the experiments and sites where the MSM have been applied. In addition, combining results from MSM with those derived under laboratory conditions (mostly static tests) on cores can improve our understanding and interpretation of rock-mechanical modelling. Our main objective here is to draw attention to in situ, high-resolution mini-seismic methods and their ability to provide real in situ results for a better understanding of in situ rock-mechanical properties. Other aspects appropriate for study using our MSM methods and concepts, such as detection and characterization of fault structures, seismic long-term monitoring to characterise evolution of the EDZ (generation and self-sealing), and evolution of backfill material (sand-bentonite), are presented in other papers in this issue (e.g., Jaeggi et al. Seismic anisotropy measured at different scales. Small-scale variability of the Opalinus Clay, Out of all the numerous results achieved during the last years, this present contribution focuses on the following issues: The mutual inspiration and open discussions between experiment partners has enabled comprehensive interpretation of the mini-seismic results and furthered continuous development of MSM. Most of the experiments were closely linked to questions concerning geological, geotechnical, or rock-mechanical questions. Since 1996, BGR has carried out MSM in the Mont Terri rock laboratory in close cooperation with experiment partners. To address these inherent complexities with an appropriate spatial resolution, we need high-resolution mini-seismic measurements (MSM). For example, each facies has a pronounced bedding-related anisotropy resulting in transverse isotropic (TVI) seismic parameters and significant small-scale variations of rock properties of different intensities at several sites due to small-scale heterogeneities. The Opalinus Clay at the Mont Terri rock laboratory can be differentiated into three facies (shaly, sandy, and carbonate-rich sandy), all of which possess different petrophysical properties (Bock 2002 Bossart and Thury 2008). Finally, we quantify seismic anisotropy at dimensions between several cm and tens of m. The evolution of borehole-disturbed zones (BdZ) was deduced from repeating high-resolution borehole measurements. We also present examples of the characterization of excavation-damaged zones with seismic parameters, including extent as well as degree of damage, and compare these to geological and structural mapping. We describe the extremely large, small-scale variability of seismic parameters normal and parallel to the bedding plane orientation and address the question of fracture detection. We were able to establish a correlation between static and dynamic elastic Young’s moduli. Both, seismic P- and S-wave velocities and dynamic elastic parameters, such as the dynamic Poisson’s ratio υ dyn and the Young’s modulus E dyn, are used to characterise the Opalinus Clay under real in situ conditions. The complexity of the local site setting always required very high spatial and parameter resolution. All these applications aimed at correlating and interpreting seismically derived parameters with relevant rock-mechanical parameters and findings. We present several mini-seismic methods developed and applied in recent years in the Mont Terri rock laboratory.
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