A PROBABILISTIC MODEL FOR PREDICTING SANDSTONE STRENGTH USING ELECTROMAGNETIC INDUCTION SOUNDING IN THE SOUTHERN YAKUTIAN PERMAFROST REGION: A CASE STUDY IN NERYUNGRI
L.G. Neradovskii
Melnikov Permafrost Institute, SB RAS, Merzlotnaya str. 36, Yakutsk, 677010, Russia
Keywords: strength, sandstone rock mass, geometric electromagnetic induction sounding, field of high-frequency vertical magnetic dipole, amplitude decrease coefficient, statistics, histograms and variograms, probabilistic model, prediction error
Abstract
This paper presents a retrospective analysis of the geometric electromagnetic induction (EMI) sounding data. The data were acquired in the 1990s in the city of Neryungri to determine probabilistic relationships between unconfined compressive strength of saturated sandstone samples and the attenuation coefficient of the harmonic field induced by a high-frequency vertical magnetic dipole at 1.125 MHz in frozen sandstone rock mass. The results indicate that the consistent increase in the attenuation coefficient with decreasing strength of sandstone rock mass is correctly described by a logistic function equation. The inverse regression relationship is adequately described by a power function equation which can be used as a probabilistic model for predicting mean values of unconfined compressive strength of saturated sandstone rock mass (but not only sandstone rock samples) from the attenuation coefficient. The relative error of model predictions at the 70-80 % confidence level is ±(27.7-32) %, which is close to the limit of allowable error (±20.0 %) for laboratory measurements of mean strength of rock samples. This provides favorable conditions for applying the geometric EMI method in rock strength mapping for geotechnical engineering in Neryungri, as well as in areas of similar geology in southern Yakutia with sporadic permafrost.
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