Comparing geological process-based and engineering data-based approaches to characterizing rock mass heterogeneities : insights from the Great Glen Fault, Scotland

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Kim, Namgwon and Shipton, Zoe K. and Kremer, Yannick and Jack, Christopher D. (2026) Comparing geological process-based and engineering data-based approaches to characterizing rock mass heterogeneities : insights from the Great Glen Fault, Scotland. Engineering Geology, 362. 108529. ISSN 0013-7952 (https://doi.org/10.1016/j.enggeo.2025.108529)

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Abstract

In rock engineering, understanding variability in rock mass properties is essential for planning engineering mitigations. The differences between engineering and geological approaches to characterizing rock masses can result in varying estimates of mechanical and/or hydraulic properties. This study applies these approaches in parallel: mapping geological domains, fracture traces and Q-values. The aim is to reveal the relationship between variability in geological and engineering parameters at a case study site in the Torcastle block, a fault-bounded sliver within the Great Glen Fault (GGF) that has a complex internal architecture. Distinct geological domains are defined based on lithology (including two generations of dyke intrusion), foliation, faults, and fracture pattern. Fractures are classified into several geometrical categories mainly based on geometrical relationships with local faults and foliations: foliation-parallel, foliation-bounded, foliation-crossing, and ladder-like fractures. Their spatial distribution correlates with the local trend of pre-existing foliations and dykes. For the engineering characterisation we used Q-value mapping, modified for surface conditions, with a moving window approach. Low Q-value zones are spatially heterogeneous but concordant with areas of high fracture density and intersections (topological X and Y nodes), typically associated with: (1) major shear or fault strands and embedded blocks; (2) intruded igneous dykes; (3) areas where faults with different orientations abut; and (4) highly rotated blocks showing re-oriented local foliations. Cross-plots of Q-value against geological fracture and engineering parameters notably reveal that increased fracture connectivity and orientation variability contribute to low Q-values, resulting from abundant foliation-crossing fractures in highly rotated blocks with relatively low fracture density. The geological and engineering variabilities in the Torcastle block highlight the close interplay between the geological deformation history and resultant rock mass conditions. We argue that combining detailed structural geological insight into engineering rock mass characterisation will result in more robust forecasting of engineering properties in rock masses, thereby reducing geotechnical risks.

ORCID iDs

Kim, Namgwon, Shipton, Zoe K. ORCID logoORCID: https://orcid.org/0000-0002-2268-7750, Kremer, Yannick ORCID logoORCID: https://orcid.org/0000-0002-5686-6351 and Jack, Christopher D.;
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