Rock Mass Characterization by High-Resolution Sonic and GSI Borehole Logging

Abstract

We investigate the relationships between the in situ P-wave velocity (Vp) of rock masses, measured by borehole acoustic logging, and their Geological Strength Index (GSI), to support a reliable assessment of equivalent continuum rock mass properties at depth. We quantified both Vp and GSI in three deep boreholes drilled in a crystalline core complex of the central Italian Alps. The boreholes were driven up to 400 m in depth and provided high-quality drill cores in gneiss, schist and metasedimentary rocks with variable lithology. Geological and geomechanical logging was carried out for over 800 m of cores, and acoustic logging was performed for more than 600 m of borehole length. High-resolution core logging in terms of GSI was obtained using an original quantitative approach. Candidate empirical correlation functions linking Vp and GSI were tested by a two-step statistical analysis of the experimental dataset, including outlier removal and nonlinear regression analysis. We propose a sigmoid Vp-GSI equation valid over a depth range between 100 and 400 m. This accounts for extremely variable lithological, weathering and rock mass damage conditions, complementing existing shallow-depth approaches and showing potential for practical applications in different engineering settings.

Damage‐Based Time‐Dependent Modeling of Paraglacial to Postglacial Progressive Failure of Large Rock Slopes

“…Intact rock properties measured in laboratory tests are scaled to field conditions by the Geological Strength Index (GSI, ranging 5–95; Hoek et al, ; Hoek et al, ). This empirical parameter describes rock mass structure and alteration, easily quantified in both outcrops (Marinos & Hoek, ) and borehole data (Agliardi et al, ). The use of GSI allows the estimation of the tensile strength and the equivalent Mohr‐Coulomb cohesion and friction coefficient of rock masses, for use within DaDyn‐RS.…”

“…Detailed geomechanical logging of high‐quality drill cores was carried out on 882 core runs for a total core length of 1,048 m. We reclassified the original descriptions of individual discontinuities (discontinuity type, shape, roughness, weathering, dip angle, aperture, and filling material) and logged fracture intensity for each core run. We processed the data set to obtain different quantitative descriptors of fracture intensity and rock mass quality, including the Weighted Joint Density (Palmstrom, ), the linear fracture intensity, P 10 (Dershowitz & Herda, ), and the Geological Strength Index, GSI (Agliardi et al, ; Hoek et al, ) for each core run (Figure a).…”

Integration of Geological, Mineralogical and Geochemical Methods in the Characterization of El Nitro and Las Alsacias Caves, Zapatoca (Colombia)

“…During karst evolution, underground cavities are controlled not only by the initial structural settings of the rock, but also by the occurrence of fractures represented by joints, faults, fissures, and bedding plane faults (Cooke et al, 1999) and the fluid flow conditions particularly within low porosity rocks (e.g., Klimchouk et al 2000a;Brown, 2004;Bakun-Mazor et al, 2009;Agliardi et al, 2016). The total annual rainfall and annual average temperature data acquired for the station of the Zapatoca stream from 1973 to 2015 (Figure 14) were provided by the information system of the Institute of Hydrology, Meteorology and Environmental Studies -IDEAM (2020), in order to know how recent climate change has been in this region and how this caves are affected, which is characterized by wet winters and dry summers.…”

Structural control on epigenic gypsum caves: evidences from Messinian evaporites (Northern Apennines, Italy)

“…Any karstic subterranean void, however, is influenced by the initial structural settings of the rock mass involved. Natural fractures are important to control stability of underground cavities (Brown and Hoek, 1988;Brown, 2004;Bakun-Mazor et al, 2009;Sciarra et al, 2010;Agliardi et al, 2016) and fluid circulation especially within lowporosity rocks (National Research Council, 1996). In karst areas, fractures represented by joints, faults, fissures, and bedding plane faults (Cooke and Pollard, 1997;Cooke et al, 2000) are often associated with karst evolution and the development of secondary permeability (Klimchouk and Ford, 2000;Klimchouk, 2012).…”