Numerical Evaluation of Top of Rock Profile, Rock Strength and Conductivity-Paper

Paper

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The paper examines how geological variability affects top-of-rock profiles, rock strength and rock-mass conductivity, and how better use of available data can improve design, construction planning and management of unforeseen-ground-condition disputes.<br /><br />For top-of-rock estimation, the authors apply a fractal statistical method that compares elevation differences between borehole pairs at different spacings. A Hong Kong case study shows that estimates from widely spaced boreholes were consistent with closely spaced diaphragm-wall pre-drilling when data came from the same geological structural domain. Including a deeply weathered fault zone produced much larger differences, demonstrating that distinct domains should not be combined indiscriminately.<br /><br />Rock strength varies widely with weathering, depth and lithology. Data from Singapore show that a small number of tests or average values may fail to represent the full strength range, including very strong or weak material. Such gaps can lead to unsuitable designs, equipment or construction methods.<br /><br />Rock-mass conductivity is governed mainly by fracture frequency, aperture and connectivity, rather than intact-rock permeability alone. Test results from granites and the Jurong Series span several orders of magnitude. Large datasets reveal potentially problematic high-conductivity zones that limited testing could miss. Comparisons of packer tests with continuous tunnel probe-hole measurements suggest broadly similar overall results, while also highlighting possible sampling bias in packer testing. Conductivity can be anisotropic, reflecting fracture orientation, drainage paths and in-situ stress.<br /><br />Overall, the paper advocates combining project-specific investigations with relevant published datasets, interpreting results within geological context, and assessing ranges and extremes—not just averages—to characterize ground conditions more reliably.

Keywords

geological variability

top-of-rock profiles

rock strength

rock-mass conductivity

fractal statistical method

borehole spacing

weathering

fault zone

packer tests

ground conditions