Summary
A joint-study of a granitic batholith recorded orientations and spacings of joint-sets at outcrop and at three separate sections of a water diversion tunnel. A second joint-survey in the tunnel determined the average joint spacing along the spring lines. Joint-set spacing studies show a 40–50% reduction of joint-set spacing underground, compared to those at the surface. Individual equal-area plots of surface joints for the two major facies of the granitic rock showed different maxima. But when the joints in the two facies were combined into one equal-area plot, the predominent facies, which represented 73% of the joints plotted, masked the prominent sets of the second facies. Hence, joint surveys for individual rock facies are warranted. Comparison of equal-area plots of surface and tunnel joints in the same rock facies reveals a striking similarity in joint-set maxima.
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References
Brown, Lynn A. (1987) Correlation of tunnel support loads with geology,Bulletin of the Association of Engineering Geologists 24, 15–26.
Tweto, O. and Pearson, R.C. (1964) St Kevin Granite, Sawatch Range, Colorado.United States Geological Survey Professional Paper 475: D 28-D 32.
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Brown, L.A. Projection of joints from surface to tunnel level — a Case Study. International Journal of Mining and Geological Engineering 5, 321–329 (1987). https://doi.org/10.1007/BF01560782
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DOI: https://doi.org/10.1007/BF01560782