Projection of joints from surface to tunnel level — a Case Study |
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| Authors: | L A Brown |
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| Institution: | (1) Division of Geology, U.S. Bureau of Reclamation, Engineering and Research Centre, P.O. Box 25007, 80225 Denver, CO, USA |
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| Abstract: | 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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| Keywords: | Site investigation joint orientation tunnel design joint spacing |
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