Engineering geology and case history experience have been relied upon as predictors for several historical East River tunnel crossings, as shown in Figure 1. Differing rock types were crossed, consisting of gneisses, schist, and limestone or dolomite nearly vertical in orientation and part of a complex tightly folded sequence, but deeply weathered along faults parallel to the river. Each crossing had vertical grade requirements, forcing the alignment through known geologic hazards of poor-quality rock and mixed face. The presence of decomposed and highly crushed zones at depth and glacial or man-made deposits further complicated the mixed face conditions for...

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