During the excavation of the underground openings of Ertan Hydraulic Project in P. R. China, a large range of longitudinal splitting cracks zone appeared in the rock pillars between the main house and transformer house that were within the deep embedded and high-pressured surrounding rock masses. In order to study and predict the failure zone and the quantities of cracks, plate theory and energy dissipation principle are used together, which have been verified by numerical analyses. The prediction formula is set up. It can estimate the crack numbers of the failure zone. In addition, using the finite differential software Flac3D. the strain-softening model is adopted, as it is appropriate for brittle rock masses, by tracing the whole process of elastic energy variation of each element and memorizing the energy difference of before and after failure. Accordingly, the splitting cracks are predicted. The numerical analysis results arc almost agreed with the results by prediction formula.
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