Breakout, stress concentration, sharp corner, stress release, stability, deviatoric stress, cross section, excavation underground excavation in rock which is subjected to stresses that are a significant fraction of the rock strength can cause failure adjacent to the excavation. Recent research on borehole breakouts has shown that a stable breakout is characterized by a stress distribution which is greatly reduced from the original stress state at locations not directly in front of the breakout "tips". Also, the stresses in front of the "tips" are almost hydrostatic. Such a shape is stable and self-supporting. If tunnels or underground excavations incorporate a cross-sectional shape similar to a stable breakout, the cost of support and longterm maintenance could be greatly reduced or possibly eliminated. The proposed research would evaluate the load bearing capacity of different excavation shapes and the feasibility of using a generic breakout shape as an excavation shape in order to reduce cost, time in construction and maintenance. If this phase of the research suggests practical and economic feasibility, phase II of the research would be large scale experiments (a cubic meter and larger) and phase iii would be the commercialization of a tunnel boring or other excavation machines, specifically designed for excavation ofa stable (breakout) cross-section.
