Abstract
Stability of multiple underground openings (tunnels) in cohesive-frictional soil subjected to surcharge pressure has been theoretically and numerically investigated assuming plane strain conditions. Unlike the case of a single tunnel, the center-to-center distance appears as a new problem parameter, which plays a key role in tunnel stability. A continuous loading is applied to the ground surface. For a series of tunnel diameter to depth ratios and material properties, rigorous lower and upper bound solutions for the ultimate surcharge pressure which can be exerted on the considered soil mass are obtained by applying recently developed numerical limit analysis. For practical suitability the results are presented in the form of dimensionless stability charts. As an additional check and also a handy practical means, upper bound rigid block mechanisms for dual tunnels have been developed and the predicted collapse loads compared with the results from numerical limit analysis.
