Stability of cohesive-frictional soils with square underground openings

Stability of foundations laying on cohesive-frictional soils with multiple underground openings (tunnels) of square shape has been analyzed under plane strain conditions. Soil domain was loaded with a uniform surface pressure and a series of tunnel size to depth ratios as well as center-to-center distances have been considered. Rigorous lower and upper bound solutions were obtained by applying numerical limit analysis and presented in the form of dimensionless stability charts for the case of dual tunnel. For comparison purposes several rigid block upper bound mechanisms have been also developed and the obtained values of collapse loads were tested against the results of limit analysis computations.