The stability of triple circular tunnels in cohesive-frictional soil subjected to surcharge loading has been numerically investigated assuming plane strain conditions. The centre-to-centre distance appears as a new problem parameter. A continuous loading is applied to the ground surface, and a smooth interface condition is modelled. For a series of tunnel diameter-to-depth ratios and material properties, rigorous lower-and upper-bound solutions for the ultimate surcharge loading are obtained by applying finite element limit analysis techniques. For practical stability, the results are presented in the form of dimensionless stability charts. Finally, a discussion is presented regarding the location of the critical tunnel spacing between triple circular tunnels where interaction no longer occurs.