Abstract The present study investigates the influences of the confining pressure and the intermediate principal stress on the mechanical behaviour of a porous limestone. True triaxial tests are carried out on a broad range of confining stresses covering both brittle and ductile regimes. The experiments included the special cases of triaxial compression, extension and isotropic compression, as well as tests at constant levels of the intermediate principal stress. The resulting stress–strain curves and yield stresses are then discussed. Three-dimensional yield envelopes are subsequently built in meridian and octahedral planes. The shape of the octahedral sections changes with the mean stress from triangular to hexagonal and then quasi circular. At even higher mean stresses, the evolution continues towards a triangle with apexes oriented in the direction of triaxial extension stress states. Various existing yield criteria are fitted and compared to the experimental data. Finally, a three-dimensional yield surface is proposed combining the previous observations.