The behaviour of three calcareous sediments-a muddy silt, a silt and a sand from offshore areas on the North-West Shelf of Australia-is studied through undrained simple shear tests. In monotonic tests, the muddy silt shows contractive behaviour and the silt and sand show dilative behaviour. In cyclic tests, a cyclic mobility failure mode is observed for the three soils. Responses in non-symmetrical cyclic tests were significantly different from those in symmetrical cyclic tests. A 'cyclic phase transformation state', which separates undrained cyclic stress paths into contractive and dilative phases, was identified: this was found to be different from the phase transformation line obtained from monotonic tests, and it is unique for a particular soil. The three soils show strain hardening behaviour in plots of stress ratio against shear strain, which can be characterised by a backbone curve and hysteresis loops.