Unsaturated constant water content triaxial compression tests with suction measurement using an Imperial College Tensiometer, and saturated consolidated undrained tests were carried out on reconstituted Brickearth, a naturally unsaturated clayey silt from London. The results show that the saturated effective stress can be applied to the critical state line (CSL) and normalised stiffness for unsaturated Brickearth but that Bishop’s effective stress variable gives a slightly improved CSL. The stiffness derived from local instrumentation demonstrates that Bishop’s effective stress is also beneficial for normalising the stiffness 16modulus over the small strain range (up to axial strainsofabout3%).