Abstract This paper presents some experimental results from hydromechanical shear tests and an improved version of the original model suggested by Barton (Office of Nuclear Waste Isolation, Columbus, Ohio, ONWI-308, 1982. 96pp.) for the hydromechanical coupling of rock joints. The original model was developed for coupling between mechanical and hydraulic aperture change during normal loading and unloading. The method was also suggested for the coupling of shear dilation and hydraulic aperture changes. The improved model has the same appearance as the original and is based on hydromechanical shear experiments on granite rock joints. It includes both the mechanical and hydraulic aperture and the mobilised joint roughness coefficient (JRC mob ).