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Mode I and II Stress Intensity Factors (SIFs) under general loading conditions were determined for a crack parallel to the surface in a two-dimensional half space. To this purpose, a parametric Finite Element (FE) analysis of the subsurface crack was set up, and the analyses were conducted for independent loading conditions. Symmetric and anti-symmetric for both normal and tangential loads were considered and the corresponding SIFs were determined at the two crack tips. Several distances of the crack with respect to the surface were analysed and general functions representing the SIFs versus this parameter were obtained by interpolating the FE results. For both KI and KII, influence coefficients were defined reproducing the FE results with a satisfactory accuracy. When the crack approaches the surface the loss of symmetry was demonstrated to produce coupling effects between modes I and II of fracture. This effect is quantified and some consequences for a general loading condition discussed.