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A general method for evaluating the fracture mechanics parameters of asubsurface crack parallel to the free surface of a semiplane is presented. A Weight Function(WF) with a matrix like structure is proposed to account for the coupling effects arising innon-symmetrical problems. An estimate of the WF accuracy is presented and a practicalapplication is considered by evaluating the Stress Intensity Factors produced by a point likeload travelling on the semiplane free surface. The complete analysis of this problemrequires crack closure (either complete or partial) to be taken into account. Indeed differentclosure conditions are expected for different load positions or inclination. A theoreticalmethod is proposed, that, starting from the matrix like structure of the WF, allows for thecalculation of the Green Functions, by which the COD components of a subsurface crack scan be calculated under general loading conditions including those produced by crackclosure.