This discussion considers the procedure proposed by Haji, Marshall and Tizani for the assessment of the structural stiffness of frame structures subjected to tunnelling. The discussion focuses on the potential contribution of both shear and bending flexibilities to the response of frame structures to tunnelling, as well as the role of the foundation scheme on the boundary conditions at the base of the structure. The validity of applying the proposed set of equations within currently available methods of prediction of tunnelling-induced deformations, based on modification factors, is also discussed.