In the literature, the plane-strain assumption usually forms the basis of inverse analyses of excavations, mainly due to the high computational cost of 3D analyses. In this paper, a procedure that quantifies three-dimensional effects of excavation is proposed. Such three-dimensional effects are represented as an uncertainty term that corrects plane-strain-based predictions, thereby offering an alternative approach to perform 3D inverse analysis without excessive computations. The results of an inverse analysis performed on an excavation case history show that (i) the procedure is able to quantify three-dimensional effects reasonably well and (ii) improved predictions of excavation field responses can be obtained.