This paper presents resistance envelope equations for open-ended caissons, considering failure of the soil inside the caisson (i.e internal scooping). Equations for assessment of failure envelopes of caissons installed in undrained soil were developed by Kay&Palix (2011) for various embedded Length (L) over Diameter (D) ratios and varying undrained shear strength profiles. One of the assumptions in Kay & Palix (2011) is a solid caisson, which implies no possibility of internal scooping failure. 3D finite element software was used to assess equations for VHM failure envelopes for open-ended caissons with various embedment (L/D) ratios in undrained soil with varying undrained shear strength profiles. The assessments show a significant reduction in VHM failure envelopes for caissons with L/D ratios less than 2, that are installed in non-uniform soil conditions. The equations can be used for design purposes.