Based on experimental data on the combined loading of an infinite layer weakened by a circular hole in a brittle material, its critical state, determined by the energy criterion, is modeled. The failure criterion is related to the free energy flow through the interaction arc and the linear size. The proposed approach allows us to reflect the dependence of the critical external load on the radius of curvature. A procedure for determining the value of the linear size is proposed and implemented. Using known experimental results, an estimate of the introduced linear parameter for a layer of GVVS-16 gypsum was obtained.