The subject of interpreting results from Propagation Saw Tests, including critical cut lengths, test slope angle, and weak-layer characteristics is studied. The Dugdale-type cohesive zone model was used to describe crack-tip stresses and evaluate weak-layer yield strengths resulting from mixed-mode loading during these field tests. The Propagation Saw Test is described analytically by applying normal and shear tractions on the saw-cut crack process zone. The model shows the interaction between far-field stresses, process zone length, and weak layer yield strengths. Field observations of process zone lengths may be a tool for characterizing weak-layer yield functions, predicted critical cut lengths, and the effects of slope angle.