The research advance and existent insufficiency of unloading relaxation in rocky slope excavation are summarized. Based on the qualitative analysis of unloading relaxation process and mechanism

the limit tensile strain of rock is proposed as the criterion of unloading relaxation. The value taking principle of limit tensile strain of rock is put forward by analyzing the relationship between lab test value of limit tensile strain of rock and its tensile strength

and by referring to the successful practice of excavation unloading relaxation analysis in Xiaowan arch dam. The calculation method of tensile strain in rocky slope after excavation is deduced. By adopting three-dimensional elasto-viscoplastic finite element method of reinforced jointed rock masses

this unloading relaxation criterion and corresponding calculation methods are applied to the numerical analysis of rocky slope excavation unloading relaxation in Jinping First-Cascade arch dam foundation plane. By comparing to the disclosed situation after actual excavation and the sonic wave testing data

the results of numerical analysis are confirmed reasonable

so as to provide beneficial guidance to the construction of project.