When designing with two-dimensional numerical analysis, the concept of stress release rate is used in order to simulate three-dimensional deformation behaviour. Generally, the stress release rate in the 2D numerical simulations is set to 40% before the support is installed and the remaining stress is released after the support is installed. However, there is no particular thing about the early closure of all sections, which has been increasingly used in recent years. Therefore, the authors derived the optimum stress release rate for the early closing of all sections by trial calculation, which is a three-stage stress release, leading displacement rate α = 40%, after installation of upper half support support β = 20%. It was also found that the semi-support + invert support = 40% could reproduce the 3D deformational behaviour more appropriately.
