[en] In order to refine and rationalize a design method of multi tunnels in the deep geological repository, 'Study on the spatially-spread behavior of EDZ (Excavation Disturbed Zone)', 'Study on the stability evaluation of the pillars', 'Study on configuration of analytical domain of the multi tunnels model', 'Remainders on an elasto-plastic FEM (Finite Element Method) analysis for the simplified model with the full width plastic deformation of pillar', and 'The suppression effect of the plasticity domain by the ground support and the auxiliary construction method' have been conducted, based on the H12 report. As the results, in case of the multi tunnels model, EDZ properties were changed by the excavation sequence of tunnels, and the whole tunnels (in panel scale) are more stabilized, however the simplified model are not possible to represent these behaviors. Each tunnel has the same design results by using the simplified model, however it is possible to design an individual tunnel by using the multi tunnels model for the detailed and rational design. The stability of the pillars on the disposal tunnels was studied by considering 'Pillar strength' and 'Pillar load'. As the results, the pillar strength and pillar load can be evaluated by numerical analysis with the multi tunnels model. The proper analytical domain of multi tunnels should be assigned 3-5W (W: width of multi tunnels) for a horizontal side from the endmost tunnel and 3-4W for below of the tunnels by an elasto-plastic FEM (Finite Element Method) analysis. In case of interference of plastic deformation domains on the pillar, FEM analysis with simplified model does not have good simulation accuracy of the pillar load. It is absolutely needed that the space between tunnels is wider than the maximum width for the full width plastic deformation of pillar. Regarding the suppression effect of the plasticity domain by the ground support and the auxiliary construction method, we confirmed that the ground support effect has different suppression effect of the plasticity domain depends on the installation time and rigidity, and the auxiliary construction method for the purpose of improvement in mechanical properties of pillar has good the suppression effect of the plasticity domain. In this study, the effect of constitutive models such as strain softening of rock masses for EDZ, and the stress relief ratio used for multi tunnels analysis were conducted. As the result, it is necessary to confirm mechanical behavior of in situ rock and it is important to choose suitable constitutive models, and it is possible for all tunnels in multi tunnels model to have same stress relief ratio. (author)