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Claystone considered as a potential host rock for high‑level radioactive waste disposal in Germany. It offers favorable long‑term safety characteristics—such as low permeability and significant sorption capacity—yet its geomechanical response is governed by low to moderate strength, pronounced anisotropy, and time‑dependent deformation mechanisms including creep, swelling, and moisture‑induced softening. These properties necessitate continuous support throughout the operational lifetime of repository galleries. Due to the unique thermo‑hydro‑mechanical (THM) boundary conditions of a deep geological repository (DGR), standardized support systems from mining and tunneling cannot be directly transferred, particularly at intersections between long‑living and short‑living drifts where stress concentrations and coupled processes are most pronounced.This study presents a constitutive rock‑behavior‑driven design methodology for concrete support structures at drift intersections in claystone. The numerical framework incorporates elastic–plastic behavior with strain softening and an exponential creep law based on viscoplastic formulations linked to time evolution. A continuum‑mechanical model developed in FLAC3D simulates excavation sequences, support installation, long‑term mechanical evolution of the claystone, and the interaction between the rock mass and elastic liners. The simulations quantify creep‑dominated stress redistribution, deformation localization, the influence of intersection geometry, and the resulting coupling forces acting on the liners. The coupling forces from numerical simulations are transferred to the other programmes like SOFiSTiK and ATENA for feasible deign and nonlinear post-peak analyses untill the collapse of support structure. The resulting conceptual design wokrflow integrates mechanically consistent loading envelopes, reinforcement strategies, and installation procedures tailored to repository‑specific operational and long‑term safety requirements.The findings demonstrate that accurate representation of anisotropy, softening, and time‑dependent behavior is essential for reliable support design in claystone‑hosted DGRs. The methodology provides a reproducible, physics‑based foundation for designing durable support structures in complex underground intersections.