The design of underground and closure structures for the Cigeo repository is mainly based on geomechanical constitutive models tested in the Meuse/Haute-Marne URL. Excavation modes adapted to the different repository components have been evaluated and tested. Specific methods for excavation and lining have been designed for access shafts and ramps, ILW and HLW disposal cells as well as sealing systems located in surface-to-bottom infrastructures and in drifts.