This experimental study aims to assess fatigue related risks in H2 storage projects. In particular, it focuses on the cyclic behaviour of caprock materials under large confining pressures. A series of monotonic and cyclic undrained triaxial tests were performed to investigate the response of the material. When subjected to cyclic loading, structured stiff clays were found to undergo a progressive destructuration, leading, eventually, to a fragile failure. This process was found to be controlled by loading frequency, maximum deviator stress and loading amplitude.

In its race towards climate neutrality by 2050, the European Union seems to be betting on green hydrogen as a high potential energy source. The French government seems to prioritize the reuse of gas networks for the transportation of H2. However, the substitution of gas by hydrogen leads to an evolution of the mechanical characteristics of steel pipelines increasing their vulnerability vis à vis external stresses, which raises a number of scientific and technical questions. The aim of this study is to synthesize the research work in the literature addressing the behaviour of buried pipelines subjected to various ground movements.

• The lower capillary porosity causes less carbonation in BNC samples because it reduces the CO2 diffusion rate in the cement matrix. • Samples with BNC have higher mechanical strength before and after carbonation. • The carbonation degree of the samples with BNC is less compared to neat cement.

Underground hydrogen storage might be the key to the success of the energy transition in Germany. Here we define positive indicators for pore storage systems and estimate hydrogen storage capacities in UGS systems and saline aquifers based on natural gas and CO2 storage assessments.