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The characterization of heterogeneous soils using common geotechnical techniques often proves impossible when the size of the heterogeneity is larger than a few tens of centimetres. Geophysical investigation techniques based on seismic wave propagation can help engineers to characterize the mechanical properties of such materials. In this paper, both refracted and surface waves are used to estimate the mechanical properties of an equivalent homogeneous medium.A summary of the main results obtained numerically using finite-element computations and homogenization theory is presented. It is shown that, for first-mode surface-wave wavelengths larger than 7.5 times the nominal size of the heterogeneity and within certain heterogeneity concentration ranges (up to 50% for matrix dominant soils), surface waves homogenize the soil in accordance with classical homogenization theory.To validate these numerical results, a reduced-scale model was built and seismograms, generated with a falling weight, were recorded. The phase-velocity dispersion curve of the generated surface waves is inverted in order to obtain the shear-wave velocity of the heterogeneous layer. The compressional-wave velocity is calculated by means of seismic refraction analysis. Velocities obtained on the reduced-scale model correspond to those predicted by homogenization theory from individual measurements of matrix and inclusion velocities.

One of the major challenges associated with CO2 geological storage is the performance of the confining system over long timescales. In particular, the occurrence of CO2 leakage through existing wells could not only defeat the purpose of storage but also badly affect human health or the environment. Indeed, cement degradation and casing corrosion in injection, production or abandoned wells can create preferential channels over time, allowing migration of CO2 from the reservoir to shallower formations (e.g. aquifers), and/or to the surface. In this paper, a risk-based approach is proposed for well integrity and confinement performance management. The approach, based on Performance and Risk Management methodology (P&RTM), serves as a decision support tool. The major steps are (i) identifying the system and the sources of degradation through characterization and system analysis; (ii) quantifying their criticity through modeling, in terms of probability and severity, and (iii) establishing a risk mitigation plan. This methodology is based on experience in material aging and risk assessment of complex systems, like nuclear structures, where probabilistic simulations are performed. It accounts for all stakes involved in well integrity management and enables the full integration of uncertainties as part of risk estimation. The methodology presented here greatly improves common approaches based on "Features, Events, and Processes" as it quantifies risk levels. It provides useful and reliable tools to support decisions for well integrity management strategies or emergency plans. To that purpose, mitigation actions such as characterization/inspection, remediation (workover), design improvement or monitoring are valued based on a cost/benefits ratio. Moreover, updating risk assessment with incoming data allows for an evolving vision of risk levels to optimize interventions in time. This approach is successfully applied, leading to recommendations for safer and more efficient design, maintenance, and monitoring strategies.