Geotechnical and environmental performance of retaining structures in unsaturated soils

Presently, environmental issues are considered as critical aspects concerning the market competitiveness in the building and construction sector. However, the construction sector is regarded as one of the main areas contributing to CO2 emissions and resource consumption worldwide. In recent years, industry and academia have been investing significantly in order to produce innovative low-carbon technologies. Other than the significant effort that has been invested in the energy and environmental efficiency of buildings, few research studies concerning geotechnical structure and infrastructure are available in the literature. These previously lacking research activities have been conducted in the framework of the European project TERRE (Training Engineers and Researchers to Rethink geotechnical Engineering for a low carbon future), which was devoted to expanding this innovation to the geo-infrastructure industry. Specifically, the performance of retaining structures in unsaturated soils is investigated in the attempt to optimize their design procedures. Moreover, the thesis deals with the quantification of the environmental impacts of geostructures by comparing conventional and low-carbon geotechnical design solutions. Geotechnical analyses and design procedures for retaining structures mainly consider the retained soils as dry or saturated. The partially saturated condition implies the presence of negative pore-water pressures (suction) that contribute to increasing both the strength and the stiffness of the retained geomaterial. Suction can be considered as a natural ‘low-carbon’ soil reinforcement that can be deployed to reduce the overdesign of both temporary and permanent retaining structures. However, the advantages provided by the condition of partial saturation can evolve with time due to the influence of environmental actions. In this regard, analytical and experimental analyses have been performed to investigate the interaction between unsaturated soils and retaining structures. Simplified geomechanical analytical solutions are implemented in geotechnical design procedures and compared with experimental results. The latter have been conducted by adopting a 1g-physical model designed and built for this purpose. The apparatus is found to be capable of investigating several soil conditions. In particular, the horizontal component of the lateral earth thrust has been experimentally measured in both the at-rest and active states. The effects of the partial saturation have been observed by considering suction profile evolution. The analytical models have been found to be in generally good agreement with the performed tests. However, the water retention curve of the involved soils is found to play a key role in the computation of the lateral earth thrust. Moreover, in collaboration with the industrial partner Nobatek/Inef4, the life cycle assessment (LCA) methodology has been employed to demonstrate the potential benefits provided by the considered eco-friendly geotechnical solutions. Two types of geostructures are considered: a retaining wall designed according to the mechanics of unsaturated soils and a thermo-activated group of piles to satisfy the heating and cooling demand of an office building. By highlighting their potentials and critical issues, the performed analyses have shown a possible significant reduction of the environmental impacts associated with the adoption of these low-carbon solutions.