Sabatino, Filomena (2023) Mechanical behaviour and durability study of cemented soils lightened by foam. [Tesi di dottorato]

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Abstract

The reuse of soil from excavation operations is an extremely interesting design strategy with a view to minimising the environmental impact of works and ensuring their sustainability. Lightweight Cemented Soils (LWCS), obtained by adding foam to a soil-cement-water mixture with self-levelling properties and a reduced unit weight by volume, are used in different geotechnical applications (e.g. embankments, backfills behind retaining structures, filling of urban cavities and excavations). The main objectives of this research work are the chemo-physical and mechanical characterisation of LWCS, together with the study of the durability of the treatment under environmental loads. Chemo-physical and mechanical characterisation of LWCS were examined via mechanical tests (i.e., unconfined compression tests, torsional shear tests and triaxial tests) and non-destructive testing methods (i.e., ultrasonic tests and electrical resistivity measurements). Results show that the development of cement hydration reactions is responsible for the formation of cement products, resulting in increased strength and stiffness of the material. Moreover, artificial porosity leads to an increase in the void index, which is associated with a reduction in strength and stiffness, when compared to a cemented soil. The results obtained following the use of non-destructive testing methods reveal a good correlation between the measured geophysical quantities and the fixed treatment parameters. The measured geophysical quantities (VP and ρ) are related to unconfined compressive strength (UCS). The applicability of non-destructive testing methods in the in situ quality control of the correct treatment is demonstrated. Subsequently, an experimental investigation on the durability of LWCS after wetting and drying cycles was developed, focusing on the evolution of their mechanical response. Wetting and drying cycles were performed in climatic chamber to test LWCS mechanical performance as function of number of cycles and the environmental conditions (50% and 90% of Relative Humidity). Unconfined compression tests and triaxial tests were performed on treated specimens after cycles in dry state. Suction of LWCS samples was measured after mechanical tests. Test results show that the wetting-drying cycles and the variations of suction are responsible for the evolution of LWCS mechanical behaviour. Moreover, strength and stiffness of the treated samples are related to the current suction level induced by environmental loading conditions. The mechanical degradation is linked to the number of cycles and to the amplitude of suction variation induced, being the latter responsible for mechanical cement bonding destructuration.

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