Mitigation of Soil Liquefaction with two Sustainable Materials: Biochar and Laponite

Abstract

Soil liquefaction is one of the causes of greatest damages during earthquakes. Even though progress has been made in understanding and mitigating its effects, liquefaction is still happening. Additionally, wastes and carbon emissions are increasing at alarming rates. Thus, new alternatives to stabilise soils are always needed, and more sustainable solutions are urgent. In this study, two materials: laponite and biochar, that possess sustainable features, are assessed on their effect on the liquefaction resistance of the host sand. Laponite is a synthetic clay that could change the viscosity of pore water transforming it into a thixotropic gel, whose viscosity and shear modulus increase with time, but flows with the application of shear stress, and recovers after the load has been suppressed. Due to this feature, it could be considered as a resilient material. Biochar, on the other hand, is the solid carbonaceous by-product of pyrolysis. Biochar is effective in managing wastes since its feedstock could be any organic waste. Besides, as it is highly recalcitrant, it can be used to sequester carbon, avoiding its emission to the atmosphere, and it could be used to promote plant growth. The main objective of the study is to assess the effect of adding these two materials on the geotechnical properties of loose saturated sand. The mitigation of soil liquefaction with these two materials is actually a multi-scale problem. For this reason, the problem was investigated at different scales, that is: (i) at nano-scale, the occurrence of laponite nano-particles interaction was investigated using SEM, and Cryo-SEM; (ii) at micro-scale, the laponite gel-pore interaction and the occurrence of biochar-pore interactions were investigated through SEM, ESEM, and the study of the chemical composition of the materials (X-ray and FTIR spectra); (iii) at medium-scale, by performing conventional elemental tests, such as various simple shear tests, resonant column tests, and rheological measurements; and (iv) at large scale by conducting a numerical simulation of model ground with a shallow foundation subjected to a series of two consecutive earthquakes. The results of this study provide evidence that these materials have the potential to be used as sustainable alternatives to mitigate soil-liquefaction. Furthermore, this study offers a starting point to understand the mechanism by which these materials could improve cyclic resistance.