Synergic effect of hydrated lime and guar gum treatments on the shear strength and retention behaviour of a pyroclastic soil

In the pursuit of sustainable ground improvement methods, numerous studies have examined the geotechnical properties of soil treated with biopolymers, such as guar gum. Only a few works have instead explored the combination of biopolymers with traditional stabilisers like hydrated lime. This study experimentally investigates the synergic effect of guar gum (GG) and hydrated lime (HL) treatment on the shear strength and water retention behaviour of a pyroclastic silty sand. Soil samples were treated with either 2%HL and 1%GG, or 1%HL and 2%GG, where percentages are relative to the dry soil mass. The soil-water retention behaviour was measured using ‘small tip’ tensiometer probes installed in near-saturated samples exposed to ambient evaporation. Retention data were interpolated using the van Genuchten retention law, which was subsequently used to interpret results from direct shear tests conducted on both near-saturated and unsaturated soil samples. Treated samples exhibit higher water retention capacity and shear strength than the untreated ones, with the 2%HL and 1%GG treatment yielding the best performance. These findings highlight the potential of combining hydrated lime with guar gum to enhance geotechnical properties of soils, offering a sustainable approach to ground improvement.