Effect of hydrated lime and guar gum treatment on the geotechnical behaviour of a Ligurian sandy silt

Biopolymers emerged in recent years as promising soil stabilisers and are increasingly investigated by the scientific community for the treatment of earthworks. The literature on the subject has mostly focused on shear strength in unsaturated rather than saturated conditions, while only a handful of studies have investigated the effect of biopolymer treatment on soil compressibility and consolidation. Moreover, there is little research about soil treatments that synergically combine biopolymers and conventional chemical stabilisers (e.g. cement or lime). The objective of the present study is to fill these gaps of knowledge by investigating the hydromechanical behaviour of a silty sand, treated with a blend of hydrated lime and biopolymer guar gum, by way of a laboratory campaign of saturated direct shear box and oedometer tests. Results indicate that the lime-treated soil exhibits the highest peak strength, while guar gum increases the strength at critical state. Under normally consolidated conditions, treated samples exhibit higher void ratio than untreated ones at any given vertical effective stress. However, this difference in void ratio reduces as the stress increases because of the progressive deterioration of bonds through loading. Finally, soil stabilisation by guar gum produces a decrease of both hydraulic conductivity and consolidation coefficient.