On the combined use of hydrated lime and guar gum for rainfall-induced shallow landslide risk mitigation

Recent studies have shown that biopolymers, like guar gum, can be employed as sustainable soil stabilisers, offering promising alternatives to traditional energy-intensive binders, like lime. While their field application is still limited, biopolymers could also be introduced at shallow depths through soil mixing for mitigating superficial landslide risks. This paper explores the application of biopolymers for the stabilisation of the pyroclastic slopes located in south-western Italy, typically affected by rainfall-induced shallow landsliding. The proposed treatment combines guar gum (GG) and hydrated lime (HL), whose potential effects are evaluated, at the slope scale, through finite element seepage models and limit equilibrium stability analyses, considering realistic interactions between the top unsaturated soil layer and the atmosphere. Treatments include two stabiliser combinations (i.e. 2%HL-1%GG and 1%HL-2%GG, with percentages by dry soil mass) to assess the impact of partially replacing HL with GG. The water retention curve, the saturated permeability and the shear strength of both untreated and treated soils are evaluated based on evaporation, oedometer and direct shear laboratory tests. Although the paper focuses on an idealised slope, the results highlight the potential of combining hydrated lime and guar gum for the sustainable mitigation of rainfall- induced shallow landslide risk.