Numerical study on stability of lignosulphonate-based stabilized surficial layer of unsaturated expansive soil slope considering hydro-mechanical effect

Numerous laboratory-based solutions have been proposed in the recent literature for the stabilization of un-saturated expansive soil by recycling lignosulphonate (LS). However, the practical assessments of these proposals for the treatment of the rainfall-induced surficial failure in unsaturated expansive soil slopes are required, considering the frequency of this failure and associated economic loss. Moreover, in conventional geotechnical practice, the slope stability is generally evaluated only with consideration of the hydraulic response of the soil, ignoring the hydro-mechanical coupling effect associated with the swelling behavior of soil. Since LS-based stabilizers mainly impart the reduction of the swelling potential of expansive soils, the assessment of the sta-bility of the LS-treated surficial layer of unsaturated expansive soil slopes requires consideration of the hydro-mechanical effect. For this purpose, the uncoupled and hydro-mechanical coupled analyses were conducted for dealing with the hydraulic and hydro-mechanical responses of the surficial layer of soil slopes, respectively. Specialized experimentations and pertinent literature review were performed to acquire the required input data for these analyses. It is observed that the LS-based surficial layer treatment affects the pore water pressure (PWP) profiles as well as wetting front depth (WFD), which are the critical aspects for influencing the stability of un-saturated expansive soil slopes. Among all LS-based stabilizers, only the stabilizer named composite cementing admixture (CCA) reasonably ameliorated the PWP profiles and WFD of the slope considering disastrous envi-ronmental impacts (i.e., wetting-drying cycles). Moreover, the heave problem of expansive soil slopes was observed to be mitigated by LS-based treatment among which the CCA performed the most efficiently. Furthermore, the critical factor of safety (FS) required for slope stability was also affected by the LS-based treatment, whereas the CCA was observed to provide the safest critical FS for slope stability.

Automated summary

Numerous laboratory-based solutions have been proposed for stabilizing unsaturated expansive soil by recycling lignosulphonate. However, practical assessments are required for treating rainfall-induced surficial failure in unsaturated expansive soil slopes. The stability of LS-treated surficial layer requires consideration of the hydro-mechanical effect. Among LS-based stabilizers, composite cementing admixture (CCA) provides the safest critical factor of safety for slope stability while mitigating the heave problem.