Influence of the type and method of bentonite addition on the liquefaction resistance of a standard clean sand

During cyclic liquefaction, sandy or gravelly soils may experience a sudden loss of shear strength and stiffness under dynamic loads such as earthquakes. Although conventional ground improvement techniques exist, most of them involve volumetric changes, limiting their applicability in liquefiable soils beneath existing structures. As an alternative, the use of plastic nanoparticles that may be permeated, such as bentonite or laponite, has been explored. However, previous studies have mainly focused on dry addition, while research using suspensions has emphasized in application aspects rather than in the cyclic resistance. This study evaluates the influence of a volcano-sedimentary bentonite on the liquefaction resistance of Ottawa sand through undrained cyclic triaxial tests. Two methods of incorporating bentonite were evaluated: (i) dry mixing sand–bentonite with 3% and 5% by mass of sand, and (ii) permeation with suspensions at 10% and 14% by mass of suspension. The suspension dosages were designed to be equivalent to the dry mixes considering sand void ratio and specific gravity. Results show that, for the same number of cycles, permeated samples exhibited cyclic resistance ratios (CRR) 13 to 40% larger than clean sand. In contrast, dry mixtures presented 3 to 30% reduction in CRR, when compared with clean sand. These reductions are related to grain size, plasticity and Na/Ca ratio of the bentonite, which all reduce the effectiveness of the dry mixes. For permeated samples, the larger concentrations and longer curing periods enhanced cyclic resistance, though at the expense of reduced permeation efficiency due to increased viscosity. • The bentonite addition method critically affects the soil liquefaction resistance. • Dry mixes of bentonite with high plasticity or Na/Ca do not improve resistance. • Bentonite suspensions are more effective than dry mixes for high plasticity or Na/Ca. • Bentonite concentration and viscosity control the effectiveness of suspensions. • Longer curing periods increase liquefaction resistance for same dosage and method