Improving mechanical behaviour of collapsible soils by grouting clay nanoparticles

The primary geotechnical concern of collapsible soils such as loess is their hydromechanical instability. Upon wetting, metastable aggregates disintegrate, leading soil to collapse under the applied load or self-weight. In situ chemical stabilisation, such as grouting, is a favoured option to improve soil mechanical behaviour; however, the low permeability of loess limits the application of permeation grouting in such deposits. Here a new approach is presented based on the injection of dilute suspensions of montmorillonite clay nanoparticles to improve mechanical behaviour of low permeable loess. In addition to clay, the grouting behaviour of an ordinary cement material was evaluated as a typically favoured soil stabiliser. Reconstituted specimens were also prepared by mixing dry clay or cement particles with soil at similar contents and curing time to compare with the grouting method. SEM images were also taken from the cured samples to visualize the soil fabric. Results revealed that clay suspensions feature a high-mobility in the soil medium as well as a remarkable performance in reducing the collapse potential due to: (1) clay effective particle size (∼0.25 μm) that facilitates its mobility in soil, and (2) formation of evaporation-driven solid bridges that reinforce the interparticle bonds during post grouting drying. Results encourage the application of clay nanoparticles over cement for an economical and eco-friendly grouting approach to improve the mechanical behaviour of low permeable collapsible soils.