Effects of initial static shear stress on cyclic behaviour of sand stabilised with colloidal silica

Colloidal silica (CS) grouting is a soil improvement technique introduced as an innovative remedial measure against seismic liquefaction. It consists of injecting soils with a time-hardening, nanosilica-based solution forming a silica gel among soil particles. This paper presents the results of an experimental study on the effects of an initial static shear stress on the behaviour of a cyclically loaded clean sand stabilised with 5% CS. Undrained cyclic triaxial tests were performed to analyse the cyclic response of loose untreated and stabilised sand specimens, isotropically or anisotropically consolidated at the same initial mean effective stress. The consolidation stage was used to provide insight on the compressibility of stabilised soil. Stress-strain behaviour, pore water pressure response and cyclic shear resistance were investigated. The results showed that: (i) stabilised sand exhibits higher compressibility than the untreated one during isotropic consolidation; (ii) cyclic strength is higher for stabilised sand than for the untreated one, increasing as the degree of anisotropic initial stress increases; and (iii) extra pore water pressure development does not depend on the degree of initial anisotropy for stabilised sand, while the same does not hold for untreated sand. Simplified relationships are proposed to describe the consolidation process and the residual extra pore water pressure build-up process.