Evaluation of Effective Strength Parameters and Micro Structural Variations of Silty Sands Stabilized with Nano Colloidal Silica

Saturated deposits of sands and silty sands are liquefiable during earthquakes. One of the new methods proposed for non-disruptive mitigation of liquefaction risk at developed sites is passive site stabilization. It involves slow injection of colloidal silica at the edge of a site and delivery of the stabilizer to the target location using natural groundwater flow [1]. Colloidal silica is an aqueous suspension of microscopic silica (SiO2) particles produced from saturated solutions of silicic acid [2]. The particles size can range in size from 2 to 100 nm, although the particle size is fairly constant in a given suspension. During manufacturing, colloidal silica solutions are stabilized against gelation so they can have long induction periods during which the viscosity remains fairly low up to a few months. A few studies have investigated the behavior of sands stabilized with colloidal silica. Persoff et al. measured short term strength of about 430 kPa at concentration of 20 wt% colloidal silica [3]. Gallagher and Mitchell found the baseline unconfined compressive strength ranged from 32 to 222 kPa in period of 7-30 days at sands samples treated with 5-20 wt% colloidal silica. They also did a series of cyclic triaxial tests and found that for passive site remediation, a 5 wt% concentration of colloidal silica is expected to be able to adequately mitigate the liquefaction risk of loose sands [4]. The stabilization of loose silty sand with colloidal silica has not been studied comprehensively so the present study was undertaken to investigate the unconfined compressive strength and microstructure analysis of silty sands stabilized with colloidal silica.