A comparative study of two different concentrations of colloidal silica gel and sand mixtures is presented. The dynamic properties, shear modulus and damping ratio, of No. 120 Nevada sand permeated with colloidal silica gel were determined using resonant column tests. The behaviour of the gelled samples is compared to untreated sand samples. The effects of the concentration of colloidal silica gel by percent weight, cyclic shear strain and aging on the dynamic properties of the gel-sand mixtures were studied. Results show there is a small difference in shear modulus with concentration of colloidal silica gel by percent weight and the gel-sand mixtures have a slightly higher shear modulus than untreated sand. The presence of the silica gel does not greatly affect the damping ratio. A 5% by weight gel-sand sample subjected to a long-term, small-strain cyclic shear resonant column test for a duration of 28 days after gelation shows an increase of 6 MPa in the shear modulus.