No abstract

The response of sand stabilised with colloidal silica aqueous gel is examined in the laboratory, under direct shear, triaxial and normal compression loading, in comparison to that of untreated sand of similar density to evaluate the effect of stabilisation on subsequent sand response. The behaviour of the treated sand differs in important respects from the behaviour of the untreated sand: a significant increase in the angle of shearing resistance is observed at lower stress levels, diminishing with increasing stress level; the peak strength envelope is curved at low stresses for the treated sand only, while at ultimate strength, the envelopes coincide for treated and untreated sands. However, at all stress levels, extreme dilation is associated with the treated sand at peak and ultimate strength conditions. Under normal compression, the treated sand is easily densified, exhibiting higher compressibility than that of sand of similar density. It appears that depending on loading conditions, the aqueous gel alters its structure and has the capacity to absorb or discharge free water; it is of paramount importance to measure volume change and/or pore water pressure change during stabilised sand testing.

To evaluate the effect of stabilisation by using a colloidal silica aqueous gel on the subsequent behaviour of sand, the dilatancy and peak and ultimate strength characteristics of M31 sand were investigated before and after stabilisation. Triaxial compression tests were performed in drained and undrained mode, at effective stresses ranging from 100 to 6000 kPa. Important changes in the sand's mechanical behaviour were observed after stabilisation, including a significant increase in stress ratio and dilatancy rate at peak and a relocation of the treated sand's critical state line in the e–p′ plane, substantially above that manifested by the untreated sand; however, the two lines converged at high stresses. The results confirm a state-dependent behaviour for the sand that is not applicable to the treated sand, which exhibits predominantly stress-dependent behaviour. A modified state parameter was used to normalise the treated sand's behaviour at peak failure.