Mechanical behaviour of sand stabilised with colloidal silica

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.

Effects of Colloidal Silica Grouting on Geotechnical Properties of Liquefiable Soils: A Review

“…Published data generally agree that the liquefaction resistance of grouted soil improves due to soil grouting, and that the level of improvement is directly related: (i) to the amount of silica particles diluted in the stabilizing grout; (ii) to the time between the end of the gelation process and the beginning of testing (known as curing time), increasing as both these factors increase [14,[23][24][25][37][38][39][47][48][49][50][60][61][62][63][64][65][66][67][68][69][70]. The same findings apply for grouted material subjected to static loading conditions [14,37,[48][49][50]60,61,[63][64][65]67,[69][70][71][72][73][74][75][76]. The behavior of grouted soil under dynamic loading at low-medium strain levels has been much less analyzed [77][78][79].…”

“…For treated soil, most of the tests reported in older studies and in some recent ones were performed without prior water saturation [14,23,63,66,68,69] to avoid disturbance to the gelled material. On the contrary, in other studies soil specimens were previously saturated [48,64,70,71,74], in some cases using very high values of the backpressure (up to 700 kPa). When back-pressure saturation is not performed, pore pressure response is not measured during the shearing phase and test results are processed with reference to total stress, or assuming that mean total and effective stresses are practically identical [68].…”

“…This decrease can be of several magnitudes, and the more the silica concentration in the grout, the more the expected permeability decreases, up to values typical of clay [13,14,17,66,72]. Finally, the effects of grouting on the soil compressibility have been scarcely investigated, even though this knowledge is fundamental for practical applications (the compressibility of soil would influence the settlements of structures and infrastructures in the area of intervention) [14,37,67,[70][71][72]. Most of the results show that the treated soil is more compressible than the untreated one, even though a strict comparison among these data is not possible due to the differences in testing conditions.…”

“…Vranna et al [68] showed the results from monotonic undrained triaxial tests on treated and untreated loose sand specimens subjected to different back-pressure values, pointing out that the magnitude of back-pressure had a strong influence on the stress-strain response of the material. Georgiannou et al [71] showed that the results of drained monotonic triaxial tests were independent from the back-pressure magnitude, which was in the range 300-700 kPa. The same range of values was adopted by Triantafyllos et al [74], who stated that increasing the back-pressure within this range does not produce damage to the gel since they observed that drained loading on similar stabilized samples gave reproducible results.…”

“…Colloidal silica treated soil can be easily subjected to unconfined compression strength (UCS) tests, with resulting UCS values that depend on the percentage of silica diluted in the stabilizing grout. Studies unanimously demonstrated that UCS values increase as silica contents and the age of samples increase (e.g., [13,23,63,69,71]). Moreover, treated soil subjected to monotonic loading shows enhanced dilative response (e.g., [48,49,61,[70][71][72]74]) (Figure 10).…”