LOW PRESSURE GROUTING WITH NANOSILICATES TO REDUCE THE LIQUEFACTION SUSCEPTIBILITY OF SAND

The paper reports an experimental laboratory study aimed at investigating the effectiveness of low pressure grouting with nano-silica compounds as a remedial against liquefaction of sandy soils and to optimize the technique rendering it more attractive from the technical and economical viewpoint. The grout herein adopted is a three-component mix of an aqueous suspension of sub-micrometric silica particles, water and an aqueous solution of sodium chloride. The latter, raising the pH of the suspension triggers the formation of the silica gel that clogging the soil pores reduces the mobility of the grains and, hopefully, produces a stiffer response and a reduced contractive tendency of the material. A preliminary set of laboratory vane tests is performed to observe the gelling time of the material and fix the curing time of the samples by measuring the increase of shear resistance. Thus, reconstituted samples of a silica sand, manufactured at two different initial levels of density are treated with nano-silica grout prepared with a silica concentration ranging from 1.2% to 5.0% in weight. The samples are transferred into a fully servo-controlled triaxial cell and subjected to monotonic drained and cyclic undrained tests at variable stress amplitudes. The comparison among the monotonic tests on treated and untreated samples reveals an increase of peak strength and a more dilative tendency, increasing with the amount of injected silica. The comparison of cyclic undrained tests shows a lower tendency of the treated material to accumulate excess pore pressures with cycles and a retarded liquefaction proving that the grouting of sands with nano-silica can be profitably adopted to mitigate the effects of liquefaction of loose sandy deposits.