Shaking Table Tests on Seismic Responses of Silica Sand Foundation Reinforced by Vibroflotation

A series of model tests about vibroflotation were conducted to investigate soil property change on silica sand foundations, especially for earthquake-resistant behavior. First, the process of double-point vibroflotation was investigated with a simulative vibrator system. Thereafter, shaking table tests were conducted to evaluate seismic responses. The results illustrated that the relative density was significantly enhanced after the first vibratory period, with the highest enhancement appearing at the vibropoint in the plane and the middle layer along the depth. As for the seismic tests, the excess pore pressure ratios show that the vibroflotation can apparently improve the liquefaction-resistance capacity of the silica sand foundation. Moreover, the shear stiffness of the unconsolidated foundation decreases distinctly under 0.2g earthquake motion, while the consolidated foundation remains capable of transmitting acceleration. Inflicting white noise before the any earthquake motion and after 0.2g earthquake, the result shows that the predominant frequency of unconsolidated foundation decreases apparently. The dynamic shear stress-strain curves were compared, while the development law of the time history was also investigated. These results demonstrated that this method can obviously prevent the shear stiffness attenuation. To sum up, the vibroflotation compaction method can make a great densification and increase the earthquake-resistant capacity.