LIQUEFACTION POTENTIAL OF LAYERED SOIL UNDER VERTICAL VIBRATION LOADS

Abstract

The risk of liquefaction phenomena increases during dynamic loading and can cause the shear failure of soil under foundations. Model tests for a small-scale model under vertical vibration loads are presented. The operating frequency was changed from 1000, 2500 to 3500 revolutions per minute and the amplitude of loading with time was applied as a sine wave. Several parameters were considered, such as the force-time history of the machine foundation, the final settlement of the foundation, the vertical stress inside the soil media, the excess pore water pressure and observed liquefaction phenomena. These observations were compared to the effect of the sub-base layer thickness under the footing and its ability to reduce the liquefaction phenomena. The results showed that the shape of the load–time history coincides with a sine wave and the increase in the operating frequency led to an increase in the measured vibration load. The settlement was observed to increase with increases in the operating frequency. The settlement depended on the state of the soil and the operating frequency applied. Increases in operating frequency of about 3 times led to an increase in the time interval of excess pore pressure and reached a maximum value. The phenomenon of liquefaction appeared clearly when sandy soil was in a loose state. When the soil changes to a medium state, the phenomena of liquefaction respond to the operating frequency more than the operating frequency in a loose state. No liquefaction occurs in a dense state. The use of a subbase layer more than 1.5 times the depth of the footing led to eliminating the liquefaction phenomena.