The effect of relative density on the response of sand to internal fluidization

Fluidization, in the geotechnical engineering context, is a failure mechanism that can occur during piping, leakage in distribution pipes or leakage through the sheet pile walls and can lead to severe consequences. This phenomenon will occur when the sand bed is subjected to an upward-facing flow. In this case, with sufficient hydraulic gradient, the effective stresses and the contact forces between soil particles will be zero, resulting in mobilization and fluidization of the soil. This paper presents small-scale laboratory tests involving two sands and relative densities (RD). The hydraulic behavior of the sand before and during the fluidization process is presented and analyzed using measurements and analytical calculations. The dimensions of the cavity and the extent of the fluidized zone are presented and investigated by performing image analysis using digital image correlation (DIC). The analysis indicates that an increase in flow rate and porosity of the sand specimen characterized the onset of soil deformation. The findings also demonstrate considerably higher hydraulic pressures just before fluidization in tests with high RD which indicates larger resistance of dense specimens to the soil fluidization. At the time of fluidization, a significantly larger failure extent is measured in tests with high RD and finer sand specimens.