Abstract
The changes of the cyclic resistance of two silty sands under unsaturated, partially saturated and fully saturated conditions are examined based on a series of undrained cyclic tests conducted using triaxial test apparatus specially equipped for testing unsaturated soils as well as ordinary triaxial test apparatus for testing partially saturated and fully saturated soils. Based on the observations of volumetric strain, pore air and pore water pressures of unsaturated soil specimens, the possibility of soil liquefaction triggering under different degrees of saturation is examined and discussed. The changes in the cyclic resistance under different degrees of saturation are then examined. Those two unsaturated silty sands with different grain size compositions are found to give rise to different responses on the volumetric strain as well as pore air and pore water pressure developments during undrained cyclic loading, leading to different relations between cyclic resistance and degree of saturation, covering unsaturated, partially saturated and fully saturated conditions.
1. Introduction
In evaluating the possibility of soil liquefaction triggering during earthquakes, any soil layers located above a groundwater table are generally assumed as non-liquefiable. Located above a groundwater table are unsaturated soil layers, where field measurements using tensiometers revealed that negative pore water pressures were observed in many geotechnical engineering applications, (Fredlund and Rahardjo, 1993 and others).
5. Conclusions
Multiple series of undrained cyclic triaxial tests were conducted on two silty sands under unsaturated, partially saturated and fully saturated conditions. The relationships between the cyclic resistance and degree of saturation were obtained for the two silty sands, and were discussed in relation to the net stress reduction and volumetric strain development. The two silty sands with different grain size compositions gave rise to different volume change characteristics during undrained cyclic excitation, resulting in a difference in the developments of pore air and pore water pressures. This led to a difference in the relationship between the cyclic resistance and the degree of saturation for the two silty sands.
