Behavior of Sand Specimens Subjected to Cyclic Loads under Drained and Undrained Conditions in Variable Loading Amplitudes

Dynamic loads with different magnitudes cause shear stress and strain in the soil and increase the pore water pressure, reducing soil strength and leading to structural failure. This article presents the behavior of natural river-sand specimens subjected to cyclic loads under both drained and undrained conditions, as observed in cyclic triaxial tests conducted in the laboratory. The experiments were performed on sand specimens with a relative compaction of 0.95 when changing the loading amplitude with three different levels of 30 kPa, 50 kPa and 60 kPa. Experimental results show that, under the condition of drained cycle load, the pore water pressure does not form; only accumulated strain and dynamic parameters are almost unchanged. Meanwhile, with the condition of undrained cyclic load, the pore water pressure increases and causes liquefaction of the specimen, then the axial strain increases dramatically and is not capable of recovery. When varying the loading amplitude under drained condition, the initial-strength values increase as the amplitude of the load increases. This trend has the opposite direction when testing under undrained condition, which means that when increasing the loading amplitude, the initial-strength values decrease and the liquefaction potential of the specimens is faster. Further, under the undrained condition, the loading amplitude of 30 kPa effect is almost negligible on the liquefaction ability of the specimen. Keywords: Sand, Drained condition, Undrained condition, Loading amplitude, Cyclic triaxial tests