General Response Of Kneading-compacted Unsaturated Silty Sand Under Drained And Undrained True Triaxial Testing

A comprehensive series of 36 drained and 36 undrained true triaxial tests was accomplished to investigate the stress-strain-strength behaviour of kneading-compacted unsaturated silty sand (SP-SM) under multi-axial stress states. Test specimens were prepared at three different initial moist contents (6, 8, 10%) to achieve different compaction-induced suction conditions prior to testing. All samples were then subjected to either a drained or undrained multi-axial stress paths, including conventional triaxial compression (CTC), triaxial compression (TC), triaxial extension (TE), or simple shear (SS) stress path. Initial compaction-induced matric suction was assessed via the SWCC of test soil. The experimental program focuses on soil response at high values of suction, that is, within the uppermost vadose zone regime. Test results were plotted in terms of octahedral stress versus principal stress response. Results show that the shear strength of kneading-compacted unsaturated silty sand, regardless of initial compaction-induced suction, increase with an increase in confining pressure. However, as the initial degree of saturation increases from 27 to 61% and the initial dry density increases from 16.4 to 18.1 kN/m3, the ultimate strength of kneading-compacted unsaturated silty sand increases. The undrained soil strength, in most multi-axial stress cases, proved to be slightly higher than that for drained conditions.