Re-examining the Influence of End Restraint on Mechanical Behaviors of Dense Quartz Sands

Mechanical behaviors of soils may be effectively observed, relying on precise and accurate experimental techniques adopted. The critical state of soils, therefore, can be determined through a series of conventional triaxial compression tests. However, some studies claim that the critical state may not uniquely exist under some conditions, such as end restraint, specimen size, confining pressure, initial relative densities, etc. The objective of this study is to revisit the end restraint condition where it could be negligible for specimens with a height-to-diameter ratio between 2.0 and 2.5, where the ratio is recommended by ASTM D7181-20. A ratio of 2.46 was adopted in this study to ensure proper comparisons under element testing, minimizing end-platen effects, and meeting the ASTM standards. The other aim of this study is to evaluate and compare the mechanical behaviors of the quartz sand with lubricated or nonlubricated end platens, including stress-strain-volume change and critical states. A series of consolidated-drained triaxial compression tests on quartz sand with an initial relative density of 75% and 85% were conducted. The results indicate that the end effect can be minimized when a height-to-diameter ratio is 2.46. Under the circumstances, the lubricated and nonlubricated end platens have few impacts on peak shear strength of the sands tested but they may affect the volume change behavior and the determination of critical state conditions.