Influence of matric suction on nonlinear time-dependent compression behavior of a granular fill material

The site formation for the construction of a new airport in a mountainous region is typically performed by cutting and filling a hill section. The fill materials are subjected to seasonal changes and large variations in water content. The water content change renders the fill material to be characterized as unsaturated or saturated. This study aims to investigate the influence of matric suction on the time-dependent compression behavior of one local soil as a fill material for the construction of a new runway of an airport in Chongqing city, a mountainous region in China. A series of unsaturated drained triaxial tests were conducted on this coarse-grained soil to obtain the relationship between the effective stress parameter, chi, and the matric suction. Subsequently, multistaged compression tests were performed on this soil using a newly designed suction-controlled oedometer apparatus. The influence of suction on the time-dependent compression behavior of the fill material is emphasized. The results indicate that the matric suction can increase the compression stiffness, and that the unloading-reloading index varies nonlinearly with suction. A linear relationship between the time-dependent compression coefficient and normalized effective vertical loading is established. The linear relationship is subsequently used to predict the time-dependent compression coefficient to describe the time-dependent behavior of the fill under unsaturated conditions. Further, a nonlinear function based on the work of Yin (Geotechnique 49(5):699-707, 1999) is adopted to describe the development of time-dependent compression. The results indicate that the prediction obtained from the two newly proposed methods are promising, and can predict the nonlinear time-dependent compression behavior of this coarse-grained soil.