“…Currently, unbound graded aggregate (UGA) is widely used in engineering constructions, such as geotechnical engineering (Youngs and Rushton, 2009a), pavement engineering (Dan et al, 2012a;Dan et al, 2012b) and railway engineering (Youngs and Rushton, 2009b); UGA can not only constitute the structure with no organic matter (it is a typical base in pavement structure) (Dan et al, 2015) but also plays a role as a drainage layers to drain efficiently the infiltrated water (Dan et al, 2013;Haider et al, 2014;Dan et al, 2018). However, the hydraulic properties of UGA materials are analyzed through a series of constant head permeability experiments to obtain the saturated hydraulic characteristic under the different compaction degree (Li et al, 2008;Sedghi-Asl et al, 2014;Dan et al, 2016;Dan et al, 2017), and it is difficult to obtain the SWRC of UGA materials in experiments under unsaturated condition.…”