RSM	Sand–rubber mixtures
DEM	Discrete element method
PSD	Particle size distribution
RC	Rubber content
PDF	Probability density function
$k^n$	The normal stiffness
$k_s$	The shear stiffness
$\mu$	The friction coefficient
$M^r$	The rolling resistance moment
$k_r$	The rolling resistance stiffness
${\mu }^r$	The rolling friction coefficient
${\sigma }_1$	The major principal stress
${\sigma }_2$	The intermediate principal stress
${\sigma }_3$	The minor principal stress
${\epsilon }_1$	The major principle strain
$q$	The deviatoric stress
$p$	The mean stress
$b$	The Intermediate principal stress ratio
${\varphi }_p$	The peak friction angle
${\varphi }_m$	The mobilized friction angle
$Z_m$	The mechanical coordination number
$Z_{s-s}$	The coordination number of sand–sand contacts
$Z_{r-s}$	The coordination number of rubber–sand contacts
$Z_{r-r}$	The coordination numbers of rubber–rubber contacts
${\varphi }_1^s$	Major principal fabric of strong contacts
${\varphi }_2^s$	Intermediate principal fabric of strong contacts
${\varphi }_3^s$	Minor principal fabric of strong contacts
${\varphi }_q^s$	Strong deviatoric fabric