The earth pressure coefficient (K) determines the nature of (tendency of) deformation of the granular mass during flow or deposition. When flow velocity is increasing, K takes its active state Kact and the flow is divergent. When the flow velocity is decreasing, K takes its passive state Kpas and the flow is convergent. The mathematical relations presented here and their 2-D and 3-D plots highlight that the passive and active earth coefficients strongly depend on the internal angle (δ) and basal angle (ϕ) of frictions. The mathematical relation for dry granular mass flow is extended to find these coefficients in soil mechanics. Results further show that active earth pressure drops as the internal angle of friction increases, but passive earth pressure rises. The earth's pressure is at rest if the wall is in its natural position

The tendency of the sliding mass to deform or deposit during the flow is dictated by the earth pressure coefficient (K) in the dynamics of a finite mass of cohesionless granular material discharged from rest on a rough inclined plane. When the flow’s velocities along the x and y-axes are decreasing, K=K_(y pas)^(x pas), the flow becomes convergent, and depositional behavior appears. On the other hand, if the flow velocity is increasing along x-axis but decreasing along y-axis, 〖K=K〗_(y pas)^(x act) and the flow is divergent and hence mass spreads. For K=K_(y act)^(x pas) and K=K_(y pas)^(x pas), the flow is neither convergent nor divergent, it remains constant throughout the domain. The mathematical relationship provided here and the associated 2D and 3D representation demonstrate how the internal angle (ϕ) and basal angle (δ) of frictions have a significant impact on the earth pressure coefficient in the dynamics of dry granular mass along a rough plane. The mathematical correlations for the soil mechanics are discussed along with these coefficients.