The role of roots in the stability of landfill clay covers under the effect of dry–wet cycles

This study investigates the role of vegetation roots in the stability of landfill clay covers subject to dry–wet cycles. Soil shear strength is tested at different depths of bare and vegetation covers before and after 1 year of seasonal dry–wet cycles. Results show that the effect of these cycles and of vegetation roots on the soil shear strength of covers mainly alters soil cohesion. By contrast, the effect on the internal friction angle of soil is inconspicuous. After 1 year of seasonal dry–wet cycles and grass root growth, the soil cohesion of the vegetation cover increases, whereas that of the bare cover decreases. The increment in the soil cohesions of two covers tends to decline exponentially with increasing cover depth. Thus, the cover stability model is established according to upper-bound solution theory based on the change rule of cover shear strength under the effect of dry–wet cycles and vegetation roots. The theoretical analysis results indicate that the increase in cover slope safety factor that was caused by vegetation roots is significant, compare that of bare cover under dry–wet cycles. Nonetheless, the effect of roots on cover slope safety factor decreases with increasing slope length and cover slope angle.