The spatial variability is an inherent uncertainty of soils. The random field theory is used to represent the spatial variability of soils

and the random field discretization is performed by the Karhunen-Loève (KL) expansion method. Using the slope upper bound analysis based on the discrete mechanism

the discretization results of the internal friction angle random field at each point in the space are considered when generating the velocity discontinuity surface. The upper bound analysis

shear strength reduction technique

bisection searching

and sequential quadratic programming method are combined to solve the safety factor of slopes. The first-order reliability method (FORM) and subset simulation (SS) are employed for slope reliability analysis. Given the characteristics of SS and the shear strength reduction technique

an optimization algorithm coupling the two is proposed to improve computational efficiency. By calculating and analyzing an earth slope

the similarities and differences between FORM and SS based on the KL expansion method in solving the slope reliability index and failure consequence are clarified. The influence of the variation coefficient of soil strength parameters on the slope reliability index and failure consequence is investigated

providing a theoretical basis for risk analysis and prevention of slopes.