The propagation characteristics and diffusion law of horizontal prestress from the slope surface to the embankment interior are key issues to be solved for the reinforcement of a prestressed subgrade. Based on the theory of elasticity

analytic formulas of the horizontal additional stress in a prestressed subgrade were derived

and the diffusion coefficient graphs of ?H under six typical slope ratios were obtained through the calculation of a number of distribution points. Meanwhile

the propagation characteristics and diffusion law of ?H were analyzed. The results show that: 1) the diffusion coefficient of horizontal additional stress (KH) at any point in a prestressed subgrade can be accurately obtained using three dimensionless parameters

i.e.

the slope rate (1:m)

the side length ratio of the lateral pressure plate (l/b) and the ratio of the calculation point’s horizontal depth to the width of the plate (h/b); 2) under different embankment slope ratios

the curves of KHD (or KHU)-h/b at the lower (or upper) corner points of the plate exhibit similar variation trends; at the lower corner points of the plate

the KHD-h/b relationship can be identified into two types determined by a critical l/b value ((l/b)c)

i.e.

first increasing and then decreasing or gradually decreasing; while the KHU at the upper corner points of the plate gradually decreases with increasing h/b; under the same embankment slope ration

KH increases with an increase in l/b

but the increase rate decreases gradually; 3) when the net spacing between the lateral pressure plate and the embankment shoulder is more than twice of the plate width

the additional stress diffusion law obtained by the interpolation of the graphic method is in good agreement with the results of the theoretical formulas and numerical simulations

which demonstrates the accuracy and applicability of the graphic method and theoretical formulas for calculating the horizontal additional stress in a prestressed embankment. The research findings form an efficient integration method and can provide a fast and simple reference for the design of a prestressed subgrade.