Abstract: To reasonably capture the magnitude, distribution, resultant force, and action point height of lateral earth pressure with depth on retaining structures for a circular foundation pit in unsaturated soils, the inclination angle of the soil sliding surface behind retaining structures was first derived. The derivation, suitable for both uniform and linear profiles of suction stress, was based on the suction stress theory of unsaturated soils and the limit equilibrium method. Subsequently, a method for calculating lateral earth pressure on retaining structures of circular foundation pits in unsaturated soils was introduced by integrating the characteristics of vertical and circumferential soil arches to account for the spatial soil arching effect. Additionally, the proposed calculation method was validated by comparing it with existing theoretical solutions and model test data, and the influence of relevant factors was analyzed. The results show that the proposed calculation method not only demonstrates excellent consistency with existing theoretical solutions and model test data, confirming its accuracy and rationality, but also effectively addresses the comprehensive effects of unsaturated formation, spatial soil arching, and structure-soil contact parameters on the lateral earth pressure of circular foundation pits. This contributes to optimizing the design and construction of circular foundation pits. Consequently, the proposed calculation method holds theoretical significance and promising practical applications. The resultant force of lateral earth pressure for a foundation pit significantly decreases with an increase in absolute value of surface suction stress, circumferential stress coefficient, and external cohesion. However, the variation in the action point height of the resultant force remains relatively minor. Lateral earth pressure under a linear profile of suction stress is greater than under a uniform profile. However, the variation in lateral earth pressure is more pronounced under the uniform profile of suction stress

Key words: circular foundation pit, lateral earth pressure, spatial soil arching effect, suction stress, limit equilibrium method