Transiently iterative solutions of spatially symmetrical earth pressure of a foundation pit in unsaturated soils

To investigate the differences in spatially axisymmetric earth pressure of a foundation pit within unsaturated soils under various transient suction conditions, two representative transient suction methods were selected for comparative analysis. These methods were evaluated for their similarities, differences, and variations in suction behavior. The differential slip line equation and a transient iterative solution for the earth pressure surrounding a spatially axisymmetric circular foundation pit in unsaturated soils were formulated. The validity of the proposed solution was confirmed by comparing it with existing earth pressure solutions reported in the literature. Subsequently, parametric studies were conducted to examine the effects of these two transient suction methods on earth pressure in different soil types—sands, silts, and clays. The results indicate that the proposed transient iterative solution for spatially axisymmetric earth pressure is not limited to any specific transient suction method and can accommodate variations in rainfall intensity, duration, and soil unit weight, thereby offering better alignment with real-world engineering scenarios. During rainfall, both transient suction methods exhibit consistent performance regarding the magnitude and profile of matric suction as well as the earth pressure of foundation pits. As initial rainfall intensity increases, matric suction decreases while earth pressure increases. However, each method has its own scope of application; misapplication of a transient suction method may lead to an overestimation of earth pressure. For sands, the earth pressure of foundation pits is only slightly affected by rainfall intensity or duration. In contrast, for silts and clays, earth pressure significantly increases during rainfall with the rise in both rainfall intensity and duration. After rainfall ceases, earth pressure initially rises and then declines over time, which can be attributed to the gradual increase in matric suction caused by evaporation, exhibiting a certain time delay.