Soil-water characteristics, which vary with hydrological events such as rainfall, significantly influence soil strength properties. These properties are crucial determinants of the bearing capacity of foundations. Moreover, shear strength characteristics of soils are inherently spatially variable, and considering them as homogeneous parameters can result in unreliable design. This paper presents a probabilistic study of the two-dimensional bearing capacity of a strip footing on spatially random, unsaturated fine-grained soil using Monte Carlo simulation. The study employs the hydro-mechanical random finite difference method through MATLAB programming along with FLAC2D software. The undrained shear strength under saturated conditions is modelled as random fields using a log-normal distribution. The generated random values are then made depth-dependent by correlating them with matric suction. Initially, matric suction is assumed to be under a hydrostatic condition and decreases linearly with depth to zero at the groundwater level. Afterward, unsaturated soil is subjected to rainfall with different durations, resulting in the non-linear distribution of matric suction and, consequently, the mean value of undrained shear strength in depth. The results showed that rainfall infiltration impacts the strength characteristics of near-surface heterogeneous strata, leading to significant effects on the bearing capacity and failure mechanism of footing.

The influence of a firm stratum on the stability of a slope under undrained conditions has long been of interest to geotechnical investigators, which has been studied in a number of previously important works in relation to slope stability analyses without considering soil spatial variability. This paper proposes another look at such a problem in the context of probabilistic slope stability analyses considering soil spatial variability. Here, the random field (RF) is used to simulate the spatially variable undrained soil strength. It is found that under stationary RF and non-stationary RF with the soil strength at the top ground surface (s(u0)) larger than 0, the depth of the firm stratum (H-f) has a significant influence on the mean and standard deviation of factor of safety (i.e., mu [FS] and 6 [FS], respectively). By contrast, under non-stationary RF with s(u0) = 0, H-f has a slight influence on mu [FS], but its influence on 6 [FS] is non-negligible. In addition, the autocorrelation distance is found to have an insignificant impact on the influential effect of H-f f on mu [FS]. However, for 6 [FS], this impact is not negligible. When the autocorrelation distance is smaller, the influence of Hf f on 6 [FS] would be more significant. Under non-stationary RF, the influence of H-f on 6 [FS] would be slight if the autocorrelation distance is large enough. Furthermore, the impacts of slope ratio, su0, u0 , isotropic and anisotropic features on the influential effects of H-f are also investigated and discussed.