Soil heterogeneity, due to variations in the subsurface stratigraphy or properties within a layer, can trigger or amplify differential settlements that affect buildings and infrastructure and can thus lead to (increase in) damage. The state-of-the-art mainly focuses on the effect of heterogeneous properties within a layer on engineering problems. From this, it is known that the variation in properties can increase the vulnerability of a structure. However, nearly always variations in the soil lithological conditions are disregarded, while they can influence subsidence potentially even more. Lithological variations are relevant both at the scale of individual buildings as well as different scales (city, regional, country), for which often detailed soil information is not available. Thus, for a better prediction of potential building damage related to subsidence, knowledge about the scale and influence of lithological variations is needed. This paper describes an approach to quantify and investigate the influence of lithological heterogeneity at the scale of a single building. Moreover, this exploratory study evaluates the influence of lithological heterogeneity on the spatial variability of settlements, intending to upscale the approach to regional application. Two independent datasets at high resolution (site-specific) and low resolution (national level) are used to retrieve the stratigraphic conditions for the area selected for the analyses. One-, Two- and Three-dimensional numerical models, based on the collected information are used to simulate the consolidation process and settlement due to a uniform load imposed on the surface level of the study area. Additional analyses investigate the influence of loading conditions and groundwater table. The parameter correlation length is used to quantify the spatial variability of the soil layer thickness and then of the computed settlements. The analyses reveal that the spatial variability of the soil strata thickness matches that of the computed settlements, ranging from 2 to 10 meters. In other words, the lithological variability of the soil leads to differential settlements occurring at the scale of man-made structures such as houses, roads, and embankments. Thus, the results encourage including the contribution of lithological heterogeneity in models and predictions of differential settlement at the scale of individual structures. Moreover, the statistical properties, in terms of mean, spread and distribution shape, of the settlement computed through in-situ specific models, match with those derived at the national scale. These results are expected to support the identification of areas potentially influenced by lithological soil heterogeneity, thus showing potential for upscaling to regional or national levels.

This study investigated the influence of sample preparation methods, moist tamping and wet pluviation, on the erodibility and mechanical behaviour of gap-graded soils with three gradations: fully stable, unstable, and on the borderline of stability. Drained triaxial tests were performed using a modified erosion-triaxial apparatus, followed by micro-CT scanning to assess pore network properties. The results indicated that for fully stable and fully unstable samples, the preparation method had minimal impact on both erosion and mechanical behaviour. However, for the samples on the borderline of stability, wet pluviation method resulted in fine particle segregation, creating a heterogeneous structure with reduced pore connectivity. This led to lower erosion rates (0.4 gr/min reduction compared to the moist tamping technique), but mechanical properties remained largely unaffected, as confirmed by similar intergranular void ratios and stress-strain responses. Micro-CT scanning quantified differences in pore structure, showing that wet pluviation samples exhibit lower connected porosity compared to those prepared by moist tamping. These findings highlight the critical role of specimen preparation in assessing suffusion susceptibility and erosion behaviour, particularly for soils near the threshold of instability.

Philip's two-term infiltration equation has been widely used to infer soil saturated hydraulic conductivity (Ks), the accuracy of which is usually influenced by the size of infiltration rings and soil conditions. Previous studies have primarily focused on exploring the ring-size dependence of Ks estimations under specific soil conditions (e.g., soil isotropy and/or uniform initial water content). This study aimed to provide a comprehensive analysis by systematically considering eight heterogeneous and anisotropic soils with nonuniform initial water contents. Specifically, we examined the validity of Philip's infiltration equation as well as the recently proposed two forms (i.e., infiltration and time forms) of Parlange's infiltration equation both theoretically and in practical applications of double-ring infiltration. Then the time form of Parlange's equation was applied to infer Ks using double-ring infiltrometer measurements with different combinations of six inner ring diameters (10, 20, 40, 80, 120, and 200 cm) and three buffer index (defined as the ratio of the difference between inner and outer ring diameters to the outer ring diameter) values (0.20, 0.33, and 0.50). For each infiltrometer set, 20 stochastic Ks fields were randomly generated by adopting five standard deviation values (0.1, 0.3, 0.5, 0.7, and 0.9). Furthermore, we investigated the effects of five horizontal correlation lengths (30, 60, 150, 300, and 600 cm) on Ks estimations. The results demonstrated that Parlange's equation, compared to Philip's equation, was more universal in describing the cumulative infiltration relationship for the test soils. The combination of inner ring diameter and buffer index of 40 cm and 0.2, respectively, which satisfied most of the practical requirements for determining Ks in the Soil Water Infiltration Global (SWIG) database was optimal. When the horizontal correlation length exceeded a threshold (i.e., 150 cm in our study), the inner ring diameter was required to increase to 80 cm. Our findings contribute to accurate Ks estimations of different soils using double-ring infiltrometers.

Landscape-scalechanges in the Arctic as a result of climate changeaffect the soil thermal regime and impact the depth to permafrostin vulnerable tundra watersheds. When top-down thaw of permafrostoccurs, oxygen and porewaters infiltrate deeper in the soil columnexposing fresh, previously frozen material and altering redox conditionsthat govern the mobility of geochemical constituents. Redox conditionsplay a critical role in the carbon cycle processes that link permafrostcarbon stocks with potential feedbacks to climate warming. As such,there remains a gap in knowledge understanding how redox stratificationsin thawing permafrost impact the geochemistry of watersheds in responseto climate change and how investigations into redox may be scaledby coupling extensive geophysical mapping techniques. In this study,we collected soils and soil porewaters from three soil pits and surfacewater samples from an Arctic watershed on the North Slope of Alaskaand analyzed for trace metals iron (Fe) and manganese (Mn) and Feoxidation state using bulk and microscale techniques, including X-raysynchrotron spectroscopy. We also used geophysical mapping and soilthermistors to measure active layer depths across the watershed torelate accelerating permafrost thaw to watershed geochemistry. Wefound that Fe(II) and Fe(III) co-occur in the soils, porewaters, andsurface waters of Imnavait Creek watershed with Fe(II) comprisingup to 37% of the total Fe concentrations in the 40-60 cm soildepth and up to 17% in the 60-80 cm soil depth. In comparisonto the surface (0-20 cm) and deeper in the permafrost (80-100cm), Fe(II) was found to be enriched in the soils at the permafrost-activelayer transition zone in two of the three soil pits and that translatedto mobilization of Fe(II) to porewaters upon thaw at 40-60cm, contributing up to 72% of the total Fe. Further, Fe(II) was foundto be mobilized in all porewater samples from 60 to 100 cm depth andcomprised 56-70% of the total Fe. In the surface water, Feand Mn concentrations were linked to seasonality with higher concentrationscoinciding with the deepest yearly extent of the active layer thawprogression. Overall, we found evidence that Fe and Mn could be usefulas geochemical indicators of permafrost thaw and release of Fe(II)from thawing permafrost and further oxidation to Fe(III) could translateto a higher degree of seasonal rusting coinciding with the warmingand thawing of near surface-permafrost.