Forest logging activities negatively affect various soil properties. In this study, we focus on the logging effects on soil water retention and associated pore size distribution. We measured the soil-water characteristic curves (SWCCs) on 21 undisturbed samples from three research plots: a reference area, a clear-cut area and a forest track. A total of 12 SWCC points between saturation and wilting point were determined for each sample with a sand box and pressure plate apparatus. The trimodal behaviour is highlighted by the dependence between soil moisture and suction. Therefore, we proposed a revised model by combining two exponential expressions with the van Genuchten model. The exponential terms describe the influence of macro-and-structural porosities, and the latter is used to calculate textural porosity. This new model with eight independent parameters was suitable to fit trimodal SWCCs in all samples. Results revealed that logging had the most destructive effect on large pores, and the soil on the forest track was the most affected. Both soil-air and available water capacity were reduced and the permanent wilting point increased as a result of damage to the soil structure and pore system. Observed increased organic carbon content in compacted soils can be attributed to slowed decomposition due to reduced air capacity and increased waterlogging susceptibility of damaged soils.

Biochar, as an environment-friendly soil amendment, has been extensively proposed in landfill cover, primarily for promoting soil hydraulic properties, such as hydraulic conductivity and soil water retention. However, the impact of biochar derived from various feedstocks on soil-biochar mix properties, particularly gas permeability under unsaturated conditions, remains under-explored. This study evaluates how different types of biochar influence gas permeability and soil water retention. Five biochars pyrolyzed using different biomass waste, such as apple wood, reed straw, walnut, corn cob and corn straw, were each mixed with sandy soil in a 5% mass ratio. Gas permeability and hydrological response (water content, matric suction) were measured during wet-dry cycles. Results indicated that biochar amendments generally enhanced water retention compared to bare soil. Apple wood biochar, in particular, significantly improved both water content (reaching 90% of the control's maximum moisture content) and suction (peaking at 2755 kPa), outperforming reed straw, walnut, corn cob and corn straw biochars. This enhancement stems from apple wood biochar's hydrophilic functional groups (e.g., -OH), which improve soil hydrophilicity and water-biochar interactions. Its large specific surface area and tightly arranged micropores further enhance suction. Gas permeability rose with increasing suction, with reed straw and apple wood biochars increasing gas permeability by 196% due to their larger average pore sizes and the formation of more meso-macro pore structures in the sandy soil. Conversely, walnut and corn cob biochars reduced soil permeability, suggesting their suitability for high-pressure applications. These findings guide the use of biochar-amended soil in landfill covers to mitigate gas emissions.

Sedimentary soils usually have an anisotropic structure, and they are generally unsaturated, especially at shallow depths. Existing models for anisotropic and structured soils mainly focus on saturated conditions, while the unsaturation effects are not considered. In this study, a bounding surface model for anisotropic and structured soils under both saturated and unsaturated conditions is developed. The model incorporates the anisotropy and structure effects on the mechanical behaviour (e.g., the loading collapse (LC) bounding surface) and considers the structure degradation and anisotropy evolution. Furthermore, based on experimental results in the literature, the increase in water retention capacity with an increasing degree of anisotropy is incorporated by a new anisotropy and void ratio -dependent soil water retention equation. The proposed hydro -mechanical model is validated against extensive experimental data. Comparisons between experimental and calculated results show that the behaviour of anisotropic and structured soils under both saturated and unsaturated conditions can be well captured.

Experimental and modeling approaches on the soil water retention of low-plasticity undisturbed silty clay were presented in this study to incorporate the combined effects of the pore structure and volume change. Two experimental procedures under the K0 stress state were performed to understand the dependency of hysteretic water retention on both pore structure and volume change effects. The water retention test results show that the hydraulic hysteresis gradually decays when either the suction or vertical compressive stress increases due to a substantial reduction in the macrostructural porosity. Distinct pore structures, including macro- and transitional extra-pore structures with a median size identified through the Mercury Intrusion Porosimetry technique, can induce a noticeable bimodal feature of the SWRC in capillary suction range. The effect of vertical stress, leading to different initial void ratios but a consistent microfabric, can also considerably restrain the irreversible suction-induced volume change and thus influence the water retention as vertical stress increases. The results from K0 compression tests indicate that the variation in the degree of saturation presents an approximate linear negative correlation with the volume change, and the hydromechanical coupling can be, therefore, interpreted through considering the effect of stress-induced volume change on the variation in the degree of saturation. A novel unified formulation of the hydraulic model was developed by incorporating the modified Gallipoli's SWRC model and an unsaturated volume change equation, which can simultaneously describe the combined effects of a heterogeneous pore structure and an elasto-plastic volume change on the variation in the degree of saturation. The proposed model was found to have a good accuracy compared to the test data, testifying to its enhanced predictive capability in modeling the bimodal water retention and the hydromechanical coupling effect.

Rehabilitation following open-cast mining aims to build a long-term functional and sustainable soil cover for a stable landscape development. The objective of this study was to assess changes in soil recovery of rehabilitation performed at different times (1980, 1998, 2009, 2016, 2017) measured as soil hydraulic and mechanical properties (shear stress) at an open-cast Yallourn mine site in south-east Australia (Victoria) in 2021. Soil hydraulic properties (SHP) were determined using the extended evaporation method and the water retention and hydraulic conductivity curves were fitted using the van Genuchten-Mualem model. The vane shear tests were performed at two depths (0-8 and 10-18 cm) combined with soil water content measurements. The results of the SHP showed a shift in the soil water retention curve when comparing 1980 and 2017 sites. While the saturated water content i.e., total porosity was the same, the saturated hydraulic conductivity (Ks) decreased from 36.7 to 1.02 cm day-1, respectively. This was mostly connected to the textural pore size distribution, as large differences in clay and sand content among the sites were observed. The vane shear test showed also large differences with rehabilitated sites indicating a larger variation compared to the reference site (exception 2016 site) and having generally higher shear resistances. The observed small-scale heterogeneity of the rehabilitated soils is most likely explained by soil heterogeneity and disturbance due to excavation activities and rehabilitation as well as availability of uniform soil material. Inevitable heterogeneity of the soil hydraulic and mechanical properties should be taken into consideration during the design and construction of various landforms as well as when implementing soil monitoring schemes.

Air entrapment in soil-pores during cyclically hydraulic loading requires a physical insight by means of both modelling and experimental works. In the present study, transient drying and wetting tests are performed in a sand column device. The device enables to perform measurements of transient water content and pore water pressure in unsaturated soils. The measurements of water content as well as the pore pressure are directly linked to soil-water retention curve. The experimental results show that it exists an entrapped air together with hysteresis in soil water retention. Based on the experimental results, a new computer model of soil water retention is proposed. Finally, numerical simulation of air -water transport in unsaturated media is implemented using this model. The comparison between measured data and numerical simulation results shows that the proposed model can improve an accuracy in simulation of the water transport in unsaturated media.

By altering the physical properties of soil through root activity, plants can act as important agents in affecting soil hydrothermal properties. However, we still know little about how plant roots regulate these properties in certain ecosystems, such as alpine meadows. Thus, we studied the influence of roots on soil hydrothermal properties in the Qinghai-Tibet Plateau (QTP). Root biomass as well as soil physicochemical and hydrothermal properties were examined at a depth of 0-30 cm at three study sites in the QTP. The relationship between root biomass and saturated soil hydraulic conductivity (K-s) was examined, as was the applicability of common soil hydrothermal properties models to the alpine meadow system. Results revealed that approximately 91.10%, 72.52%, and 76.84% of root biomass was located in the top 0-10 cm of soil at Maqu, Arou, and Naqu, respectively. Compared with the bulk soil, the water-holding capacity of rhizosphere soil was enhanced by 20%-50%, while K-s was decreased by at least 2- to 3-fold. The thermal conductivity (lambda) of rhizosphere soils was lower than that of the bulk soil by 0.23-0.82 W m(-1).K-1 on average. Lastly, soil hydrothermal properties models that do not explicitly consider root effects overestimated the Ks and lambda in the rhizosphere soil of these systems. Overall, our results revealed distinctive differences in soil hydrothermal properties between the rhizosphere soil and the bulk soil in the QTP. This research has important implications for future modeling of soil hydrothermal processes of alpine meadow soils.