The generation of polyethylene mulch film (PEMF) has promoted the rapid development of agriculture, while the non-degradability of it has caused the serious damage for the ecological environment. Currently, the biodegradable mulch film is considered as the most promising green substitutes for petroleum-based PEMF, owing to its environmental friendliness and biodegradability. Hence, this study fabricated a biodegradable mulch film (PSGA) through the crosslink (the esterification/amidation reactions and hydrogen bonds) between polylactic acid waste liquid (PLAWL) and sodium alginate (SA)/gum arabic (GA). Then attapulgite (ATP) was added to improve the mechanical properties. Therein, PLAWL was a kind of waste liquid from the fabrication process of polylactic acid (PLA) based on straw. At the same time, PSGA had similar insulation and water retention performance to PEMF and great UV resistance, thermal stability, and hydrophilicity surface. Additionally, pot experiment showed that PSGA could significantly promote the growth of Chinese white cabbage and the degradability ratio of that could reach 50% in a month. The total amounts of Rhizobiaceae (Ensifer and Allorhizobium-Neorhizobium-Pararhizobium, fixing free nitrogen gas and providing nitrogen nutrients for plants) in soil with PSGA was 12%, which was obviously higher than that in blank (4.5%). Therefore, this study provides a high-value recycling route for industrial waste liquid, offering an alternative solution to PEMF.

The shear strength of compacted bentonite is crucial for preventing tilting and damage of the waste canisters in deep geological repositories (DGRs). The shear strength evolution along the confined wetting path also needs to be investigated, given the long saturation time of the bentonite buffer. This study conducted direct shear tests on densely compacted Gaomiaozi bentonite after suction control under confined conditions to determine its peak shear strength and strength parameters. Furthermore, the shear strength evolution along the confined wetting path was modeled on the basis of the effective stress principle. The results show that, for a given dry density, the peak shear strength at a given vertical pressure and the strength parameters exhibit an overall decrease along the confined wetting path. Moreover, the peak shear strength of the specimen that underwent confined wetting was considerably lower than that of the as-compacted specimen with the same total suction, indicating that the suction value and microstructure codetermine the peak shear strength of compacted Gaomiaozi bentonite. For this reason, the peak shear strength in the as-compacted state and the dual-porosity water retention curves established along the confined wetting path were used to model the shear strength evolution along the confined wetting path. The substitution equation for the effective stress parameter chi was selected on the basis of the experimental evidence. Finally, the model parameters were calibrated from the shear strength evolution at a given vertical pressure, and they reasonably reproduced the shear strength evolution under other vertical pressures. These findings can be helpful for the design and safe operation of DGRs under extreme geological conditions.

Agricultural soils are often affected by compaction due to machinery loads, which alters pore-size distribution and thus hydraulic properties. Up to date most studies on traffic and its impact on soil functions lack a detailed analysis of the effect on pore-size distribution (PSD). Our study aimed to understand how different machinery types, load levels, and moisture conditions impact the water retention curve (WRC) and PSD at various soil depths and field areas (headland or inner field). Eight field campaigns were conducted between 2016 and 2019 on a variety of sub-fields within one agricultural farm site with a clayey-silty soil. Undisturbed soil samples were collected before and after the harvest of winter wheat, silage maize, and sugar beet, and before and after digestate application. The van Genuchten model was fitted to the laboratory data, and parameters were interpreted to deduce WRC features. Additionally, the pore water pressure head at the pore-size density maximum (PSDmax) was determined and interpreted. The parameter alpha responded to all types of field traffic and decreased with increased load, indicating a shift from coarser to finer pores. The parameter n generally increased due to field traffic, suggesting a narrowed pore-size distribution. The theta s parameter, associated with porosity, decreased in all trials, with the tendency of lowest values occurring after wheeling under moist conditions. Load-induced shifts in the PSDmax towards finer pores were obvious down to 50 cm depth, even with relatively low loads. Our findings indicate that the majority of vehicles utilized in conventional agricultural operations can lead to severe soil compaction.

This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials (CREFMs) using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique (ATT). Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio, matric suction, and confining pressure on the properties of CREFMs. Key findings reveal a primary suction range of 0-100 kPa characterized by hysteresis, which intensifies with decreasing density. Notably, the air entry value and residual suction are influenced by void ratio, with higher void ratios leading to decreased air entry values and residual suctions, underscoring the critical role of void ratio in hydraulic behavior. Additionally, the critical state line (CSL) in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction, significantly affecting dilatancy and critical states. Furthermore, the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction. A novel modified dilatancy equation was proposed, which enhances the predictability of CREFMs' responses under variable loading, particularly at high stress ratios defined by the deviatoric stress over the mean effective stress. This research advances the understanding of CREFMs' performance, especially under fluctuating environmental conditions that alter suction levels. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Water scarcity is a critical problem around the world, and superabsorbent hydrogels has attracted growing attention in water management for handling water deficiency during agricultural and forestry practices. Herein, intending to apply gelatin hydrogel as soil conditioner, humic substances (HS) extracted from Chinese medicine residue compost were used to modify gelatin hydrogel through either physical mixing or chemical cross-linking. The results demonstrated that low level of HS could improve the hardness and rheological properties of the hydrogels, however, the gel strength significantly decreased when the concentration of HS rose up to 16 g/L. As revealed by TEM and XRD, chemical cross-linking reaction promoted the development of denser network structures, thereby improving the hardness and rheological properties of the hydrogels. Subsequently, applying HS at a concentration of 3 g/L was found to be preferable for enhancing the swelling ratio of the gelatin hydrogels, and lightweight substrates amended with the resultant hydrogels displayed superior water retention ratio (17.23 +/- 0.79 % for GelHS3 and 17.74 +/- 1.31 % for GelHS3-EDC). Furthermore, it was proved that HSincorporated hydrogels can effectively keep moisture for the growth of Melaleuca alternifolia (Maiden & Betche) Cheel saplings under drought stress. These findings suggest that humic substances can be utilized to modify hydrogels for use as soil conditioners.

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.

The variation in soil moisture can lead to unfavourable deformation of highway embankments, threatening their long-term stability under seasonal groundwater level fluctuations and frequent changes in evaporation and precipitation. This paper conducted unsaturated soil triaxial tests to examine soil water retention and volumetric deformation behavior during wetting-drying cycles. The results show that soil water retention decreases with increasing wetting-drying cycles, particularly in the low suction range from 0 to 100 kPa, where gravimetric moisture content (GMC) declines sharply. With more wetting-drying cycles, the soil's capacity for volumetric deformation diminishes. The soil has a loose soil structure and is more prone to plastic deformation. Furthermore, three soil water retention models, the Gallipoli, Tarantino, and Hu models were employed to analyse soil's hydromechanical behaviours and evaluate the effect of wetting-drying cycles. It was found that Tarantino's model used only three fitting parameters, which were more concise and maintained a good fitting effect. This study clarifies soil-water retention and volumetric deformation behavior during wetting-drying cycles, which is essential for effective water control in subgrade construction and operation.

Featured Application The findings of this study establish the behavior of sanitary landfill cover materials, such as compacted clay and compacted polyurethane-clay, in unsaturated conditions under several wet-dry cycles, which would aid in predicting the performance of the material under varying environmental conditions. By predicting the unsaturated hydraulic conductivity and understanding the effects of environmental stresses, the findings can aid in the design and implementation of more durable and efficient landfill liners and covers.Abstract Sanitary landfill covers are exposed to varying environmental conditions; hence, the state of the clay layer also changes from saturated to unsaturated. The study aimed to predict the unsaturated hydraulic conductivity of the locally available compacted clay and clay with polyurethane to determine their behavior as they change from wet to dry using matric suction and empirical models proposed through other studies. The specimens underwent three wet-dry cycles wherein the matric suction was determined for several moisture content levels as the specimen dried using the filter paper method or ASTM D5298. The results showed that the factors affecting the soil structure, such as grain size difference between clay and polyurethane-clay, varying initial void ratios, and degradation of the soil structure due to the wet-dry cycles, did not affect the matric suction at the higher suction range; however, these factors had an effect at the lower suction range. The matric suction obtained was then used to establish the best fit water retention curve (WRC) or the relationship between the matric suction and moisture content. The WRC was used to predict the unsaturated hydraulic conductivity and observe the soil-water interaction. The study also observed that the predicted unsaturated hydraulic conductivity decreases as the compacted specimen moves to a drier state.

Traditional water retention models often overlook the dynamic interplay between soil structure and moisture content, leading to inaccurate predictions of unsaturated soil behaviors. In this research, based on laboratory data, van Genuchten's soil water characteristic (van Genuchten, 1980) is modified to establish two bounding surfaces that define the permissible range of soil states in terms of the void ratio (e), suction (s), and degree of saturation (Sl). Considering a bounding surface technique, the model effectively captures hysteresis in the soil water retention behavior, encompassing main curves and scanning paths. This approach presumes that within the permissible range of soil states, which is included between two main surfaces, the derivative of the degree of saturation by void ratio and suction relies on the soil state's proximity to the main bounding surface. This hypothesis guarantees that the wetting-drying or compressing-swelling scanning curves transit smoothly toward their corresponding main surfaces. The derived equations for Sl are integrated into closed forms, allowing all scanning curves to be distinguished by varying values of the integration constant. Model necessitates the determination of two parameters (b and beta) related to the slope and intercept of the linear line interpolating experiments in the ln(s)-ln(eSl/s) plane, which can be defined based on at least a single wetting-drying test. The model predictions are validated against various data sets, including sands and clayey soils, published in the literature. This validation demonstrates the model's ability to reflect the behavior observed in experimental tests accurately. This new technique offers a significant advantage in the simplicity of parameter determination. Finally, this hysteretic water retention procedure is implemented into a finite element program (Code_Bright), and its performance is evaluated by simulating the behavior of a representative slope subjected to rainfall conditions.