Frozen soil, covering most of the Tibetan Plateau (TP), critically influences land surface and climate simulations. Although some studies have made advancements in simulations, further investigation into the distinct mechanisms underlying relevant parameterization schemes remains essential. This study compares two frozen soil permeability schemes in Noah-MP (NY06: high-permeability; Koren99: low-permeability) to elucidate their distinct hydrological mechanisms. Although significant disparities exist in the simulation of soil water and ice content between the two schemes in permafrost regions, the simulated soil water content in the shallow layer exhibits similarity. Their underlying physical processes behind this similarity differ fundamentally: Koren99 relies on cross-seasonal ice melt recharge, whereas NY06 depends more on current-season precipitation and snowmelt. With greater soil depth, soil water differences progressively propagate downward, amplifying variations in hydraulic conductivity, and soil memory effects become increasingly dominant. Meanwhile, the Koren99 scheme more effectively impedes bottom-up melting water transport than top-down effect. However, the aforementioned disparities are not apparent in seasonally frozen soil. Notable disparities also exist in simulated evapotranspiration and surface runoff over permafrost regions, particularly during the summer months. This research investigates the differences in water transport within frozen soil over the TP, elucidates the distinct hydrological mechanisms underlying different frozen soil permeability schemes, and highlights that similar soil hydrothermal simulations are associated with different physical processes, leading to varying degrees of effectiveness in soil memory. Furthermore, this research elucidates the dual role of soil ice (permeability restriction and water storage) in hydrological processes, providing a theoretical basis for improving frozen soil parameterization.

Hydraulic conductivity plays a significant role in the evolution of liquefaction phenomena induced by seismic loading, influencing the pore water pressure buildup and dissipation, as well as the associated settlement during and after liquefaction. Experimental evidence indicates that hydraulic conductivity varies significantly during and after seismic excitation. However, most previous studies have focused on experimentally capturing soil hydraulic conductivity variations during the post-shaking phase, primarily based on the results at the stage of excess pore water pressure dissipation and consolidation of sand particles after liquefaction. This paper aims to quantify the variation of hydraulic conductivity during liquefaction, covering both the co-seismic and postshaking phases. Adopting a fully coupled solid-fluid formulation (u-p), a new back-analysis methodology is introduced which allows the direct estimation of the hydraulic conductivity of a soil deposit during liquefaction based on centrifuge data or field measurements. Data from eight well-documented free-field dynamic centrifuge tests are then analysed, revealing key characteristics of the variation of hydraulic conductivity during liquefaction. The results show that hydraulic conductivity increases rapidly at the onset of seismic shaking but gradually decreases despite high pore pressures persisting. The depicted trends are explained using the KozenyCarman equation, which highlights the combined effects of seismic shaking-induced agitation, liquefaction, and solidification on soil hydraulic conductivity during the co-seismic and post-shaking phases.

This paper presents a comprehensive investigation into the role of soil permeability variation on the stability of slopes reinforced by retaining walls, with a focus on the Huizhou slope failure as a case study. The study demonstrates that rising groundwater levels diminish the Factor of Safety (FoS) for retaining walls, with stability most compromised under combined loading from adjacent soil and lightweight concrete. These findings emphasize the need for enhanced drainage or structural support in retaining wall designs subjected to elevated groundwater conditions. It integrates advanced numerical simulations, utilizing Abaqus and GeoStudio, with empirical field data to analyze the interactions between soil permeability, pore water pressure, moisture content, shear strength, and the overall stability of the slope. The dynamics of water infiltration are influenced by permeability, moisture content, and the groundwater table. These factors change the pore pressure and decrease shear strength, which causes shear failure in the slope mass. This research also looks at how surcharge loading affects slope stability. Higher permeability soils cause faster infiltration rates, leading to higher pore pressures, lower effective shear strengths, and a higher likelihood of slope failure. The opposite is true for reduced permeability, which makes drainage more difficult and ultimately leads to hydrostatic pressure building up behind retaining walls, which in turn makes the slope even more unstable. This study demonstrates the critical need for optimized drainage systems to reduce the hazards of infiltration-induced failure and the role of precise permeability evaluation in geotechnical design. Geotechnical engineers can use these results to better understand how to construct and maintain slope stabilization systems.

This study investigates the long-term effects of landfill leachate contamination on soil hydraulic conductivity and shear strength parameters over a 12-month period, addressing the current lack of comprehensive long-term experimental data in this field. Laboratory permeability tests and direct shear tests were performed on sandy clayey silt samples contaminated with leachate at concentrations ranging from 5% to 25%. Microstructural and mineralogical analyses were conducted using SEM and XRD to identify the mechanisms behind observed changes. The results identify a critical threshold at 15% contamination where soil behavior transitions from granular to cohesive characteristics, marked by significant changes in both hydraulic and mechanical properties. Hydraulic conductivity increases at low contamination levels but decreases significantly at higher levels, while friction angle shows an immediate reduction from 36.5 degrees to 31-31.5 degrees and cohesion exhibits a three-phase evolution pattern, reaching peak increases of 151.5% at 15% contamination. The hydraulic conductivity changes are controlled by contamination level rather than exposure time, maintaining stable values throughout the testing period, whereas shear strength parameters demonstrate more complex temporal evolution patterns. These findings provide essential parameters for landfill design and stability assessment, demonstrating how leachate concentration affects long-term soil behavior through mineral formation and structural modification.

Saturation development and distribution at the soil-bedrock interface are important for predicting shallow landslide occurrence. Previous studies have indicated that saturation is generated in bedrock depressions and valleys and that bedrock groundwater seepage generates locally saturated areas. However, the effects of soil permeability, which is known to be heterogeneously distributed, on saturation development and distribution are poorly understood. In this study, we performed unprecedented high-resolution (approximately 50 cm grid) soil pore water pressure and soil temperature monitoring using 141 tensiometer-thermocouple sets in a plot measuring approximately 5 x 4 m to investigate the effects of topography and bedrock groundwater seepage on saturation development and distribution. We then measured permeability distribution of two soil profiles, including at the soil-bedrock interface, using the Guelph Permeameter method (GP method) for comparison with saturated zone distribution and saturation duration. The results indicated that a perennial saturated area was formed by bedrock groundwater seepage and was distributed downstream from a certain bedrock surface altitude in the lower region of the study plot. After a peak of rainfall, the perennial saturated area expanded upslope owing to the increased seepage. In areas without the influence of bedrock groundwater, saturation was observed to retreat rapidly at high permeability points and persist over long periods at low permeability points; however, the saturation duration was inconsistent with the bedrock surface topography. Therefore, it is suggested that the bedrock altitude controls the saturation distribution generated by bedrock groundwater, whereas the distribution of saturation that is associated with direct rainwater infiltration may be controlled by the permeability distribution during recession periods. Although the plot size was small, the unprecedented high-resolution observations suggest that the permeability distribution, rather than the bedrock topography, may control the saturated zone distribution following rainfall.

Grouting is normally undertaken to reduce the permeability of rock or soil formations and this process is used extensively in the construction of hydraulic structures such as dams, tunnels and in a wide variety of special cases. Even though the application of the grouting technique to reduce the permeability of rock formations has been reported in literature, no serious attempts are reported about the effective use of this technique to reduce the permeability of soil formations. In this paper, an attempt has been made to study the effectiveness of grouting in reducing the permeability of the granular medium. Constant head permeability tests were carried out on the sand medium treated with different grouting materials such as cement, bentonite, lime, locally available clay and different combinations of the above materials. By grouting with different grout materials (e.g., in the case of cement - bentonite grout) the permeability of the medium sand got reduced from 10(-4) m/s to 10(-9) m/s. The present study undoubtedly proves the effectiveness of using grouting as an efficient technique in reducing the permeability of sandy soils.