Energy piles, which serve the dual functions of load-bearing and geothermal energy exchange, are often modeled with surrounding soil assumed to be either fully saturated or completely dry in existing design and computational methods. These simplifications neglect soil saturation variability, leading to reduced predictive accuracy of the thermomechanical response of energy piles. This study proposes a novel theoretical framework for predicting the thermo-hydro-mechanical (THM) behavior of energy piles in partially saturated soils. The framework incorporates the effects of temperature and hydraulic conditions on the mechanical properties of partially saturated soils and pile-soil interface. A modified cyclic generalized nonlinear softening model and a cyclic hyperbolic model were developed to describe the interface shear stress-displacement relationship at the pile shaft and base, respectively. Governing equations for the load-settlement behavior of energy piles in partially saturated soils were derived using the load transfer method (LTM) and solved numerically using the matrix displacement method. The proposed approach was validated against experimental data from both field and centrifuge tests, demonstrating strong predictive performance. Specifically, the average relative error (ARE) was less than 15% for saturated soils and below 23% for unsaturated soils when evaporation effects were considered. Finally, parametric analyses were conducted to assess the effects of flow rate, groundwater table position, and softening parameters on the THM behavior of energy piles. This framework can offer a valuable tool for predicting THM behavior of energy piles in partially saturated soils, supporting their broader application as a sustainable foundation solution in geotechnical engineering.

This study investigates the strain-rate-dependent mechanical properties of unsaturated red clay under varying temperatures and matric suction conditions through triaxial shear tests on red clay fill materials from the Sichuan-Tibet Railway region. The tests were conducted with multiple shear strain rates, complemented by advanced microstructural analysis techniques such as mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM), to examine the evolution of pore structure. The results indicate that high matric suction significantly reduces the rate-dependency of strength in red clay fill materials, whereas temperature has a relatively smaller effect. As matric suction increases, the strain-rate parameter decreases across different temperatures, with a diminishing rate effect observed at higher suction levels. Compared to temperature, strain rate has a more pronounced influence on failure time. An increase in strain rate leads to a significant reduction in failure time. At low strain rates, failure time exhibits substantial variability, while at high strain rates, the effects of temperature and matric suction on failure time become less significant. Under high-temperature conditions, the strength of red clay is enhanced, and failure time is delayed. These findings provide critical theoretical support for controlling settlement deformation and predicting failure times of subgrade fill materials under complex climatic conditions, offering valuable insights for engineering applications.

This study numerically evaluates the stability of RS walls with select, marginal, and fly ash backfills under rainfall infiltration. A transient seepage, global stability, and lateral deformation were analyzed considering different rainfall intensities. As infiltration flux increases from 10 mm/h (low rainfall) to 80 mm/h (very heavy rainfall), wall stability decreases significantly due to the excessive buildup and inadequate dissipation of pore water pressure. Pore water pressure increases considerably due to infiltration. Fly ash fill exhibits approximately 125% higher pore water pressure than select fill. To allow for the dissipation of pore water pressure, the effect of chimney drains of various thicknesses was analyzed on the stability of the RS wall. It was observed that the stability of the wall increased with increasing thickness of the chimney drain.

Intense rainfall and extreme modifications to the slope are the immediate triggering factors of landslides and slope instability in the Western Ghats of Kerala, India. An increase in the frequency and intensity of rainfall and its adverse impact on the stability of slopes have demanded slope stability analysis and the adoption of suitable mitigation measures to retard slope failure. This study examines the role of matric suction and pore water pressure variations caused by rainwater infiltration in slope stability. Suction is one of the factors that hold the soil particles together and provide necessary shear strength, hence improving slope stability. During monsoons, water infiltrates the soil which leads to a reduction in soil suction and therein the shear strength and increasing susceptibility to landslides. The study focuses on the rainfall-induced slope failure at Kormala, Muvattupuzha in Kerala, India, where a devastating landslide took place. A laboratory study was conducted on soil samples obtained from the location to obtain the soil properties and soil suction parameters. The resilience of the slope in proximity to Muvattupuzha was assessed numerically for slope stability using a combination of finite element and limit equilibrium analysis software. The variation in pore water pressure across various sections of the slope by varying rainfall intensities was analysed and the change in the factor of safety (FOS) with respect to time at different intensities was compared. The results indicate that infiltration-induced changes in matric suction significantly influence slope stability. At lower rainfall intensities (I = 0.2 Ksat), suction reduction was minimal and the slope remained stable while for moderate intensities (I = 0.4 Ksat and I = 0.6 Ksat), noticeable reductions in suction occurred, particularly near the surface and at the slope toe, leading to a marginal decline in FOS. However, at higher rainfall intensities (I >= 0.2 Ksat), infiltration exceeded the hydraulic conductivity of the soil, causing a rapid decrease in suction and led to near-saturation conditions, especially at the crest and toe sections. Hence, proper and periodic monitoring of the rainfall intensities and soil suction is required for enhanced resilience to slope instability and landslides in this and surrounding regions.

Rigid pile composite foundation (RPCF) has been widely used in Yellow River Alluvial Plain (YRAP) due to remarkable reinforcement and economical effects. However, current design of RPCF in this area are typically based on saturated soil mechanic principles assuming drained condition, despite the fact that the soil is typically in unsaturated condition. Due to long time water scouring, the silt in YRAP generally exhibits high particle sphericity and poor particle gradation. Even after standard compaction, it is still in a relatively loose state with developed capillary pores. Water content increment induced by infiltration can lead to considerable soil mechanical properties degradations due to matric suction reduction associated with soil micro-structure rearrangement. Consequently, the RPCF will suffer serious bearing characteristic deteriorations, exhibiting additional settlement. In this study, extending unsaturated soil mechanics, initially the influences of matric suction on mechanical properties of YRAP silt were demonstrated. Then total RPCF settlement was calculated as the sum of the compression deformation of the soil between piles in the reinforcement zone and the underlying soil stratum. The former one was estimated through the modified load transfer curve method considering the pile-soil interface behaviors deteriorations with matric suction reduction, while the later one was estimated through the traditional stress diffusion method. The feasibility of the proposed method was validated through a model RPCF test subjected to ground water level fluctuations. Good comparisons on RPCF mechanical behaviors indicate the proposed method can be a valuable tool in the design of RPCF in YRAP under extreme weather conditions.

Rigid pavements built on an expansive subgrade often sustain damage due to differential movement caused by variations in the subgrade moisture content and the resulting swelling pressure. This study aims to introduce an approach based on swelling pressure for analyzing the deformation of rigid pavements. The analysis takes into consideration the effect of soil matric suction on the modulus of subgrade reaction and potential swelling pressure. The numerical analysis was carried out using the pasternak foundation model, wherein the pavement was idealized as an Euler-Bernoulli beam, the pasternak shear layer represented the granular sub-base supporting the pavement, and the expansive soil was modelled using winkler springs. To demonstrate the practical applicability of the proposed model, a case study is presented for an Indian site and the outcomes are presented. The parametric study clearly illustrates that the modulus of subgrade reaction of expansive soil is the most sensitive and significant parameter for improving the flexural response of the pavement. A flowchart outlining the evaluation procedure is included to provide a visual representation of the analysis process.

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.

Soluble salts significantly influence the freezing characteristic parameters of frozen soil. Previous studies have either insufficiently addressed the effect of sodium sulfate on matric suction or not comprehensively revealed the mechanism by which temperature affects matric suction at freezing temperature. In this study, the moisture and suction sensors were used to quantify the freezing temperature (FT), unfrozen water content (UWC), and matric suction (MS) of Ili loess with varying soluble salt contents. The impact of soluble salt content on three freezing characteristic parameters were investigated with the underlying mechanisms revealed. The results indicated that there was an initial decrease in both freezing and supercooling temperatures as the soluble salt content increased. Beyond a soluble salt content of 14 g/kg, an increase in both the freezing and supercooling temperatures was observed. Specimens with different soluble salt contents exhibited distinct UWC, which could be categorized into three stages based on temperature. A crystal precipitation stage was observed beyond the soluble salt content of 14 g/kg. Moreover, the proposed fitting model for UWC by incorporating the soluble salt content into the Gardner model demonstrated high accuracy. The MS can also be divided into three stages with temperature. Notably, specimens with soluble salt contents of 20 and 26 g/kg exhibited nonlinear increases in MS at temperatures of 5 degrees C and 10 degrees C due to crystal precipitation. Furthermore, theoretical calculations indicated the complete precipitation of sodium sulfate during the positive temperature stage.

The structure of loess is an important physical property indicator. Just like grain size, moisture content and density, it also affects the physical and mechanical properties of loess. Based on the definition of the constitutive degree index, the definition of structural parameters was redefined. And conventional triaxial shear tests were conducted on undisturbed soil samples and remolded soil samples with different moisture contents and different dry densities. Firstly, the deformation characteristics and strength changes of the soil samples were analyzed. Then, based on the definition of structural parameters, the structural change laws of the soil were analyzed. Finally, the relationships between the structural properties and soil moisture, grain size and density were analyzed, thereby verifying that the newly proposed definitions of the structural parameters are reasonable.

The residual shear strength (RSS) of unsaturated soils is a crucial parameter for the reliable analysis and design of geostructures constructed with or within unsaturated soils undergoing large shear deformation. For investigating the RSS of unsaturated soils, two sets of data are specifically generated on the poorly graded sand with silt and Indian Head till using suction-controlled ring shear tests and three more sets (i.e., silty sand (SM), silty clayey sand, and fat clay) are gathered from the literature. A model is proposed extending two approaches for predicting the RSS for both coarse- and fine-grained unsaturated soils. In this model, the suction contribution was calculated considering the loss of degree of saturation due to shearing, which was described as a nonlinear function of degree of saturation. The capability of the proposed model is validated with the five sets of data using two different approaches. The best-fitting approach that is based on three fitting parameters provides good predictions. The approximate approach performs well for four studied soils, except for SM soil; this approach is simple for use in engineering practice because no fitting parameters are required. The proposed model is valid for the suction range where degree of saturation is higher than the residual degree of saturation.