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.

With the advantages of low construction costs and rapid installation, suction caissons are widely used as foundations in offshore engineering. This paper investigates the behavior of suction caisson foundations located in sandy soil under horizontal cyclic loads. The upgraded simple anisotropic sand constitutive model with memory surface (SANISAND-MS model) is employed to accurately capture the sand's cyclic behavior. To calibrate the parameters of the upgraded SANISAND-MS model, a series of triaxial drained monotonic and cyclic tests was performed. The effects of load idealization and loading sequence on the cyclic behavior of sand are studied based on the element test results, and the effects of load idealization on the cyclic response of suction caissons are studied from a finite-element simulation perspective. The triaxial test results indicate that load idealization slightly affects strain accumulation in both loose and dense sand. Based on simulation results, it is found that the loading sequence of load packages with varying amplitudes has a minor effect on the rotation accumulation of the suction caisson. The current load idealization method used in the engineering design practice of suction caissons is acceptable under drained conditions.

Seismic activity often triggers liquefaction in sandy soils, which coupled with initial vertical tensile loads, poses a significant threat to the stability of suction bucket foundations for floating wind turbines. However, there remains a notable dearth of studies on the dynamic response of these foundations under combined seismic and vertical tensile loads. Therefore, this study developed a numerical method for analyzing the dynamic response of suction bucket foundations in sandy soils under such combined loading conditions. Through numerical simulations across various scenarios, this research investigates the influence of key factors such as seismic intensity, spectral characteristics, as well as the magnitude and direction of tensile loads on the seismic response of suction buckets. The results revealed that the strong earthquake may cause the suction bucket foundation of floating wind turbines to fail due to excessive vertical upward displacement. This can be attributed to that the accumulation of excess pore water pressure reduces the normal effective stress on the outer wall of bucket, and consequently decreases the frictional resistance of bucket-soil interface. Additionally, the above factors significantly influence both the vertical displacement of the suction bucket and the development of pore pressure in the surrounding soil. The findings can provide valuable insights for the seismic safety assessment of suction bucket foundations used in tension-leg floating wind turbines.

Suction anchor foundations serve as a critical anchoring solution for submerged floating tunnel (SFT) cable systems. In marine environments, these foundations must endure not only static loads but also long-term oblique cyclic loading caused by wave excitation, which can result in soil weakening and a reduction in bearing capacity. This study systematically examines the oblique cyclic bearing behavior of SFT suction anchors using a combined experimental and numerical approach. The results demonstrate that (1) the cyclic load ratio initially increases with increasing wave periods, then decreases, before rising again; (2) displacement accumulation at the mooring point occurs rapidly during the initial wave loading cycles, gradually stabilizing as cycling progresses; (3) during foundation failure, tension redistribution displays asymmetric characteristics, with connected cables experiencing load reduction while adjacent cables are subjected to amplified forces; (4) numerical analyses quantify key parametric relationships, revealing that the weakening coefficient (alpha) decreases with increasing loading angle, exhibits a positive correlation with zeta b, and shows a negative correlation with zeta c. These findings advance the understanding of cyclic performance in SFT anchors and offer essential insights for SFT safety evaluations.

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.

The laboratory experiment is an effective tool for the rapid assessment of the unsaturated soil slopes instability induced by extreme weather events. However, traditional experimental methods for unsaturated soils, including the measurement of the soil-water characteristic curve (SWCC), soil hydraulic conductivity function (SHCF), shear strength envelope, etc., are time-consuming. To overcome this limitation, a rapid testing strategy is proposed. In the experimental design, the water saturation level is selected as the control variable instead of the suction level. In the suction measurement, the suction monitoring method is adopted instead of the suction control method, allowing for simultaneous testing of multiple soil samples. The proposed rapid testing strategy is applied to measure the soil hydro-mechanical properties over a wide suction/saturation range. The results demonstrate that: (1) only 3-4 samples and 2-5 days are in need in the measurement of SWCC; (2) 7 days is enough to determine a complete permeability function; (3) only 3 samples and 3-7 days are in need in the measurement of the shear strength envelope; (4) pore size/water distribution measurement technique is fast and recommended as a beneficial supplement to traditional test methods for unsaturated soils. Our findings suggest that by employing these proposed rapid testing methods, the measurement of pivotal properties for unsaturated soils can be accomplished within one week, thus significantly reducing the temporal and financial costs associated with experiments. The findings provide a reliable experimental approach for the rapid risk assessment of geological disasters induced by extreme climatic events.

The unified effective stress equation based on suction stress, a widely accepted method for calculating effective stress in unsaturated soils, provides a closed-form solution that enables the characterization of soils in both saturated and unsaturated states. The effect of desaturation on the water content of natural and treated soils was studied with respect to unconfined compressive strength (UCS) and indirect tensile strength (ITS). The soil's moisture-dependent behavior was characterized by the van Genuchten (Soil Sci Soc Am J 44:892-898, 1980. https://doi.org/10.2136/sssaj1980.03615995004400050002x) and Lu et al. (Water Resour Res, 2010. https://doi.org/10.1029/2009wr008646) models and implemented using the equation. Suction tests were conducted using the dew point and filter paper methods, alongside UCS and ITS tests, on silty clay soil and microsilica-treated soil with microsilica contents of 5%, 10%, and 15%. The equation was validated by comparing mean total stress (p) and mean effective stress (p ') to deviatoric stress (q) and analyzing the friction angle at different suction levels. It proved applicable to both natural and treated soils, with valid moisture content ranges of 4-17.5% and 6-20%, respectively. This study experimentally confirms the equation's effectiveness in characterizing the hydro-mechanical behavior of soils under varying moisture conditions.

In this study, a novel 2D method for measuring soil surface suction, leveraging infrared thermal imaging technology is presented. The main principle of this method is the establishment of a correlation between soil surface water content and a normalized interfacial temperature difference. Subsequently, we link unsaturated soil surface suction to the normalized interfacial temperature difference through the soil-water characteristic curve. To validate the proposed method, an in-situ calibration test was conducted to ascertain the requisite parameters. Then, the method was tested under varying meteorological conditions at two distinct in-situ sites using the same test protocol as the calibration phase. The results demonstrate a strong agreement compared to measured values, affirming the feasibility and robustness of the proposed approach. This method offers several noteworthy advantages, including rapidity, non-contact operation, non-destructiveness, and robustness to environmental fluctuations. It holds promise for advancing investigation of the spatial and temporal evolution of hydro-mechanical properties of in-situ soil under the influence of climate change.

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.

This study investigates slope stability under rainfall infiltration using numerical modeling in Plaxis 2D, comparing poorly graded sand (6.5% fines) and well-graded sand (11.9% fines) under high-intensity rainfall of 30 mm/h for durations of 8, 12, 18, and 24 h. The results indicate that, as rainfall duration increases, soil saturation rises, leading to reduced suction, lower shear strength, and decreased safety factors (S.F.s). Poorly graded sand shows minimal sensitivity to infiltration, with the S.F. dropping by only 4.3% after 24 h, maintaining values close to the initial 1.126. Conversely, well-graded sand demonstrates significant sensitivity, with its S.F. decreasing by 25.4% after 8 h and 73.7% after 24 h, due to higher water retention capacity and suction. This highlights the significant contrast in stability behavior between the two soil types. The findings emphasize the critical role of soil hydro-mechanical properties in assessing slope stability, especially in regions with intense rainfall. This study establishes a methodology for correlating safety factor variations with rainfall duration and soil type, offering valuable insights for modeling and mitigating landslide risks in rainy climates, considering the hydraulic and mechanical parameters of the soil.