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Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils

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A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Geomechanics".

Deadline for manuscript submissions: closed (31 October 2025) | Viewed by 5485

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Prof. Dr. Laureano R. Hoyos

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Guest Editor

Department of Civil Engineering, University of Texas at Arlington, Arlington, TX 76019, USA
Interests: characterization and modelling of unsaturated soils
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Prof. Dr. Dunja Perić

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Guest Editor

Department of Civil Engineering, Kansas State University, Manhattan, KS 66506, USA
Interests: characterization and modelling of unsaturated soils
Special Issues, Collections and Topics in MDPI journals

Dr. Aritra Banerjee

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Guest Editor

Department of Civil and Environmental Engineering, South Dakota State University, Brookings, SD 57007, USA
Interests: geotechnical engineering; climate change; biogeotechnics; unsaturated soils; expansive soils

Special Issue Information

Dear Colleagues,

Over the last few decades, research on coupled hydro-mechanical processes—essential for understanding and modelling unsaturated soil behaviour—has been expanded to include the effects of thermal gradients. This advancement has led to significant breakthroughs in both the development and refinement of experimental techniques, as well as the formulation of more robust constitutive and computational models.

The present Special Issue of Geosciences aims to expand the scope of unsaturated soil mechanics by incorporating thermo-hydro-mechanical and biochemical couplings. It highlights key scientific advances essential for the thorough characterization and modelling of the interactions between unsaturated soils and their natural or engineered environments. Integrating fundamental concepts from core science subjects—including physics, chemistry, and biology—within the realm of unsaturated soil mechanics is crucial for a sustained progress in the production and storage of clean energy, the bioremediation of contaminated soils, and the development of bio-inspired technologies within the practice of geotechnical engineering.

From a broader perspective, the development of experimental and computational techniques to understand and model the behaviour of geotechnical systems—where soil materials are subject to mechanical and biogeochemical changes due to human-made amendments and/or exposures to extreme conditions—is essential for building resilient and sustainable civil infrastructure.

The main goal of this Special Issue is to gather some of the most pivotal advances in the thermo-hydro-mechanical and biochemical (THMBC) characterization and modelling of unsaturated soils. This Issue serves as a follow-up edition of a recent open access Special Issue published by Geosciences: Advances in Thermo-Hydro-Mechanical Characterization and Modelling of Unsaturated Soils (http://mdpi.com/si/178396).

Prospective contributions to this Issue will undergo a rigorous review process. Submissions are expected to primarily focus on recent advances in experimental THMBC-based characterization of unsaturated soils, including developments in equipment, protocols, and data interpretation, as well as the proposal of refined computational modelling frameworks grounded in robust experimental evidence.

Contributions that exclusively focus on hydro-mechanical, thermo-hydro-mechanical, or biomechanical processes—considered as independent and discrete couplings—are also welcome. The present Special Issue aims to serve as a valuable reference for both scholars and practitioners.

Prof. Dr. Laureano R. Hoyos
Prof. Dr. Dunja Perić
Dr. Aritra Banerjee
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Geosciences is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

unsaturated soils
hydro-mechanical, thermo-hydro-mechanical, and biochemical characterization
hydro-mechanical, thermo-hydro-mechanical, and biochemical modelling

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Advances in Thermo-Hydro-Mechanical Characterization and Modelling of Unsaturated Soils in Geosciences (11 articles)

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Research

19 pages, 1446 KB

Open AccessArticle

Fungal Network Effects on Coupled Thermo-Hydraulic Behavior of Sand Under Controlled Surface Heating

by Anna D. Kwablah, Emmanuel Salifu and Aritra Banerjee

Geosciences 2026, 16(6), 210; https://doi.org/10.3390/geosciences16060210 - 23 May 2026

Viewed by 160

Abstract

Drying in granular porous media is governed by coupled thermal and hydraulic processes that can be substantially modified by biological activity. This proof-of-concept study investigated how surface heating and fungal colonization influence the evolution of thermal conductivity (λ) and matric suction (ψ) as [...] Read more.

θ_{v}

in Ottawa 20/30 sand. Four treatments were examined: sterile sand at 22 °C (T1), sterile sand at 28 °C (T2), fungal-amended sand with 10% biomass and 9-day incubation (T3), and fungal-amended sand with 15% biomass and 30-day incubation (T4). Samples were instrumented to monitor

θ_{v}

, λ, and ψ during controlled evaporation using synchronized HYPROP and VARIOS measurements on the same specimen. Across all treatments, λ increased with

θ_{v}

(that is, λ declined as drying progressed), and ψ reflected the transition from hydraulically connected to disconnected pore water. Heating shortened the drying time but did not materially change the form of the λ–

θ_{v}

relationship or generate strong matric gradients in sterile sand. Low biomass (T3) produced thermal and hydraulic responses comparable to the heated sterile control (T2), indicating limited pore-scale modification at early colonization. In contrast, high biomass (T4) widened the effective saturation range, maintained low and nearly uniform ψ across depth, and exhibited the steepest mid-range λ–

θ_{v}

slope with a higher peak λ (~4 Wm⁻¹K⁻¹), consistent with hyphae and extracellular polymers stabilizing thin water films. A soil water retention curve (SWRC) analysis using the van Genuchten model further indicated increased water retention and delayed air entry with an increasing fungal biomass, with approximate air-entry values increasing from ~1.8 kPa (T3) to ~3.0 kPa (T4). Tests were terminated upon tensiometer cavitation rather than complete gravimetric dryness, constraining observations at very low

θ_{v}

. These results indicate that heating primarily affects the rate of drying, whereas fungal networks alter the pathway by preserving hydraulic and thermal continuity at relatively high

θ_{v}

. This behavior suggests a potential role of bio-mediated structuring in influencing near-surface thermo-hydraulic processes relevant to energy foundations, soil covers, and desiccation management in biologically active or bio-engineered soils. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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18 pages, 3243 KB

Open AccessArticle

Modeling Thermal Conductivity of Sandy Soils Under Unfrozen Temperature Conditions

by Aashish Pokhrel, Laureano R. Hoyos and Xinbao Yu

Geosciences 2026, 16(5), 175; https://doi.org/10.3390/geosciences16050175 - 27 Apr 2026

Viewed by 373

Abstract

Soil thermal conductivity is a key parameter in modeling heat transfer, temperature-driven moisture migration, artificial ground freezing, and geothermal systems. However, most existing thermal-conductivity models do not account for temperature effects. This study aims to determine the temperature-dependent thermal conductivity of silty and fine sandy soils at elevated temperatures using a steady-state heat cell method, addressing the limitations of transient probe techniques, which are affected by air voids and heat loss at the needle–soil interface. The experiment employs a heat cell under one-dimensional steady-state heat-transfer conditions, with sufficiently small temperature gradients to prevent temperature-induced moisture migration, and measures the soil’s thermal properties at steady state by indirect temperature and heat-flux measurements using various sensors. The test observations showed well-correlated thermal conductivity readings from steady state and transient probe methods at room temperature. Furthermore, the measured thermal conductivity of the sandy soil demonstrated a near-linear increase with temperature, with the highest dependence at 15.1% and 22.5% saturation for Benbrook (SM) and fine-grained Ottawa (SP) sands, respectively. Several commonly used existing thermal conductivity models were used to fit the measured thermal conductivity. A new thermal conductivity model was developed, incorporating a temperature-dependent correction based on the best-fit model. The proposed model could more accurately capture the increased thermal conductivity of soils with temperature. The findings will significantly improve the modeling of soil-temperature-dependent multi-physics behavior. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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21 pages, 3990 KB

Open AccessArticle

Enhancing Thermo-Mechanical Behavior of Bio-Treated Silts Under Cyclic Thermal Stresses

by Rashed Rahman, Tejo V. Bheemasetti, Tanvi Govil and Rajesh Sani

Geosciences 2026, 16(1), 48; https://doi.org/10.3390/geosciences16010048 - 21 Jan 2026

Viewed by 635

Abstract

Freeze-thaw (F-T) cycles in seasonally frozen regions induce progressive volumetric strains leading to degradation of soils’ mechanical properties and performance of earthen infrastructure. Conventional chemical stabilization techniques often are not adaptive to cyclic thermal stresses and do not address the fundamental phase changes of porous media, underscoring the need for sustainable alternatives. This study explores the potential of extracellular polymeric substances (EPS) produced by the psychrophilic bacterium Polaromonas hydrogenivorans as a bio-mediated soil treatment to enhance freeze-thaw durability. Two EPS formulations were examined—EPS 1 (high ice-binding activity) and EPS 2 (low ice-binding activity)—to evaluate their effectiveness in improving volumetric stability and thawing strength of silty soil subjected to ten F-T cycles. Tests were conducted at four moisture contents (12%, 18%, 24%, and 30%) and three EPS concentrations (3, 10, and 20 g/L). Volumetric strain measurements quantified freezing expansion and thawing contraction, while unconfined compressive strength assessed post-thaw mechanical integrity. The untreated soils exhibited maximum net volumetric strains (γ_Net) of 5.62% and only marginal strength recovery after ten F-T cycles. In contrast, EPS 1 at 20 g/L mitigated volumetric changes across all moisture contents and increased compressive strength to 191.2 kPa. EPS 2 yielded moderate improvements, reducing γ_Net to 0.98% and enhancing strength to 183.9 kPa at 30% moisture. Lower EPS concentrations (3 and 10 g/L) partially mitigated volumetric strain, with performance strongly dependent on moisture content. These results demonstrate that psychrophilic EPS, particularly EPS 1, effectively suppresses ice formation within soil pores and preserves mechanical structure, offering a sustainable, high-performance solution for stabilizing frost-susceptible soils in cold-regions. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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23 pages, 7328 KB

Open AccessArticle

Assessing the Influence Zone and Drainage Efficiency of Geotextiles with Enhanced Lateral Drainage Abilities in Unsaturated Soil Systems

by Shakeel Abid Mohammed and Jorge G. Zornberg

Geosciences 2026, 16(1), 22; https://doi.org/10.3390/geosciences16010022 - 1 Jan 2026

Viewed by 813

Abstract

The hydraulic performance of woven geotextiles is frequently overlooked in roadway design, despite their extensive use for reinforcement applications. Woven geotextiles are typically manufactured from hydrophobic polymers such as polypropylene or polyester and can act as capillary barriers under unsaturated conditions. This results in moisture accumulation at the soil–geotextile interface, adversely impacting long-term pavement performance. Such problems can be effectively mitigated using geotextiles with enhanced lateral drainage (ELD) capabilities, which are engineered with hydrophilic fibers to facilitate capillary-driven lateral water movement under unsaturated conditions. This functionality facilitates the redistribution of moisture away from the interface, mitigating moisture retention and enhancing drainage performance. The hydraulic performance of geotextiles with enhanced lateral drainage capabilities under unsaturated conditions remains insufficiently understood, particularly in terms of their influence zone and drainage efficiency. For this reason, the present study evaluates the lateral drainage behavior of an ELD geotextile using a soil column test, compared against a control setup without a geotextile and with a non-woven geotextile. Two moisture migration scenarios, namely capillary rise and vertical infiltration, were simulated, with the water table varied at multiple depths. Moisture sensors were embedded along the column depth to monitor real-time water content variations. Results show that the ELD geotextile facilitated efficient lateral drainage, with a consistent influence zone extending up to 2 inches below the fabric. Under infiltration, the ELD geotextile reduced moisture accumulation by 30% around the geotextile, highlighting its superior drainage behavior. These findings encourage practicing engineers to adopt rational, performance-based designs that leverage ELD geotextiles to enhance subgrade drainage and moisture control in pavement and geotechnical applications. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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21 pages, 4646 KB

Open AccessArticle

A Non-Linear Suction-Dependent Model for Predicting Unsaturated Shear Strength

by Kalani Rajamanthri and Claudia E. Zapata

Geosciences 2026, 16(1), 12; https://doi.org/10.3390/geosciences16010012 - 23 Dec 2025

Cited by 1 | Viewed by 798

Abstract

Accurate evaluation of unsaturated shear strength remains a significant challenge in geotechnical engineering because of the nonlinear interaction between matric suction and shear strength. Existing models often assume a linear contribution of suction and are generally restricted to low suction ranges, limiting their predictive capability under highly unsaturated conditions. This study investigated the nonlinear response of unsaturated shear strength through single-stage direct shear tests conducted under constant water content. Two soil types: a high-plasticity clay and a low-plasticity silty clay were examined across a wide suction range extending beyond the air-entry value (AEV). The results revealed a nonlinear behavior expressed as a distinct bi-linear trend, with shear strength increasing with suction up to the optimal moisture condition and then exhibiting a clearly altered rate of increase at higher suction levels. To capture this nonlinear behavior of unsaturated shear strength with suction, an exponential shear strength equation was proposed and validated using eight additional published datasets encompassing different soil classifications and suction magnitudes. The proposed formulation demonstrates that accounting for non-linearity is essential for accurately estimating the unsaturated shear strength of the soil. Moreover, the proposed exponential model outperforms both the well-established linear model of Fredlund and the nonlinear power law model of Abramento and Carvalho, thereby providing a unified framework for capturing the nonlinear interaction of matric suction on unsaturated shear strength. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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14 pages, 3569 KB

Open AccessArticle

Persistence of Soil Water Repellency After the 2022 Bolt Creek Fire

by Mustafa Demir, Peter R. Robichaud and Idil Deniz Akin

Geosciences 2025, 15(12), 472; https://doi.org/10.3390/geosciences15120472 - 15 Dec 2025

Viewed by 627

Abstract

Wildfire ash and water-repellent soil are new materials that are formed after a wildfire that change the mechanical and hydraulic behavior of wildfire-burned slopes. Wildfire ash is known to be typically hydrophilic and to retain water, whereas the water-repellent soil layer acts as a hydraulic barrier. However, there is limited in situ soil water content data to understand the short- and long-term impacts of wildfire ash and a water-repellent soil layer on the hydromechanical behavior of burned slopes. This study investigates the trends in water content of wildfire ash, water-repellent soil, and subsurface soil after the 2022 Bolt Creek Wildfire near Skykomish, WA. The ash deposit averaged 10 cm, with a maximum 30 cm thickness in channels immediately after the fire, which allowed the in situ measurement of ash water content. Soil water content sensors were installed in the ash and subsurface soil layers, and changes in the water content were monitored for a year after the fire. The surface ash layer was above a thin (<1 cm) water-repellent soil layer, which was followed by the soil that did not show any apparent effects from the fire. The results showed a reduction in ash thickness and the persistence of the water-repellent layer over a year. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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21 pages, 2749 KB

Open AccessArticle

A Novel Poly-Potassium Salt Osmotic Technique for High-Suction Water Retention in Compacted Kaolin

by Abolfazl Baghbani, Yi Lu, Sankara Narayanan Murugesan, Hossam Abuel Naga and Eng-Choon Leong

Geosciences 2025, 15(12), 461; https://doi.org/10.3390/geosciences15120461 - 4 Dec 2025

Cited by 1 | Viewed by 547

Abstract

Accurate suction control underpins thermo-hydro-mechanical (THM) characterization of unsaturated soils, yet conventional polyethylene-glycol (PEG) osmotic methods suffer from membrane degradation, polymer intrusion, and marked temperature sensitivity. This study evaluates a potassium-neutralized poly (acrylamide-co-acrylic acid) hydrogel (PP) as a high-suction osmotic medium for water-retention testing of compacted kaolin using a sealed cell with a grade-42 filter paper separator (no semi-permeable membrane). The water-activity–suction relation of PP was calibrated with a chilled-mirror hygrometer (WP4C) over the high-suction domain, and temperature effects were assessed between 20–30 °C. The PP imposed stable target suctions across the practical engineering range, with cross-validation to WP4C of R² ≈ 0.985 and RMSE ≈ 0.09 MPa, and exhibited modest thermal sensitivity (~2–3% per 10 °C). Mass–time records showed a two-regime equilibration (rapid first-day moisture loss then slowing to asymptote), with time to 95% equilibrium t₉₅ ≈ 3–7 days depending on suction, and equilibrium within ~2 weeks under a normalized mass change,

\frac{1}{m} |\frac{∆ m}{∆ t}| < \frac{0.1 %}{24 h}

criterion. The resulting kaolin water-retention curves are smooth soil moisture factor (SMF) reproducible, and exhibited minor wetting–drying hysteresis (~20–25% gap at matched suctions). Collectively, the results indicate that PP provides a practical, membrane-free (in the semi-permeable sense) and accurate means to control high-range suction for unsaturated soil testing, showing only modest suction variations within the tested 20–30 °C range, while mitigating long-standing PEG limitations and simplifying laboratory workflows. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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21 pages, 5847 KB

Open AccessArticle

Probabilistic Slope Stability Assessment of Tropical Hillslopes in Southern Guam Under Typhoon-Induced Infiltration

by Ujwalkumar Dashrath Patil, Myeong-Ho Yeo, Sayantan Chakraborty, Surya Sarat Chandra Congress and Bryan Higgs

Geosciences 2025, 15(12), 453; https://doi.org/10.3390/geosciences15120453 - 29 Nov 2025

Cited by 1 | Viewed by 748

Abstract

Uncertainty and variability in soil properties strongly impact slope stability under extreme rainfall. This study applies a probabilistic hydro-mechanical slope stability assessment to unsaturated volcanic hillslopes in southern Guam, covering a range of slope angles and subjected to four major 2023 typhoons. The slope scenarios analyzed include bare slopes, vegetated slopes with root water uptake, and vetiver with both uptake and root reinforcement. Laboratory-derived variability in effective cohesion, friction angle, and unit weight was incorporated via Latin hypercube sampling. Gentler slopes (≤40°) remained stable with a probability of failure (PoF) = 0%. For steep slopes (45–60°), vetiver root reinforcement improved the mean factor of safety by up to 12–15% and reduced variability in outcomes to less than 2%. Probabilistic predictions advanced failure timing compared to deterministic estimates, with differences more pronounced on steeper slopes. By integrating soil variability and vegetation effects within probabilistic frameworks, this approach provides a more accurate and comprehensive assessment of tropical slope failure risks, thereby informing more effective and resilient slope management strategies. Full article

(This article belongs to the Special Issue Advances in Thermo-Hydro-Mechanical and Biochemical (THMBC) Characterization and Modelling of Unsaturated Soils)

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