Moisture Load Research Articles

Memory response on hygrothermal three-phase-lag hollow cylinder due to heat and moisture loading

Memory response on hygrothermal three-phase-lag hollow cylinder due to heat and moisture loading

Assessing the effectiveness of cross-laminated timber (CLT) roof assembly moisture control and mitigation strategies: A field laboratory

Exposure to moisture and wetting is a concern in mass timber construction and service. Understanding the moisture conditions and the drying response of mass timber during construction and service can impact durability of the building material and occupant health because of the potential for biological degradation and mould growth, respectively. Cross-laminated timber (CLT) used in roof assemblies is particularly susceptible to high moisture loading from exposure to driving rain and extended periods of ponding and water retention on roofs during construction. The field research conducted in this study utilises a purpose-built CLT test facility in Toronto, ON to test and assess the impact of three specific moisture control strategies towards both mitigating moisture and increasing the dry-out rate of CLT used in roof assemblies. The moisture control strategies tested were: (1) the integration of an air cavity directly above the CLT within the roof assembly, (2) the protection of CLT during exposure and moisture loading periods on site, and (3) the permeability of membranes installed in the roof assembly and during site exposure. The CLT roof panels underwent four months of exposure to exterior environmental conditions followed by two months of bulk water inundation at the CLT test facility site immediately prior to installation and enclosure. Moisture content was monitored at evenly distributed depths in the CLT panels throughout exposure and inundation periods and for one year of simulated service conditions, post-enclosure. Comparative analysis of the moisture control strategies tested during this field laboratory demonstrate that the presence of an air layer above the CLT in the roof assembly consistently doubled the dry-out rate compared to the assemblies without an air cavity. The results also found that unprotected CLT panels took approximately 2.5 times longer to dry-out to below 15 % MC than protected panels and finally, that in comparing the results of using impermeable vs. permeable air/vapour barrier membranes on the surface of exposed CLT, that the impermeable membrane slowed the dry-out rate of wetted CLT by approximately 20 %. The results of this research support the implementation of specific moisture mitigation and control strategies during design and construction towards promoting rapid dry-out of CLT in roof assemblies in service.

Evaluation of the performance of different internal insulation systems in real-life conditions ‐ A case study

Thermal retrofitting of historic buildings is essential to reducing heat loss in all buildings. Although exterior insulation often is hygrothermally a better solution, internal insulation is the only option in facades worthy of preservation (e.g., solid masonry external walls). However, mold growth has frequently been discovered in buildings with internal insulation at the interface between the insulation and the original wall, while simulations and lab tests show minimum risk, and vice versa. Therefore, real-life testing is required so that the building owners are more likely to accept these measures.This paper presents a case study of an 1837-built typical historic building. The study focuses on the building's top floor, a residential area (commune). Eight different rooms have four different types of internal insulation installed. The performance of the insulation systems was determined by monitoring the interior and exterior climate and the temperature and relative humidity at the intersection of the insulation and the existing wall for 20 months. The risk of mold growth was estimated based on the measurements. In the wall interfaces, the Mold Index indicated that the risk for mold growth is not severe. Hygrothermal simulations for the measured period and ten years were also performed. To increase simulation accuracy, the original exterior masonry bricks underwent laboratory testing to determine their precise material properties. The main outcome from the simulations was that the three vapor-open systems were more susceptible to indoor moisture load changes and had an elevated risk of mold growth, whereas the vapor-tight system was more robust to variation in insulation thickness and internal moisture level changes, and in this case, demonstrated the best performance in respect to moisture safety.

Assessing the Moisture Resilience of Wood Frame Wall Assemblies

Resilience has been used as a building performance metric that measures the building’s capability of absorption, response, and recovery from one or a series of disruptive events, e.g., extreme weather events or power outage events. With respect to resilience, in relation to the moisture performance of the building envelope (moisture resilience), this aspect has not yet been thoroughly explored nor defined. Given the expected increase in annual precipitation in certain regions of Canada as induced by climate change effects occurring both currently and in the future, the moisture resilience of building envelops will require immediate attention given that wall assemblies of buildings are predicted to be subjected to excessive moisture loads in the coming years. In this study, the moisture resilience of wood frame wall assemblies to mould growth was described from three aspects: (i) absorption—the ability of the wall to maintain a low level of relative humidity on the OSB; (ii) response—the fluctuation of the relative humidity on the OSB; and (iii) recovery—the rate at which the relative humidity recovers to an acceptable level. The metrics used to demonstrate the relative impact of these factors on moisture performance were also developed. The results have revealed a robust correlation between moisture performance and the relative influence of various newly defined aspects of moisture resilience.

Experimental performance investigation on a desiccant-assisted two-stage evaporative cooling system in hot and humid areas

The escalating demand for energy-efficient and eco-friendly air conditioning systems in buildings has spurred the development of comfortable, efficient, and cost-effective air handling system configurations. Desiccant cooling has shown a higher coefficient of performance (COP) compared to traditional vapor compression refrigeration (MVCR) systems. However, current desiccant cooling facilities struggle to decouple and efficiently handle indoor heat and moisture loads. The complexity of these facilities has kept intricate cooling systems remaining theoretical, requiring simplification and experimental investigation. This paper presents an experimental study on a compact, two-stage evaporative cooling system assisted by a liquid desiccant. A key innovation of this system is the inclusion of a two-stage heat exchanger that adeptly manages the decoupling of indoor heat and moisture loads under challenging high-temperature and high-humidity conditions. Performance analysis was conducted experimentally under three hot and humid climatic conditions using an optimized operating parameter scheme. Starting from an initial condition of 36.22 °C and a humidity ratio of 0.028 kg/kg, the proposed system achieves COP values ranging from 11.3 to 18.4 without compromising indoor comfort or facility compactness. Under high heat and high humidity conditions, the optimized system extracts 20 % of the product air as the secondary air source. It can reach a minimum supply air temperature of 18.44 °C, achieved under optimized conditions of low wind speed (1.0 m/s), high desiccant concentration (35 %), and substantial desiccant flow (0.09 kg/s). Experimental studies of this new system provide the possibility of achieving high efficiency in air handling over a wide range of temperatures and humidity.

Requirements of the Vapour Barrier in Wood-Frame Walls

This paper examines the water-vapour diffusion resistance (Z-value) of vapour versus wind barriers by determining their Z-value ratio in exterior wood-frame walls thermally insulated with six different materials to prevent mould growth. Using WUFI Pro, the water-vapour diffusion resistance requirements were determined for thermal insulation using mineral wool and biogenic materials: wood fibre, straw, flax, grass, and hemp. Hygrothermal simulations determine the minimum Z-value ratio between these materials with vapour versus wind barriers in temperate and cold climates. Wind barriers with Z-values between 1 and 8 GPa s m2/kg were used in walls with U-values of 0.15 and 0.10 W/m2 K. The indoor moisture load was defined from classes of 1 to 5 with a U-value of 0.15 W/m2 K and classes of 2 and 3 were used for a U-value of 0.10 W/m2 K. The Z-value ratio depends on the Z-values of the wind barrier and thermal insulation material, moisture load class, and U-value. The required Z-value ratio declines with an increased wind-barrier Z-value. The vapour-barrier Z-value approaches a fixed threshold for wind-barrier Z-values approaching lower values (1 GPa s m2/kg) and those approaching higher values (8 GPa s m2/kg), depending on the thermal insulation material. This parameter study examines wind barriers with a Z-value ranging between 1 and 8 GPa s m2/kg, which characterises typical wind barriers used in Denmark For the water-vapour diffusion resistance requirement of the vapour barrier, the Z-value increases for increased moisture load classes and thermally insulated walls with lower U-values. The conversion between the Z-value, the Sd-value, and the water-vapour resistance factor µ can be found in DS/EN ISO 12572:2016.

Studying Impact of Moisture, Node Position and Loading Rate of Paddy Straw on its Mechanical Properties

In this study, mechanical properties of paddy straw such as bending strength, shear strength and Young's modulus were determined through force-deformation curve using textural analyzer with 50 kg load cell. The mechanical properties were determined at three moisture contents, i.e., 18.4% (M1), 13.5% (M2) and 10.8% (M3), at three node positions, i.e., N1, N2 and N3 and three loading rates, i.e., 25, 30 and 35 mm min-1, respectively. The results revealed that moisture content and loading rate at different node positions significantly (p<0.01) affected the bending strength, shear strength, and Young's modulus of straw, whose values varied from 5.35 to 17.34 MPa, 4.99 to 7.35 MPa, 0.43 to 1.39 GPa, respectively, through N1 to N3 with decrease in moisture content; likewise, other findings also indicated increase in output values on increasing loads through N1 to N3. Cutting force was also significantly affected (p<0.01) by shear angle and moisture content, which varied from 6.39 to 22.9 N, and cutting energy ranged from 142 to 511 J by Straw Management System serrated blade and was found to be minimum at 20° shear angle. The mechanical property of the straw for residue management in the context of cutting force for node position N3 at the initial moisture content was found optimum.

Evaluating the Impact of Moisture Content and Loading Orientation on the Geometrical Characteristics and Mechanical Behavior of Cassava Tubers

This study investigates the geometrical and mechanical properties of two cassava varieties: ‘Newly Elected No. 48’ and ‘Jin Yue HRMUS’. We analyzed various properties, including width, length, geometric diameter, thickness, compression firmness, shape ratio, surface area, shear strength, rupture force, and shear rupture force (SRF), at different moisture content (MC) levels ranging from 35.0 to 80.0% wet basis. Our findings indicate that all mechanical properties of cassava (MPC) were significantly influenced by moisture content within this range. Specifically, as moisture content decreases, the compression rupture force (CRF) increases linearly in the vertical direction, while a quadratic relationship is observed in the horizontal direction, characterized by an initial increase followed by a decrease. Additionally, a quadratic relationship was established between moisture content and firmness. In contrast, shear fracture force and strength exhibited a quadratic relationship that decreased initially and then increased with rising moisture content. Furthermore, both compression and shear fracture forces were significantly higher in the vertical loading direction compared to the horizontal direction. Notably, the ‘Jin Yue HRMUS’ variety demonstrated greater mechanical strength than the ‘Newly Elected No. 48’. These findings provide valuable insights for developing, optimizing, and evaluating cassava harvesting and processing machinery.

Shelf-Life Extension and Quality Changes of Fresh-Cut Apple via Sago and Soy-Oil-Based Edible Coatings

In-demand fresh-cut fruits are highly perishable and require shelf stability. Starch, such as sago, is a naturally available polysaccharide with good gas barrier properties. The study aimed to develop an edible coating and examine the effect of its application on the quality parameters of fresh-cut apples. The coating solution was prepared with sago and soy oil in concentrations of 3, 4, and 5% and 0, 0.25, and 0.50%, respectively. Lecithin (0.50%) was used as an emulsifier and glycerol (1.5%) as a plasticizer. Coated fresh-cut apples were evaluated for physicochemical properties (TSS, pH, non-enzymatic browning index, moisture content, weight loss, headspace gas, and color attributes) during a 12-day shelf-life study at 4 °C. Sensory analysis was also performed to assess consumer acceptability, and microbial analysis to investigate its inhibiting effect against yeast and mold. Compared to the control, developed coatings reduced browning, respiration rate, moisture, weight loss, and microbial load in fresh-cut apples. The study indicates that the blend of 5% sago and 0.5% soy oil produced the best coatings which were most effective for retaining the original quality attributes and in extending the shelf life of apple slices for 12 days in storage at 4 °C.

Investigation of physicochemical and antibacterial properties of dill (Anethum graveolens L.) microencapsulated essential oil using fluidized bed method

The present study delves into the encapsulation of dill essential oil utilizing the fluidized bed coating methodology. The investigation focused on the impact of essential oil concentration and the application of maltodextrin and arabic gum as the primary and secondary coating agents. The dominant compounds in the dill essential oil were identified as limonene (32.32%), carvone (35.43%), and cis-dihydrocarvone (5.43%). The antimicrobial potency of the dill essential oil was evaluated, demonstrating notable inhibition against Streptococcus mutans with inhibition zone diameters ranging from 5.4 mm to 16 mm for concentrations between 250 μg/mL and 2000 μg/mL. For Streptococcus sobrinus, the inhibition zones measured from 6.6 mm to 18 mm across the same concentration gradient. An increase in maltodextrin concentration was associated with a decrease in moisture content, bulk density, and tapped density, while it improved microencapsulation efficiency and loading capacity. In contrast, a higher concentration of arabic gum increased moisture content, loading capacity, and encapsulation efficiency, but reduced bulk density and tapped density. Elevating the essential oil concentration increased all physicochemical properties of the microcapsules, except for tapped density. The optimal conditions for microencapsulation involve using a 2000 ppm concentration of dill essential oil with 75% maltodextrin and 0.1% arabic gum as carrier agents. Scanning electron microscopy images indicated that the microcapsule particles were nearly spherical with a smooth, intact surface. The release rate of phenolic compounds in a simulated saliva environment reached its maximum at 98.32% after 20 min, showcasing an efficient release profile.

Hygrothermal assessment of three bio-based insulation systems for internal retrofitting solid masonry walls

The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls retrofitted internally with three diffusion-open bio-based insulation materials (two loose-fill cellulose and one hemp fibre), installed in test containers with controlled indoor climate. Focus was on bio-based insulation materials, as these are upcoming due to necessary CO2 reductions and because the hygroscopic properties of bio-based materials are different from traditional insulation materials like mineral wool therefore, some manufacturers claim a vapour barrier is unnecessary, even in relatively cold climates. The project was a large experimental study in two reefer containers with reconfigured facades, in which solid masonry walls with embedded wooden elements were constructed. The study focused on the conditions in the masonry/insulation interface and in the embedded wooden elements. The effect of hydrophobization and different indoor moisture loads were also investigated. Moreover, the bio-based insulation systems were compared with a wall insulated with the traditional mineral wool and vapour barrier system. Relative humidity and temperature were measured at several locations in the test walls for 1 year and 9 months. Measurements show that exposed masonry walls retrofitted internally with diffusion-open bio-based insulation materials resulted in unacceptably high moisture levels (>80% RH over longer periods). Lower moisture levels were observed when the internal insulation was combined with hydrophobization against wind-driven rain, but unacceptably high moisture levels still occurred (60%–70% in summer and 95%–100% in winter in the interface). Hydrophobization reduced the moisture levels in the interface and embedded wooden elements only in walls facing southwest, which is the direction with the most wind-driven rain. Mould growth tests showed no growth in the interface in walls insulated with cellulose insulation (mycometer surface value <25). Meanwhile growth was found in all four walls insulated with hemp fibre matts (mycometer surface value >400).

Hygrothermal resilience of typical lightweight steel-framed wall assemblies in hot-humid areas under future climate uncertainty

Ensuring the hygrothermal performance of lightweight steel-framed (LSF) wall assemblies is critical for the sustainability of LSF buildings in hot-humid regions; however, climate change poses new challenges. Therefore, this study aimed to bridge the gap in understanding the characteristics of hygrothermal load changes and the hygrothermal resilience of different LSF wall assemblies. Future climate data for each decade of this century (from 2030 to 2090), under various carbon emission scenarios, were generated based on a typical meteorological year (TMY) for hot-humid areas to evaluate the impact of climate change on hygrothermal loads. The hygrothermal resilience of four typical LSF wall assemblies, with either ventilated rainscreen cladding or face-sealed stucco cladding, with or without external insulation, was evaluated through simulation and comparative analysis. The results indicated that the thermal load would increase with increasing carbon emissions and over time, with the annual average external temperature peaking at 25.8 °C by the end of this century. The frequency of months with a high or critical moisture load would increase, although the moisture load may fluctuate across scenarios and years. Consequently, the cooling and dehumidification loads may increase by 52–60 % and 40–88 %, respectively. The hygrothermal risk within the walls may increase, with maximum increases of 2.8–8.0 % in the annual average relative humidity, 2.7–3.0 °C in the annual average temperature, and 10–35 % in the wetness duration. However, the impacts could be reduced by using ventilated rainscreens and external insulation, with further precautions needed to mitigate the increasing hygrothermal risk in areas with thermal bridges and rainwater leakage, as well as at the outer interface of the external insulation. These findings could provide a reference for the design of LSF buildings adapted to climate change in hot-humid areas.

Applying and Evaluating the Modified Method of the Rothermel Model under No-Wind Conditions for Pinus koraiensis Plantations

Pinus koraiensis is one of the important tree species in Northeast China. Due to its high pine-needle-oil content and the density of human activities in its habitat, the forest-fire prevention situation is severe in the context of climate change. The rate of surface-fire spread is one of the key indicators for scientifically advancing early fire prevention and is crucial for guiding forest firefighting operations. In this study, we investigated how moisture content, load, and slope impact the surface-fire spread rate using indoor-simulated fire-spread experiments. Furthermore, we analyzed the limitations in the Rothermel model for predicting the surface-fire spread rate in P. koraiensis plantations and proposed modifications to the model by the modification method of priority to no-wind or slope conditions and slope conditions. Additionally, we evaluated the prediction accuracy of the original Rothermel model and two other modified models on the surface-fire spread rate. A high moisture content and low slope demonstrated an absolute inhibitory effect on the rate of surface-fire spread, whereas the promotional effect of a low moisture content and high slope was easily disturbed by the other factors. Under high-slope conditions, an overestimation situation was observed in the Rothermel model. Both of the modification methods involving priority to no-wind or slope conditions and slope conditions could improve this situation. Furthermore, the modification method demonstrated a better improvement effect on the prediction accuracy. Our findings provide valuable insights for refining the Rothermel model and offer guidance for improving the accuracy of predicting fire spread rates and behavior for Pinus koraiensis. This bears immense significance for advancing the understanding and calculation of the ROS of forest fires in the region.

Features of the formation of cohesive and adhesive strengths by non-structured and structured polyvinyl acetate films during wood gluing

The formation of a higher number of hydrogen bonds in the structured polyvinyl acetate film compared to the unstructured one was established by means of infrared spectroscopy method. It was concluded that the structured polyvinyl acetate film has a higher cohesive strength than unstructured. It was revealed that the films subjected to moisture loads (with the amount of sorbed moisture lower than the swelling limit of the adhesive film) would show greater cohesive strength compared to the films which were not subjected to moisture loads due to the formation of a higher number of hydrogen bonds. Based on the obtained results, it was predicted that the system "structured film after moisture loads/wood substrate" would exhibit the highest adhesive strength, explained by an increase in the number of hydrogen bonds between the film components and the wood cellulose. It was theoretically predicted that in order to provide high cohesive and adhesive strengths of polyvinyl acetate adhesive joints of wood ensuring, moisture saturation should be lower than the saturation limit of the wood fiber and the adhesive film simultaneously.

Use of Polylactic Acid Added with Calcium Oxide and 3-Iodo-2-Propynly Butyl Carbamate as an Antifungal Agent and Bio-degradable Soil Remediator

This work studied the use of polylactic acid added with calcium oxide (CaO) and 3-Iodo-2-propynly butyl carbamate (IPBC) for agricultural applications. CaO content of 30 pph was fixed, while IPBC contents were varied at 0, 2.5, 5.0, 7.5 and 10.0 ppm in the polymer matrix. All ingredients were mixed by the extrusion process for receiving the PLA, PLA/CaO, and PLA/CaO/IPBC granules. The pH value, antifungal activities of Phytophthora parasitica, tomato growth, and disposal degradation were also investigated. The experimental results indicated that the acidic condition of the PLA granules increased with increasing IPBC contents but was compromised by CaO. An IPBC was an effective antifungal agent. It was also promoted and activated by CaO. Growth of P. parasitica can be inhibited by CaO synergized IPBC for the PLA/CaO granules with four different IPBC contents and the PLA/CaO granules with the four different IPBC contents were an effective antifungal agent. A PLA/CaO granule with an IPBC content of 2.5 ppm can be developed to compete with an unused condition. A PLA/CaO granule with an IPBC content of 10 ppm was recommended for agricultural applications. A PLA/CaO/IPBC 10 acted as an effective antifungal agent and compostable for soil bioremediatory before planting. Over the 45-day experimental period, the maximum percentage of weight loss of a PLA/CaO granule with an IPBC content of 10 ppm was influenced by moisture and initial PLA loading. A PLA/CaO granule with an IPBC content of 10 ppm (47.2%) had a faster degradation rate than a PLA/CaO granule (45.3%) and a neat PLA granule (15.0%).

Effect of the porous structure on the hygrothermal vibration analysis of functional graded nanoplates using nonlocal high-order continuum plate model

This study delves into the thermomechanical vibration behavior of functionally graded porous nanoplates under extreme thermal temperature and humidity conditions. The equation of motion of the nanoplate was derived using advanced theories in elasticity and deformation. The nanoplate consists of metal (SUS304) on the bottom surface and ceramic (Ni3S4) on the top surface, with the material distribution changing according to the power law across the plate thickness. The nanoplate was modeled with uniform and symmetric distributions of porosity reaching as high as 60%. Upon incorporating the thermal and moisture loads from the humid surroundings into the equations of motion derived from Hamilton's principle, the equations were solved using Navier's method and simplified to the eigenvalue equation. Analyzed within a broad framework are the thermomechanical vibration behavior of the nanoplate, temperature impact, humidity influence, porosity and its distribution, material grading parameter effects, and nonlocal integral elasticity effects. Observations indicate that variations in thermal temperature, humidity, and nonlocal parameters can lower the thermomechanical vibration frequency of the nanoplate, whereas porosity has the opposite effect. The effects mentioned are influenced by factors, such as the porosity ratio, porosity distribution, material ratios, and the size of the nonlocal parameter in the plate. The primary objective of this work is to uncover the nonlinear frequency response of nanoplates with high porosity in conditions characterized by high temperature and humidity.

Polyurethanes Thermal, Hydrolytic and Soil Degradation: Systematic Literature Review

A search in the Scopus and Web of Science databases covering the period from 2016 to 2021 was carried out and used to update the methodology of polyurethanes hydrolytic, thermal and soil degradation assessment. To that effect, three groups of search words were used: (1) polymer degradation AND “hydrolytic degradation” AND polyurethane; (2) polymer degradation AND “thermal degradation” AND polyurethane; and (3) polymer degradation AND “soil degradation” AND polyurethane. It was observed that the studies on the degradation of polymers are disseminated in different research groups and on a continuous basis during the survey period. The main methodologies found to perform the degradation of polymers were: method of immersion of samples in aqueous solution to evaluate hydrolytic degradation, thermogravimetric analysis, differential exploratory calorimetry and accelerated weathering to evaluate thermal degradation and inoculation of the polymer in soils with different characteristics, such as pH, moisture and organic load to assess soil degradation. Polymers can become a biodegradable solution to the environmental issues generated by plastic waste.

Sewage sludge co-gasification in a pilot-scale two-stage fluidized bed gasifier for improved hydrogen production: Effects on sewage sludge moisture, metal species, and metal loading amount

Theabundant mineral olivine was applied as second-stage-gasifier bed materials to increase the H2 content in the syngas produced during the co-gasification of the sewage sludge and the simulated municipal solid waste. Regardless of the second-stage bed material used, the hydrogen-to-syngas ratio in the syngas output from the second stage increased when the S/B ratio increased from 0.02 to 0.13. This demonstrates that adding steam enhances the hydrogen-to-syngas ratio in the second-stage syngas. Under the same S/B conditions, the H2 content in the syngas varied when the original and modified olivine were separately used as bed materials in the second-stage gasifier. The H2 content was 23.12 mol.% when the original olivine was used and increased to 25.27 and 26.99 % mol.% when the olivine was respectively impregnated with 1 wt% Ni and 1 wt% Fe. These results evidenced that Ni and Fe could efficiently catalyzed the co-gasification of sludge and simulated municipal solid waste and improved the hydrogen production efficiency.

Overview of the Influence of Static Water Saturation on The Mechanical Properties of Concrete

This paper reviews a series of experimental and theoretical research results on the influence of existing pore water on the static and dynamic properties of concrete. This paper summarizes the current experimental research methods and conclusions, analyzes the influence mechanism of moisture content and loading speed on the elastic modulus and strength of concrete, and points out that the influence of pore water on concrete properties should be the result of the joint action of multiple factors.

Permanent deformation characteristics of unsaturated subgrade soils under cyclic loading

Excess permanent deformation of subgrade may cause critical rutting in pavements, and subsurface water significantly affects the accumulation of permanent deformation. This study aims to reveal the permanent deformation behaviour of unsaturated subgrade soils. Subgrade box tests were performed at varying moisture content, stress levels and loading frequency, respectively. The test results show that the permanent deformation significantly increased with moisture content. The concept of a permitted moisture content-applied dynamic load envelope was proposed. Based on curve fitting, a prediction model of permanent deformation of subgrade soils was developed, and the effects of moisture content and loading cycles were included. The validation results show that the model exhibited reasonably good performance in modelling the deformation. This study may provide an alternative way for predicting the permanent deformation of unsaturated subgrade soils.