skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Modeling Resilient Modulus of Unsaturated Subgrade Soils under Concurrent Changes in Water Content and Temperature
Seasonal variations and climatic events cause fluctuations of water content and temperature in shallow unsaturated soils. Such fluctuations can alter the resilient modulus (MR) of subgrade, which is an important parameter in the design and evaluation of pavements. This paper presents a new model to determine MR of unsaturated subgrade soils under concurrent changes in water content and temperature. The proposed analytical model offers the following two new features distinguishing it from alternative models: (1) the model separately accounts for two different soil water retention mechanisms, namely capillary and adsorption, which enables it to predict MR over a wide range of suctions, and (2) it explicitly incorporates the effect of temperature in the calculation of MR through employing temperature-dependent expressions for matric suction and the soil water retention curve (SWRC). The proposed model showed high accuracy when validated against experimentally measured MR values for several different soils reported in the literature. The presented model is simple and can readily be employed in practice to determine MR of subgrade soils under concurrent variations of water content and temperature.  more » « less
Award ID(s):
1951636
PAR ID:
10379265
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Proc. Geo-Congress 2022: Site and Soil Characterization, Computational Geotechnics, Risk, and Lessons Learned, Geotechnical Special Publication No. 333
Page Range / eLocation ID:
374-384
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, E3S Web of Conferences)
    Cardoso, R.; Jommi, C.; Romero, E. (Ed.)
    Near-surface unsaturated soils can be exposed to elevated temperatures due to soil-atmospheric interactions under drought events, wildfires, heatwaves, and warm spells, or the heat induced by emerging geotechnical and geo-environmental technologies such as geothermal boreholes and thermally active earthen systems. Elevated temperatures can affect the hydro-mechanical characteristics of unsaturated soils, which in turn can alter lateral earth pressures developed in the backfill soil. The main objective of this study is to quantify the effect of elevated temperatures on active and passive earth pressures of unsaturated soils. For this purpose, the paper presents the derivation of an analytical framework to extend Rankine’s earth pressure theory to account for the effect of temperature under hydrostatic conditions. The equations are derived by incorporating the effect of temperature into the soil water retention curve and a suction stress-based effective stress representation. The proposed effective stress equation considers the temperature-induced changes in the contact angle, surface tension, and enthalpy of immersion. To investigate the impact of temperature on active and passive earth pressures, the proposed method is then used in a set of parametric studies to determine active and passive earth pressure profiles for three hypothetical soils of clay, silt, and sand at different temperatures. Results suggest that elevated temperatures can cause variation in active and passive earth pressures for all the soils considered. The findings of this study can contribute toward analyzing earth retaining structures subjected to elevated temperatures. 
    more » « less
  2. ; ; ; (, Geo-Congress 2020: Geo-Systems, Sustainability, Geoenvironmental Engineering, and Unsaturated Soil Mechanics, Geotechnical Special Publication No. 319)
    null (Ed.)
    Key engineering properties of unsaturated soils such as volume change and shear strength can be defined using the effective stress principle. Several problems like prolonged drought, high-level radioactive waste, buried high voltage cables can subject surface and near-surface unsaturated soils to elevated temperatures. Such elevated temperatures can affect the hydraulic and mechanical behavior of unsaturated soils. It is very important to develop a closed-form model that can reasonably estimate the effective stresses under different elevated temperatures. For this purpose, the current study incorporates the temperature effect into a suction stress-based representation of Bishop’s effective stress. The proposed model accounts for the effect of temperature on matric suction and degree of saturation. A temperature-dependent soil water retention curve is used to account for thermal effects on surface tension, contact angle, and enthalpy of immersion per unit area. The proposed effective stress model is then used to calculate the effective stress for two soils, Pachapa loam, and Seochang sandy clay, at various temperatures ranging from 25°C to 100°C. The validity of the model is examined by comparing the predicted effective degree of saturation and suction stress values against the experimental data reported in the literature for GMZ01 bentonite. At a constant net normal stress, the results for both soils show that the impact of temperature on effective stress can be significant. The proposed model can be used for studying geotechnical and geoenvironmental engineering applications that involve elevated temperatures. 
    more » « less
  3. ; ; (, International Journal for Numerical and Analytical Methods in Geomechanics)
    Summary This study presents a thermo‐hydro‐mechanical (THM) model of unsaturated soils using isogeometric analysis (IGA). The framework employs Bézier extraction to connect IGA to the conventional finite element analysis (FEA), featuring the current study as one of the first attempts to develop an IGA‐FEA framework for solving THM problems in unsaturated soils. IGA offers higher levels of interelement continuity making it an attractive method for solving highly nonlinear problems. The governing equations of linear momentum, mass, and energy balance are coupled based on the averaging procedure within the hybrid mixture theory. The Drucker‐Prager yield surface is used to limit the modified effective stress where the model follows small strain, quasi‐static loading conditions. Temperature dependency of the surface tension is implemented in the soil‐water retention curve. Nonuniform rational B‐splines (NURBS) basis functions are used in the standard Galerkin method and weak formulations of the balance equations. Displacement, capillary pressure, gas pressure, and temperature are four independent quantities that are approximated by NURBS in spatial discretization. The framework is used to simulate strain localization in an undrained dense sand subjected to plane strain biaxial compression under different temperatures and displacement velocities. Results show that an increase in the displacement rate leads to reduction in the equivalent plastic strain while an increase in the temperature leads to an increase in the equivalent plastic strain. The findings suggest that the proposed IGA‐based framework offers a viable alternative for solving THM problems in unsaturated soils. 
    more » « less
  4. ; ; ; ; ; ; ; (, Journal of Geophysical Research: Biogeosciences)
    Abstract Due to their large carbon storage capacity and ability to exchange subterranean CO2with the atmosphere, soils are key components in the carbon balance in semi‐arid ecosystems. Most studies have focused on shallow (e.g., <30 cm depth) soil CO2dynamics neglecting processes in deeper soil layers where highly CO2‐enriched air can be stored or transported through soil pores and fissures. Here, we examine the relationship among variations in subterranean CO2molar fraction, volumetric water content, soil temperature and atmospheric pressure during three years within soil profiles (0.15, 0.50, and 1.50 m depths) in two semi‐arid grasslands located in southeastern Spain. We applied a wavelet coherence analysis to study the temporal variability and temporal correlation between the CO2molar fraction and its covariates (soil temperature, soil moisture and atmospheric pressure). Our results show that CO2dynamics are strongly influenced by changes in atmospheric pressure from semidiurnal, diurnal and synoptic to monthly time‐scales for all soil depths. In contrast, only weak daily dependencies were found at the surface level (0.15 m) regarding soil temperature and volumetric water content. Atmospheric pressure changes substantially influence variations in the CO2content (with daily fluctuations of up to 2000 ppm) denoting transportation through soil layers. These results provide insights into the importance of subterranean storage and non‐diffusive gas transport that could influence soil CO2efflux rates, processes that are not considered when applying the flux‐gradient approach and, which can be especially important in ecosystems with high air permeability between the unsaturated porous media and the atmosphere. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Water Resources Research)
    Abstract The size and spatial distribution of soil structural macropores impact the infiltration, percolation, and retention of soil water. Despite the assumption often made in hydrologic flux equations that these macropores are rigid, highly structured soils can respond quickly to moisture variability‐induced shrink‐swell processes altering the size distribution of these pores. In this study, we use a high‐resolution (180 m) laser imaging technique to measure the average width of interpedal, planar macropores from intact cross sections and relate it to matrix water content. We also develop an expression for unsaturated hydraulic conductivity that accounts for dynamic macropore geometries and propose a method for partitioning sensor soil water content data into matrix and macropore water contents. The model was applied to a soil in northeastern Kansas where soil monoliths had been imaged to quantify macropore properties and continuous water content data were collected at three depths. Model‐predicted macropore width showed significant sensitivity to matrix water content resulting in changes of 15%–50% of maximum width over the 15‐month period of record. Transient saturated hydraulic conductivity predicted from the model compared favorably to a previously developed model accounting for moisture‐induced changes to structural unit porosity. Following periods of low soil moisture, infiltrating meteoric water filled highly conductive macropores increasing by several orders of magnitude which subsequently decreased as water was absorbed into the matrix and macropores drained. This model offers a means by which to combine measurable morphological data with soil moisture sensors to monitor dynamic hydraulic properties of soils susceptible to shrink‐swell processes. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email