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1. Suction and thermal conductivity of unsaturated loess from Northern France

   Nguyen, V (January 2018, UNSAT 2018)

   Loess covers large areas around the earth. Loess deposits are typically composed of silt with clay and fine sand particles and it is usually distributed with a few meters thick. Literature review shows that, the thermal conductivity of loess varies in a relatively large range from 0.2 to 2 W/(mK), depending on the particle composition, texture and moisture content of soil. In this study, loess samples were taken at shallow depth from the Northern France. Suction, volumetric moisture content and thermal conductivity of soil were measured simultaneously while wetting/drying cycles were applied to the sample. The results show that, the degree of saturation significantly affects the thermal conductivity of the soil. The relationship between these two parameters is reversible under wetting/drying cycles while hysteresis can be observed while plotting the thermal conductivity versus suction. 

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2. Centrifuge tests to assess seismic site response of partially saturated sand layers

   https://doi.org/10.1016/j.soildyn.2017.01.024  

   Mirshekari, Morteza; Ghayoomi, Majid (March 2017, Soil Dynamics and Earthquake Engineering)

   Seismic response of unsaturated soil layers may differ from that of saturated or dry soil deposits. A set of centrifuge experiments was conducted to study the influence of partial saturation on seismic response of sand layers under scaled Northridge earthquake motion. Steady state infiltration was implemented to control and provide uniform degrees of saturation profiles in depth. The amplification of peak ground acceleration at the soil surface was inversely proportional to the degree of saturation, especially in low period range. The cumulative intensity amplification of the motion was also higher in unsaturated soils with higher suctions. The lateral deformation and surface settlement of partially saturated sand with higher stiffness were generally lower than that in dry soil. Although neglecting the effect of partial saturation in sand layers might be conservative with respect to seismic deformations, it may result in underestimating the surface design spectra. 

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3. Cyclic Triaxial Test to Measure Strain-Dependent Shear Modulus of Unsaturated Sand

   https://doi.org/10.1061/(ASCE)GM.1943-5622.0000917  

   Ghayoomi, Majid; Suprunenko, Ganna; Mirshekari, Morteza (September 2017, International Journal of Geomechanics)

   Dynamic shear modulus plays an important role in the seismic assessment of geotechnical systems. Changes in the degree of water saturation influence dynamic soil properties because of the presence of matric suction. This paper describes the modification of a suction-controlled cyclic triaxial apparatus to investigate the strain-dependent shear modulus of unsaturated soils. Several strain- and stress-controlled cyclic triaxial tests were performed on a clean sand with various degrees of saturation. Suction in unsaturated sands increased the shear modulus in comparison with the ones in dry and saturated conditions for different shear strain levels, with a peak modulus in higher suction levels. Also, shear modulus decreased with an increase in the shear strain for specimens with similar matric suction. The normalized shear moduli of the unsaturated sand specimens followed a similar trend to the ones predicted by the available empirical shear modulus reduction functions but showed lower values. The modulus reduction ratios of unsaturated sands shifted up as a result of higher effective stress and suction-induced stiffness. These trends were consistent for both strain- and stress-controlled tests. 

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4. On the Differential Effects of Salinity and Sodicity on Particulate Emissions from Agricultural Soils

   Khatei, Ganesh; Rinaldo, Tobia; Van_Pelt, Scott; D’Odorico, Paolo; Ravi, Sujith (December 2024, American Geophysical Union, Fall meeting)

   Wind erosion and dust emissions affect regions of the world with sparse vegetation cover or affected by agricultural practices that expose the soil surface to wind action. Research in this field has investigated the impact of soil moisture, land use, and land cover on soil susceptibility to wind erosion and dust emissions. The effect of soil salinity and sodicity, however, remains poorly appreciated. Salt accumulation in agricultural soils is a major concern in agroecosystems with high evaporative demand, shallow water tables or irrigated with water rich in dissolved solids. The understanding of how salts can affect aeolian processes in arid and hyper-arid landscapes remains incomplete. Recent studies focused on the effect of soil salinity on soil erodibility in dry atmospheric conditions, while the effect of soil sodicity and more humid conditions still needs to be investigated. Here we use wind tunnel tests to detect the effect of varying atmospheric humidity on wind erodibility and particulate matter emissions under saline and sodic conditions.Through a series of controlled wind tunnel experiments of soils treated with different concentrations of saline and sodic water, we find that the threshold velocity for wind erosion significantly increases with increasing soil salinity and sodicity, provided that the soil crust formed by soil salts is not disturbed. Indeed, with increasing soil salinity, the formation of a soil crust of increasing strength is observed, leading to an increase in the threshold wind velocity and a consequent decrease in particulate emissions. However, if the crust is destroyed by trampling, no significant changes in threshold velocity for wind erosion are found with increasing salinity and sodicity levels. Interestingly, after the threshold velocity was exceeded, soil crusts were readily ruptured by saltating sand grains resulting in comparable or sometimes even higher particulate matter emissions in saline and sodic soils compared to their untreated ('control') counterparts. Finally, understanding the role of atmospheric humidity under changing climate scenarios will help to modulate the wind erosion processes in saline-sodic soils and will help mitigate better dust emissions and soil management policies in arid and semi-arid climate zones. 

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5. Stability of kangaroo rat burrows in the Sonoran Desert: Evidence of biocementation

   https://doi.org/10.1139/cgj-2024-0225  

   Tirkes, Sera; Aydin, Duygu; Thompson, Madison; Collins, Clint E; Beyenal, Haluk; Akin, Idil Deniz (October 2024, Canadian Geotechnical Journal)

   Kangaroo rats (Dipodomys deserti) construct complex burrow systems in loose desert sand that survive temperature and relative humidity fluctuations and storms. Animals that burrow in desert sand typically burrow in compacted sand, near plant roots, or when the soil is unsaturated. However, these processes are insufficient to explain tunnel stability of kangaroo rats. Our goal is to understand how kangaroo rat burrows remain stable in loose desert sand, intending to translate this knowledge to geotechnical engineering. A kangaroo rat habitat in the dunes of The Sonoran Desert, AZ, was selected for the study. Dynamic cone penetrometer tests performed at active, abandoned, and no-burrow sites demonstrated that the animals prefer loose sand for burrow construction. Soil samples collected from the burrows' ceilings, subsurface, and surface were characterized. Brazilian tensile strength test results showed that burrow soil has approximately 3 times greater tensile strength than the rest at dry state, which indicates increased interparticle attractive stress in burrow ceilings due to biocementation. Laboratory experiments, scanning electron microscopy, and confocal microscopy images showed that fungal and microbial biofilms provided 17 kPa increase in interparticle attractive stress at less than 1% biomass concentration, indicating potential to be used in soil improvement applications. 

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