More Like this

1. Monotonic, Cyclic, and Post-Cyclic Response of Willamette River Silt at the Van Buren Bridge

   https://doi.org/10.1061/9780784484043.042  

   Dadashiserej, Ali ; Jana, Amalesh ; Ortiz, Susan C. ; Walters, James J. ; Stuedlein, Armin W. ; Evans, T. Matthew ( March 2022 , Geo-Congress 2022)

   Lemnitzer, A. ; Stuedlein, A.W. (Ed.)

   This study presents a laboratory investigation of the monotonic, cyclic, and post-cyclic responses of a lightly overconsolidated, low plasticity silt deposit conducted to support the geotechnical design of a proposed bridge replacement crossing the Willamette River in Corvallis, OR. The design seismic hazard corresponded to the 975-year return period with the Cascadia Subduction Zone contributing the greatest portion of the hazard. The response of the intact, natural specimens was compared to that of specimens reconstituted from the same material for comparison of the effect of soil fabric. Constant-volume cyclic stress controlled direct simple shear tests (CDSS) conducted on the low plasticity silt deposit showed cyclic mobility type behavior and increases in cyclic resistance with OCR. The exponent of the power relationship between cyclic resistance ratio (CRR) and the number of cycles, N, was shown to be smaller than that commonly assumed within the simplified method for cyclic softening of fine-grained plastic soil. Despite higher density, the reconstituted specimens exhibited approximately 16% lower cyclic resistance than their undisturbed counterparts, indicating the importance of soil fabric on the cyclic resistance of natural silt soils. The post-cyclic volumetric strain of the silt deposit was found to be independent of OCR and increased with the maximum excess pore pressure ratio generated during the cyclic tests. 

   more » « less
2. Effect of Drained Heating and Cooling on the Preconsolidation Stress of Saturated Normally Consolidated Clays

   https://doi.org/10.1061/9780784482780.061  

   Samarakoon, Radhavi A. ; McCartney, John S. ( February 2020 , GeoCongress 2020)

   The thermo-mechanical behavior of saturated clays during a heating/cooling cycle is relevant from the perspective of understanding different types of energy geostructures as well as understanding the use of heat for soil improvement. This paper involves a study of the effect of a heating/cooling cycle on the preconsolidation stress of saturated normally consolidated clays. Although many studies have observed a decrease in preconsolidation stress (thermal softening) after heating of overconsolidated soils, fewer studies have investigated changes in preconsolidation stress of normally consolidated soils. Available thermo-elasto-plastic models indicate that a heating-cooling cycle will lead to thermal contraction and an apparent overconsolidation effect for normally consolidated soils (thermal hardening), but inconsistencies in the literature have been observed. This study involves the use of a thermal triaxial cell to first consolidate kaolinite clay to normally consolidated conditions, apply a drained heating or a heating/cooling cycle, followed by mechanical loading to higher mean effective stresses. The tests presented in this study confirm that cooling also induces an apparent overconsolidation effect on the initially normally consolidated clay, but with a preconsolidation stress greater than that expected from the initial virgin consolidation line before heating. The results are a positive finding regarding the possible use of heat to improve the mechanical response of soft clays. 

   more » « less
3. Analysis of thermal drains in soft clays

   Samarakoon, R. ; McCartney, J.S. ( October 2020 , GeoAmericas 2020)

   null (Ed.)

   This paper focuses on the thermo-hydro-mechanical behavior of soft clay surrounding a prefabricated thermal drain. A prefabricated thermal drain combines features of a conventional prefabricated vertical drain (PVD) and a closed-loop geothermal heat exchanger by placing plastic tubing within the core of the PVD through which heated fluid can be circulated. The prefabricated thermal drain can be used to increase the temperature of the surrounding soft clay, which will generate excess pore water pressures due to differential thermal expansion of the pore fluid and clay particles. As these excess pore water pressures drain, the soft clay will experience volumetric contraction. The elevated temperature leads to an increase in the hydraulic conductivity and the volumetric contraction leads to an increase in thermal conductivity, making this a highly coupled process. Although thermal drains have been tested in proof of concept field experiments, there are still several variables that need to be better understood. This paper presents numerical simulations of the coupled heat transfer, water flow, and volume change in the soft soil surrounding a prefabricated thermal drain that were validated using the results from large-scale laboratory experiments. Numerical simulations were found to agree well with the experimental data. A further analysis on the performance of the thermal PVD indicates an increase in surface settlement with an increase in drain temperature and a significant reduction in the surcharge required when using a thermal PVD. 

   more » « less
4. CO 2 Dynamics Are Strongly Influenced by Low Frequency Atmospheric Pressure Changes in Semiarid Grasslands

   https://doi.org/10.1029/2018JG004961  

   Moya, M. R. ; Sánchez‐Cañete, E. P. ; Vargas, R. ; López‐Ballesteros, A. ; Oyonarte, C. ; Kowalski, A. S. ; Serrano‐Ortiz, P. ; Domingo, F. ( April 2019 , Journal of Geophysical Research: Biogeosciences)

   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. Integrating observations and models to determine the effect of seasonally frozen ground on hydrologic partitioning in alpine hillslopes in the Colorado Rocky Mountains, USA

   https://doi.org/10.1002/hyp.14374  

   Rey, David M. ; Hinckley, Eve‐Lyn S. ; Walvoord, Michelle A. ; Singha, Kamini ( October 2021 , Hydrological Processes)

   This study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long‐Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time‐lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process‐based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.

    

   more » « less