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1. 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. 

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2. Role of initial effective stress on the thermal volume change of normally consolidated clay

   https://doi.org/10.1051/e3sconf/202020509001  

   Samarakoon, Radhavi; McCartney, John S. (January 2020, E3S Web of Conferences)

   McCartney, J.S.; Tomac, I. (Ed.)

   This paper focuses on the results from thermal triaxial tests on normally consolidated Georgia Kaolinite. The hypothesis evaluated in this study is whether the initial mean effective stress has an impact on the thermal volume change encountered during drained heating. To that effect, specimens at three different initial mean effective stresses were considered in this study. The clay specimens were first isotropically consolidated to a normally consolidated state, then subjected to a drained heating cooling cycle followed by further mechanical loading to higher effective stresses. The results indicate contractive volumetric strain during drained heating where the volumetric strain was found to increase with increasing initial mean effective stress. A rebound in volume was observed during subsequent cooling where the net change in volume transitioned from zero volume change of the specimen to net contraction of the specimen after a heating cooling cycle as the initial mean effective stress increased. The results indicate the need for considering the effect of initial mean effective stress when assessing in-situ heating as a method of soil improvement. 

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3. A Study on Thermal Consolidation of Fine Grained Soils Using Modified Consolidometer

   https://doi.org/10.1061/9780784482117.014  

   Joshaghani, Mohammad; Ghasemi-Fare, Omid (March 2019, Geo-congress 2019)

   In order to fully understand the thermo-hydro-mechanical behavior of the geotechnical infrastructures, the effects of temperature variations on soil properties and soil behavior have to be studied. Hydraulic conductivity, strength, volume change, moisture content, and pore pressure generation and dissipation rates depend on temperature variations. Thermal loading might induce excess pore water pressure and volumetric changes. Temperature changes in the fine-grained soils will cause expansion in water and soil particles. Since the coefficient of expansion for soil particles is much smaller than that for water, a generation of pore water pressure is expected. This thermally induced pore water pressure and then its dissipation during the relaxation period results in a time dependent consolidation. Thermal consolidation in fine grained soil is more dominant and can be irreversible in normally consolidated clay. However, the volumetric changes of highly over consolidated soil caused by temperature increment is reversible by temperature reduction. In this research, a modified consolidation testing device is used to study the effect of temperature increments (e.g., increasing step by step temperature increments to 80ºC) on the consolidation of fine grained soils. In another words the effect of temperature increments during the test on the consolidation process is studied. Time of applying the heating, target temperature, and initial void ratio are parameters affecting the rate and the amount of consolidation in the samples. 

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4. Partially Drained Responses of Dense Sand under Monotonic Simple Shear

   https://doi.org/10.1061/9780784486016.048  

   Kwan, Wing_Shun; Leal, Cesar; Nunez, Elizabeth; De_Jesus, Brandon (February 2025, American Society of Civil Engineers)

   Marine structures placed in the shallower seabed can experience pore water drainages with more complexity than those in onshore environments, particularly in coarse-grained soils where drainage is neither purely “drained” nor “undrained,” but Partially Drained (PD). However, current laboratory approaches for characterizing soil behavior are limited to modeling drainage conditions as fully drained or undrained. This paper presents results from a series of confined monotonic saturated simple shear tests under various drainage conditions on reconstituted medium dense to dense Monterey sand specimens to fill this knowledge gap. Although others have performed limited PD element-level tests under triaxial conditions, no documentation exists for tests using a simple monotonic shear configuration. To achieve PD, a special filter was fabricated and connected between the bottom of the specimen and the backpressure controller. The hydraulic filter comprises a series of needle valves to provide various hydraulic impedances. All simple shear tests in this paper were backpressure-saturated. Two different degrees of PD were considered and compared with fully drained and undrained conditions. Results show that the excess pore water pressure generation and measured volumetric changes in the PD tests are bounded between those measured from fully drained and undrained, proving the PD filter provided the hydraulic resistance to achieve PD condition. 

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5. PM4Silt (Version 1): A silt plasticity model for earthquake engineering applications

   Boulanger, Ross W.; Ziotopoulou, Katerina (January 2018, Report No. UCD/CGM-18/01, Center for Geotechnical Modeling, Department of Civil and Environmental Engineering, University of California, Davis, CA, 108 pp.)

   The PM4Silt plasticity model for representing low-plasticity silts and clays in geotechnical earthquake engineering applications is presented herein. The PM4Silt model builds on the framework of the stress-ratio controlled, critical state compatible, bounding surface plasticity PM4Sand model (version 3) described in Boulanger and Ziotopoulou (2015) and Ziotopoulou and Boulanger (2016). Modifications to the model were developed and implemented to improve its ability to approximate undrained monotonic and cyclic loading responses of low-plasticity silts and clays, as opposed to those for purely nonplastic silts or sands. Emphasis was given to obtaining reasonable approximations of undrained monotonic shear strengths, undrained cyclic shear strengths, and shear modulus reduction and hysteretic damping responses across a range of initial static shear stress and overburden stress conditions. The model does not include a cap, and therefore is not suited for simulating consolidation settlements or strength evolution with consolidation stress history. The model is cast in terms of the state parameter relative to a linear critical state line in void ratio versus logarithm of mean effective stress. The primary input parameters are the undrained shear strength ratio (or undrained shear strength), the shear modulus coefficient, the contraction rate parameter, and an optional post-strong-shaking shear strength reduction factor. All secondary input parameters are assigned default values based on a generalized calibration. Secondary parameters that are most likely to warrant adjustment based on site-specific laboratory test data include the shear modulus exponent, plastic modulus coefficient (adjusts modulus reduction with shear strain), bounding stress ratio parameters (affect peak friction angles and undrained stress paths), fabric related parameters (affect rate of shear strain accumulation at larger strains and shape of stress-strain hysteresis loops), maximum excess pore pressure ratio, initial void ratio, and compressibility index. The model is coded as a user defined material in a dynamic link library (DLL) for use with the commercial program FLAC 8.0 (Itasca 2016). The numerical implementation and DLL module are described. The behavior of the model is illustrated by simulations of element loading tests covering a range of conditions, including undrained monotonic and cyclic loading under a range of initial confining and shear stress conditions. The model is shown to provide reasonable approximations of behaviors important to many earthquake engineering applications and to be relatively easy to calibrate. 

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