13 research outputs found
Role of initial effective stress on the thermal volume change of normally consolidated clay
Full text linkThis 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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Thermal Improvement of Normally Consolidated Clay
Full text linkConstruction on soft clay deposits poses challenges to geotechnical engineers due to low shear strength, high compressibility, and complex dynamic response. The main soil improvement technique used in practice requires the placement of a surcharge load in conjunction with vertical drains, which is time consuming, requires transporting significant amount of surcharge material, and can only be used in onshore applications. As an alternative, this study investigates the improvement of soft clays using in-situ heating with geothermal heat exchangers. Heating of soft clays leads to differential expansion of the pore water and soil solids, causing pressurization and drainage of the pore water resulting in permanent volumetric contraction. While the impact of temperature on soft soils has been widely investigated, a key missing piece of information is the effect of initial mean effective stress of the soft clay on thermal volume change and corresponding increase in undrained shear strength. To address this limitation, the overall objective of this study is to understand the effects of subjecting saturated normally consolidated clays with different initial mean effective stresses to drained heating. Innovative testing approaches include glass thermal triaxial tests which permits use of image analysis to track thermal volume changes, and a thermal triaxial cell with embedded bender elements to measure the shear wave velocity of clay specimens. The magnitude of thermal volumetric strain increased with increasing initial mean effective stress, which is a departure from expected trends in established constitutive models. A corresponding increase in undrained shear strength with both temperature and initial mean effective stress was observed. Further, an increase in the shear wave velocity was observed during heating and no significant change was observed during cooling, indicating permanent hardening of the clay.
Experimental results were useful in calibrating a new constitutive model for the thermal volume change of normally consolidated clays, which was implemented into numerical simulations of heat transfer and water flow around a vertical drain containing a geothermal heat exchanger. Overall, this study provides the technology behind an exciting new thermal soil improvement technique that can have positive long-term energy savings for civil infrastructure in soft soil regions
Computational Code for Optimization of Thermal Treatment of Fine Grained Soils as a Method of Expediting their Load Induced Consolidation
Full text linkConstruction in soft soils has been a challenging task for engineers due to the excessive time taken for dissipation of construction induced pore water pressure and the ensuing postconstruction settlement. Use of vertical drains has proven to be an effective and economical method for soft ground improvement and hence extensive research has been carried out to further improve its efficiency. Effect of temperature on radial consolidation is one aspect of such research among many others that have been pursued.
Elevated temperature certainly has a pronounced effect on the hydraulic conductivity due to the reduction it causes in the viscosity of water. Furthermore, temperature also generates excess pore water pressure due to the tendency for differential volumetric expansion between the soil grains and pore water. Thermally induced volumetric strains can have an effect on the magnitude of settlement as well. A numerical methodology based on the NavierStokes equations of flow and thermoelasto-plastic soil compressibility relationships was developed to model transient fluid flow in a clay under thermal treatment. Experimentally verified soil compressibility relationships coupling the loading and thermal effects obtained from literature were employed in this model. The transient temperature distribution within the consolidation soil was modeled using the Fourier’s equation of heat transfer.
The effect of temperature on consolidation of clay was investigated by a parametric study involving different maximum temperatures, surcharge loads and initial porosities of clay. It was concluded that the improvement in the magnitude and rate of settlement at elevated temperature is more significant at relatively smaller surcharges and low initial porosities. Since there is a possibility for thermally induced volumetric expansion even in normally consolidated clays, an optimum combination of surcharge and thermal treatment should be employed for given initial conditions of the soil, in order to achieve the maximum improvement in settlement. The developed numerical model will provide the framework to carry out further investigations and determine the viability of the practical implementation of coupled thermomechanical consolidation using prefabricated vertical drains
Effect of Drained Heating and Cooling on the Preconsolidation Stress of Saturated Normally Consolidated Clays
Full text linkSimulation of thermal drains using a new constitutive model for thermal volume change of normally consolidated clays
No full textImpact of Drained Heating and Cooling on Undrained Shear Strength of Normally Consolidated Clay
No full textEffect of Drained Heating and Cooling on the Preconsolidation Stress of Saturated Normally Consolidated Clays
No full textSimulation of thermal drains using a new constitutive model for thermal volume change of normally consolidated clays
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Impact of Drained Heating and Cooling on Undrained Shear Strength of Normally Consolidated Clay
Full text linkUse of Bender Elements to Evaluate Linkages between Thermal Volume Changes and Shear Modulus Hardening in Drained and Undrained Thermal Triaxial Tests
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