| dc.description.abstract | Dynamic Response of Cohesive-Frictional Soils Under Thermo-Controlled Constant Water Content
Cyclic Simple Shear Testing
Daniel R. C. Green
The University of Texas at Arlington, 2023
Supervising Professor: Dr. Laureano R. Hoyos
A considerable portion of the emerging geothermal infrastructure in the country is located in earthquake prone areas while being supported and/or surrounded by soil deposits located well above the groundwater table. Geotechnical earthquake research in the country, however, continues to be mostly focused on soil response under saturated conditions, especially soil liquefaction phenomena, while most of the work on dynamic response of compacted soils has not taken thermal conditioning of pore-fluids into account as critical environmental factors. To date, there is hardly any comprehensive study at the laboratory scale that has focused on a thorough assessment of the dynamic properties of compacted soils, particularly shear modulus and material damping ratio of cohesive-frictional soils, for a relatively large range of cyclic shear strain amplitudes (0.001% to 10.0% shear strain amplitudes) under controlled moisture content and simultaneous thermal conditioning of pore-fluids.
In the present study, an existing Cyclic Simple Shear (CSS) apparatus has been upgraded to investigate the dynamic response of three distinct types of cohesive-frictional soils, namely, CL (w=9.0%), CL (w=13.6%), CL (w=17.0%), ML (w=14.8%), SC (w=10.0%), particularly in terms of shear modulus and damping ratio, under controlled moisture, confinement, and thermal conditioning of the pore-fluids, from 23oC (room temperature) to 60°C. A digital convection heater, featuring two heating elements and a thermocouple, was adapted to the main cell of the CSS apparatus for measurement and control of thermal gradients in the test samples. However, because thermocouple probes cannot be inserted into the sample during testing, for risk of disturbing the compacted soil and puncturing the latex membrane, a thorough thermo-calibration of the upgraded CSS chamber was necessary prior to thermo-controlled testing to ensure proper heating and heat distribution within the soil samples.
After thermo-calibration, a comprehensive testing plan was followed to investigate the effects of increased temperatures on shear modulus and damping ratio of all three test soils for a wide array of shear strain amplitudes (from 0.001% to 10.0%). Experimental variables and procedures are described in detail. Experimental results are presented and analyzed via the Bilinear and Ramberg-Osgood Models. Results and analysis suggest that increased temperatures caused a decrease in peak shear stress under a fixed shear strain amplitude, suggesting a decrease in shear modulus and an increase in material damping ratio. | |
