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ABSTRACT This study investigates linkages between volume change, pore fluid drainage, shear wave velocity, and temperature of soft clays using a thermal triaxial cell equipped with bender elements, a measurement approach that has not been explored widely in past thermo-mechanical studies. Two kaolinite specimens were consolidated mechanically to a normally consolidated state and then subjected to drained and undrained heating-cooling cycles, respectively. After cooling, the specimens were subjected to further mechanical consolidation to evaluate changes in apparent preconsolidation stress. Both specimens showed net contractive thermal strains after a heating-cooling cycle and overconsolidated behavior during mechanical compression immediately after cooling. The shear wave velocity increased during drained heating, but negligible changes were observed during drained cooling, indicating permanent hardening because of thermal consolidation during the heating-cooling cycle. The shear wave velocity decreased during undrained heating because of a reduction in effective stress associated with thermal pressurization of the pore fluid but subsequently increased when drainage was permitted at elevated temperature. The shear wave velocity increased slightly during undrained cooling but decreased when drainage was permitted at room temperature. Net increases in small-strain shear modulus of 17 and 11 % after heating-cooling cycles under drained and undrained (with drainage after reaching stable temperatures) conditions, respectively, provide further evidence to the potential of thermal soil improvement of normally consolidated clays. Transient changes in shear modulus also highlight the importance of considering drainage conditions and corresponding changes in effective stress state during heating-cooling cycles.
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Role of initial effective stress on the thermal volume change of normally consolidated clay
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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- Award ID(s):
- 1941571
- PAR ID:
- 10251003
- Editor(s):
- McCartney, J.S.; Tomac, I.
- Date Published:
- Journal Name:
- E3S Web of Conferences
- Volume:
- 205
- ISSN:
- 2267-1242
- Page Range / eLocation ID:
- 09001
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1051/e3sconf/202020509001
