Nonisothermal Shear Strength of Compacted Silt at Residual Saturation

Abstract

This paper focuses on the results from a new triaxial cell developed to measure the shear strength of unsaturated soils under elevated temperatures and high suction magnitudes. Suction control is implemented by circulating vapor through a soil specimen having an initially low degree of saturation while the temperature of the soil specimen is controlled using heating elements within the cell fluid. A mechanical load frame was also modified to be capable of performing both load and constant displacement control triaxial tests. Volume changes were assessed using axial displacements and by tracking changes in the cell fluid volume. In addition to presenting the details of the new cell, the results from a set of drained triaxial tests performed on compacted silt specimens under different combinations of total suction and net normal stress at both ambient and elevated temperatures are presented.

Thermal Volume Change of Unsaturated Silt under Different Stress States and Suction Magnitudes

“…Similar observations have been observed for unsaturated silt by Shanina and McCartney (2016). Alsherif and McCartney (2015) found that heating at low suctions leads to contraction while heating at high suctions leads to expansion for similar stress states and temperature changes. This behavior was explained using different hardening and softening mechanisms by Alsherif and McCartney (2016).…”

“…This is a feature that cannot be captured using thermo-elastoplastic models, but may be considered using a thermal creep model. The rate of thermal axial strain with change in temperature for the results from Vega and McCartney (2015) are compared with those from Alsherif and McCartney (2015) in Figure 7. In order to make the comparison in this figure, the mean effective stress and mean effective preconsolidation stress for the high suction tests of Alsherif and McCartney (2015) were back-analysed by Alsherif and McCartney (2016) using a thermo-elasto-plastic model.…”

“…The rate of thermal axial strain with change in temperature for the results from Vega and McCartney (2015) are compared with those from Alsherif and McCartney (2015) in Figure 7. In order to make the comparison in this figure, the mean effective stress and mean effective preconsolidation stress for the high suction tests of Alsherif and McCartney (2015) were back-analysed by Alsherif and McCartney (2016) using a thermo-elasto-plastic model. When plotted in terms of the effective stress OCR, similar behavior is noted for the saturated and unsaturated specimens, regardless of the fact that the specimens tested by Alsherif and McCartney (2015) were under very high suction magnitudes and those tested by Vega and McCartney (2015) are saturated.…”

“…In order to make the comparison in this figure, the mean effective stress and mean effective preconsolidation stress for the high suction tests of Alsherif and McCartney (2015) were back-analysed by Alsherif and McCartney (2016) using a thermo-elasto-plastic model. When plotted in terms of the effective stress OCR, similar behavior is noted for the saturated and unsaturated specimens, regardless of the fact that the specimens tested by Alsherif and McCartney (2015) were under very high suction magnitudes and those tested by Vega and McCartney (2015) are saturated. This indicates that an effective stress analysis of thermal volume change tests is critical to correctly interpret trends in the data.…”

Thermal behaviour of unsaturated silt at high suction magnitudes

“…More details on specimen set-up and test procedures can be found in Alsherif and McCartney (2014b). Although this rate is relatively fast for a drained test, as no change in relative humidity at the boundaries was noted during shear, it was assumed to correspond to drained conditions.…”