No abstract

The present work documents some of the most recent experimental evidence of the thermohydro-mechanical behavior of compacted soils over a whole range of suction- and/or thermo-controlled stress paths and modes of deformation, including data from a series of triaxial, true triaxial, plane strain, ring shear, and resonant column tests conducted on different types of cohesive-frictional soils in the low-to-medium matric suction range under either room temperature or thermally controlled conditions. The work has been accomplished at the Advanced Geomechanics Laboratory of the University of Texas at Arlington, focusing primarily on the following essential features of unsaturated soil behavior: (1) Loading-collapse and apparent tensile strength loci assessed from suction-controlled triaxial and true triaxial testing on clayey sand, (2) Critical state lines from suction-controlled plane strain testing on silty soil, (3) Peak and residual failure envelopes from suction-controlled ring shear testing on clayey soil, (4) Frequency response curves and cyclic stress-strain hysteretic loops from thermo-controlled, constant-water content resonant column testing on clayey soil, and (5) Residual failure envelopes from suction/thermo-controlled ring shear testing on clayey soil. The work is intended to serve as a succinct yet reasonably thorough state-of-the-art paper contribution to PanAm-UNSAT 2021: Third Pan-American Conference on Unsaturated Soils, Rio de Janeiro, Brazil, July 21-25, 2021.

The impact of thermal gradients on the stiffness response of soil materials subjected to monotonic loading has been reasonably well documented. The combined effect of simultaneous thermal and cyclic loadings on soil stiffness, however, has not been as thoroughly investigated. In the present work, a comprehensive series of thermo-controlled constant-water content resonant column (RC) tests was carried out to experimentally assess the effect of increasingly elevated temperatures on small-strain stiffness properties, namely maximum shear modulus and minimum damping ratio, of three different types of cohesive-frictional soils. An existing RC apparatus was upgraded by the incorporation of immersion heaters and a thermocouple inside the main RC cell to control and monitor the thermal conditioning of the test samples. A thorough calibration of the upgraded RC device was first performed to determine the suitable thermal-equalization time required to reach reasonably steady heat distribution within the typical RC test samples of each type of soil. Results from the series of thermo-controlled RC tests showed a mostly detrimental effect of increasing temperature on the small-strain shear moduli of cohesive-frictional soils. The small-strain damping ratios, accordingly, either remained unchanged or experienced a gradual increase with increasing soil temperature.

The shear modulus and damping ratio are arguably the two most crucial soil parameters to be used in seismic site-response analyses and a wide variety of other geotechnical engineering applications involving soil materials subjected to dynamic loading. The dependency of these parameters on the level of load-induced shear strains in the field has been investigated rather extensively for different types of soil. Most experimental studies, however, have relied on a limited set of controlled environmental factors and stress variables, mainly soil moisture and confinement. The present work is an attempt to gain further insights on the possible impact of an additional critical factor: soil temperature. A resonant column (RC) apparatus was upgraded to assess the dynamic response of three types of cohesive-frictional soils as they transitioned from linear to nonlinear behavior under thermo-controlled cyclic torsional loading. Emphasis was placed on shear modulus degradation, and hence variation in damping ratio, with increasing shear-strain amplitude (cyclic torque magnitude). Results showed a mostly detrimental effect of increasing soil temperature on the normalized shear modulus, damping ratio, and threshold shear strain of clayey, silty, and sandy soils when subject to small-to-medium shear strain levels.