Temperature- and Rate-Dependent Stress–Strain–Time Behavior of Sands and Its Simulation Using a Modified Nonlinear Three-Component Model

Understanding the time-dependent deformation of granular materials under coupled thermal and mechanical loading is essential for the safe design of geotechnical structures subjected to temperature variations. This study investigates the temperature- and rate-dependent stress–strain–time behavior of three sands—KMUTT, Hostun, and Ottawa sands—through temperature-controlled consolidated drained triaxial compression (CDTC) tests conducted at constant temperatures ranging from 30 to 60 °C. The experimental program included monotonic loading, sustained loading (creep), and strain-rate change tests to characterize elastic, inviscid, and viscous responses. The results reveal clear material-dependent thermal effects: KMUTT and Hostun sands, composed of sub-angular to angular particles, exhibit thermal weakening characterized by reductions in peak shear strength and elastic stiffness with increasing temperature, whereas Ottawa sand, composed of rounded particles, exhibits thermal strengthening with enhanced strength and stiffness at elevated temperatures. In contrast, the intrinsic viscous properties of the sands, including the rate-sensitivity coefficient and viscosity type, were found to be essentially independent of temperature within the tested range. To simulate these coupled behaviors within a unified framework, a modified Nonlinear Three-Component (NTC) model was developed by introducing a temperature effect parameter into the elastic and inviscid components while maintaining temperature-independent viscous parameters. The model successfully reproduces temperature- and rate-dependent stress–strain responses, transient stress jumps associated with strain-rate changes, and time-dependent creep behavior. The contrasting thermal responses are interpreted in terms of particle shape, where thermal expansion disturbs particle interlocking in angular sands but enhances inter-particle contact forces in rounded sands.