Thermal Effects on Shear Characteristics of Unbound Granular Materials under Drained Conditions

Abstract

In this study, the thermally induced changes in the shear characteristics of unbound granular materials (UGMs) were investigated. A series of drained shear tests were conducted using a large-scale triaxial apparatus under controlled temperatures. The thermal dependence of the peak strength, critical strength, internal friction angle, and dilatancy of UGMs were investigated under different temperatures, initial mean effective stresses, and relative compaction. Dense UGMs tended to expand during heating and slightly contract during cooling. In the heating and cooling process, a nonlinear relationship was observed between thermal deformation and temperature. Thermal deformation was attributed to the deformation, movement, and rotation of soil particles and closely related to the initial mean effective stress and relative compaction. A thermal softening effect was observed during the shear test, and the peak strength decreased with increasing temperature. However, negligible thermal effects were observed relative to residual strength. The effect of temperature on the shear characteristics of UGMs was primarily related to the thermal expansion of pores in the soil skeleton. The relationship between peak strength and initial thermal volumetric strain was found to be exponential. Considering the thermal effect, a normalized semi-empirical model of the parabolic Hvorslev envelope for dense UGMs was proposed to supply guidelines for road base design.