Volume change characteristics of fine-grained soils due to sequential thermo-mechanical stresses

摘要

Know-how of volume change characteristics, VCC, of the fine-grained soils, exposed to thermal stresses, is essential for design of various thermo-active structures. These stresses are known to induce excess pore-water pressure, Delta u(theta), in the saturated state of such soils, which in turn affects their compression and shear strength characteristics. In this context, through several experimental studies, the effect of thermo-mechanical stress-path, the over-consolidation ratio (OCR) and degree of saturation on VCC (viz., thermally induced volumetric strain, epsilon(v theta), compression and re-compression indices, c(c) and c(r)) of the fine-grained soils has been demonstrated by earlier researchers. However, the response of these soils when exposed to sequential thermal and mechanical stresses, STMS, due to temperature fluctuation and continued infrastructure development, on VCC has seldom been studied. This motivated us to investigate the VCC of the fine-grained soils, by subjecting them to STMS in a suitably modified oedometer setup which facilitates temperature controlled tests. From the results of STMS tests, it is seen that the epsilon(v theta) of these soils exposed to thermal cycles (20.60-20 degrees C) is independent of the thermal stress history experienced at different applied vertical stress, sigma(v), (= 60, 125, 250 kPa). Furthermore, from the analysis of deformation-time curve of the thermal loading phase, a methodology for direct determination of the volume change component of fine-grained soils, due to structural rearrangement, Delta V-s theta, has been proposed. The methodology enables direct computation of the coefficient of volume change due to structural rearrangement, alpha(s theta), that would aid in direct prediction of Delta u(theta) from the deformation-time curve of thermal loading phase.