Experimental researches of thermal diffusivity and conductivity in embankment ballast under periodically fluctuating temperature

The experimental approach to evaluating the thermal diffusivity and conductivity in the porous ballast was studied. For tight-test and open-test, heat transfer characteristics in porous ballast cylindrical specimens under a periodically fluctuating surface temperature were analyzed. For tight-test, the theoretical and experimental studies show that natural convection may be negligible and heat conduction is the main mechanism of heat transfer. For the slender cylindrical specimen in the tight-test, the damping of temperature amplitudes in the upper part of the porous ballast specimen is in good agreement with the exponential damping. Due to larger lateral conduction and the convective heat transfer boundary at the upper surface in the open-test, the exponential damping of temperature amplitudes with depth is not completely satisfied. The thermal diffusivity and conductivity values in the porous ballast with three grain sizes of 6–8, 4–6 and 2–4 cm were evaluated by the slender cylindrical specimen in the tight-test.