年平均気温から地盤の最大凍結・融解深度を推定する方法

Abstract

A method is described for the prediction of maximum freeze/thaw penetration depth in snow-and vegetation-free ground as a function of the mean annual air temperature. Annual variation in ground surface temperature was fitted by a sinusoidal curve with the amplitude, Tos. The meteorological data show that the value of Tos ranges from 11° to 16°C in Japan. Three sinusoidal curves with the Tos values of 11°, 13° and 15°C were used for the calculation of the freeze/thaw depth. The Aldrich equation allowed the calculation to be made. The freezing and thawing indices involved in this equation were determined for every degree of the mean annual ground surface temperature. The maximum freeze/thaw depth was calculated for four kinds of ground materials, i.e., volcanic ash, sand/silt, gravel and rock, and then plotted against the mean annual surface temperature. The diagram indicates that the freeze/thaw depth increases as mean annual surface temperature approaches 0°C and with rising both thermal conductivity and volumetric water content of the ground material. The relationship between the mean annual air temperature and the maximum freeze/thaw depth was obtained using the empirical relation between the mean ground surface and air temperatures. The predicted depths agreed fairly well with the measured depths in various cold environments where the mean annual air temperature is known.