Hydro-thermal Coupled Mechanism Of Residual Soil Slope In The Short-term Frozen Soil Zone

The northern part of Fujian Province is located in the short-term permafrost zone, in this region, short-term frozen soil slope has many characteristics of short freeze-thaw-cycle and great frequency of short-term freeze-thaw, the frozen deep is very shallow and high moisture content after the condition of snow infiltration. The results of the field investigation show that shallow collapse disease of residual soil slope occurred frequently, these issues caused many difficulties in the local road maintenance. Unfortunately, the related basic theory has not been given enough attention.Based on above, this article combined the literature and engineering research, laboratory tests, field tests and theoretical analysis as technical means, obtained the hydrothermal parameters and freezing characteristics of granite residual soil, compiled a calculation procedure to calculate the hydrothermal coupling of granite residual soil slope in short-term frozen soil zone, analyzed the short-term frozen soil regions climate and soil hydrothermal characteristic, drawn the hydrothermal variation of frozen-soil slope variation in northern Fujian. The main conclusions of the study are as follows:(1) From the freezing tests of two types of typical granite residual soil, the freezing temperature of yellow-soil range from -1℃～-2℃ while the freezing temperature of red-soil range from -6.5℃～7.5℃;The soil freezing temperature rise while the higher moisture content and the lower salt content.(2) Integrated use of function fitting and averaging to determine initial conditions, the outer boundary condition are main considered evaporation, solar radiation, net radiation, convective heat and latent heat of vaporization, based on the Harlan model, through the MATLAB programming to get the calculation program which is suitable for short-term freezing zone of residual soil slope hydro-thermal coupling.(3) In the test section,the freeze period is between 2013.12-2014.2,the minimum temperature can reach about -4.4℃; during freeze period weather are mainly cloudy and overcast, radiation is generally lower than 850W/m2 and the lowest of day-peak-radiation is 21W/m2; the low temperature days of each month are 8d, 10d, 14d, freeze-thaw is frequently happen during freeze period, there were 18 times of freeze-thaw cycle,include 16 times of one day freeze-thaw,1 time of two days freeze-thaw and 1 time of six days freeze-thaw; the northern of Fujian Pro vice extremely low temperature can reach -7℃～-8℃, the area temperatures reduces while the latitude or altitude get increasing;the influence depth of slop by the air-temperature-reduce is 25cm; the slope soil temperature-time changes showed a positive cosine law and relative lag 2h～3h than the air temperature changes; the range of daily evaporation of soil moisture content is 0.001/d～0.003/d.(4) The model calculate results shows that:the range of slope frozen depth is about 0-15cm in the northern of Fujian Provice; slope is easy to form a stable ice surface if the freezing-thawing time of soil gets more than five hours;in the test zone,the freezing-thawing time of soil can reach five hours during the one-day freeze-thaw and the calculate results of six-day freeze-thaw is thirty-two hours; when the duration of the air temperatures below the soil freezing temperatures less than 1.5h, the soil is not easily to get freezing; the higher humidity and less evaporation can increase the frost depth and the duration time of freeze-thaw.(5) The influence factors sensitivity order of soil factors on the depth of soil freezing is:salinity> initial water content> dry density> soil aggregate heat; the influence factors sensitivity order of outer boundary factor on the depth of soil freezing is:daily minimum temperature> solar radiation> air humidity.