Hydro-thermal-mechanical Coupled Numerical Simulation Of Granite 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 methods of the literature and engineering research.test analysis,theoretical research and numerical simulation and so on to obtain the short-term frozen soil regions climate and soil hydrothermal characteristic of Fujian.besides;this article analysed the mechanism of hydro-thermal-mechanical coupled in short-term residual soil slope.The main achievements are as follows:(1)In the test section,the freeze period is between 2014.12?2015.2,there were 11 times of freeze-thaw cycle in one day.The minimum temperature can reach about-2.5?.The maximum wind speed can reach 11.6m/s,The average wind speed is about 3.4m/s and the average humidity is about 80%,The total rainfall day is up to 27 and the maximum rainfall strength can reach 41.6mm/h.During the short-term freeze-thaw cycles of air temperature,the daily maximum temperature generally appear from 13:00 to 15:00 while the daily minimum temperature generally appear from 5:00 to 7:00;the diurnal temperature is about 10?;the highest radiation peak can reach 772W/m2 while the lowest is 15W/m2;the weather was cloudy and overcast most.(2)The influence depth of slop by the air-temperature-reduce is about 25cm;the slope soil temperature-time changes showed a positive cosine law and relative lag 2h?3h than the air temperature changes.(3)The finite element software COMSOL Multiphysics was verified reliability and effectiveness through the comparative analysis of laboratoty test and field test to the numerical simulation results.The external environment influence to the depth of water content is about 12cm.(4)Numerical results by the weather condition of 12.17 show that the shallow slope freezing depth is about 4cm.In the soil daily minimum temperature of 8:00 and 24:00,the lowest temperature is-1.57? and-1.62? respectively.so the slope appear freeze.In the soil daily maximum temperature of 14:00,the minimum temperature is about 2.9 ?.so the slope is thawed soil.It may be infered that the slope soil can appear freeze-thaw cycles which from thawed soil to frozen soil in one day.The maximum frost heave stress and maximum frost heave displacements appear in the slope top surface which numeric is respectively 0.52MPa and 0.12mm.(5)Increasing the heat capacity of soil and reducing the coefficient of thermal conductivity of soil can improve the insulation performance of soil which reduce the frost heaving failure and improve the stability of the shallow slope.The larger initial moisture content of soil,the higher freezing temperature and longer freezing time,so the displacement of frost heave and frost heaving stress is larger which is unfavorable to slope stability.(6)The warm frozen soil can appear freeze-thaw cycle in one day.while the low temperature frozen soil is in the frozen state during a whole day.when the environment low temperature is-2.5 ? the frozen depth is about 4 cm,while-5.5 ? is about 6 cm,and under-8.5 ? the frozen depth can reach about 10 cm.