Experimental Study On The Salt-frost Heaving Characteristics Of The Natural Saline Soil Under Different Cooling Conditions

Xinjiang is located in inland of cold and arid areas,where saline soil is widely distributed.The saline soil of different regions has unique properties.The natural saline soil from Lop nur and Aydingkol Lake area as the experimental soil is selected to do the salt-frost heaving test and stepwise freeze-thaw cycling test under different cooling rate,to study the influence of cooling rate on the salt-frost heaving characteristics and the law of salt-frost heaving and dissolved collapse deformation after freez-thaw cycles.The main conclusions are as follows:(1)The amount of salt-frost heaving of the sub-chlorine saline soil in lop nur area increases with the decreasing of temperature,the temperature interval of the main salt-frost heaving is from -5? to -25?.While sulfurous acid saline soil of Aydingkol Lake starts to bulge at higher temperature,there is obvious deformation of salt expansion at 20?,and the temperature interval of the main salt frost heaving is from 15? to -5?.When the temperature is below -15?,the salt frost heaving tends to be gentle,and the final salt frost heaving is very large.Overall the salt frost heaving of saline soil in the area of Lop Nur is less than that of Aiding Lake.(2)The increase of salt heaving rate of saline soil shows the power exponential function with the decrease of the cooling rate.When the cooling rate is small,the cooling gradient is also small,the micro-migration of water and salt occurs continuously during the cooling process,resulting in the large amount of salt frost swelling,or the lower the amount of salt swelling.(3)The salt frost heaving process of chlorine soil saline in the Aydingkol Lake area has good accumulative effect under the freeze-thaw cycle.Under the condition of optimum water content,the maximum salt expansion can reach to 42 mm after 9 freeze-thaw cycles.In the stage of rising temperature,the salt frost heaving drops,but it will not return to the initial equilibrium state.(4)The temperature range of violent salt frost heaving phenomenon of chlorine saline soil in Aydingkol Lake area is from 5? to -15?,and the temperature range of the larger dissolved collapse deformation is from 5? to 15?.There are no obvious laws of deformation when the temperature rises.Under different water content,the period of maximum deformation and the period of large increase in salt swelling are different.In the first 3 cycles,the salt frost heaving amount increases greatly,which can reach to 68% of the total salt heaving.In the vicinity of the optimal water content,the salt frost heaving tends to be stable after 9 freeze-thaw cycles.While the water content is much larger than the optimal water content,the accumulative salt heaving is still increasing after 9 freez-thaw cycles.(5)The amount of salt frost heaving in saline soil is determined by many factors,such as the location of salt solution in saline soil,the cohesive force,internal friction force and gravitational attraction between soil particles.The decrease and increase of temperature is the main reason of salt expansion.