Freezing Point Of Saline Loess Under Freeze-thaw Cycle

Seasonal saline soil in China is mainly distributed in the northwest and the qinghai-tibet plateau.Due to the combined action of freeze-thaw cycle and water and salt,the cooling,freezing and thawing process of saline soil is quite different from that of non-saline soil,The freezing point is a direct physical indicator to judge whether the soil mass is in the frozen state.The hydrothermal characteristics of the soil mass are different at different freezing points,and the temperature gradient changes in different trends,so the frozen state of the soil layer at different positions is different In recent years,due to the repeated action of freezing-thawing cycle,the temperature field of the slope in the saline soil area shows different variation trends under different freezing points,and different freezing points will affect the freezing depth of the slope soil layer,making the slope prone to significant engineering geological disasters.As a widely distributed salt,chlorine plays a significant role in geological disasters in loess region,which seriously affects the stability of loess slope.Therefore,it is of great engineering significance to study the freezing point and its changing mechanism of soil in salt-bearing loess region under the action of water salt and freeze-thaw for the stability of slope.This paper takes the chlorinated loess in Xi'an area of Shaanxi as the research object,and mainly completes the following research work:The variation trend of freezing point of saline loess under different water content was studied by indoor freezing test,and the change mechanism of freezing point was explained.The results show that the freezing point of saline loess increases nonlinearly with the increase of water content and is close to 0?.Through freezing test,the variation trend of freezing point of saline loess under different salinity conditions was studied,and the mechanism of freezing point variation was explained.The results show that the freezing point decreases linearly with the increase of salt content.In the process of ionic hydration in saline soil,the freezing point decreases during the freezing process,and the higher the salt content,the lower the freezing point.Through freezing-thawing cycle test,the influence of freezing-thawing cycle on freezing point of saline loess was analyzed,and the change mechanism was explained.The experimental results show that the freezing point decreases with the increase of freeze-thaw times and finally tends to be stable.The freezing-thawing cycle changes the microstructure of soil,the pore distribution index of soil changes,affects the heat transfer process of soil in the freezing process,and finally causes the freezing point to change.The effects of water and salt migration on freezing point during freezing-thawing cycle were analyzed.The results show that there is no water-salt migration in the loess samples after freezing-thawing,so the initial water content and initial salt content of the soil are the main factors affecting the freezing point of the saline loess in this paper,and the influence of water-salt migration on the freezing point of the loess can be ignored.Based on the relationship curve between freezing point and water content,salt content and freezing-thawing times,the empirical formula describing freezing point and water content,salt content and freezing-thawing times is established,and the empirical formula of freezing point is also applicable to qinghai-tibet silty clay and lanzhou loess.Based on the COMSOL Multiphysics software,the temperature field of a loess slope in shaanxi province was simulated in the process of freezing and melting,and the relationship between the freezing depth of the slope and the freezing point of the soil was analyzed.Numerical simulation shows that the internal temperature of the slope is constantly exchanging heat with the outside world,and during the freezing process,the cold quantity is continuously input from the upper boundary to the inside of the slope,and the temperature gradient keeps increasing,making the freezing range and freezing depth of the slope keep increasing.In other words,the lower the freezing point is within a certain temperature range,the greater the freezing depth of the soil layer is.Besides,the freezing depth of the slope under different freezing points is within the range of the average freezing depth of the stratum in xi'an city,shaanxi province in winter,and the range of the seasonal freezing layer is 0?0.2m.