Study On The Micro-structure And Mechanical Properties Of Frost Heaving Saline Alkali Soil And Their Relationships With Salt Discharging Mechanism And Engineering In The Yellow River Delta

With the increasingly serious salinization of the land,a large number of cultivated land lost its planting ability,which makes the food problem become more and more acute.In this paper,we take the typical saline-alkali soil in the Yellow River Delta as the object,and make a qualitative observation and a quantitative analysis respectively on the micro structures of the original saline soil and the saline soil frozen under different initial conditions(temperature and moisture content)so that we can obtain their change rules.Through studying the mechanical characteristics of frozen saline soil,the change rules of stress-stain behaviors and intensity and the destructive morphological characteristics of frozen saline soil under different freezing conditions are obtained.Based on the above research results,the connection between the micro structure of saline-alkali soil in the Yellow River Delta region and its salt removal mechanism,as well as the relationship between its mechanical characteristics and salt-emission engineering,is discussed.Further,we give some specific suggestions on salt-draining work of the salinealkali soil in the region.The conclusions are as follows:(1)Under the natural condition,the porosity of saline-alkali soil in the Yellow River Delta is 28.52% at the maximum and 19.5% at the minimum,and most of the data are concentrated in 20%~23%.There are few internal pores and poor connectivity,and the structure is relatively dense,which is an important reason for the difficulty of salt drainage in this area.(2)The increase of moisture content and the decrease of freezing temperature will lead to the increase of porosity increment,and the change of moisture content has larger influences on porosity increment,compared with the change of freezing temperature.(3)When the moisture content is constant,in the temperature range of-10?~-20?,the increase of porosity caused by the change of freezing temperature is the largest.When the freezing temperature is constant and the moisture content is in the range of 20%~24%,the increase of porosity caused by the change of moisture content is the largest.Changing the freezing condition in these two intervals will increase the porosity to a maximum extent.(4)The best condition for using frost heaving to change the porosity is to choose the freezing temperature in the range of-10?~-20?and the moisture content in the range of 20%~24%.(5)When the freezing temperature is fixed,the peak strength and ultimate strain show a backward trend with the increase of moisture content,that is,the peak strength and ultimate strain both increase while the moisture content is increasing.When the moisture content is fixed,the peak strength increases with the decrease of freezing temperature,while the limit strain has no obvious regularity.Thus,the frozen efficiency is higher when the freezing temperature is lower than-15?.After freezing,the brittleness of saline alkali soil increases obviously.(6)In reference to the Yellow River Delta region,the minimum winter temperature is below-10 ° C,the natural moisture content is about 22%,and the porosity exceeds 31.36% after freezing.It is suggested that irrigation in the region be used to increase the water content of saline-alkali soil in the early winter.After the frost heaving effect of the whole winter,the salt should be drained in time after the frozen soil melts.Under the conditions of temperature and moisture content,the strength of frozen saline-alkali soil exceeds 477.3157 kPa,so large open trenches and concealed pipes are constructed in winter,and then reinforced to a certain degree,a more significant salt drainage effect can be obtained during salt drainage.In this paper,the mesostructure and mechanical properties of saline-alkali soil in the Yellow River Delta under frost heave were studied.The theoretical research is applied to actual working conditions,which has a certain degree of guiding significance for salt drainage in the Yellow River Delta.