Research Of The Specific Surface Area Of Loess Based On Nitrogen Adsorption Method

The specific surface area?SSA?is the basic parameter of soil,it plays an important role in many physical and mechanical properties of soil.The specific surface area of loess can reflect the intensity of interaction between loess and water,and also affect the sorption and swelling shrinkage of loess.More importantly,the collapsibility of loess express the special relationship between loess and water.Studying the SSA of loess has certain price for analyzing collapsibility and other properties of loess.The most classic BET specific surface area analysis methods based on nitrogen adsorption test is used to analyze the characteristics of SSA of loess in the typical northwest region in this paper.The main results are as follows:?1?The main minerals of the loess are illite,kaolinite,montmorillonite,chlorite.The mainly component soluble cationic of loess are Na⁺and Mg²⁺and so on.The SSA of loess ranges between 15.0m²/g and 40.9m²/g.On the upper surface of loess,clay mineral content is relatively small,and the SSA is relatively small.The BET method is applied to dry soil particles under dry conditions,covering the surface of soil particles and measuring the SSA.The process can maintain the pore and structure of the soil.The MB method is carried out in the solution,so the SSA of the loess measured by the MB method is larger than that of the BET method,still,the error is acceptable.?2?The SSA of loess in different regions is predicted and compared with the physical model and empirical model.When the relationship between the liquid limit and the SSA is refitting after considering the various liquid limit value,the formula obtained will be relatively good correlation.The result from the physical model is very small,only the value of BET 1%³%can be got.There are two reasons.On the one hand,the physical model assumes that the body of the loess is granular,in fact,the surface of the soil particles has more a large amount of pores.On the other hand,the content of the particles below 1um cannot be measured,while the part of it has the most important role in the SSA.?3?The SSA of loess is gradually decreased with the increment of quicklime mixing ratio,when the mixing ratio is 6%,SSA show a turning point.The SSA of loess damages 60%.?4?With the increase of acid concentration,the SSA of loess is gradually decreased and the number is only 10 m²/g.The loess particles is relatively“bigger”.?5?After salt solution immersion of the loess,with the increase of concentration of salt solution,the SSA of loess increases gradually,after all kinds of salt solution immersion,the change rule of SSA is:potassium loess<Sodic loess<Magnesia loess<Aluminum loess.?6?The SSA of Tongchuan loess in Shanxi is slightly larger than the SSA of Tianshui loess in Gansu,but the increment of SSA of Tianshui loess is greater than the Shanxi loess after changes of salt solution processing.