Study On The Sulphate Saline Soil's Salt Expansion Characteristics And Empirical Formula Of Salt Expansion Coefficient

Based on the engineering characteristics of the Iranian Deyi high-altitude saline soil and the salt expansion and dissolution mechanism research project,this paper conducts experiments on the salt expansion characteristics of the indoor remodeling artificial saline soil based on the exploration data of the saline soil along the line.For the coarse and fine grain saline soil,the effects of soil physical structure,salt,water and temperature on the salt expansion characteristics were studied.The importance of the soil thickness and gradation type on the salt expansion was revealed.The influence factors of the influence factors on the salt expansion of saline soil were established.The salt expansion coefficient of coarse and fine grain saline soil was established.The main research results and conclusions are as follows:(1)It was found that the content of soluble salt in sodium sulfate saline soil was generally between 1.05%and 2.32%,and the content of sodium sulfate in undisturbed soil was between 0.0285%and 0.175%.The optimum moisture content of coarse-grained saline soil is between 10%and 18%by compacting tests on various grades of different salt-bearing native sodium sulfate soils.(2)Through the test results of the weighting factors of the factors affecting the salt swelling of coarse-grained sodium sulfate saline soil,the difference analysis shows that the main factors affect the salt expansion of saline soil from high to low:sulfuric acid Sodium content>soil gradation>temperature>moisture content.(3)Based on the quadratic orthogonal test,the formulas for calculating the salt expansion coefficient of the soil with coarse and fine particles are established respectively.The salt expansion coefficient can be preliminarily calculated according to the formula to determine whether it meets the requirements of the code and provide effective reference for on-site construction.Through the established empirical formula of salt expansion coefficient,the trend chart of salt expansion coefficient of coarse and fine particle soil with sodium sulfate content under the most unfavorable working conditions is analyzed,which provides a safe and simple calculation process for design and calculation.(4)Comparing the swelling characteristics of chlorine salts and sulfate salts,it is found that chlorine salts have certain inhibitory effect on the salt swelling characteristics of saline soil.When the content ratio of sodium sulfate/sodium chloride is 1,the inhibitory effect is weak under the condition of relatively low salt content(sodium chloride content is less than 0.25%).With increasing test soil samples in the content of sodium chloride,sodium sulfate/sodium chloride content ratio to 1,the saline as the expansion coefficient of the proportion compared with pure sodium sulfate salt expansion coefficient of soil samples showed a trend of decrease rapidly,when sodium chloride content in the soil sample was 2%,the ratio of the saline as the expansion coefficient is only 0.47 times that of the pure sodium sulfate salt expansion coefficient of soil sample.Therefore,it is reasonable to use sodium sulfate as the index and the content of sodium sulfate as the index to establish the empirical formula for salt swelling.(5)By studying the influencing factors of sodium sulfate soil,it is found that the salt expansion coefficient increases with the increase of sodium sulfate content.When the sodium sulfate content and temperature are combined,in order to maintain the same salt expansion coefficient,when the sodium sulfate content increases,the temperature will also increase;When the sodium sulfate content and moisture content act together,in order to maintain the same salt expansion coefficient,when the sodium sulfate content increases,the soil moisture content will decrease.When the sodium sulfate content and the gradation type work together,in order to maintain the same salt expansion coefficient,when the sodium sulfate content increases,the gradation test variable also increases(i.e.,the content of d<5mm decreases).The salt expansion coefficient decreases with the increase of temperature.When temperature and moisture content work together,in order to maintain the same salt expansion coefficient,when temperature increases,moisture content will also increase;When temperature and gradation type work together,in order to maintain the same salt expansion coefficient,when temperature increases,the gradation test variable will be reduced(i.e.,the content of d<5mm increases).The salt expansion coefficient increases with the increase of water content.When moisture content and gradation type work together,in order to maintain the same salt expansion coefficient,when moisture content increases,the gradation test variable should also increase(i.e.,the content of d<5mm decreases).Salt expansion decreases with the increase of gradation test variable.(6)Through ABAQUS numerical simulation analysis,it is found that salt heaving is mainly concentrated in the surface layer of the foundation,and no salt heaving occurs when the depth of the stratum reaches a certain position.With the increase of time,the total salt expansion tends to be stable and converges.