Studies On Engineering Improvement Of Songnen Plain Carbonate Saline Soil

There is a large area of alkaline saline soil in Songnen plain of China, through which segments from songyuan to jinbaotun of the national highway No.203 goes. The highway construction of local area is imperiled increasingly by the geological hazards such as saline soil because of adverse engineering properties affect of saline soil, suffering from subsidence and collapse of the roadbed. This thesis studies chemical, physical and mechanical properties of alkali saline soil to research on improvement of saline soil, taking section from songyuan to jinbaotun of the national highway No.203, K198+300 bidding section as trial section, on basis of supervisor's scientific research project. The main content of the research are as follows:(1)Identify physical index such as Artberb limits, grain size and chemical properties of saline soil, basic mechanical properties (compaction, shear strength, compressive, swelling and shrinking properties) and so on, in order to research on improvement of saline soil. (2) research on engineering properties of improved saline soil through a series lime tests of heavy compact test, Artberg test, CBR test, swelling and shrinking test for improved saline soil, ascertain feasibility of saline soil improved by calcareousness used as filling materials of the expressway roadbed. Base on the above, research the strength of improved saline soil and analysis preliminarily mechanism and feature of lime improving saline soil through shear strength test, consolidation test.The results showed that:(1) Saline soil researched of the thesis consists of NaHCO₃ and Na₂CO₃ mainly, belong to saline soil with main component of carbonate, called alkali or soda saline soil also. (2) Liquid limit of the saline soil improved changes a little, but plastic limit changes much and plastic index reduces greatly. Compactness has obvious change from saline soil to improve saline soil by lime. (3) Saline soil before improved can't be used expressway roadbed filling material because of small CBR value. The CBR value of the improved saline soil increases with quantity of lime added. The optimumadding ratio of lime is 6%. (4) Shear strength index, cohesiveness and friction angle increases with quantity of lime added, until adding ratio of lime reached 6%. (5) Swelling rate of saline soil increases with water content, but line shrinking rate and volume shrinking rate reduces with water content. Swelling and shrink of saline soil hazard to roadbed, lime adding can reduce swelling with no pressure and shrinking rate and volume rate, therefore it can not only eliminate swelling but also reduce shrinking deformation. (6) Lime improvement is realized through ion exchange, crystallization and hardening, volcanic ash, carbonation function; thereof carbonation is main function for lime improving saline soil.