Frost Heaving Characteristic And PFC-3D Numerical Analysis Of Saline Soil In Western Jilin Province

The west area of Jilin province is located in southern Songnen plain of China,which is the typical seasonal frost region in northeast China. The climate is semi-aridtemperate continental monsoon in western Jilin. Some seriously salinized soil werewidely distributed on Songnen plain in western Jilin. Soil salinization will causecultivated land and grass degeneration, which will threat the human environmentactivity. For the purpose of improve the ecological environment of Jilin province, thegovernment took the land consolidation and rehabilitation project of western Jilin.This project leads the water from downstream of Nen river and second Songhua riverto wash the saline soil of western Jilin. However, because of the special climaticcharacteristics of western Jilin, the seasonal frost action during washing progress madea series of industry and agricultural problems such as road frost heaving, collapse,power transmission line drawing out and secondary salinization, which will restrict theeconomic development and human activities.For the purpose of investigate the characteristic and material composition ofsaline soil in western Jilin, this article took the soil samples from4research areas asZhenlai， Da’an， Qian’an and Nong’an, the samples were taken from differentsample collection spot, different season and different depth. According to theexperiment result: the most soil samples were clay soil, the silt particle content werehigh of most samples, but the clay particle content were high of Da’an and Nong’ansamples; some samples showed out dispersibility of shallow layer, but the clay particles dispersed after the dispersing agent was added into soil of soil samples takenfrom Nong’an and other deep layer, which showed out the―fake silty‖features; theoriginal mineral was the principal minerals of soil samples, the clay minerals mostlywere illite and kaolinite, few samples contained illite-montmorillonite mixed layer.Those results provided the basis of analysis the frost heave characteristic of saline soilin western Jilin province.Mercury injection tests were taken to investigate the pore distributioncharacteristic of soil samples quantitatively. The tests results showed that the poreswere smaller but more of soil samples in Da’an, the pores were lager but less of soilsamples in Zhenlai. Besides, pH, CEC content and organic matter content were alsotested in lab, all those tests results showed different effect to the salinization progressand frost heave action.Meanwhile, unsaturated soil theory was also used to investigate the soil-watercharacteristic of soil samples. Arya-Paris prediction model was chosen to predict theSWCC of saline soil in western Jilin. The prediction results showed that the waterholding capacity of soil samples in Zhenlai area location I were strong, the waterholding capacity of soil samples in Da’an area location II were highly affected bydepth, the water holding capacity of soil samples in Qian’an area were weak, and thewater holding capacity of soil samples in Nong’an area were strong. Those resultsprovided the reference to the water-salt transport characteristic and unsaturated soiltheory of saline soil in western Jilin.For the purpose of study the water and soil migration law of saline soil sample,nature water content and salt content were tested of samples collected from differentseasons and depth. By analyzing the tests results, the conclusions were drawn that thesoil which nearby the ground was highly affected by evaporation effect, the saltycontents were higher than0.3%of most soil samples, and water and salt migration lawwas quite different in each season. Therefore, the climate feature of research areasshould be studied to analyze water and salt migration law. For this reason, the data oftemperature, rainfall and evaporation in last10years were investigated of4researchareas in western Jilin. The analysis results showed that the dry season was long and wet season was short in research areas; spring and autumn were drought and windy,summer was warm and rainy, winter was chilliness and long, the temperaturedifference was quite large of whole year, annual evaporation capacity was highlystronger than precipitation. Combining those results and the water and salt contentstests results in research areas, referring to the water contents, ground temperature, andfreeze depth of frozen soil in Changchun city, the conclusion were drawn that inunfreezing period, the evaporation effect took the lead in arid season, provided thedriving force come from below, and made the salt migrate upwards with water in soil,so the water contents were low and salt contents were high of soil nearby the groundsurface, the salt gathered on the surface; summer time was rainy, made the elucidationeffect took the lead and provided the driving force come from top, the water carriedsalt migrated downwards, so the salt contents were low of soil samples nearby theground surface collected in summer of Zhenlai, Da’an and Qian’an, but theevaporation capacity was highly stronger than precipitation of whole year, so the saltcontents were still showed the law of decreasing by the depth. Because of the uniquecorrosion landform in Qian’an―mud forest‖scenic spot, the eluviations effect wasvery strong in summer when there was no plants on the soil ground, the salt contentsincreased by the depth; in freezing period, because of the combining action of solutepotential gradient and temperature gradient, the driving force still came from belowand made the salt migrated upwards with water in soil, so the salt contents wereextremely high on the ground surface in spring. Besides, the evaporation influencedepth were20～30cm in research areas. Those results provided the basis ofsalinization progress of saline soil in western Jilin.In order to study the frost heaving characteristic of saline soil in western Jilin, thesoil sample collected from Da’an and Zhenlai were chosen to do the indoor closedsystem frost heaving tests, during the tests, the water contents, salt contents andcompaction degree were designed differently of testing soil samples. The tested resultsshowed that the frost heaving ratio was increased with the temperature decreasing, butby the-10℃the frost heaving ratio was stabilized; the samples with low watercontents were more easily affected by compaction degree, the frost heaving ratio was increased with the compaction degree increasing of most test samples; the frostheaving ratio were lager of high salt content samples, but it took longer time to bestabilized. The largest frost heaving ratio of Da’an samples occurred at the sampleswith1.5%salt content,26%water content and90%compaction degree, it’s3.5%; thelargest frost heaving ratio of Zhenlai samples occurred at the samples with3.0%saltcontent,26%water content and95%compaction degree, it’s2.58%. By those results,the frost heaving characteristic and affection features of saline soil in western Jilinwere studied deeply from the angle of mechanism, and provided the physical modelsupport to build the frost heaving grain flows numerical model in next part.At last, the research combing with the properties of the soil samples, aiming thefrost heaving process, establish the indoor closed system frost heaving grain flowsnumerical model of saline soil in western Jilin for the first time. The model reflectedthe frost heaving process of Da’an and Zhenlai samples under the circumstance of sidewall and bottom wall limitation. And the particle migration, porosity characteristic andinner stress changing law were discussed during the frost heaving process. Aftercomparing with the indoor frost heaving test, the conclusions were drawn: for theinitial period of frost heaving process, the pore got lager because of the ice got lager,the porosity increased obviously, but with the frost heaving continue, soil particlesbalanced their relative locations because the ice expanse, the porosity increased slowlyin this period, the frost heaving got to steady gradually. With the frost heavingdeveloping, the inner pressure stress of soil were getting smaller, by reason of the topboundary was liberty, the inner stress was small but decreased faster in the upper soil,the inner stress was large but decreased slower in the bottom soil. The particlecomposition showed direct influence to frost heaving result, with the effect of particlecomposition, the frost heaving action of Da’an sample was stronger than Zhenlaisample.This research was based on laboratory tests, material composition, physicalchemistry and mercury injection test were used, SWCC of soil samples were predictedby using unsaturated soil theory, investigated and analyzed a large number of climaticdata and took the temperature and water data of frozen soil in Changchun as reference, proposed the water and salt migration law and salinization progress in western Jilin.On the base of indoor test, analyzed the frost heaving characteristic of soil samples inwestern Jilin from macro-perspective angle, and established the indoor closed systemfrost heaving grain flows numerical model of saline soil in western Jilin, discussed thefrost heaving characteristic frome micro-perspective angle. The research provided thebasis of prevention the secondary salinization and frost heaving disease of saline soilin western Jilin province.