Study On The Salty And Frost Swelling Of Sulfate (Sulfurous) Salty Soil Fills In Shuimohe Plain, North Of Tianshan

There is a great distribution of sulfate (sulfurous) salty soil in West China. Due to the additional constitution of crystal-soluble salt, the solid phase and liquid phase in sulfate (sulfurous) salty soil are different from normal soil. The salt can exchange between solid phase and liquid phase under the influence of temperature, water content, salt content, soil structure, etc. With the increase of water content and temperature, or the change of salt, the solid crystal salt can transport into liquid phase salt; vice versa. When sodium sulfate (Na₂SO₄), the main salt in sulfate (sulfurous) salty soil, changes to Glauber's salt (Na₂SO₄. lOH₂O), the volume will swell by 3.18 times, which results in salty swelling。The emergence engineering destruction problems result from salty and frost swelling due to sodium sulfate crystallization in sulfate (sulfurous) salty soil. So it is very important to deeply investigate salty and frost swelling in sulfate (sulfurous) salty soil, in order to guarantee the safe project operation. Taking sulfate (sulfurous) salty soil in Shuimohe Plain, north of Tianshan, as subject investigated, the author made many field investigations, laboratory tests, and microscopy observations. The salty and frost swelling deformation and swelling force were examined. The goal of this study was to understand the mechanics and the influencing factors of salty and frost swelling deformation and swelling force, and to investigate the corresponding influence to projects. This included not only in situ observation to build forecasting model but also the analysis of application in engineering. Firstly, single salty and frost swelling deformation test was performed. The new findings were as follows: â‘ With the decrease of temperature, salty and frost swelling rate of sulfate (sulfurous) salty soil increased. Before freezing, solubility of sodium sulfate decreases with the decrease of temperature, which makes the calculated concentration greater than solubility, and sodium sulfate in solution will crystallize. Then soil will swell to 4.18 times. This swelling process is salty swelling. With the decrease of temperature, the water in soil will freeze and the volume will swell to 1.09 times. Due to the surface energy of particles, there will be some non-freezing water in which some sodium sulfate solves. The decrease content of non-freezing water will result in some sodium sulfate crystallization. The swelling process after freezing is salty and frost swelling. The content of non-freezing water and the decreasing rate of non-freezing water are very little when below -15。C, so salty and frost swelling of soil mass stabilize. â‘¡The inception temperature of swelling of sulfate (sulfurous) salty soil depends on sodium sulfate crystal temperature, sodium sulfate crystal content, soil mass microstructure, internal frictional resistance, cohesion, attraction among soil particles, and degree of adsorption of sodium sulfate in pore. â‘¢Single salty and frost swelling rate of sulfate (sulfurous) salty soil is second-degree parabola related to dry density of soil when dry density is less than second critical value. With the increase of initial dry density, single salty and frost swelling rate decreases; the rate increases when dry density is above first critical value; when dry density is above second critical value, the rate decreases with the increase of dry density. The range of large single salty and frost swelling rate occurs when compacted density is around 1.84 g/cm3 and lower dry density. The change of dry density results in the change of internal frictional resistance, cohesion, attraction among particles, pore structure, and the position of fluid in soil mass. The interaction of these factors leads to single salty and frost swelling rate changing with dry density. â‘£Single salty and frost swelling rate of sulfate (sulfurous) salty soil is second-degree parabola related to water content. Maximum single salty and frost swelling range occurs when water content is around optimum water content, and the rate will decrease if water content changes. When water content decreases, the rate decreases due to increasing of internal frictional resistance, cohesion, and attraction among particles. In addition to the decrease of internal frictional resistance, cohesion, and attraction among particles, sodium sulfate content in pores will decrease greatly when water content increases, which also will result in lower salty and frost swelling rate. ⑤Single salty and frost swelling rate of sulfate (sulfurous) salty soil is second-degree parabola related to sodium sulfate content. Single salty and frost swelling rate will be less than 1.3% when sodium sulfate content is be less than 0.5%; when sodium sulfate content is between 0.5¹%, the rate will be less than 2%; when sodium sulfate content is between 1¹.5%, the rate will be less than 4%; when sodium sulfate content is between 1.5²%, the rate will be less than 7%; when sodium sulfate content is between 2³%, the rate will be less than 10%; when sodium sulfate content is between 3⁴%, the rate will be less than 20%; when sodium sulfate content is between 4⁵%, the rate will be less than 27%.â‘¥On the condition of optimum water content (ω≈13%) and maximum dry density (ρd≈1.84g/cm3), single salty and frost swelling rate of sulfate (sulfurous) salty soil will be greater, which is rather dangerous to engineering. Further more, on the condition of load or no load, it studied the multiple salty and frost swelling experiment of the sulfate(sulfurous ) salty soil of the fine earth region of no relief of Shuimohe in north Tiansha. After the multiple salty expansion and frost swelling experiment of no load, there was some new discovers: â‘ There is great distinction between the "multiple freeze-thaw salty and frost swelling"and "single salty expansion and frost swelling"experiment of sulfate(sulfurous) salty soil, and there is the problem of the development of salty and frost swelling in sulfate (sulfurous) salty soil. In the multiple freeze-thaw salty and frost swelling experiment of the soil mass of different Na2SO4 content and dry density, with the increase times of freeze-thaw, in the all, the soil mass salty and frost swelling increases, the remain deformation (also structure deformation) also increases, the non-structure deformation also increases, the deformation increment decreases, and drives to stabilize stage. â‘¡In the multiple freeze-thaw salty and frost heaving expansion experiment of sulfate(sulfurous) salty soil, the times of freeze-thaw circulation and "the soil dry density of salty and frost swelling"is the law of second-degree parabola curve; also the law between different Na2SO4 content and the decrease rate of dry density finally, between different Na2SO4 content and "maximal salty and frost swelling rate". â‘¢It is almost equal of multiple freeze-thaw salty and frost swelling rate in the condition of same Na2SO4 content and different dry density. Then, the initial dry density effected the salty and frost swelling rate little, so it couldn't reduce the salty and frost swelling rate effectually by increasing dry density. As the multiple freeze-thaw salty and frost swelling experiment of load, there were new discovers: â‘ It is divided three phase of the multiple freeze-thaw salty and frost swelling experiment of load as so as experiment of no load: First phase, the salty structure deformation phase arousing by theseparation and crystallization with the temperature decrease and outside pressure; Second phase, it is the salty swelling freeze-thaw structure deformation phase after freeze arousing by water frosting,salty separation and crystallization,outside pressure; Third phase, it was the structure deformation phase arousing by the thaw of ice and solution of Na2SO4 crystal with the temperature of soil mass increasing. â‘¡In the multiple freeze-thaw salty and frost swelling experiment, the freeze-thaw circulation times and "the dry density of salty and frost swelling"fitted the law of second-degree parabola curve of the soil mass of 13 percents water content, 1.84g/cm3 dry density, different pressure and Na2SO4 content; the same law as the times of freeze-thaw circulation and "salty and frost swelling rate"of the soil body of different pressure and Na2SO4 content, different Na2SO4 content and "maximal,finally salty and frost swelling ratio"; the law of different pressure and "maximal,finally salty and frost swelling ratio"fitted the logarithm curve.â‘¢In the experiment of multiple freeze-thaw salty and frost swelling of sulfate(sulfurous) salty soil, the maximal salty and frost swelling rate of soil mass of 13 percents water content, 1.84g/cm3 dry density, different pressure, different Na2SO4 content : PPPCPPCCPCPssbssssss0.06837ln0.1798(ln)1.33814ln0.005627ln0.1300368.6525690.0098390.426060.00026222???+η=++?? Finally salty and frost swelling rate: PPPCPPCCPCPssessssss0.68411ln0.068229(ln)1.32479ln0.00698ln0.5426338.5612230.0086230.413830.000096222?+??η=++?+ â‘£In the multiple freeze-thaw salty and frost swelling experiment of sulfate(sulfurous) salty soil, the salty and frost swelling rate of soil mass of 13 percents water content, 1.84g/cm3 dry density, different pressure,different Na2SO4 content,different freeze-thaw times: 0.657ln0.2610.418ln9.8055 .0950.41722.605ln1.9040.0720.175(ln)2?+??=?++??CpnCnpCCpnnpssssηNssss Finally, it studied the salty and frost swelling force of sulfate(sulfurous)soil of the fine earth region of no relief of Shuimohe in north Tiansha. There was new discovers as follows by the research of salty and frost swelling experiment .â‘ "The salty and frost swelling force of sulfate(sulfurous) salty soil "and dry density fit the exponential curve. For the equal Na2SO4 content, dry density increases, then the porosity decreases, salty and frost swelling force enhances.â‘¡The relation between salty,frost swelling force of sulfate (sulfurous) salty soil and water content fit the second-decree parabola. The maximal interval of salty and frost swelling force is near the optimum water content, and the soil salty and frost swelling force is decreased whether enhancing or reducing the water content. With the decrease of water content, the internal frictional resistance,cohesion,attraction among particles increases, so that soil salty and frost swelling force decreases; with the increase of water content of soil mass, the internal frictional resistance,cohesion,attraction among particles decreases, so that soil salty and frost force decreases.â‘¢The salty and frost swelling force of sulfate(sulfurous) salty soil and Na2SO4 content fit the second-degree parabola curve. With the Na2SO4 content increase, the salty and frost swelling force enhances. For less than 1 percents Na2SO4 content, the salty and frost swelling force increases slow, because the pore and tangency grain absorb part of Na2SO4 crystal. For more than 1 percents Na2SO4 content, the soil salty and frost swelling force increases fast.â‘£In the experiment of salty and frost swelling force of sulfate(sulfurous) salty soil , the maximal salty and frost swelling force of soil mass of different dry density,different Na2SO4 content,different water content: 222249.5235.94513.3458.608676.974147.3513.396ρωρω?=?+?+?+dPb CssdCss the salty and frost swelling force of different dry density,different Na2SO4 content,different water content: 222261.3065.792467.68257.586712.030143.6523.101ρωρω?=?+?+?+dPe CssdCss ⑤In the condition of optimum water content,maximal dry density for light hitting apparatus, there is the large salty and frost swelling force and great...