Study On Frost Heaving Behavior Of The Carbonate-Saline Soil In Nong’an, Jilin Province

Nong’an County in Jilin province is located in the Midwest, in the central region of Songliao plain. Because the area is low and the terrain is flat, the drainage is not smooth. The mineralization of shallow groundwater is very high, the salt ions in the water with the water transfer, resulting in the area of soil salinization is more serious. The water soluble salt were detected most content is sodium bicarbonate, local area of the saline soil types to carbonate saline soil. Nong’an county belongs to the seasonal frozen region, in cold winter conditions, soil because of geological disasters caused by the frost occurred. At the same time, the addition of salt to the frost heaving and makes frost heave process process than the saline soil region is more complex.This paper to carbonate saline soil in the Nongan area, Jilin Province as the research object, derived by use of Nongan area upland soil sample of frost heave and indoor experiment, study the characteristics of frost heaving of the carbonate saline soil. By rough set theory with the characteristics of carbonate saline soil frost heave factors of attribute reduction, reduction to obtain the factors affecting frost heave the biggest after using Matlab based on BP neural network of carbonate saline soil heave simulation model. Finally, then delete the different parameters in the simulation model to influence factors on frost sensitivity analysis. This paper draws the conclusion as follows:1. In critical Frost temperature a critical frost(shrinkage) moisture content(fht) and critical frost heaving compaction degree(fhd). When the saline soil water content and the compaction degree reaches a critical value of soil sample to frost or cold shrink.2. When start to cool(5℃~-2℃), samples of different degrees of shrinkage, this is the kind of "cold" process of soil. When the temperature is in the range of-8 ℃ to-2 ℃, with the decrease of temperature, soil volume change. When the soil moisture content and compaction is lower than the threshold value of critical frost heave two factor(fhc), with decreasing temperature soil samples showed "cold shrink"; when the soil moisture content and compaction degree is larger than critical frost heaving of soil samples of the two factorlimit value(fhc), with decreasing temperature, soil samples for "frost heave".-2℃ to-8℃ this interval is the interval of experimental soil samples the biggest change. When the temperature is in the range of-8℃ to-25℃, with the decreasing of the temperature, the soil sample tends to be stable, and the temperature will not fluctuate until the end of the experiment.3. Each group of soil samples are more than double factor frost group critical limit value fhc. Under normal circumstances, critical frost heaving compaction(fhd) more and soil critical frost(shrinkage) moisture(fhw) lower and critical frost heaving compaction(fhd) smaller soil critical frost(shrinkage) containing water(fhw) will be greater.4. The soil moisture content and compaction degree did not reach the critical frost heave two factor limits(fhc) containing salt content in the range 0 to 1% range, with the increase of the salt content of sample freezing shrinkage increased; salt content in 1% to 3% range, with the salt increased freezing shrinkage reducing, but different containing salt freezing shrinkage is insignificant. When the soil moisture content and compaction degree did not reach the double factor limits of critical frost heave value(fhc) containing salt content in the range 0 to 1% range, with the increase of the salt content, small sample quantity of frost heaving; salt content in 1% to 3% range, the frost heave amount increased with increasing salinity, but different with salt content between frost heaving amount difference is very small.5. With the increase of salt, the starting temperature of the test piece is reduced, at 0%, the starting temperature of-2℃, to 1% when the salt content, the swelling temperature reached-4 ℃. This is because the increase in salinity decreased soil salt solution freezing point.6. According to the theory of rough sets, frost heaving of the 10 factors(degree of compaction, moisture content, temperature, plastic limit, salt content, organic matter content, pH, cation exchange capacity, silt content, clay content) of the attribute reduction, ultimately selected the four largest factors influence on carbonate saline soil, respectively is: compaction degree, moisture content, temperature, moisture of salt. The remaining factors on the frost heave of carbonate saline soil has no obvious effect or limited impact.7. In the training of BP neural network, 500 experimental data were randomly selected, and 90 of the data were randomly selected in the model prediction. Model input layer neuron is 4, the hidden layer neuron number is 10, the output layer 1, the simulation precision is0.001. The simulation results and the actual value of the correlation coefficient R2=82.32%, the error is relatively small, the training convergence speed, high precision. This shows that the prediction model can predict the variation trend of frost heaving ratio, can correctly reflect the influence parameters on the choice of frost heaving ratio.8. By removing the model in a certain parameter prediction results and comparing the different parameters of carbonate saline soil frost heave effect sizes, the delete moisture content after R2=25.36%, delete compaction degree after R2=54.66%, delete after temperature R2=47.81%, remove salt content R2=59.06%. Finally get the frost heave of carbonate saline soil parameters affecting the largest order: water content > temperature > degree of compaction > salt content.