Research On Water And Salt Transport Law And Salt Frost Heave Characteristics Of Sulfate Saline Soil With Different Fine Grain

Ningxia Hongshibao area is located in the central arid zone,due to the severe cold in winter,hot and dry in summer,large temperature difference between day and night,and high mineralization of shallow groundwater,resulting in serious salinization of the soil in the region,and its soluble salt is usually sodium sulfate,which is sulfate and sulfite impregnated soil.Influenced by the local environment and climate,the moisture and salt in this type of soil constantly changes,which is easy to produce salt swelling,melting and sinking,and dissolving sink,thus triggering the disease of foundation projects.In this paper,we investigate the water and salt transport law and salt swelling characteristics of saline soils under different temperature,water content,salt content and fines content,and establish an artificial neural network model to analyze and predict the salt swelling rate,and conduct a simulation to verify the test results.The results are as follows:(1)With the increase of fines content,the capillary effect of soil increases,the upward migration of water and salt increases,and the effect of gravity on water and salt decreases,while the downward migration of water and salt decreases due to the blockage of seepage channels in the soil by the increase of fines.(2)The vertical deformation of soil in the freeze-thaw process is divided into five zones:?fast growth zone,rapid expansion of soil;? complete freezing zone,basically completely frozen;? slow thawing zone,sodium sulfate crystal melting;? fast thawing zone,sodium sulfate crystal and ice crystals start to melt at the same time;? complete thawing zone,when the thawing and sinking is basically completed.(3)Under the action of the same freeze-thaw cycle,with the increase of salt content and fines content,the larger the soil deformation.The first freeze-thaw cycle has a great influence on the deformation and the soil with low salt content has freeze-shrinkage phenomenon,while the soil with high salt content has only freeze-swelling phenomenon.(4)The maximum freeze swelling and maximum thawing amount at 0%salt content are decreasing with the increase of the number of freeze-thaw cycles.When the salt content is 2%,the maximum freeze swelling and the maximum thawing amount are decreasing with the number of freeze-thaw cycles and then increasing.The maximum freeze swelling and maximum thawing amount of 5%salt content are increased with the increase of freeze-thaw cycles.(5)In this paper,artificial neural network learning method is used to predict the freezing swelling rate of saline soil under closed system,and the prediction results show that the fit of artificial neural network learning method is relatively high.Sensitivity analysis of the four factors affecting the frost swelling rate of saline soils showed that the importance of the factors affecting the model prediction was in the order of temperature,time,salt content,and fines content.