Study On Water-salt Transport And HTSPE Coupled Model Of The Saline Soil In Western Jilin

The soil in Western Jilin,has the properties of seasonal frozen soil,saline soil and dispersive soil.Since the special protolith and the weather conditions,the soil has special engineering geological characteristics.The winter lasts 5 months,which prompts coupling process of the different fields of flow-solid-thermal-stress-strain.As a result,different disease in engineering and agriculture is induced.In freezing,the distribution of temperature field,water field,salt field,strain field and stress field change,which leading to frost heave.Besides,water migration affects salt transport,and the salt accumulate at the soil surface,which leading to salinization and environmental disaster.Thus,study of the multi-field mathematical coupled model is the research foundation for the study of environmental engineering geology disastrous mechanism in the study area.This article selected Nong’an county,which is the typical saline soil area in Western Jilin,as the study area for study.And some conclusion are drawn as following,Through the indoor test for the soil samples collected in the Spring of 2015,we obtained the characteristics of the content,basic physical properties and the thermal parameters.The results indicated that the proportion of the primary mineral for the soil is high.The secondary mineral is mainly dominated by kaolinite.The soil is carbonated saline soil.The positive ion is mainly Na~+,and the negative ions are mainly bicarbonate radical and sulfate radical,which affect the pH value.In the soil,the silt has a large content.While 30cm is the boundary for the particle distribution,the soil that less than 30cm is mainly low liquid limit clay,and the soil at the depth over 30cm is mainly high liquid limit clay.Besides,the soil at the depth less than30cm has low water content and high salt content.Comparing with the water content and salt content of the soil in 2014,the influence depth of evaporation for the soil is obtained,and the reason for the soil salinization is primarily investigated.The soil samples with different water contents and different compaction degrees,which is subjected to freezing and thawing,are studied for the structures observation.With the assistance of scanning electron microscope,it was found that after freezing and thawing,the proportion of the small particles increases firstly and then decreases,and the bigger particles decreases firstly and then increases.Through the analysis,it is considered to be influenced in two parts.On the one hand,the volume will increase if the pore water transfer into ice,and the volume will decrease if the ice melt into water,which leading to the particles transformation or broken.On the other hand,water migration induces the changes of the pore water pressure,and freezes into ice in a new position,or even breaks the structural connection.The unfrozen water content for the soil samples with different water contents or different salt contents is tested by using nuclear magnetic resonance.Then we analyzed the influence of the initial water content and salt content on the unfrozen water content curve.By using“Rock&soil Freezing-Thaw Trial and Error imitating comprehensive experimental platform with ultracold condition”that independently designed and invented by our research group,the freezing tested is developed on the soil samples with the optimum water content.Then we obtained the freezing curve and freezing temperature.And based on the thermometry,the unfrozen water content is forecasted.As a result,the forecasted results is proved to be valid by comparing with the testing result by the nuclear magnetic resonance.Upon considering the capillary water raising under unfrozen condition and water migration under freezing condition,we carried out the capillary water raising experiment and water migration tests under different conditions(whether there is water recharging,unidirectional or bidirection freezing),which are subjected to freezing.And the freezing time is 5 days.By comparing the experimental results,the driving force for the water migration is determined,and the temperature potential and the pressure potential is the main reason for water migration,gravitational potential affects water a little,and the matric potential has little influence on water migration.On the basis of the reasonable assumption,we systematically established the mathematical coupled model coupled water-heat-salt-stress-strain by analyzing three-dimensional representative elementary volume.And then simplified the model into one-dimensional coupled model.The model is based on the conservation law of energy and mass,principle of effective stress,constitutive equations,Darcy law and clapeyron equation.And the mathematical equation set contains some parameters including unfrozen water content,thermodynamic parameter,osmotic coefficient.The concept of total void ratio is proposed to determine the formation of ice lenses,and the positions of the salt crystallization is determined by solubility.Unidirectional freezing test with the water recharge is carried out by means of“Rock&soil Freezing-Thaw Trial and Error imitating comprehensive experimental platform with ultracold condition”,considering the freezing speed,initial condition and boundary condition.And the temperature,frost heaving amount are monitored.Also,the water content and salt content is tested after the experiment.Through using the PDE module of COMSOL Multiphyscis,the experiment is simulated based on the mathematical coupled model of hydraulic-thermal-salt-pressure-elastic(HTSPE).The simulated results have an agreement with the experimental results,which verified the validation of the model.Thus,the special engineering boundary condition is considered for simulation.The calculated results of the water content and salt content indicated that the calculated results are agree with the monitored data.While the water content of the monitored water content for the soils at the depth less than 30cm is small and the salt content is high,which is considered to be influenced by evaporation,which leads the moisture go into the air and the salt accumulated at the soil surface.