Distribution Of Subgrade Humidity Field Under Environmental Field

Due to the increasing shortage of high-quality fillers in China,fine-grained soils are widely used in subgrade filling.In the process of long-term service,the atmospheric environment and groundwater exchange water and heat with the fine-grained soil subgrade with strong capillarity and water-holding capacity by means of rainfall,evaporation and capillarity,resulting in the soil moisture content in the subgrade far exceeding the optimal moisture content controlled in the construction process.Subgrade wetting leads to the degradation of subgrade support capacity and the deterioration of road service performance,which brings a series of engineering problems such as local subgrade settlement and subgrade soil mudding,which greatly reduces the service life of subgrade.Therefore,a correct understanding of the evolution process of the subgrade humidity field under the influence of the atmospheric environment and groundwater during the service period of the fine-grained soil subgrade can provide more scientific and rigorous decision-making for the preliminary design of the subgrade,the evaluation of the subgrade state during the operation period,and the later maintenance.Based on the above problems,this paper is based on saturated-unsaturated seepage theory and water-vapor-heat multi-field coupling theory.through laboratory experiments and numerical simulation,the evolution law of subgrade humidity field under the action of groundwater,rainfall and evaporation is explored,and the main results and conclusions are obtained as follows:(1)The hydraulic parameters of the fine-grained soil subgrade filler are obtained through the laboratory tests,and the maximum capillary water rising height of silty clay subgrade is calculated based on the Hessen formula.(2)The water migration model of unsaturated soil subgrade under capillary action is established,and the reliability of the model is verified by laboratory model tests.The equilibrium humidity magnitude of three groundwater level height subgrades is obtained by software steady-state calculation,and the results show that the water content is approximately linear along the depth direction under the influence of three groundwater levels.The comparison with the recommended value of the specification shows that the matrix suction distribution is the same as the reference value provided by the specification,but the saturation distribution based on the soil-water characteristic curve is larger than the reference value provided by the specification.(3)A rainfall infiltration boundary switching equation is proposed to verify the reliability of the boundary setting method.Difference with the existing infiltration conditions,this method can more truly reflect the variation law of the boundary infiltration rate during the rainfall infiltration process.(4)The seepage analysis model of unsaturated soil subgrade under rainfall infiltration is established,and five rainfall intensities(light rain,moderate rain,heavy rain,rainstorm,and extreme precipitation)are selected,and the rainfall process and the variation of rainfall infiltration range and humidity in the two stages after the end of the rainfall are analyzed.Changes in humidity in the seepage range.The relative size of rainfall intensity(qs)and soil saturation permeability coefficient(Ks)is an important factor affecting the law of rainfall infiltration,When qs<Ks,the infiltration slope will not produce transient saturation zone during rainfall.When qs>Ks,the soil infiltration area is all transient saturation zone.After the end of rainfall,the transient saturation zone of the slope gradually dissipates,Rain Water begins to infiltrate into the deep soil of the subgrade,and the infiltration-depth increases with the slowly increase of the initial rainfall intensity.(5)Using the COMSOL Multiphysics numeric calculation software as the calculation platform,establishes the multi-field coupling numeric calculation model of soil H-V-T under atmospheric evaporation,and the variation law of temperature and humidity field inside the subgrade under typical weather in Jinan area is obtained.Numeric calculation results present that the process of unsaturated subgrade soil shows two stages:deceleration evaporation stage and residual evaporation stage,in which the residual evaporation stage is dominated by water vapor migration.(6)In the process of temperature field transfer under fixed temperature boundary conditions,the internal temperature of soil gradually changes from curvilinear distribution to linear distribution with the slowly increase over time along the depth direction,and the alltransfer process will be divided with three stages.They are fast transfer stage,slow transfer stage and stable transfer stage.(7)The migration of vapor water is a non-negligible part of subgrade moisture transfer under the action of evaporation.The change of soil moisture content at the subgrade level mainly depends on the vapor water migration driven by the temperature gradient inside the soil.