Study On The Precise Characterization Of Subgrade Balance Humidity Under Complicated Environment Factors

Modulus of resilience is an important parameter to describe subgrade mechanicalproperties in mechanics-experience method for asphalt pavement. It changes with thesubgrade humidity and temperature. Subgrade humidity actual state and its variationcharacteristics must be considered in pavement structure design.Taking the literature research, numerical simulation, field investigation, theoreticalanalysis and other technical means and putting soil-water characteristic curve, thematrix suction, subgrade humidity and subgrade performance, the paper discussessubgrade humidity change rule in the case of rainfall and underground water levelfluctuation. The subgrade humidity forecast model is established in differentenvironmental factors and the influence of subgrade humidity to subgrade performanceis analyzed. The main research content is as follows:①Though extensive literature research at home and abroad and in combinationwith the result of field investigation for subgrade humidity, subgrade humidity will bebalanced in3to5years. So the humidity in balance is the state in subgrade humiditydesign. On the basis of the sources of subgrade humidity and various influence factors,climate and underground water level are two major control factors. The atmosphericrainfall is the dominant of climate factor.②Using the numerical simulation software SEEP/W, it analyzes change rule ofsubgrade humidity under the condition of rainfall intensity, rainfall duration, type ofroad surface and crack.. The results show that:1)When dirt road shoulder, subgradeslope and medial strip are the main way of rainwater infiltration. Arc disturbance zone isformed within subgrade.2)Disturbances and rainfall intensity range conforms to directproportion function. Volumetric water content in subgrade soil and rainfall intensityconforms to logarithmic function relationship within the scope of disturbance.3)Volumetric water content in disturbance range soil and rainfall duration conforms tologarithmic function relationship.4)Under the condition of the pavement waterproof,the road bed and the upper embankment area is the most affected by rainfall,nevertheless the under embankment area is the lest affected. Subgrade humiditydisturbance depth in the pavement of road central line is diffused linearly as the growthof the time.5)In the existence of crack in subgrade pavement, if the rainfall intensity isless than the pavement permeability coefficient, the whole unsaturated subgrade seepage field change does not affect. For a heavy rainfall, unsaturated subgrade seepageoccurs obvious change.6)Subgrade humidity disturbance range is diffused linearly asthe growth of the time around the subgrade cracks.③Using the numerical simulation software SEEP/W, the changing rule of thesubgrade humidity under the condition of the underground water level fluctuation isanalyzed. The results show that:1)Under the condition that the underground water levelis constant, subgrade humidity disturbance range for underground water is increasingwith the growth of time. Finally, it is into balance and up to capillary maximumheight.2)For that the influence of groundwater on subgrade humidity field is limited,silty clay’s capillary water maximum lifting height is6.75m, whose degree ofcompaction is96%. disturbance distance changing over time conforms toD at2bt.3)When the groundwater is back, the volumetric water content of subgrade soilchanging conforms tom ae btv cwithin the influence by groundwater.④According to the difference of main factors that influent the subgrade humidity,the subgrade is divided into3classes. The paper puts forward the subgrade humidityforecast model TMI wPI, which is suitable for I type, and improve the undergroundwater level model forecasting subgrade humidity of type Ⅲ. The process offorecasting subgrade humidity is given.⑤Indoor triaxial test is done for3kinds soil. The test concludes conventionaldynamic modulus of resilience of subgrade soil and permanent deformation. The resultsshow that modulus of resilience of each subgrade soil is sensitive to moisture contentchanges. The higher the moisture content, the bigger the permanent deformation.