The Evolution Of Highway Subgrade Humidity Field In Westernarid And Semi Arid Regions

The state of subgraded humidity field in concentrated rainfall period is a very importantbasis for correct evaluaion of subgrade strength and bearing capacity，and for reasonableselection of pavement structure design parameters. The general evolution rules of subgradehumidity field in western arid and semi arid regions influenced by compaction degree，initialhumidity，pavement layer rainfall，and groundwater level were studied systematically byfield investigation，numerical simulation，similar physical model experiment，theoreticalanalysis and field measurement. A prediction model of humidity characteristic value wasestablished based on witch a determination method to the most unfavorable distribution ofsugrade humidity field in a given condition was proposed in the light of high grade highwayin western arid and semi arid regions. The main contents and conclusions are as follows：（1）The general evolution rules of sugrade humidity field influenced by compactiondegree were revealed by numerical test and similar physical model experiment and analysis.The results show that humidity values and horizon distances gradually diminish withincreasing of compaction degree in subgrade humidity disturbance，and front disturbancearea reduce with increasing of humidity gradients；as sugrade using compaction degreecombination the humidity increment of lower disturbance diminish when compaction degreeof upper disturbance is larger because of water downward migration difficulties.（2）The general evolution rules of sugrade humidity field influenced by initialhumidity were revealed by numerical test and analysis. The results show that influences ofslope surface moisture affected by initial humidity are very slight outside that sugradehumidity and disturbance area show linear growth with increasing of initial humidity；humidity gradients of front disturbance area show exponential gradual decreasing withincreasing of initial humidity.（3）The general evolution rules of sugrade humidity field influenced by pavementlayer were revealed by numerical test and analysis. The results show that horizontal andvertical expansion distances of humidity disturbance show linear increasing along withrainfall time with permeable pavement，at the same time，humidity gradients of frontdisturbance area show binomial variation.（4）The general evolution rules of sugrade humidity field influenced by rainfall wererevealed by numerical test and analysis. The results show that sugrade humidity at everyhorizon positions show binomial distribution in rainfall humidity disturbance；humidity ofslope surface logarithmic grow with increasing of rainfall strength and duration；humidity disturbance expand in logarithmic form to stable，and hysteresis effect of rainfall strengthemerge corresponding to stable state；influences of disturbance areas affected by rainfallstrength become smaller with rainfall duration becoming longer；Influences that sugradehumidity and range of rainfall back disturbance area and non-disturbance area influenced byinterval time are every slight，however，humidity of front disturbance slightly reduce withincreasing of interval time，and humidity distribution of intermittent rainfall become morecloser to it of continuous rainfall with increasing of rainfall strength.（5）The general evolution rules of sugrade humidity field influenced by groundwaterlevel were revealed by numerical test and analysis. The results show that rainfall disturbancehumidity outside slope surface enlarge with increasing of groundwater level，but theamplitude trend to weak with horizon high；certain conditions will correspond to a balancegroundwater level above witch subgrade humidity amplitude of rainfall disturbance showlogarithmic decreasing with dropping of groundwater level，at the same time，subgradehumidity gradients of groundwater intrusion disturbance show linear decreasing.（6）The subgrade humidity field distributions in western arid and semi arid regionswere revealed by numerical and field test and analysis. The results show that it is verysignificant that rainfall strength and groundwater level influence disturbance areas extensionwith impermeable pavement，however，with permeable pavement what significantlyinfluencing disturbance areas extension are initial humidity and groundwater level；it is verysignificant that initial humidity and groundwater level influence groundwater intrusiondisturbance extension；a prediction model of humidity characteristic value was establishedusing BP neural network，based on witch a determination method to the most unfavorabledistribution of sugrade humidity field in a given condition，considering rainfall returnperiod，was proposed in the light of high grade highway in western arid and semi aridregions.