Moisture Distribution Of Loess Subgrade Under Atmosphere

Unsaturated loess exists widely in northwest China.It is necessary to study unsaturated loess of its special physical mechanic properties and inevitability in practical engineering application.Lanzhou unsaturated loess,as the investigation object,is proveded to carry out the outdoor evaporation test in summer and autumn.By observing the temperature and humidity field of unsaturated loess and comparing with the potential evaporation strength outside,we can analyze the sensible factors of the unsaturated loess.Indoor soil test,outdoor evaporation test and numerical simulation method were carried out to achieve the purpose of research.The related knowledge of unsaturated soil and loess is systematically studied and summarized,providing theoretical preparation and framework support for subsequent outdoor evaporation test and numerical simulation.By testing the basic physical parameters of soil samples(the maximum dry density,the optimum moisture content and the liquid plastic limit),we can have a basic understanding of the soil properties,which prepate for the follow-up outdoor evaporation test.With the help of the tutor,the outdoor evaporation experiment of unsaturated loess is designed.The change of temperature field and humidity field of unsaturated loess with different initial volume and different degree of compaction in different evaporation time is observed.It is found that:(1)The soil temperature will increase with the increase of the outdoor evaporation time.In the range of 30 cm distances to surfaces,soil temperature is "?" distribution,and the soil temperature is relatively lowest in the range of 5cm~10cm range from the earth surface.The soil temperature at 30 cm is higher than the soil surface temperature.(2)When the compaction degree is same,the larger the initial volume water content is,the lower the soil temperature is.(3)When the initial volume water content is same,the smaller the compaction degree is,the lower the soil temperature is.(4)The initial volume water content plays a leading role in the factors affecting the soil moisture content.(5)The water content relationship between different samples with the same compaction degree and different initial volume water content won't be changed after the same evaporation time.The water content of the sample with a bigger initial volume water content is still relatively higher after outside evaporation.When the initial volume and moisture content are the same,the moisture content of the samplel with small compactness is relatively high.The numerical simulation of unsaturated loess roadbed coupled by three fields of water,heat and gas is carried out by using COMSOL software.It is found that:(1)The soil temperature and moisture content of subgrade change from the surface to the inside.(2)Under the continuous sunshine,the moisture content of subgrade will decrease to a certain number then stop dropping.(3)Not the whole subgrade's temperature can increase to the same temperature as atmosphere.(4)The sunshine is the major element influence the subgrade's temperature and moisture content changing.(5)The longer the sunshine is,the easier the subgrade get wet.The evaporation process of unsaturated loess in the outdoor is complicated and influenced by many factors.This paper only selects two of the internal factors of the soil,and considers the effect of the atmospheric environment into the potential evaporation strength,and the quantity of the tested parts is limited,and the measurement error is added,so there are still many shortcomings.The exploration of evaporation law of unsaturated loess remains a far and hard journey.