Study On Evaporation Effect And Influencing Factors Of Remoulded Loess In Lanzhou

Lanzhou area belongs to arid and semi-arid climate.It has the characteristics of strong evaporation,weak rainfall,more drought and less rainfall,and distributes a large number of unsaturated loess.Due to the influence of various climatic factors and soil properties,geotechnical engineering problems related to greeningin the plateau dry area,slope protection and soil moisture migrationare more seriousin the loess area of northwest China in recent years.Therefore,it is of great practical significance to study the law of water migration and its influencing factors in shallow surface soil under evaporation for preventing and controlling geotechnical engineering problems caused by the change of water content.On the basis of summarizing the previous research results,this paper takes Lanzhou unsaturated remodeling loess as the research object,indoor soil column evaporation experiments under different temperatures,different wind speeds and different initial water content conditions were carried out,and numerical simulation was carried out by HYDRUS-1D software.The influencing factors of soil evaporation and its water migration law were studied,and the influence depth of evaporation on soil moisture was explored.Temperature is the direct factor that causes the evaporation effect of the soil,and the effect of the wind speed is to transfer the gaseous water evaporated from the surface of the soil to the atmosphere.The water content of the soil determines the water supply capacity for evaporation.The indoor soil column evaporation test was carried out under different conditions.The results show that the evaporation of unsaturated loess can be divided into stable evaporation stage,deceleration evaporation stage and residual evaporation stage.The cumulative evaporation of soil column shows a nonlinear increase with time,while the cumulative potential evaporation shows a linear increase trend.At the same evaporation time,the evaporation of soil column is lower than the potential evaporation.The higher the temperature,the greater the wind speed,the greater the initial moisture content,and the greater the cumulative evaporation of the soil;The potential relative evaporation varies by about 5% when the wind speed changes by 1 m/s or the temperature changes by 10?,but the initial moisture content has nothing to do with the potential evaporation.The change of soil temperature of 23 cm high soil column corresponds to the change of ambient temperature.Along the depth direction,the rate of water content decrease gradually from top to bottom,and the average rate of water content migration along the depth increases by 0.18%/d when the temperature rises by 15?.Based on the experimental data,the range of variation of the evaporation coefficient is obtained.According to the experimental model parameters and boundary conditions,the numerical simulation analysis is carried out,and compared with the measured values.it is found that the simulated values are basically consistent with the measured values,and the water migration laws are basically the same.By simulating the change of the moisture content of the natural foundation of 5.7 meters,the influence depth is about 160 cm when the initial moisture content is 15%,and the influence depth is more than 200 cm when 20%.In the depth range of 0 to150 cm,the soil moisture content and temperature change range is large.