Experimental Study On Wet Heat Transfer And Pollutant Migration In Unsaturated Soil Under Temperature

In recent years,the study of heat,water,force coupling and pollutant migration in porous media is an important part of the environmental geotechnical field.It has good practical value in the fields of geothermal resource development and nuclear waste disposal.Through related researches,there are few experimental studies on the transfer of heavy metal ions in the unsaturated soil under the action of cyclic temperature rise and temperature and the action of temperature.Therefore,in this paper,through the self-developed test device,the experimental research on the influence of the wet heat transfer,heating time,initial water content and dry density of unsaturated soil on the process of lead ion migration during different temperature rise and fall processes was carried out.The main work contents are as follows:(1)It has been observed that the volumetric moisture content measured by the moisture sensor is greatly affected by the temperature change,so the moisture sensor used in the test is calibrated.It was found that there is a linear relationship between them,and the quantitative relationship is used to calibrate the data measured by each sensor in subsequent experiments.In addition,the permeability coefficient of different dry density kaolin was tested to determine the relationship between the permeability coefficient and the dry density.(2)The wet heat transfer test during the single temperature rise and fall of the soil column with different initial moisture content was carried out.The results show that the farther away from the heat source end,the higher the initial water content and the lower the temperature value is,the slower the temperature changes,and the longer the time for stabilization requires.Temperature has a certain range of influence;The cooling process is similar to the heating process,but the temperature values at the time of stabilization tend to be the same.The distribution of the humidity field during the heating process is:the closer to the heat source end,the lower the initial water content,the more obvious the peak humidity phenomenon is,the lower the humidity value when stable,the shorter the time to reach the steady state.Also,humidity has a certain range of influence.During the cooling process,the change in humidity depends on the humidity value at the start of cooling and the initial moisture content.(3)The wet heat transfer test during the cyclic temperature rise and fall of the soil column with different initial moisture content was carried out.The results show that the temperature and humidity changes during the cycle temperature rise and fall are similar to the single temperature rise and fall process,but as the number of cycles increases,the temperature and humidity values become higher during the stabilization;no matter which cycle,the soil temperature value of the column in vertical position is lower than that in the horizontal direction,but the humidity value is higher than that in the horizontal direction.This phenomenon is more obvious at the near-heat end;When the soil column is placed horizontally,the temperature value and humidity value of each measuring point can be consistent during the cooling process;when the soil column is placed vertically,the humidity value of the near-hot end measuring point changes greatly,and the distance is measured.The humidity value of the point varies a little less.(4)In a single heating process,the migration test of lead ions in unsaturated soil under various conditions was carried out.The effects of heating time,initial water content and dry density on the lead ion migration process were analyzed.The results show that the longer the heating time,the farther the lead ions migrate.The larger the initial moisture content,the farther the lead ions migrate.For the soil column with lower initial water content,the effect of dry density on the lead ion migration process is not obvious,while for the soil column with higher initial water content,the smaller the dry density,the farther the migration under the same conditions.However,in general,the lead ion migration process is very slow,and the amount of ions that migrate is small.The migration of lead ions in unsaturated soil is a very complicated process affected by many factors.