Study On Heat And Moisture Migration Characteristics And Mechanism Of Remolded Loess

The natural conditions in the central and western regions are harsh and the ecological environment is fragile.The frequent construction of projects and human activities have also brought challenges to disaster prevention and reduction and coordination between human and the environment.With the arrival of the 14 th Five-Year Plan,the realization of ecological protection and high-quality development of the Yellow River Basin has become a difficult problem we are facing in the new era.Among them,the heat and moisture migration characteristics of rock and soil and its environmental disaster effect deserve attention.Therefore,this paper takes the disturbed loess site as the background,and studies the thermal characteristics,structural characteristics,heat and moisture migration and multi-field coupling of the loess by means of experimental testing,numerical simulation and theoretical analysis.The aim is to deepen the understanding of the characteristics of soil heat and moisture migration,environmental and disaster effects,so as to provide a scientific basis for engineering construction,disaster prevention and mitigation and ecological livability in the Loess Plateau.Firstly,the thermal parameters of remolded loess were tested by the steady-state heat flow method.Through statistical and fitting analysis,the relationship between thermal conductivity or specific heat capacity and dry density and water content was obtained,and the empirical model was also,and the heat transfer and storage mechanism of soil was discussed.The results show that the difference of loess thermal parameters in different areas depends on the material composition,while the same area is mainly affected by the dry density,water content and other state parameters.The thermal conductivity or specific heat capacity has a good surface fitting relationship with dry density and water content,and the contribution of water to thermal parameters has a duality.Secondly,based on the structural characteristics of loess and the migration characteristics of water and air,the relationship between the structural characteristics and the transport of water and air is clarified.The analysis shows that the like-aggregates can be divided into three forms: aggregates,bridge-like linkages and "core-coating" structures,which form the basic structural units together with single particles.Clay particles often gather together to act as cements or form aggregates.Loess pores are mainly divided into macropores,intergranular pores,intragranular pores and cement pores.The first two are the main channels of water and air transport and contribute significantly,followed by intragranular pores.Cemented pores are poor in connectivity and water and air permeability.Under the action of soil-water potential difference,water migrates from high potential to low potential area.The form and amount of migration are closely related to the water-bearing state,and the direction and rate of migration depend on the gradient of temperature and humidity.The water-air phase coexists and interacts with each other,so the saturated hydraulic conductivity can be predicted by air permeability.Finally,the characteristics of heat and moisture migration of soil were studied from the indoor soil column test,and the environmental impact of heat and moisture migration was summarized.The coupled heat and moisture migration and its disaster effect were discussed through the simulation corresponding test and the heat and moisture distribution of the high fill slope of loess.It is found that the temperature redistribution is obvious and the humidity changes little in the soil with uniform initial water content under the action of temperature gradient alone.Under the combined action of temperature gradient and humidity gradient,the water migration is active and the change of temperature and humidity is complex.The heat and moisture migration in the soil affect each other,and the redistribution process of the two is related to each other.Under the influence of natural environment change or human activities,soil heat and moisture migration phenomenon exists widely,which has an impact on irrigation and water conservancy,engineering construction and ecological protection,etc.Therefore,the coupling problem of soil heat and moisture migration must be considered when studying it.The increase of deformation,decrease of strength and adjustment of stress state caused by heat and moisture change is actually a multi-field coupling problem of thermalhydraulic-mechanics(THM).Therefore,the disaster effect caused by heat and moisture migration of soil cannot be ignored.