Bound Water Properties And Moisture Migration In Unsaturated Loess

In this dissertation,isothermal adsorption and thermogravimetric analysis were used to determine strongly and weakly bound water content of loess samples.Experimental results show that bound water content in loess is mainly related to clay minerals content,and bound water content increase with the increase of clay mineral content.A linear relationship between the content of clay minerals and the amount of bound water was established.The density of the different types of bound water and water film thickness were also determined by experiments and theoretical analysis.Suction is the core variable in unsaturated soil,soil with different water content level may have different suction types that may have different effect on seepage problem of the soil.However,the existing classification of suction cannot explain the seepage problem in unsaturated soil.Therefore,it is necessary to reclassify the unsaturated soil suction based on the occurrednce state of pore water in unsaturated soil.The occurrednce of pore water is divided into bound water state,capillary edge water state and capillary water connected state.Migration of bound water can be neglecte under natural conditions.When pore water in unsaturated soil is capillary edge water state,gaseous water migration is the main moisture migration form.When pore water in unsaturated soil is connected,moisture migration is domainated by liquid water migration.Suction is divided into adsorption force,local capillary force and capillary force corresponding to the three kinds of unsaturated soil pore water occurrence state.The theoretical calculation formulas of adsorption force and capillary force were provided based on the physical chemistry principles and the effect of local capillary force was also evaluated.Adsorption force can be assessed by the adsorption potential energy between bound water and soil particles.However,the application of the theoretical calculation formula of capillary force is limited by undetermination of sol-id-liquid contact angle and randomness of pore size distribution.Therefore,the high air entry materials represented by ceramic plate were often used to measure soil suction.Based on the analysis of water-gas-ceramic plate-unsaturated soil system,we pointed that the water-gas-ceramic plate-unsaturated soil system just can be used to measure suction of unsatured soil when capillary water in unsaturated soil is connected.Based on the above analysis,the experiment of moisture migration in unsaturated loess with connacted pore water due to matric potential gradient was carried out.Experimental results show that the quantities of moisture migration in unsaturated loess were incrised with matric potential gradient.A statistical relationship between quantities of moisture migration and matric potential gradient was also established,which can be used to evaluate the effect of matric potential gradient on moisture migration.Gaseous water transfer and liquid water transfer test of unsaturated loess under the effect of temperature gradient of were also carried out.Experimental results show that temperature gradient,as driving force,has great effect on gaseous water migration than liquid water migration.Temperature effect in gaseous water migration is remarkable than it in mixed water migration.Within the scope of certain moisture content,temperature effect in gaseous water migration increased significantly with the increase of soil initial water content.Temperature effect in mixed state water migration is not obvious with the increase of initial moisture content.Two-dimensional unsteady finite element numerical method of unsaturated soil was improved based on the above research results.Then,the numerical calculation to predicte the dynamic changes of the water field of shallow unsaturated loess on the loess plateau was carried out by it.Numerical calculation results of the shallow unsaturated loess' s water filed under the condition of continuous drought were consistent with the measured results,which indicated the reliability of numerical calculation method.The variation law of shallow stratum's water field in arid loess plateau under the condition of continuous drought was found out based on measured and calculated results.The results of numerical analysis can provide a reference for the plant protection engineering construction in arid loess plateau.