Experimental Study On Water Transfer Property Of Unsaturated Loessial Silt With Capillary Action

As the continuously prosperous development of urban economy and the enlargement of construction scale,the transport resources become increasingly important.Especially under the"the Belt and the Road Initiative" policy,the number of roads and railway are growing rapidly.At present,lots of unsaturated soils are used for subgrade as filling materials,such as silt,loess.Water migration as a core role in unsaturated soils has an important effect on engineering quality of unsaturated soils.Based on tests of the compacted unsaturated loessial silt,this paper takes two different kinds of loess for research objects,and shows the indoor one dimensional soil column capillary test.The capillary effects of unsaturated loessial silt have been obtained through analyzing data and fitting curves.And the effective element influencing factors is discussed also.Experiments indicate that the speed of capillary water going up slows down as the height of capillary water is increasing.When capillary water gets one section,the volume water content of soil increases slowly first,and then grows quickly,finally turns to be stability.Also,matric suction in this section decreases slowly at beginning,then falls sharply,finally tends to be stability.The curve of volume water content with time and the curve of matrix suction with time can be divided into four stages,i.e,the initial invariant segment,the abrupt change segment,the slow change segment and the stable segment.After stability,the volume water content of each cross-section is generally decreasing with the increase of the section level,and the matrix suction of each cross-section gradually increases with the increase of the section level.At last,the soil at all section position does not reach the saturation state in this test.The capillary properties of the soils are mostly similar when the slendernesses of the soil columns are 4.68 and 9.54 respectively.Therefore,it can be drawn out that when the slenderness?4.68,the soil column can be considered as one dimensional column.The microstructure of soil has an essential influence on its macroscopic properties.As a result,when the size distribution of loessial silt is different,matric suction in each cross-section and its decreasing rate,the volume water content of each cross-section and its increasing rate,the speed rate of capillary water going up,SWCC and permeability function of unsaturated soil are certain different,when the particle size distributions of loessial soil are different.The instantaneous profile method is generally applied to determine the unsaturated permeability of compacted loessial silt.The analysis results show that the permeability coefficient of unsaturated compacted loessial silt varies in a range of several orders of magnitude.Matric suction has a significant effect on permeability coefficient.Permeability coefficient reduces as the matric suction is increasing,and its reducing rate is slowly decreasing.By the statistical analysis to the experimental date,a function of y = axb can be used to express the relationship between the height of capillary water going up and action time for compacted loessial silt.Meanwhile its adaptability is verified by the scholar's rsults.And the Boltzmann Equation can be used to express the SWCC of the compacted loessial silt.Finally,the relationship of permeability coefficient and matric suction for compacted loessial silt fits the Gardener model well.Therefore,all above functions will be applied in the analyses of permeability problem for the compacted loessial silt.