Experimental study of the upward seepage law of the intact unsaturated Lishi loess

A special kind of seepage phenomenon,the upward seepage,occurs in the loess( unsaturated soil)if the groundwater( phreatic water) level rises. In order to study the upward seepage law of the intact unsaturated Lishi loess under different conditions,an upward permeameter is designed in the unsaturated soil,and four groups of specimens( the height is 20 cm and the diameter is 8 cm) are selected to implement the upward seepage test under the constant pressure heads of 1,5 and 10 cm. The process of upward water seepage and the shape and change of the seepage front in the loess are observed. The relationship between seepage frontal displacement and time( seepage velocity) and the relationship between seepage pressure and seepage velocity are obtained. The results show that( 1) the curve showing the relationship between the seepage frontal displacement and time is a parabola.( 2) According to the change in the seepage rate,the seepage process consists of three stages,i. e.,the fast,slow and stable stages,and comparison and analysis reveal the effects of constant head pressure,dry density and natural moisture content on the seepage rate.( 3)It is found that the wormhole development and good connectivity can accelerate the rate of upward seepage.Using the obtained experimental data to run a regression, the fitting formula between seepage frontaldisplacement and time is attained.