Experimental Study On Water Exchange Between Clay And Fractur

Fractures in soils provide significant preferential pathways for contaminant transport, rainfall infiltration and evaporation. The definition of the water exchange between the soils and the fractures is the movement of water getting in or out the soils. The water exchange between the soils and the fractures includes two directions: infiltration and evaporation. For the infiltration directions, it is crucial to estimate the preferential flow, which is often quantitatively described by a water exchange ratio. Current studies on the water exchange ratio mainly focus on the fractures in sand. The water exchange ratio between the fracture and clay is still unclear. The difficulties in investigating the fractures in clays include two aspects: the fractures close upon wetting and re-open upon drying; the width of the fracture is very small in the clay. For the evaporation model, current studies only get the conclusion that the fracture increases the water loss from bare soil. But it is unknown that how the fracture impacts the evaporation of the soils. The difficulties in investigating the evaporation of soil with fracture are that it has many factors needed to consider including the soil environment and meteorological conditions. It is hard to get an equation to calculate the fracture evaporation.This study designed a novel experiment setup with advance water content and suction measuring system to investigate the water exchange of the deformable fracture in clays. Result show that the water exchange ratio is the highest at the initial stage and decrease with decreasing suction in the clay. The hydraulic conductivity of the fracture-clay interface is about one order of magnitude larger than that of the saturated soil matrix. For the experiment with different width of fracture, result shows that the water exchange ratio is also the highest at the initial stage and decrease with decreasing suction in the clay. The maximum of the hydraulic conductivity of the fracture-clay interface is about one order of magnitude larger than that of the saturated soil matrix. At the initial of the experiment, the difference between the water exchange ratios of the three experiments is the biggest during the process of the experiment and the difference decreases in the progress of the experiments.This study also designed a novel experiment setup with advance water content and suction measuring system to investigating the evaporation in fractured clay. Result shows that the evapotranspiration is the highest at the initial stage and decrease to the stable value at the end of the experiment with different initial water content and different widths of fracture. The water content of the soil around the fracture increases with the increasing depth in vertical direction and the increasing distance in horizontal direction to the crack.