Improvement On Instantaneous Profile Method And Equipment For Unsaturated Hydraulic Conductivity Measurement

The instantaneous profile method (IPM) is a commonly used method for measuring unsaturated hydraulic conductivity. In this method, the profiles of water content and pore-water pressure are obtained by fitting discrete raw data measured along water flow direction in a soil sample. Various measurement spacings and measurement time intervals have been used by different researchers. Furthermore, the interpolation method for fitting water content data and the difference method for calculating hydraulic gradient are different in the literature. However, the assessment on these discrepancies is still in the lack. Therefore, it is necessary to study the effect of data processing methods on unsaturated hydraulic conductivity determined by IPM for improving the accuracy of IPM and in better planning future experiments based on IPM. In addition, the soil column existed can not measure the water flow in the evaporation test. So that the unsaturated hydraulic conductivity in the evaporation process can not be measured. It is also necessary to improve the soil column for better use.Instead of carrying out experiments, a capillary-rise test on a silt column was simulated numerically to produce raw data of water content and pore-water pressure in this study. Subsequently various data interpretation methods were adopted to calculate hydraulic conductivity according to the procedures of IPM. The results were then compared with the input hydraulic conductivity function used for numerical simulation. The comparison shows that:(1)For sand soil, the polyline function is a bette interpolation method for fitting water content data than the cubic hermite spline. The backward diffenence method is better for calculating hydraulic gradient than forward and central difference methods.(2)For silt soil, the cubic hermite spline is a bette interpolation method for fitting water content data than the polyline function. The central diffenence method is better for calculating hydraulic gradient than forward and backward difference methods.(3)For clay soil, the ubic hermite spline is a bette interpolation method for fitting water content data than the polyline. The central diffenence method is better for calculating hydraulic gradient than forward and back difference methods.(4)For the three kinds of soils mentioned above, the accuracy of calculated unsaturated hydraulic conductivity is found to decrease with increased measurement spacing and measurement time interval. The effect of measurement time interval on the accuracy is especially obvious. The error increased the same times with the time interval increased nearly. So the measurement spacing and time interval should be short reasonblely for accurate results. This study is useful in improving the accuracy of IPM and in better planning future experiments based on IPMThen the equipment was improved based on the above results. The spacing between the sensor positions was determined and the top of the equipment was sealed for measuring the water outflow during the evaporation process. And then an evaporation test was constructed with the improved equipment. According to the results determined by the IPM with better data processing methods of the evaporation test, it is found that the improved equipment is easy and time-saving for measuring the unsaturated hydraulic conductivity with nonzero flow boundary conditions.