هدايت هيدروليكي خاك ها و نحوه كاربرد آن در طراحي شبكه هاي زهكشي

Soils Hydraulic Conductivity and Its Applications in Drainage Designs

Hydraulic conductivity is one of the soilʹs dynamic properties, which plays a major role in water flow and salts transport within the soil. A saturated hydraulic conductivity value is needed for drainage projects design, which is almost constant. Different methods can be used in determining insitu hydraulic conductivity and they can be divided into two groups, e.g. above and below water table methods. Preliminary investigations showed that there was a significant difference between the results of these methods. The objectives of this study were 1) to investigate and compare the hydraulic conductivity values obtained using the above-mentioned methods in Iran and other countries; 2) to find the reasons of differences between the results of these two methods; and 3) to present practical solutions to minimize these differences. Generally, the results obtained by the above water table method were lower than those of under water table one. Rased on the results of this research, values of under water table method were 0.5 to 32 times bigger than those of the above water table method. The reason for such a difference can be explained by various factors, e.g. water quality, the collapse of well walls, trapped air bubbles within soil pore, and the difference in flow patterns. Lower values obtained by the above water table method compare with under water table one may indicate that the saturated hydraulic conductivity cannot be accurately determined using the above water table method. Therefore, the results of this kind of method need to be closer to those of under water table one. In this regard, the suitable methods can be ranked as following: Natural model method, field model method, geostatitical method, Macnill method and correlation between texture and structure method.