DETERMINATION OF THE HYDRAULIC CONDUCTIVITY
The constant-head test is used to determine the hydraulic conductivity of coarse-grained soils. A typical constant-head apparatus is shown in Figure 6.7. Water is allowed to fl ow through a cylindrical sample
of soil under a constant head (h). The outfl ow (Q) is collected in a graduated cylinder at a convenient duration (t).
With reference to Figure
The fl ow rate through the soil is qz 5 Q/t, where Q is the total quantity of water collected in the measuring cylinder over time t.
where kz is the hydraulic conductivity in the vertical direction and A is the cross-sectional area. The viscosity of the fl uid, which is a function of temperature, infl uences the value of kz. The experimental value (kT8C) is corrected to a baseline temperature of 208C using
where m is the dynamic viscosity of water, T is the temperature in 8C at which the measurement was made, and RT 5 mT8C/m208C is the temperature correction factor that can be calculated from