Soil and Water Conservation Engineering · Soil Mechanics · 2 marks · Numerical answer
A constant-head permeability sample is 70 mm in diameter and 100 mm long. Head loss is 80 mm and 60 mL water is collected in one minute. Find hydraulic conductivity in mm/s, to two decimals.
Darcy’s relation is $Q=KA\Delta h/L$. Flow is 60000 mm³/60 s=1000 mm³/s and area $A=\pi70^2/4=3848.451$ mm². Thus $K=1000(100)/(3848.451\cdot80)=.324806$ mm/s, rounded **.32 mm/s**. The sample length and head difference must use the same length units.