ABSTRACT
Eq. (4.29) expresses for a given hydraulic gradient i, the velocity of water in a circular pore channel is proportional to the square of the diameter of the pore channel. The average diameter of the voids in a soil at a given porosity increases practically in proportion to the grain size, D
Extensive investigations of filter sands by Hazen (1892) led to the equation k(rn/s) = CD 2
where De is a characteristic effective grain size which was determined to be equal to D IO (10% size). Fig. 4.10 gives a relationship between k and effective grain size DIO of granular soil which validates Eq. (4.30). The permeability data approximates a straight line with a slope equal to 2 consistent with Eq. (4.30). These data indicate an average value of C = 10-2 where k is expressed in rn/s and D IO in mm. According to the data in Fig. 4.10, Eq. (4.30) may underestimate or overestimate the permeability of granular soils by a factor of about 2.
