Geotechnical Engineering

DHARM

674 GEOTECHNICAL ENGINEERING

Franki Pile Company has suggested the following:

Table 16.8 Correlation between qc and N (Franki Pile Co.)

Type of soil qc/N

Silty clay 3

Sandy clay 4

Silty sand 5

Clayey sand 6

Schmertmann (1970) suggests the following:

Table 16.9 Correlation between qc and N (Schmertmann, 1970)

Type of soil qc/N

Sandy silts, silts 2.0

Silty sands, fine to medium sands 3.5

Coarse sands 5.5

Sandy gravel, gravel 9.0

These values are applicable for N-values equal to or greater than 75. qc will be obtained
in kg/cm^2.

Piles in granular soils

Meyerhof (1959) has shown that the ultimate point-bearing capacity of a pile, qb, ranges from

2/3 to 112 times the static cone penetration resistance, qc.

On the average, therefore,

qb = qc ...(Eq. 16.31)

Meyerhof proposed the following equation:

qb = qc = 4N ...(Eq. 16.32)

(qb and qc will be obtained in kg/cm^2 )

qb = qc = 400 N ...(Eq. 16.33)

(qb and qc will be in kN/m^2 )

Similarly, it has been found that the observed values of skin friction, fs, varies from 141

to 3 times the static skin friction, fc.

On the average, therefore,

fs = 2fc ...(Eq. 16.34)

However, for small displacement piles such as H-piles,

fs = fc ...(Eq. 16.35)

Meyerhof suggests the following:

fs = qc/200 ...(Eq. 16.36)

fs = N/50 or fs = 2N ...(Eq. 16.37)

(kg/cm^2 ) (kN/m^2 )