Overburden Pressure Corrections

$(N_1)_{60} = C_N \cdot N_{60}$

$C_N \le 2$

Gibbs & Holtz (1957)

$C_N = \dfrac{350}{\sigma_o + 70} \, \sigma_o \le 280kN/m^2$

Note

$\frac{N_c}{N_{60}}$ should lie between 0.45 and 2.0, if $\frac{N_c}{N_{60}}$ is greater than 2.0, :math:N_c should be divided by 2.0 to obtain the design value used in finding the bearing capacity of the soil.

Peck and Bazaraa (1969)

$ C_N = \dfrac{4}{1 + 0.0418 \cdot \sigma_o}, \, \sigma_o \lt 71.8kN/m^2 $

$ C_N = \dfrac{4}{3.25 + 0.0104 \cdot \sigma_o}, \, \sigma_o \gt 71.8kN/m^2 $

$C_N = 1 \, , \, \sigma_o = 71.8kN/m^2$

Peck et al. (1974)

$C_N = 0.77 \log \left(\dfrac{2000}{\sigma_o} \right)$

Liao & Whitman (1986)

$C_N = \sqrt{\dfrac{100}{\sigma_o}}$

Skempton (1986)

$C_N = \dfrac{2}{1 + 0.01044 \cdot \sigma_o}$