Modification of Teraghi and Peak Correlation by Peak, Hanson and Thornburn

Peck, Hanson and Thornburn (1974) | Modification of Teraghi and Peak Correlation by Peak, Hanson and Thornburn

Peck, Hanson and Thornburn (1974) have modified the original Terzaghi and Peck (1948) recommendations and presented charts as shown in Fig.1 to obtain allowable bearing pressure to give a settlement of 25 mm for a footing of known width, B with its base at a depth, D_f resting on a granular deposit in which N (corrected SPT) values are measured.

Procedure | Modification of Teraghi and Peak Correlation by Peak, Hanson and Thornburn

• N (corrected SPT) value  should be corrected with respect to dilitancy and overburden.
• Average of the corrected value is considered.
• q_a is obtained from the graph of (D_f/B) verses N (corrected SPT) value.
• If the water table is not deep the Correction is applied on the obtained allowable soil pressure (q_a) by a correction factor of R_W = 0.5 + 0.5 D_W/(D+B

Where, D_W = Depth of water table measured from the ground surface. D_w is equal to 1 if the water table is at great depth. If the water table is in between the ground surface and sum of depth and width of foundation then D_w lies between 0.5 to l.

q_a(corrected) = q_a(graph) × R_W

The value of bearing capacity factors can be found out from the approximate correlation between the N value and the angle of shearing resistance proposed by Peck, Hanson and Thornburn (1974) as shown in Fig.2 below.

Peck, Hanson and Thornburn (1974 have also given an equation for net safe bearing capacity of spread footing to give a permissible settlement s and a differential settlement of 3/4th of s. The equation is:

q_ns = 0.042 R_WN_s   ———- (1)

Where, N = Average SPT value corrected  for dilatancy and overburden pressure

s = Permissible settlement, mm

R_W = Water table correction factor