Skempton Method (CPT)
This solution for cohesive soils use a Skempton theory, where the bearing capacity of foundation soil is given by a formula:
It is recommended to use a safety factor FS = 3 when calculating the bearing capacity using this method.
bearing capacity of foundation soil
load inclination factor
Skempton bearing capacity factor
undrained shear strength
unit weight of the soil in the footing bottom
depth of the footing bottom
The formula is derived for imperial units [tsf, tcf, ft] - the program calculates automatically in the units used in the program.
horizontal component of resultant load
vertical component of resultant load
This method should not be used for ratio H/V > 0,4.
Skempton bearing capacity factor Nc depends on the ratio of effective width bef and effective length lef and on the ratio of the footing bottom depth d and effective width bef.
Determination of Nc factor (From Peck, Hanson a Thornburn, 1974)
Undrained shear strength Su is determined as follows:
average value of cone penetration resistance
average value of vertical stress measured at depths from footing base to 1,5.bef below the footing base
Cone factor (range <10;20>)
average value of cone penetration resistance measured at depths from footing base to 0,5.bef below the footing base
average value of cone penetration resistance measured from the depth 0,5.bef below the footing base to 1,5.bef below the footing base
The influence of inclined terrain and inclined footing bottom is considered in the same way as in the Schmertmann method.
FHWA-SA-91-043: THE CONE PENETROMETER TEST
Bridge Engineering Handbook (Wai-Fah Chen, Lian Duan, 1999)