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Schmertmann Method (CPT)

This solution for cohesionless soils use a Schmertmann 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.

where:

Rd

-

bearing capacity of foundation soil

Kq, Kγ

-

reduction factors

γ

-

unit weight of the soil in the footing bottom

bef

-

effective footing width

Nq, Nγ

-

bearing capacity factors

d

-

depth of footing bottom

The formula is derived for imperial units [tsf, tcf, ft] - the program calculates automatically in the units used in the program.

where:

qc1

-

average value of cone penetration resistance measured at depths from footing base to 0.5*bef bellow the footing base

qc2

-

average value of cone penetration resistance measured from the depth 0.5*bef bellow the footing base to 1.5*bef bellow the footing base

where:

iq, iγ

-

load inclination factors

sq, sγ

-

footing shape factors

dq

-

footing depth factor

bq, bγ

-

footing bottom inclination factor

gq, gγ

-

ground inclination factor

Inclination factors iq and iγ are determined as follows:

where:

H

-

horizontal component of resultant load

V

-

vertical component of resultant load

lef

-

effective footing length

θ

-

angle between horizontal component of resultant load H and longer axis of footing (in the direction lef)

determination of angle θ

This method should not be used for ratio H/V > 0.4.

Footing shape factors sq and sγ are determined as follows:

where:

φ

-

angle of internal friction in the footing bottom

Footing depth factor dq is determined as follows:

Footing bottom inclination factor bq and bγ are determined as follows:

where:

η

-

angle of footing bottom inclination

Ground inclination factor gq and gγ are determined as follows:

where:

β

-

angle of ground inclination

Literature:

FHWA-SA-91-043: THE CONE PENETROMETER TEST

Bridge Engineering Handbook (Wai-Fah Chen, Lian Duan, 1999)