Developments in Earthquake Geotechnics by Susumu Iai

Author:Susumu Iai
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

9.3.1 Bearing Strength Surface

The following equation gives the standard estimation of the bearing strength of a shallow foundation under vertical load, horizontal shear, and moment:

(9.4)

where:λcs, λqs, and λγs are shape factors;

λcd, λqd, and λγq are depth factors;

λci, λqi and λγi are inclined load factors;

and c, q, qu, B, Nc, Nq and Nγ have their usual meanings.

A set of shape, depth, and inclined load factors for use in Eq. 9.4 are given by Pender (2017). Equation 9.4 provides a way of estimating what combinations of vertical load, horizontal shear, and moment mobilise all the available shear strength of the soil underlying and surrounding a shallow foundation. The locus of these combinations forms a three dimensional Bearing Strength Surface (BSS). There are two surfaces to consider, generated using appropriate rearrangements of Eq. 9.4, one for the undrained case and another for the drained case.

A convenient way of presenting the surfaces is to use axes defined in terms of dimensionless parameters, one for vertical load, another for horizontal shear, and a third for moment applied to the foundation. The normalising parameter is the ultimate bearing strength of the foundation subject to vertical load only; a possible suite of dimensionless parameters is then:

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