1.3*G*

=

(9-9)

(b) Capacity parameters.

2.

The lateral capacity of a footing

1. In the absence of moment loading, the

should be assumed to be attained when the

vertical load capacity of a rectangular footing of

displacement, considering both base traction and

width *B *and length *L *is

passive pressure stiffnesses, reaches 2.0 percent of the

thickness of the footing. Upper and lower bounds of

(9-10)

twice and one-half of this value, respectively, also

apply.

For rigid footings subject to moment and vertical

load, contact stresses become concentrated at footing

(3) Pile Foundations.

edges, particularly as uplift occurs.

The ultimate

moment capacity, *M*c, is dependent upon the ratio of

(a)

General.

Pile foundations, in the

the vertical load stress, *q*, to the vertical stress

context of this paragraph, refer to those foundation

capacity, *q*c.

Assuming that contact stresses are

systems that are composed of a pile cap and

proportional to vertical displacement and remain

associated driven or cast-in-place piles, which

elastic up to the vertical stress capacity, *q*c, it can be

together form a pile group. A single pile group may

shown that uplift will occur prior to plastic yielding

support a load-bearing column, or a linear sequence

of the soil when *q/q*c is less than 0.5.

If *q/q*c is

of pile groups may support a shear wall. Generally,

greater than 0.5, then the soil at the toe will yield

individual piles in a group could be expected to be

prior to uplift. This is illustrated in Figure 9-6. In

less than 2 feet (0.6m) in diameter. The stiffness

general, the moment capacity of a rectangular

characteristics of single large-diameter piles or

footing may be expressed as:

drilled shafts are described in Paragraph 9-2c(4).

(b) Stiffness parameters. For the purpose

1 -

(9-11)

2 * q*c

of simplified analyses, the uncoupled spring model

as shown in Figure 9-1b may be used where the

footing in the figure represents the pile cap. In the

where:

case of the vertical and rocking springs, it can be

assumed that the contribution of the pile cap is

relatively small compared to the contribution of the

piles. In general, mobilization of passive pressures

by either the pile

9 - 10

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