Page 168 - Civil Engineering Formulas

CHAPTER 4
PILES AND

PILING FORMULAS

ALLOWABLE LOADS ON PILES

A dynamic formula extensively used in the United States to determine the
allowable static load on a pile is the Engineering News formula. For piles dri-
ven by a drop hammer, the allowable load is
2WH
P a (4.1)
p 1
For piles driven by a steam hammer, the allowable load is
2WH
P a (4.2)
p 0.1
where P allowable pile load, tons (kg)
a
W weight of hammer, tons (kg)
H height of drop, ft (m)
p penetration of pile per blow, in (mm)
The preceding two equations include a factor of safety of 6.
For a group of piles penetrating a soil stratum of good bearing characteris-
tics and transferring their loads to the soil by point bearing on the ends of the
piles, the total allowable load would be the sum of the individual allowable
loads for each pile. For piles transferring their loads to the soil by skin friction
on the sides of the piles, the total allowable load would be less than the sum on
the individual allowable loads for each pile, because of the interaction of the
shearing stresses and strains caused in the soil by each pile.

LATERALLY LOADED VERTICAL PILES

Vertical-pile resistance to lateral loads is a function of both the flexural stiff-
ness of the shaft, the stiffness of the bearing soil in the upper 4 to 6D length of
shaft, where D pile diameter and the degree of pile-head fixity.

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