UFC 4-151-10
10 September 2001
hardened tips into the refusing stratum, drilled sockets, or drilled dowels to
secure the tips of the piles against lateral displacements due to
eccentricities and intentional lateral forces. Develop a minimum lateral
resistance of at least 5 percent of the pile's design axial load. Increase the
effective length factors as described above.
2-1.2.2
Tolerances on Installation. For piles fully, or near fully, embedded in the
ground, the provisions of Unified Facilities Guide Specifications apply. The following
provisions relate to piling installed for elevated platforms where the piles project several
feet above the mudline:
A slope within 4 percent of plumb or the specified batter, as a reasonable
compromise between the design requirements and the practicality of
installation.
In locating the pile head, there is no limit, provided the structure can tolerate
the revised pile spacing. However, consider residual stresses in the piles
due to forcing the pile into the pile cap in evaluating the capacity of the pile.
Do not apply an increase (or additional increase) in allowable stress to
stress-combinations that include these residual stresses.
NOTE: For effective un-braced length, divided by radius of gyration (Kl/r)
between about 40 and 100, these effects can be substantial. But for fully embedded
piles, Kl/r commonly is less than 40 and locked-in stresses can be neglected. Exercise
caution when using driving frames because they prevent lateral movements of the head
of the pile and mask the existence of locked-in stresses. Provide ample edge distances
so that the piles will fit into the cap without excessive force or restraint. Allow for
tolerance in the location of the pile head of at least 1.5 percent of the exposed height up
to a maximum of 152 mm (6 inches).
2-1.2.3
Minimum Spacing. The minimum spacing requirements of piles are as
follows:
Provide for adequate distribution of the load on a pile group to the
supporting soil. Recommend 1 m (36 inch) spacing.
No minimum values are specified other than practical limitations to avoid
piles interfering with or intersecting each other. One technique is to use a
center-to-center spacing equal to 5 percent of the pile length for parallel
piles.
2-1.2.4
Pile Caps in Contact With the Ground. Design piles to carry the entire
superimposed load with no allowance made for the supporting contribution of the material
between the piles.
2-3
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