28 July 2005
These loads are applied at and near the water level and may be significant where
large size piles are used in high-current waters. An estimate of current and wave
forces can be made using the UFC 4-150-06.
Sloping Fill Loads.
These loads are transmitted along the shaft of the piles by the lateral movement of
the soil surrounding the piles beneath the structure, such as may occur along a
sloping shoreline at marginal wharves, as shown in Figure 2-9. The maximum
moments in the piles for this category of loadings are determined by structural
analysis and the methods outlined in UFC 3-220-01N after the conditions of pile
support in the pile cap and the soil have been established and the effective length of
pile has been determined.
a. Piles of relieving platform types of solid wharves, shown on Figure 2-10,
may be subjected to lateral earth loads if the stability of the slope beneath the
platform is minimal and soil creep occurs. In such cases, stabilizing
measures should be introduced, prior to installation of piles, to prevent
movement of the soil along the slope. Among the stabilizing measures that
may be used are surcharging (preloading), installation of sand drains or soil
compaction piles, or replacement of unstable materials. If the piles
supporting the structure are used to increase slope stability, or if time-
dependent stabilizing measures are introduced after the piles are in place,
calculate the resistance to soil movement provided by the piles and the piles
checked for the bending moments induced by the calculated lateral earth
loads, in addition to the increased loading caused by the downdrag of the
b. The pile resistance to soil movement may be obtained from a stability
analysis by determining the additional resistance, provided by the piles, which
will provide a factor of safety that corresponds to zero soil movement. The
minimum factor of safety required for this tape of analysis varies and should
be selected after evaluating the soil conditions, which exist at the site. The
embedment length of piles needed for developing the required lateral
resistance may be determined in accordance with the criteria given in UFC 3-
Pile Driving Loads.
Piles are subjected to high compressive and tensile stresses during driving and
should be proportioned to resist these in addition to the service loads. Where
prolonged driving in alternately soft and hard layers of soil or driving through stiff
"quaky" clays is anticipated, very high tensile stresses are set up and will require a
higher level of prestress (1000 psi [6894.8 kPa] or more) in prestressed concrete
piles. Give attention to controlling driving stresses by specifying frequent cushion
replacement, and by requiring use of hammers capable of adjusting driving energy.