241 First, the results of the structural assessment (Step 6) should be used to determine whether a change in the pile preliminary structural design (diameter,
reinforcement, etc) is needed. If any element affecting the pile lateral response is modified, the analyses should restart from Step 2 based on the new proposed structural design. If the structural assessment
is considered adequate, and no modification to the pile structural section is needed, then a check on the pile length should be performed. This can be verified by analyzing the top pile lateral deflection for
different trial pile lengths, and constructing a plot relating pile top lateral deflection versus total pile length. This plot can automatically be generated by available programs such as LPILE. For the example being analyzed, Figure B shows such relationship. Note that Service loads should be used to generate this graph since it is built by calculating a displacement.
Figure B Pile top lateral deflection vs. pile length. 0 1
2 3
4 5
6 0
5 10 15 20 25 30 35 40 45
Pile Top Lateral Deflection (in
)
Pile Length (ft)
Pile Lateral Deflection vs Pile Length (Service Loads)
The plot shown in Figure B shows that for this example the pile top lateral deflection is relatively constant once the pile length exceeds about 20 feet. From this perspective, a shorter pile could be selected and reanalyzed. Other considerations such as settlement
of the soft clay layer, pile axial resistance, and other owner constraints which are not discussed in this example may still require the pile to extend below the bottom of the soft clay layer (Layer 3). It is important to consider that a reduction in the pile length will have an impact on the pile bending moment and shear. A similar plot to the one shown in Figure B could be constructed relating pile length to maximum bending moment and maximum shear Strength Loads shall be used for this plot as bending moment
and shear are being evaluated, as shown in Figure B. Nevertheless, if a reduced
pile length is selected, the analyses should restart from Step 2 utilizing the reduced pile length and any other structural modification to the pile structural section as selected by the structural engineer. This additional process is not presented in this example, but could be carried out to optimize the pile design.
