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DISCUSSION, CONCLUSIONS, AND RECOMMENDATIONS
Discussion
A literature review, users' experience, laboratory tests, and site visits of PVC installations all
suggest that PVC as a material is suitable for sheet piles and has a clear advantage over steel in
lightness, cost, and durability. For the currently available UV-resistant PVC sheet pile materials,
severe exposure to UV produced some discoloration and skin hardening. Except for impact
resistance and creep, much of the apprehension of its degradation in mechanical properties over
time is not well founded. However, the rate of change of both creep and impact resistance are
quantifiable and can be accounted for at the design stage for a given life-cycle estimate. This
would, of course, require a suitable design protocol for the specific PVC grade that has been
selected and applications of an appropriate safety factor. If discoloration by sun exposure is a
factor, then that too needs to be considered in the design. This would ensure that the installation
functions satisfactorily over the designed life.
It became clear during the study that sheet pilings are used for multiple purposes, for
example, seepage reduction, waterfront bulkhead or retaining walls, and protection from waves or
stormwater floods. As discussed in Section 3, steel has a clear superiority over PVC in terms of
strength, stiffness, impact resistance, and many other parameters; however, in many installations,
for the sake of economy, design engineers must consider whether those superior properties are
truly needed for the functional requirements of the installation. Obviously, such considerations
will need a detailed structural analysis of the piling with accurate estimates of the loads (both
quasi-static and dynamic), environment (temperature, humidity, exposures, etc.), and input of the
accurate mechanical properties of the materials under those environments. Commercial software
(e.g. PileBuck, 2003) are available for designing retaining walls or bulkheads. However, design
for the dynamic load as might occur from wave action, storm flood, debris impact, etc. may need
a more sophisticated design analysis using numerical tools. Appendix C gives an example of a
model for numerical analysis, which can be further developed to take into consideration various
loadings to determine the maximum anticipated stress and strain levels.
For designing PVC sheet piling it is necessary to consider the failure criteria that should be
applied to the design. PVC fails only after a very large deformation. As discussed in Section 2,
the tensile modulus of PVC is about one eightieth of steel, so for a given load and shape of a
beam, PVC deflects about 80 times more than the steel. The design must set a limit on the
allowable strain over its life from all sources (creep, temperature, and load) besides the stress.
The issue of vulnerability of vinyl sheet piling to damage from vandalism or fire was
discussed with the field experts (Agostinelli, 2003, Appendix D). These are issues that would
have to be considered in the decision process to use vinyl. Vinyl walls, because of their relatively
low hardness and low melting point, would be much more likely to be damaged from vandalism
and fire than steel or concrete walls. A simple grass or brush fire could severely damage a vinyl
wall and its ability to function as designed. This problem could be reduced by providing a gravel
bed next to the wall, this eliminating grass and the potential for fire. These considerations must be
addressed on projects that have life safety implications.
Satisfactorily addressing all the concerns described above would present vinyl sheet piling as
a great opportunity to save money in materials, installation, and maintenance cost. The Westwego
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