may stick out above the ground level (Fig. 6d) and the water level may rise against the sheet pile
wall. In these applications the integrity of the wall should be adequate to resist the hydraulic load
and the storm wave impacts. Most retaining walls and flood walls have anchor bolts to stabilize
the wall from the excessive backpressure of the ground. Engineering design guidance documents
are usually available from the suppliers of the sheet piles for use in designing the sheet pile walls
and their driving methods.
General guidance
The U.S. Army Corps of Engineers Engineering Manual, EM 1110-2-2504 of 1994, gives the
guidelines for sheet piling installation with recommendation for proper coordination among
hydraulic, geotechnical, and structural engineers. Final decisions are usually taken after close
coordination between design engineers and local interests for alignment and construction.
Geotechnical considerations are paramount in determining the driving conditions and stability.
Structural considerations will lead to the decision on the wall type (cantilever vs. anchored type),
materials (heavy-gauge steel, light gauge steel, wood, concrete, PVC, or composite). The designer
must consider the possibility of material deterioration and its effect on the structural integrity of
the system.
Basic engineering design considerations
Sheet piles basically work as cantilever beams. For a given load condition, the stresses and
deflections in beams are primarily controlled by two basic parameters: E, the modulus of
elasticity of the material, and I, the moment of inertia. While E is the fundamental property of the
material, I depends on the thickness and section profile of the beam. The corrugation provided by
the `Z' shape of the common sheet piles simply enhances the value of I. A cursory look at the
heavier-duty sheet piles of any of the manufacturers would show higher section depths and
thicker gages. The key design equation for limiting beam deflection takes the form
δ = f(P)/(EI)
which shows that the deflection δ depends on the product EI, which is called flexural stiffness.
The higher the value of EI, the lower will be the deflection. As we discussed before, because the
value of E for steel is so high (i.e. 30 106 psi, as opposed to 0.38 106 psi for PVC), for the
same section profile (i.e. the same moment of inertia), the deflection of the PVC sheet pile would
be 30/0.38, or approximately 80, times more than steel.
The work performed by the ERDC Construction Engineering Research Laboratory,
Champaign, IL, (Lampo et al., 1998) under the Construction Productivity Advancement Program
(CPAR) has defined three classes of commercial sheet piles:
Minimum EI = 2.48 105 kip-in2/ft
Light duty:
Medium duty: Minimum EI = 1.0 106 kip-in2/ft
Minimum EI = 5.5 106 kip-in2/ft.
Heavy duty:
The values of moment of inertia, I, of the heavy-duty PVC sheet piles available commercially
were observed to be around 90 in4/ft. For new installations of PVC sheet piles, E = 375,000 psi
and I = 90 in4/ft, so EI is 3.38 105 kip-in2/ft, which definitely meets the light-duty requirement
but not the heavy- or medium-duty requirement as per the CPAR classification above.
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