Frequently Asked Questions
Q: How can NASSPA help me?
NASSPA can assist the owner, engineer and contractor compare the cost of using steel sheet piling versus other retaining wall alternatives. It is generally accepted that for temporary applications steel sheet piling is the best alternative. However, as our comparison studies demonstrate steel sheet piling is often the most cost effective and efficient retaining wall system for permanent applications as well.
NASSPA also publishes the NASSPA - Best Practice Sheet Piling Installation Guide.
Q: What is steel sheet piling?
Sheet pile is a hot-rolled structural shape with interlocks on the flange tips. The interlocks permit individual sections to be connected in order to form a continuous steel wall which is earth tight and virtually water resistant.
Q: What are the advantages of hot-rolled sheet piling?
Hot rolled steel sheet piling is an engineered product meeting ASTM specifications. These specifications, and the producer’s QC program, provide a quality product which is both ductile and durable. In addition, steel’s strength will not change over the years, i.e., the material produced today will have the same properties during the entire life of the structure when properly maintained.
The hot-rolled process enables the producer to engineer profiles by placing metal where it will be most efficient in maximizing section properties. The process also permits the design and production of interlocks with structural integrity.
Additional advantages of hot rolled steel sheet piling are:
- Steel sheet piling is usually the lowest cost retaining wall alternative, even in permanent applications (refer to the NASSPA Permanent Retaining Wall Comparison Study).
- Steel sheet piling is a top choice in water retention systems, particularly with cofferdams, port & harbors, locks & dams and flood protection. It is also excellent for retaining soils that are below the water table.
- Sheet piling will maintain it's shape during installation.
- Driven sheet piles displace soil rather than remove it. Therefore: the support of adjacent structures is not compromised due to soil movement.
- Steel sheet piling is environmentally friendly. In addition to being produced with recycled steel the sheet piles are installed in manner that produces no spoils. Therefore there is no risk of exposure and disposal of potentially hazardous or contaminated materials.
- Retention walls using steel sheet piling have excellent stability, especially in areas with earthquakes. Hot rolled sheet piling is also useful in very soft clay soils that have little or no strength.
- Steel sheet piling has a long, successful history and awareness in the industry is relatively high.
Q: Why would I use steel sheet piling?
There are numerous reasons to use sheet piling. Because it is readily available and transportable it is in many cases a fast and economical solution to an owner’s need for a durable, long lasting wall system. For permanent construction, some uses include retaining walls, bulkheads, bridge abutments, graving docks, cut-off walls, mooring dolphins and pier protection cells. Temporary structures would include cofferdams used to construct building excavations, trenches, piers for bridges, and lock & dams on our inland river system.
Q: Who can I contact for further design or construction guidance on my project or for specific sheet piling information?
Please refer to the following manufacture web sites:
Q: What is a cofferdam?
A cofferdam is a temporary structure (could be several weeks or several years) built to keep earth and/or water out of an area in order that a permanent structure may be constructed within its boundaries.
Q: Why are there so many different sheet piling sections?
Different producers have different profiles and different interlock systems. All of the available sections, however, can be broken into two types based on end use.
The most common end use requires sections which resist bending moment. This requirement for beam strength, or section modulus, is provided by "Z-profiles" and "U-profiles". The second end use is for sections which require interlock strength. This need for interlock strength is created when sheeting is installed as a circular cell and backfilled with granular material. The confined fill pushes outward and thereby creates hoop tension in the cell wall. The "flat sheet piling" sections transmit the hoop tension through their interlocks.
Q: How long will sheet piling last?
With proper engineering and maintenance you can expect steel sheet piling walls to give you a very long service life. There are examples of sheet piling structures installed prior to 1920 that are still in service and performing well.
Q: Is sheet piling a "Green Product"?
Hot-rolled sheet piling is very "green".
The producers of this product obtain their steel from the electric arc furnace process which utilizes selected recycled steel scrap, producing steel to exacting specifications. The scrap content of the finished steel is in the range of 90 to 95 per cent or more.
Q: Will my sheet piling wall be aesthetic?
It can be! The first step in creating an attractive wall is to contract with an experienced pile driver who uses proper procedures and takes the time to properly set and drive the sheet piling wall. The next step is to pay attention to details. This can be accomplished by capping the wall with an architecturally pleasing concrete cap, placing the wale behind the wall, and applying a durable attractive coating system. In some cases the use of weathering steel (ASTM A588) might be considered in lieu of a coating system.
Q: What is the availability of sheet piling?
In most cases sheet piling is readily available either from mill rollings or stock. For the availability of particular sections and specifications contact the member companies of NASSPA. For them to efficiently handle your inquiry you should have available the required sections, lengths, approximate quantities, steel specifications, and your desired delivery schedule.
Q: How long is sheet piling rolled?
Typical sheet piling lengths required for projects range from 15 to 70 feet. Some projects require much longer lengths, perhaps in excess of 90 feet. Contact member companies for availability of this longer length material.
Q: Sheet piling is produced to what specifications?
Hot-rolled sheet piling is available to several ASTM specifications. ASTM A328 with a yield point of 39 ksi is the original ASTM sheet piling specification. Most sheet piling is currently produced to ASTM A572-Grade 50 and it is also available in Grades 60 and 65. For atmospheric weathering applications it is available to ASTM A588. For increased corrosion resistance in the splash/tidal zone in a marine environment it is available to ASTM A690. Both A588 and A690 have yield points of 50 ksi. With the exception of A572-Grade 50, you should contact the member companies for availability.
Q: What is the allowable design stresses for sheet piling?
Accepted engineering practice is to design to 0.65 Fy in longitudinal bending. This would apply to "Z-profiles" and "U-profiles". Based on research in recent years it is becoming more apparent that in addition to longitudinal stresses, transverse stresses should also be considered. When designing cellular structures, accepted engineering practice is to limit the interlock load on the "flat sheet piling" sections to one-half the minimum ultimate interlock strength.
Q: Are interlocks waterproof?
The interlocks of hot-rolled sheet piling are fairly water tight, but not waterproof. Sheet piling is used as cut-off walls under hydraulic structures such as locks & dams. It is also utilized for cut-off walls at hazardous waste sites. There are products available to seal the interlock and reduce or eliminate seepage through the interlocks. Contact the member companies for additional information on interlocks and sealant products.
Q: Can I place vertical loads on sheet piling?
Yes! There is the tendency to view sheet piling as a structural system used only to carry lateral loading from soil and water pressures. In fact, there is no reason that sheet piling can’t be designed to carry both lateral and vertical loads. It is of course necessary for the engineer to insure, as with H or pipe piles, that the underlying soils can support the vertical loads.
Q: What should I do if I need a bulkhead to develop my water front property?
Step number one would be to retain a registered professional engineer who is experienced in steel sheet piling design. The engineer would contract with a geotechnical firm and obtain soil borings. With the soil profile and properties known your engineer can than design and specify the requirements for your bulkhead. The next step would be to solicit prices from contractors experienced in steel sheet piling installation.
Q: Who installs sheet piling structures?
In most areas you will find foundation contractors who specialize in pile foundations, including steel sheet piling installation. It is very important that the contractor retained to install your wall be experienced in using sheet piling.
Q: How is sheet piling installed?
Sheet piling is normally installed with impact or vibratory hammers. Impact hammers types include air, hydraulic, or diesel. Vibratory hammers clamp onto the top of the sheet piling sections and through a combination of vibration and hammer weight push the piling into the soil. The type of hammer used will depend upon site conditions and available types of hammers.
Q: Will the piling installation create noise or vibration problems?
At most sites there will be no concerns. However, when installing sheet piling in residential or urban areas there may be noise complaints by nearby residents. These concerns can be minimized by limiting the hours of pile driving. There are also installation tools available which press the sheeting into the ground, thereby eliminating both impact noise and vibrations.
Q: Will the sheet piling installation create ground heave?
Steel sheet piling, as compared to a closed ended pipe pile, has very little cross-sectional area. It is, therefore, a non-displacement pile which does not cause soil heave or cause additional lateral pressures on nearby existing walls.
Q: Who is eligible to join NASSPA ?
NASSPA membership is open to producers of hot rolled steel sheet piling with a presence in North America. If you would like to apply for a NASSPA membership please email us for further details.