The most common methods of installing steel sheet pile walls include vibrating, impact driving, hydraulic pushing, jetting, and trenching. The type of sheet piling often governs the method of installation. Contract specifications at times may prohibit the installation of sheet piling until the contractor’s methods and equipment are approved.
The types of pile driving hammers used for the installation of steel sheet piles include vibratory pile hammers, diesel, air-steam, hydraulic impact pile hammers, hydraulic sheet pile “pushing rigs”, a high pressure jet w/jet pump or a simple drop hammer. Vibratory Pile hammers are widely used because they usually can drive sheet piles faster, do not damage the top of the pile, and can easily extract piling when necessary. Provided of course the soils are granular, a vibratory hammer can drive steel sheet piling far faster than impact hammers. When a hard driving condition is encountered, there have been situations whereby a vibratory hammer can cause the interlocks to literally emit flames and melt. If the penetration rate is 1 foot or less per minute, it might be best to reconsider the use of a vibratory hammer as an impact hammer may be more effective.
With the innovations of Hydraulic Excavator Mounted Vibratory Pile Driver/Extractors with the ability to grab Sheet Piling from not only the Top of the Sheet but from the Side via a “Side Grip” Clamp Assembly the installation of Sheeting has become a far less cumbersome act. These units combined with the advent of numerous “smaller” compact, free hanging vibros from various manufacturers a contractor now has numerous choices when it comes to the installation of virtually any type of Sheet Piling; be it, Steel, Composite, Vinyl, Timber, Concrete or Aluminum.
The selection of the type or size of the hammer is based on the soil in which the pile is driven. The designer should be aware of the soil stiffness and possibility of obstructions which could cause failure or weakening of the sheet pile during driving. When installing lighter weight aluminum, vinyl sheet piling or composite sheet piling obviously the aforementioned does not apply. These lighter weight sheet piling sections have become increasing popular for residential, municipal bulkheads and retaining walls and more. Some of the more effective hammers utilized for these installations are small air hammers as well as excavator mounted vibratory pile driver/extractors.
To ensure that piles are placed and driven to the correct alignment, a guide structure or templates should be used. Many contractors recommend at least two templates be used in driving each pile or pair of sheet piles. Templates should also be used to obtain the proper plumbness of the sheet pile wall. Sheet pilings properly placed and driven generally are interlocked throughout their length.
Tips for installing Sheet piles –
- Always set-up a template system
- Rule of thumb: When driving long, heavy sections of Steel Sheet Piling, Crane Boom length should be twice that of the sheets one is driving
- Drive the Sheets with the “male” interlock leading in order to avoid annoying soil plugs
- If the “female” interlock must lead, place a bolt or other object at the bottom to avoid debris filling the female end
- A panel of sheet piling should be threaded and set prior to driving any sheets to grade
- Align and plumb the first two sheets and drive carefully and accurately
- Drive sheets in pairs when possible placing the hammer in the center of the pair
- Some contractors recommend not driving a sheet more than 1/3 its length before driving the adjacent pile
- Letting the sheets “free-fall” and drop in order to aid in penetration will generally cause the sheets to fall “out of plumb”
- Sheet piling should be threaded and allowed to “slide” until it stops by its own weight. A hairpin can be used to assist penetration at this point.
- When walls are being constructed, sheet piling should be checked periodically (at a minimum, every 5th single sheet or 3rd double) as to ensure the wall is plumb.
- Never rush the Pile Foreman.