Setting & Driven Tips for Sheet Piling

Improper setting and driving practices result in problems and costs that far out-weigh the initial expense of applying correct methods from the start. Although setting and driving techniques may vary according to the site conditions and/or the contractor's level of experience, several basic principles can be applied.

USE AN ADEQUATE TEMPLATE
The utilization of an adequate steel template will facilitate the installation process and result in a superior end product. The purpose of the template is to both properly align the sheet piling during the setting process as well as to keep the sheet piling in alignment during the driving phase. Since a typical sheet weighs one ton or more, the template obviously needs to be of rugged construction. Also, bear in mind that the template will normally be used and moved multiple times at the job site; this is another reason for a well-designed and solidly constructed template.

MARK THE TEMPLATE
To maintain the published laying width of the sheeting, it is very important to mark the template for each sheet, or pair of sheet piling. By following this procedure, the contractor can observe if the line being set is gaining or losing wall length. This procedure is important for installations such as: cofferdams, which must be closed; or anchored bulkheads, where tie-rod locations are critical. Depending upon the length of the sheet piling, the template might be one, or two - or more - tiers high. In order to maintain a plumb wall when driving sheet piling in excess of 50 feet (15 meters), a two-tier template is always suggested as a minimum.

SET A PANEL OF PILING
The length of the panel will vary depending upon site conditions, the contractor's experience, and other factors. In general, you might expect a panel length of 25 to 45 feet (8 to 14 meters). As each sheet, or pair of sheet piling, is set, the sheet piling may be rotated as necessary in the interlock (as shown below) in order to match the marks on the template.

SET AND DRIVE WITH THE BALL-END LEADING
When the piles are set and driven with socket-end leading, the socket becomes clogged with soil and the ball must force the soil out of the opening. In some types of soils, such as very fine and dense sand, the resistance of the soil in the socket can be such that driving becomes impossible without damaging the sheet piling. Under such conditions - particularly with a vibratory hammer - it is possible to actually weld interlocks together.

If for some reason, the sheet piling must be driven with the socket-end leading, such is the case when using an interlock sealant like WADIT, then place a bolt or some object in the socket at the bottom end to at least minimize clogging.

KEEP THE SHEET PILING PLUMB
It's of utmost importance that, as each pair is set, the sheet piling are plumb and secured before the next pair is set. Once the wall is allowed to get out of vertical alignment, the mistake will only get worse; and at some point the contractor will simply have to quit, extract the out of plumb sheet piling, and start over. The most important tool of the pile driving crew is a long level: 3 feet (1 meter) or more in length.

DRIVE THE PANEL OF SHEET PILING IN STAGES
Piles driven full length in one operation are more prone to deflect and go off line. This is particularly true when the soil contains debris, boulders, or other obstructions. Subsequent piles are guided by the deflected section; and within a short length of wall, pile driving comes to a halt. The sheeting must then be pulled, and the wall has to be restarted. The preferred process to minimize, if not eliminate, this problem is to first set a panel of sheet piling and then work the panel down as a unit. This is accomplished by driving the sheet piling (singles or paired), in increments using a defined sequence. The magnitude of the increment will be determined by the soil conditions. In general, the harder the driving, the less the driving increment - perhaps 6 feet (2 meters) in easy driving, versus 3 feet (1 meter), or less, in denser soil. Panel driving allows the piles to be guided by previously driven piles, and it lessens the possibility of driving the piles out of interlock. During this phase, as during the setting process, it's important that constant attention be paid to maintaining a plumb wall. Any deviations from being plumb that are detected should be quickly corrected before things get out of hand.

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