subject: Vinyl Seawalls [print this page] Author: Ben Kaylor Author: Ben Kaylor
Vinyl sheet piling used for vinyl seawalls, bulkheads, wave breaks, retaining walls and other various geotechnical applications has been around for roughly 20 years. The earliest vinyl sheet pilings were very thin and had a geometric profile that did not provide for much strength. Since the earliest vinyl sheet pilings, profiles have come through a renaissance of improvements including thickness and shape. The vinyl seawalls that you see on the market today are designed to achieve taller wall heights and are therefore made of thick, rigid vinyl that is extruded in a z or box shape that allows for a very strong, structurally sound part.
Just as important as the shape and thickness of the PVC vinyl sheet piling, is to consider the type of plastic to use in the extrusion process. When manufacturing vinyl seawalls it is of utmost importance to utilize the co-extrusion process. Co-extrusion is the preferred way to extrude exterior PVC parts. Whether making vinyl siding, vinyl fencing, window frames, or vinyl seawalls, exterior grade PVC that is co-extruded is the preferred manufacturing process. Co-extrusion is a process that allows plastic pellets or regrinds to be molecularly bonded to a 100% virgin cap stock to make up the exterior of the sheet. Having a 100% weatherable capstock that can be as thick as a credit card ensures two primary functions. First, it ensures that the exterior grade PVC is weatherable and can stand up to the harshest environments. Additionally co-extrusion can guarantee color consistency so that each and every time the part is made you can expect to see the same color. In the co-extrusion process impact modifiers are also added to the formula so that the exterior grade vinyl can be rigid and can withstand the rigors of installation and the longevity of performance in the ground
When vinyl seawalls are manufactured using the mono-extrusion process, regrinds (often classified as misruns, or seconds) often purchased on the open market, are run through a die. UV stabilizers are added in a way that makes it difficult to ensure that the entire product is receiving an adequate amount of chemical. The TiO2 that is used is often added at a very rough rule of thumb of 8 lbs. of TiO2 per 100 lbs. of compound. This way of winging it, although much cheaper to produce than a co-extruded part can often result in a part that chalks, becomes brittle due to UV damage, fades excessively and eventually can fail due to UV degradation, creep failure, and strength loss. Vinyl Seawalls made using the co-extrusion process are more likely to perform as designed irregardless of UV performance.
Once vinyl seawalls are extruded they can generally be cut to any length. The length that the sheet piling is cut at is often a result of how tall a wall height needs to be. For instance, there is generally as much sheet in the ground as is out of the ground. A 16ft. sheet would have approximately 8 foot in the ground and 8 foot exposed. As is the case with any seawall or bulkhead, if poor soils are prevalent, it may be necessary to put more sheet piling in the ground. In poor soils, sheet piling must be driven to greater depths where better soil conditions may exist or where you may be achieve more surface friction in the ground by having more surface area buried.
Another use for vinyl seawalls is to utilize them in an underground cutoff wall application. At many petrochemical plants, industrial plants, land fills, and superfund sites vinyl sheet piling is being used as an underground curtain or cut-off wall. If there is a known or suspected chemical leaching into soil or ground water, vinyl sheet piling can be driven below grade to cut off the movement and seepage of the harmful chemicals. Additionally if the transmissivity numbers need to be reduced even further, the use of a water expanding sealant can be applied to the interlocks. Once this sealant comes into contact wit any type of moisture, it will expand in the interlocks of the vinyl seawalls making it nearly impossible for any leaching of chemicals to occur. This system has proven to be cost effective; the long term benefits of using vinyl seawalls for cutoff wall applications will do nothing but continue to improve and find additional ways to save projects time and money while providing a long-term solution. Visit our website for more information on Vinyl Seawalls.About the Author:
