Plastic is very sustainable, but it has a lower E-modulus than wood and steel. Softwood offers much strength and is cheap, but it rots away when it is applied at water surface. However, immersed softwood has a very long life span.

Therefore Profextru developed a sheet piling system which combines the characteristics of plastic with the benefits of softwood. The plastic screen is applied at the height where water is present up to ground level (and depending on the type of earth up to approx. 50 cm in the bottom), while the wooden pole is installed under the lowest water level, where it has to provide strength and the wood cannot rot.

What does this really mean?

When an engineer designs a retaining wall, the sheet pile is selected that will have the properties required to support the predicted loads, and it will have a length stated that provides sufficient penetration to gain reaction to employ these properties.  If the wrong pile is selected, the wall will bend over regardless of the penetration obtained, likewise if too short a length is used or not driven to depth then the wall can fail, although the sheet pile has not - i.e the wall would lean forward.

The sheet pile would also be selected to ensure that not only does it have sufficient strength for the application, it must have sufficient strength to be driven to the design depth.

If the sheet pile does not have sufficient driving strength, the design depth will not be achieved, the pile will be damaged by the hammer and ultimately the retaining wall would fail.

A sheet pile must therefore be selected that meets both these criteria, and therefore it is not unusual for the sheet pile to be more heavy duty that really needed.  So applications with predicted difficult driving regardless of how low the retaining loads are, would still need a much heavier expensive sheet that the application really warrants.

This is where ProLock and MultiLock really break the mould.  For applications where the pile specifications exceed the retaining load requirements, these products can be use in conjunction with untreated or treated timber piles.  The design is based upon the strength of the plastic pile, but this system only requries around 50cm of penetration, as the timbers, subequently driven to conventional depths are the anchoring elements that provide the reaction force needed to stop the wall leaning.  

Timber piles above ground level, will over time rot away, but that beneath the ground - away from oxygen - will last very long periods of time; even in the absence of timber treatments.

In otherwords, ProLock and MultIlock provide a means of using the interlocking sheet piles solely where they are really needed - this keeps your costs down.  Further a measure of conservatism is provided in the short term, as the bending moments are much higher than that calculated.

The flexibility of the product goes much further, if high bending moments are required for longer term applications then treated timber or steel tubes can be used with design lifes providing that extension.

Research and Development – A market lead approach.

After an extensive market research, in February 2002 Profextru started with the development of the plastic sheet piling system  ProLock® . In September 2003, the Overijssel Province commissioned Profextru to install the first 80 metre ProLock® sheet piling along the bank of the canal Steenwijk-Ossenzijl. The Overijssel Province was searching for a sustainable alternative for the protection of the 100 kilometre waterway which it is managing and maintaining.

The pilot with the  ProLock®  sheet piling system was a first step for the province in the transition to sustainable and innovative bank protection. Prolock was nominated by the Overijssel Province for the Overijssel Innovation Award 2004.

Reduction of the Energy Burden

In order to investigate the possibilities of a further reduction in environmental burden in the lifecycle of the sheet piling, Profextru has conducted an Energy Innovation Scan (EIS) in cooperation with engineering consultancy Energy Experts Int. B.V. and SenterNovem. On the basis of the ideas that were developed in this scan, Profextru has developed a lighter version of the plastic sheet piling. This sheet piling (MultiLock®) has a thinner wall and can therefore be applied for banks that only require light weight constructions up to 1.5 metre.

When considering the energy burden of a specific product, it is important to consider the energy spent actually installing the product, rather than simply compare initial transportation variations.  In terms of speed of installation, driving wider sheets reduces the handling time, enablng site to run more efficiently.  The increased rigidity of the section reduces hammer inefficiency, that occurs with more flexible options.

Clearly using this system you combine the best of recycling (pile) with sustainability (post).  Further, the overall amount of pile used on similar application is reduced dramatically.

Now, all UK end users can benefit from this technology, brought to you by APE.

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