Inferior geocomposite drainage layers threaten landfill slips

Whether or not due to recessionary pressures on profits for contractors, or inexperienced contractors bidding outside their normal expertise and winning landfill/geo-engineering work, environmental experts ABG are reporting that inappropriate separation layers are increasingly being offered in drainage layer geotextiles.

These inferior materials crush, or simply bend under the normal soil loading and the drainage path between the underside of landfill capping sub-soils, and the low permeability capping layer which these drainage geotextile composites are intended to provide becomes non-existent.

The very real concern is that if these defective materials are accepted for use in the works, slip failures on the restored landfill surfaces will be inevitable during wet weather conditions. Water will build up on the layer between the top of the capping layer and the sub-soil creating a slip plane, and eventual failure.

The remediation costs after such slips, and disruption to use of the land, caused are to be avoided at all cost. Contractors and Designers and Site Engineers accepting geotextile drainage materials which subsequently block when the drainage path void becomes flattened and filled with soil, could also quite possibly be sued for negligence after such slip failures.

And yet, use of such materials is easily avoided by carrying out a simple test which can be carried out in less than 60 seconds on a small sample of any drainage geotextile composite offered. It is done by squeezing in the hand a sample (geomembrane, protection layer and the drainage stone (equivalent) layer) of the material between two resilient rubber pads to imitate the soft pressure exerted by the soil.

Inspection of the extent to which compression of the separation layer can be seen to occur is a good indication of their capability. Low performance of geocomposite drainage layers is due to combinations of drainage core compression and textile intrusion into the drainage core. Some products on offer will compress visibly to the point that the drainage void space can be seen to have been greatly reduced, and some very inferior samples show almost complete loss of open drainage voids.

Other more rigorous tests should also be considered appropriate to the application of these materials, but by use of this simple action alone the worst performing products would be discounted.

Goran Erak, Business Development Director for ABG, Environmental Geosynthetics and producers of the original Pozidrain product is very concerned about the loss of reputation of drainage geo-composites posed to the landfill remediation and restoration industry by the use of inferior products. He gave my company a set of rubber pads to use when we are offered these materials, plus a sample of their Pozidrain product, which shows no such problems.

Goran was also keen to point out that reliance on the supplier’s data on plate compression testing could also bring problems unless the supplier/manufacturer’s test protocol was checked in detail. Test results offered by some suppliers had been found to show compliance for stiff steel plate tests, whereas soft pads would give an entirely different and more accurate reflection of soil conditions in-situ. It is the requirement that standard flow capacity test must be carried out with soft platens, so any use of hard platens is a non standard test.

The closest you can get to a list of the top contractors doing Construction Quality Control (CQC) work on landfill developments (basal development and capping/restoration) is probably the following list.

New Civil eEngineer Magazine, which is the weekly news magazine of the Chartered Institution of Civil Engineers, provides through eMapInform an annual contractor listing and ranking report across all civil engineering construction disciplines.

This years edition provides the following list for “waste” contractors. these are the top twenty waste contractors by turnover. These companies normally also work in building recycling facilities and composting plants.

1. Ascot Environmental
2. J N Bentley
3. Edmund Nuttall
4. Fitzpatrick Contractors
5. Balfour Beatty
6. Norwest Hoist Civil Engineering Division
7. North Midland Construction
8. J Breheny Contractors
9. Fox Owmby
10. Amalgamated Construction Company
11. Dean and Dyball
12. Raymond Brown Construction
13. Alun Griffiths Contractors
14. Forkers
15. UCS Civils
16. Wrenco Contractors
17. Highland Quality Construction
18. Interserve Project Services
19. Barhale Construction
20. Buckingham Croup Contracting

Although the top listed players above, are well known and respected within the waste industry they are not household names outside the waste industry, and the really large national contractors are under-represented with only Balfour Beatty present. This is a very specialist area of work and has the large value contracts have the past been dominated by landfill development and restoration works, with some work also in waste facility construction.

The split of the value of the work will soon reverse with increasing demand for waste treatment and processing facilities rising fast to eventually exceed landfill type projects. This will happen as the largest of the UK’s planned PFI integrated waste management contracts move into the construction phase and the start of their operational contract periods.

The UK government plans to pump a lot of money into this sector, to have the necessary effect on the redirection of waste away from landfills in a big way, over the next few years.

Whether the name Dean and Dyball will be around for very long, or even next year in this list, is unknown as they were taken over by Balfour Beatty in March 2008.
Archive information etc on the top contractors of past years is available at the Landfill Site Top Twenty Contractors.