Introduction. Geomembrane lining systems are used in a variety of different applications. Landfill Lining Landfill Capping Salt Piles Lagoons / Ponds

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2 Contents 1. Introduction/Overview 2. Traditional Methods of Anchoring Geomembrane Liners 3. What can go wrong? 4. Net Down 5. Theory and how Net Down works 6. Installation Details 7. Technical Information 8. Cost Benefit 9. Risks 10. Conclusion

3 Introduction Geomembrane lining systems are used in a variety of different applications Landfill Lining Landfill Capping Salt Piles Lagoons / Ponds

4 Introduction cont. Exposed liners (whether permanent or temporary) can be extremely susceptible to loadings generated by wind: This damage can be costly to repair, disruptive to site operations, and potentially a hazard to health and safety of personnel and property.

5 So What is the Challenge? A major factor is how to deploy the plastic membranes and geotextiles, in the knowledge that they will not end up displaced or damaged as a result of wind damage. The waste management industry has used a number of approaches to the problem of wind loading on plastic membranes/geotextiles on landfill sites including; - placement of sandbags; - placement of tyres; - installation of soil windrows; - installing ground anchors; and

6 Traditional Methods of Anchoring Geomembrane Liners Sandbags Tyres Soil Fingers Ground Anchors

7 So What Can go Wrong? Wind loading is created from 2 main effects: Cross Wind Wind Uplift or Negative Pressure Cross wind pushes air trapped under the liner until it creates a larger bubble. This bubble then acts as a sail catching more wind that creates a tensile force which can then rip/tear the liner..and this is what happened in this case

8 Theory of Wind Uplift Wind blowing over a land form where the geometry expands (such as a landfill), will generate a recirculation pattern, as shown below: This causes the recirculating air to be sucked back into the main flow at the top of the slope creating negative pressure (or uplift of the liner).

9 Build Up of Air/Gas under Geomembrane Trapped air / landfill gas can be seen ballooning the liner at the top of the slope.

10 Theory of Wind Uplift So what we need is something that can either withstand this force or cancel it out. Traditional methods of anchoring liners withstand this force through a downward force to pin/hold down the liner. But this can be unpredictable, time consuming and expensive.

11 Net Down How It Works Net Down acts as a diffuse layer between the wind and the geomembrane liner. The magnitude and location of the negative pressures created by recirculating flows can vary due to the fluctuation of the air velocity (turbulence). This effect is also scalable (i.e. the effect is proportionate to the size of the site that creates the condition e.g. height of the slope). It relies upon the law of the Conservation of Mass and Momentum Imagine a sealed box of air and you try to draw the air out of a hole As you draw out the air, the external pressure exceeds the internal pressure and the box will want to collapse. If you now add an opening in the other side of the box, air will rush in to replace the air you are drawing out and reduce/cancel the pressure difference.

12 Net Down How It Works Net Down behaves in a similar manner. During a period of negative pressure the air is drawn up from the surface of the liner causing it to want to lift. Net Down allows the air trapped between itself and the geomembrane to feed air into this zone of negative pressure. This air is replaced by air which is drawn back into the gap which generates an opposite downward force. Net Down Geomembrane Liner Upward Force/Air Downward Force/Air

13 Net Down Net Down replaces traditional anchor systems. It is a polyethylene mat that is deployed directly over the geomembrane. It directly blocks UV light reaching the geomembrane by 47% - thus allowing a thinner geomembrane to be used in addition to being UV resistant itself. Panels can be shaped and cut on site to suit the desired pattern of the site.

14 Net Down - Installation Panels are pre-fabricated off site and are typically 20m wide and up to 100m long. Panels are stitched together on site to create a continuous panel. A panel plan can be developed to ascertain dimensions and number of different panels to be fabricated.

15 Net Down - Installation Net Down must be anchored at the perimeter of the installation anchor trenches/bunds are typically between 0.5-1m 2 in section, depending on the size and geometry of the site.

16 Cost Benefit Method Cost /m 2 Tyres & Rope Sandbags & Rope Soil Fingers (typically 0.1m equivalent loaded needed) Anchor Pins Net Down

17 Risks What are the key risks to be considered when deciding what product to use: Cost From previous cost benefit variable costs associated with different techniques Purpose Need to understand the purpose Accessibility Permanent or temporary Can plant access the slopes Steep for personnel working on slopes Material availability How Are other materials available or allowed to be used Soils Tyres

18 Risks What are the key risks to be considered when deciding what product to use: How long is the application required Weathering of soils UV degradation of materials e.g. sandbags UV protection of liner Visual What finish is acceptable? or Removal of material Are tyres/soils required to be removed? How much time and at what cost?

19 Net Down- Considerations What are the key considerations when deciding to use Net Down: Gas generation or trapped air pockets Area / Shape to be covered Wind Speed / Direction Surface Shape / Geometry Geomembrane being Covered Installation Other factors (e.g. gas extraction / pipework) All to be considered to optimise efficiency of Net Down Net Down s application is based on sound engineering judgement and consideration of the above factors.

20 Net Down Considerations Key Issues Slack liner due to installation or shape of site; Generation of gas bubbles or presence of trapped air;

21 Net Down Considerations Area / Shape Smaller areas less risk What are size / shape limitations Largely dependant on all factors previously described Typically: If, W < 50 meters L - any size If, 50 < W < 110 meters L < 110 meters (Area = 12,000 meters) If Area > 12,000 meters 2 consider additional/intermediate surcharge These dimensions can increase if all other conditions are favourable. L W

22 Net Down Considerations Wind Speed Direction Wind Speed Determines potential negative pressure (uplift) Potential Force on Material (cross wind force) Wind speeds typically kph Gusting can be greater

23 Net Down Considerations Wind Speed Direction Main consideration is accumulating wrinkles: Solution: Minimise wrinkles during installation Remove (cut-out) wrinkles (follow up monitoring/ maintenance)

24 Net Down Considerations Surface Shape Optimum condition is for geomembrane and Net Down to be tight to the surface. Flat Good Convex Good Concave Unfavourable

25 Net Down Considerations Undulations Undulations can cause slack material to generate during installation. Solution keep tight during installation, or remove wrinkles once accumulated

26 Net Down Considerations Underlying Geomembrane Net Down and the Geomembrane overcome lift by self weight and then properties of Wind Defender to diffuse uplift. The larger the weight of the combined lining system, the less it will deform for a given force.

27 Net Down Considerations Gas Extraction Accumulation of trapped air or generation of landfill gas can inflate a geomembrane

28 Net Down Considerations Gas Extraction Active gas extraction can assist with generating a downward force on the liner on to the landfill. Secondary anchorage from pipework.

29 Net Down Considerations Solutions Preparation of surfaces (to minimise undulations) Installed by experienced / trained personnel Induce negative pressure onto the slope with gas extraction if possible Monitor site and remove wrinkles if developed Consider intermediate surcharge In-built sand-bags Linear bunds/anchor trenches Large agricultural tyres

30 Net Down Considerations Post Installation and other considerations: Needs to be relatively tight when installed Post-installation wrinkles may gather down stream from principal wind direction. Wrinkles can be cut-out and ends re-stitched providing tight installation. Migration wrinkles can catch on site infrastructure such as gas wells Need to monitor Provide slack Provide pipe-boot detail with slack in system to accommodate Holes / Tears Can be patched or stitched

31 Net Down Considerations Post Installation and other considerations: Monitoring Regular monitoring to observe if any movement of liner After initial installation due to wrinkles After storm event

32 Net Down Conclusion Wind loading can create cross flows and negatives pressure which can cause lining systems to rip and tear, which subsequently allows more air to enter beneath the liner creating more damage. This damage is costly to repair and is a risk to health and property. Net Down is a deployable and re-usable lining system that counters and diffuses the negative pressures generated by wind flows thus protecting the underlying lining material. It can be installed to suit any shape of surface and can be quickly repaired or extended as required. It is unaffected by rainfall/water. It is a re-usable, low maintenance and cost effective solution.

33 Questions

34 Thank You Contacts: Bruce Craik M 0044 (0) T/F 0044 (0) E bcraik@hbbgeosales.co.u Frank Smyth M 0044(0) E fsmyth@hbbgeosales.co.uk