EMBANKMENTS & EARTHWORKS
Controlling E
mbankment stabilisation remains a key facet within Network Rail infrastructure management; creating stable and protected embankments results in less maintenance and a reduction in track possession.
One of the key issues is how slopes and embankments are protected from erosion damage caused by moving water – whether by rainfall or surface – flow. In broad terms the engineer can pick from one of four choices when addressing this: • Do nothing • Apply temporary erosion protection • Apply permanent erosion protection/ reinforcement
• Install hard armour
Taking the ‘do nothing’ option accepts that the risk of erosion is low and that there is time for ‘natural protection’ to establish before the ‘design erosion incident’ occurs.
It relies on nothing other than vegetation cover to be established.
Martin Lambley, marketing manager at ABG Geosynthetics, looks at options for erosion control on trackside embankments.
The application of temporary erosion protection is an assessment that the ‘design erosion incident’ will occur before natural protection can
be established. Temporary
protection is intended to provide sufficient protection in the short to medium term to allow robust development of vegetation which, in the longer term, will provide protection against erosion.
Permanent erosion protection is intended as a long-term solution; allowing the vegetated
protection to resist higher erosive forces than an unreinforced slope. Typically these products are known as Turf Reinforcement Mats (TRMs) and provide both matrix within which vegetation can establish whilst at the same time providing reinforcement to the surface of the soil and enhanced shear strength.
More demanding conditions require protection through the application of hard armour such as stone pitching, rip-rap or concrete revetment or rock armouring.
The approach to the selection of erosion protection varies. In the ‘mid-range’ the historical approach was to base the selection of protection on the flow velocity to which the slope is exposed, however this has been largely superseded by a more rigorous approach based on design shear stress applied to the slope protection.
FOR MORE INFORMATION
E:
rail@abgltd.com W:
www.abgltd.com/erosion-control
78 | rail technology magazine Jun/Jul 13
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