You are here: RailwayPeople.com » Rail News » Natural hazard protection solutions

Natural hazard protection solutions

September 19th 2008

The railway infrastructure includes many hill sides, embankments and cutting slopes which sometimes present railway earthworks and geotechnical engineers with challenges. For those situations where the risks have been assessed as high and require action, solutions are needed which are economic, practical, durable and can be implemented with minimal disturbance.

Over the decades since the railways were constructed, weathering has often taken place, sometimes causing instabilities which pose a risk to the running line. In other cases, vegetation removal or drainage issues can result in slope movements.

In hilly areas, potential rock falls present serious hazards to safe railway operations. Abnormally high rainfalls can cause devastating debris flows covering tracks and blocking culverts. None of these problems are new to civil engineers involved in railway slope design or maintenance, but some of the modern techniques available to solve these problems are ingenious and cost effective.

In cases where the slope is high, uneven or heavily vegetated, the installation of mesh or other support systems may well be impractical. New slopes for track widening or to provide room for new structures are often steeper than the natural ground will safely stand on its own, so these too require to be stabilised.

Flexible rock fall barriers

Recent advances in flexible rock fall barrier design (especially on the Continent) now enable engineers to provide cost effective protection in these circumstances. The Swiss are acknowledged leaders in this field and have had government guidelines for the design, testing and installation of rock fall barriers for many years. Many flexible rock fall barriers are now in place to protect the Swiss railway (SBB) infrastructure, which handles 2,300 freight trains per day in Switzerland and between Germany and Northern Italy and over 9,000 trains travelling on SBB’s 3,000 km network. However on 1st February 2008, the European Union also endorsed new EOTA-Guidelines (ETAG27) for Rock Fall Protection Kits, the standard that UK organisations are likely to adopt.

Flexible rock fall barriers meeting these guidelines and using flexible nettings have advanced considerably in recent years. For example Geobrugg’s ROCCO® range of barriers is able to deal with impact energies ranging from 100 kJ to the world record capacity of 5,000 kJ. An energy of 5,000 kJ is equivalent to a 16 tonne rock, free-falling 32 metres! These cutting-edge barriers are tested at the Swiss government test site at Walenstadt and have proved their worth in arresting rock falls around the world.

Recent advances have included optimised designs to reduce anchor loads, and remote monitoring linked to the mobile phone network to enable instant notification of an event occurring.

UK installations have included Golspie in the Scottish Highlands for Network Rail as well as sites as diverse as Whitehaven in Cumbria and below the cliffs at Hastings. At Golspie, the cutting varies between 5m and 30m in height with the crest being vegetated with grass, gorse and birch trees. The crest itself varies between four and six metres. The protection work, which was undertaken by Ritchies, consisted of scaling and de-vegetating some 1,500 m2 of rock face, installing 180m2 rock mesh and 42 rock dowels and erecting a 2.5m high by 70m long Geobrugg RXI-025 ROCCO® catchment fence.

Barriers meeting the new ETAG 27 and carrying the full ETA certification (leading to CE marking) are currently under development and will be available for installation soon. Where there are isolated rock boulders in precarious locations, Geobrugg’s new SPIDER® mesh is very effective, owing to its high strength and ease of installation when compared with old style rope lacings. The value of this system is currently being demonstrated by the installation of over 35,000 m2 at St Helena in the South Atlantic, to protect the Jamestown Wharf - the main access to and from the island.

Debris flow barriers

Debris flows are phenomena that happen frequently in places such as California, Japan and Korea. However, there have been events occurring in the British Isles in recent years, notably at Boscastle, Lochgilphead, Strome and Dooncarton where considerable infrastructure damage has been caused. Geobrugg’s Debris Flow Barriers are being developed in conjunction with the Swiss government and installations around the world have already proved their worth with volumes up to 3,000 m3 having been successfully restrained.

Soil nailing

Recent years have seen the significant increase in the use of soil nails for slope stabilisation. This cost effective solution results in a green finished slope with little ongoing maintenance that can often be installed with minimal interruption to traffic operations. The CIRIA guidance document C637 Soil Nailing: Best Practice Guidance is now used by leading slope stabilisation designers to facilitate best practice design. The three key elements of a soil nailed slope are the nails themselves, drainage and facing. Good design of the facing will allow economical nail spacing while ensuring soil retention and hence good ’greening’ of the slope.

High strength active support

Geobrugg’s advanced TECCO® mesh system, developed in Switzerland, has been successfully used on numerous railway slopes worldwide and in the UK on sites spread across the country from Cornwall to north Scotland. The wire used in this high strength mesh has a UTS of 12.5 kN and is coated in Geobrugg’s durable zinc/aluminium Supercoating for long life. For locations where corrosion is likely to be a serious issue, TECCO® mesh can be manufactured using stainless steel.

The system uses specially developed spike plates to transfer loads from the facing to proprietary soil nails. Unlike hexagonal twist wire-based netting installation, a high tensile and tensioned system provides active and positive support to the slope face. This prevents movement occurring in the first place. This benefit is particularly important close to the track, where any movement may encroach into the kinetic envelopes of trains, resulting in expensive possession work to remove material causing bulges to weaker nettings. For very steep slopes, soil retention matting may be used under the mesh.

Currently, there is no similar system on the market which has these benefits. Sprayed concrete is the most comparable with regard to strength, but it is expensive, cannot be ’greened’ and a recent report has calculated that the ’carbon footprint’ is four times greater. Design may be undertaken using bespoke design software. Such software is simple to use and can quickly optimise the design solutions, using the minimum number of nails to match the facing and slope requirements.

Flax Bourton slope stabilisation

The cost effectiveness of the TECCO® system has been amply demonstrated at Flax Bourton cutting. Over 50,000 m2 of this high tensile mesh and soil nails have been installed, stabilising weathered marls at a cost and programme time approximately half of that of alternative solutions - whilst maintaining normal traffic operations. Slope heights at Flax Bourton have been up to 20 metres high and at an angle of 45-50 degrees to the horizontal. Access and installation has been by rope supported rigs and personnel secured on tested anchors, which are used for both temporary and permanent works.

Soil nails installed on the face are Dywidag GEWI bars installed in drilled holes between four and eight metres long. In addition, various drainage measures have been installed. The TECCO® system is suitable for both soil and rock slopes. Significant rock slopes on the Kyle line in Scotland have been made safe successfully using the unique active support of this high strength mesh.

Natural hazard protection solutions

Subscribe or spread the word: