It has long been recognised that the provision of drainage in permanent way work is a vital factor in ensuring the effectiveness and long-life of ballast. Recently, designers have put a greater emphasis on good drainage design. This has resulted in product development to ensure that not only is any drainage system guaranteed to perform its primary function but that it offers advantages in terms of speed and safety of installation.
Draining Swiss track
A good example of this new product development was seen recently at Lake Thun in the Bernese Oberland, Switzerland. Here, BLS Netz AG operates a rail network spanning more than 900 km. Direct proximity to Lake Thun and Lake Brienz as well as minuscule differences in altitude regularly cause the groundwater level to rise and penetrate the track bed. After more than 30 years of service, it was decided to renew the railway line. In parallel with permanent-way renewal, the existing drainage system – made of concrete pipes in an open drain trench along the railway line – and the cross drainage to a navigational canal also had to be modernised. According to the requirements of RTE 21110 (Swiss Railway Technical Code of Practice governing requirements for roadbed and ballast), the piping system required for railway line drainage in the roadbed and ballast has to meet the figures specified by the operator, e.g. a clear water inlet opening of at least 100cm² and a minimum slot width of 6mm. To ensure reliable operation of such a drainage system over a period of decades, demanding static, dynamic and mechanical requirements also have to be met. The gradient requirements are 0.65 to 11.05 per mil.
This construction project was realised with Simodrain® drainage pipes with an outside diameter of 250mm, SDR (Standard Dimension Ratio) 21, and 10mm slotting, specially developed for traffic route drainage by local company Simona. These extruded smooth-wall pipes meet the requirements of such a system, and with their large water inlet area they are capable of handling the specified 100cm. Using a special slot geometry and slot arrangement, and with the excellent hydraulic properties of the polyethylene (PE) material, the drainage provided by the system is ‘best in class’ and designed for the long term. End-milled slotting avoids undercuts, and hence deposits and incrustations. In addition, the pipes are easy to rinse out, making them the perfect solution for the Swiss railway infrastructure operator.
In the UK, Burdens, who have been involved in drainage since the company was founded in the 1920s, is currently working with Network Rail to introduce the Simona range of heavy-duty solid-wall PE pipes for use in pressure zones and critical track drainage applications.
Installing catchpits, a traditionally time-consuming process, is another area where new thinking can pay dividends. Now Cubis Industries, a company with three manufacturing sites in Ireland and the UK, has developed the STAKKAbox Ultima access chamber. This is claimed to have numerous advantages over existing systems, particularly as regards speed of installation. Indeed, because the chamber comes complete to site, they can be installed in as little as 18 minutes by a two-man team. Other advantages are a loading strength of 12.5 tonnes, high chemical resistance, and design flexibility. Manufactured from recycled materials, the chambers offer a high level of safety in installation and use, all of which makes the product very cost-effective. Cubis drainage catch pits are approved by Network Rail and by Manchester Metrolink, and supplied in the UK by Burdens.
Another innovative product, which has been mentioned in the rail engineer before, is so-called Concrete Cloth, a flexible cement-impregnated fabric that hardens when hydrated. It comes in a roll format with a PVC waterproof backing and has been used on several Network Rail contracts where a traditional concrete pour would have been difficult. This flexible, strong and durable material is also easy to lay, allowing around 400m of ditch to be installed in one day with minimal staff. Concrete Cloth has achieved a Euroclass B-sl fire rating.
In September 2009, a 140m section of ditch was lined using Concrete Cloth by Amalgamated Construction (AMCO). The project was commissioned by Network Rail to provide drainage at the top of a railway embankment in Chipping Sodbury, Gloucestershire. This was the first time AMCO had used this product for ditch lining and the project was heralded as a major success. Concrete Cloth proved significantly quicker and easier to install than conventional concrete slab construction, reducing the project cost and time on site. The cloth was supplied in portable rolls for ease of use on a site with limited access. Andrew Gurd, construction manager for contractor Amalgamated Construction Ltd, said “Concrete Cloth is incredibly quick and easy to use. It allowed us to line over 100m of ditch in less than 8 hours, with the minimum of manpower and plant.”
Installation begins with digging a V-shaped ditch with smooth, flat sides. Concrete Cloth can be supplied by Burdens either in man portable-lengths (8 linear metres weighs 105kg) or in large rolls (120m, 1400kg) if the necessary plant is available. Once unrolled and positioned, the cloth is hydrated by controlled spraying with water – even sea water may be used – with care being taken to avoid washout. An excess of water should be used as Concrete Cloth cannot be over-hydrated. Once hydrated, it remains workable for about two hours, although warm ambient temperatures may reduce the working time. It hardens to 80% of its 28-day strength in 24 hours and is ready for use.
Drainage products may be largely hidden from view, but that doesn’t mean that innovation is not taking place. After all, every high-technology engineering project needs good drains…