Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/1223154
44 | APRIL 2020 | WWT | www.wwtonline.co.uk The Knowledge: pipes & drainage Relation to the Adoption of Sewerage Assets by Sewerage Companies in England' water and sewerage companies in England will be able to adopt some SuDS components. This is expected to encourage the implementation of SuDS by providing an alternative route for adoption and maintenance. New and evolving standards for geocellular design The CIRIA 2016 report C737 'Structural and geotechnical design of modular geocel- lular drainage systems' gives guidance on the calculation of the loads on 'tanks'. The 2018 BPF Pipes Group 'Guide to De- signing Geocellular Drainage Systems to CIRIA Report C737' supplements this by provid- ing a worked example for designers to do the structural calculations based on parts of C7371. What has been missing, un- til now, is how a manufacturer can demonstrate the perfor- mance of their system, in par- ticular the long-term strength over the typical 50-year design life. The strength of a plastic material changes with time, due to creep, and the resist- ance to structural loads will decrease. The reassurance that the long-term strength of the system is higher than the structural loads is key to avoiding system failure. The loads acting on 'tanks' are compressive so the normal tensile tests commonly used for polymeric material are not applicable. The strength of a 'box' is a combination of mate- rial, design (geometry) and stability of production process and so tests need to be carried out on the 'box' and not just on the material alone. In supporting the develop- ment of a cohesive approach to SuDS specification the BPF Pipes Group has been directly involved in the production of three new European Stand- ards, which came out on 21 August 2019 a"er eight years' work. l EN 17150 gives a standard method for testing the short- term compressive strength of plastic boxes; l EN 17151 gives a test method for long-term testing using creep rupture; l EN 17152-1 is the product standard giving the charac- teristics needed to measure and control, for example long-term and short-term strength. The final element is the as- sessment of conformity and third party certification. Work is ongoing on other standards, covering for example, assess- ment of conformity and audits. In the meantime, British Board of Agrément (BBA) certification gives the designer confirmation that the product has been made and tested in conformance with the new standards and that the values for the short- and long-term strengths are as the manufacturer declares. The BBA protocol for geo- cellular systems certification not only covers the product itself and the manufacturing quality plan, but incorporates sample calculations based on the BPF Pipes Group Guidance to C737 (see it at https://www. bpfpipesgroup.com/support- downloads/guidance-notes/) that will allow designers to have confidence that the prod- uct will perform as expected under given conditions. The geocellular toolset The elements described now work together. Calculation of loads can be made accord- ing to C737 and BPF Pipes Group guidance. Resistance to the calculated loads can be demonstrated through the new standards and assured by BBA certification. Design- ers now have an effective and more complete toolset at their fingertips to help them ensure that the underground attenua- tion elements of SuDS systems are correct and purpose-built. www.bpfpipesgroup.com/ support-downloads/guid- ance-notes/