How does CIRIA C737 impact the design of modular geocellular drainage systems?

As a member of the BPF Pipes Group and manufacturer of a range of plastic water management and drainage solutions, we join them in welcoming the recent publication of CIRIA C737.

A rise in use of plastic geocellular drainage systems

There has been a significant increase in the use of plastic geocellular drainage systems over recent years, including our AquaCell systems, and we are pleased that the practical knowledge gained from this growth is reflected in this revised document.

Such systems are essential components in delivering the changes needed in the UK to address flood resilience, a topical issue following the House of Commons’ rejection of the Lords’ amendment on SuDS. They can be complex geotechnical structures which are increasingly being used as part of holistic SuDS solutions across a wide range of construction industry sectors.

How does C737 improve on C680?

C737 recognises that good design, testing and installation is essential to deliver long-term, whole life performance. It aligns with the Eurocodes and acknowledges the ongoing development of European test standards. For companies like Wavin, this is a significant step as our systems have always been built on the basis of high performance quality materials that meet prescribed standards allied with a robust design methodology.

This document improves upon the previous edition (C680) with increased emphasis on long-term testing and a more scientific approach to risk management. Whilst it provides a general introduction to systems, materials and applications, additional guidance will be required to enable practitioners to apply the principles in practice.

Guidance from the BPF Pipes Group

With this in mind, the BPF Pipes Group has emphasised that:

a) These products have been in use for over twenty years and, as Section 2.5.1 of the document recognises, failures of installed systems are rare. Investigation has shown that previous failures could have been further reduced by a more rigorous approach to design, preparation and installation.

b) The process for evaluating products against the overall performance parameters in this document is not yet fully defined and this may lead to differences in interpretation.

c) At the time of drafting, a target date for manufacturers to comply with testing requirements was discussed (Section 1.7), however it is not now possible to meet this deadline due to the time taken to finalise the report and the ongoing work to develop appropriate test methods and a consistent approach. Once test methods are agreed and defined product manufacturers will able to proceed with the testing required to make the design methodology work.

d) The document provides a lot of general information on materials which means that the specific guidance on design of geotechnical structures is difficult to identify. The practical application of the design methodology is difficult to use as it is overly rooted in theory.

Commitments from the BPF Pipes Group

To move this forward, the BPF Pipes Group is committed to:

a) Remaining actively involved in the development of European standards referenced in this document and working with 3rd party certification bodies to ensure consistency of approach.

b) Developing practical guidance targeted at designers and specifiers.

It is acknowledged that this will take time, and until this work is complete the BPF Pipes Group members firmly believe that C680 (Structural design of modular geocellular drainage tanks, 2008) continues to provide an effective and conservative approach to designing and installing plastic modular geocellular drainage systems.