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Cellular confinement systems and ground protection – New good practice guidance

Last Updated:  02/07/2018

There are a variety of uses for Cellular Confinement Systems (CCS) in the construction industry but the proposed new guidance document will focus on creating hard surfacing near trees. When CCS, or “geocells”, are infilled with compacted material a new composite entity is created that possesses enhanced mechanical and geotechnical properties.

© Wrekin Products

© Image courtesy of Wrekin Products

Geocells provide confinement, creating a tensioned membrane effect, and a wider distribution of the applied stress, which result in increased bearing capacity and stiffness of the base course. This limits mechanical damage to the ground surface and also minimises compaction of the surrounding soil. If the right thickness of geocell is used (for the loads experienced during its use) compaction of the soil adjacent to trees can be avoided, preventing tree roots from being starved of moisture and oxygen.

The use of CCS to install hard surfacing near trees has been employed in the UK for approximately 15 years. The accepted approach to creating hard surfacing near trees involves laying geocells on a non-woven geotextile, filling them with stone aggregate, and topping this with a wearing course. Unfortunately this concept has been frequently misused by the construction industry because it is seen as a ‘silver bullet’ that allows surfacing to be created within the root zones of trees, but the use of geocells is not always a simple matter and the limitations of the approach are often overlooked.

With increasing pressure to open up land for development it is now common to require the installation of driveways, car-parking, cycle paths and footpaths near trees. CCS are briefly discussed in BS5837:2012 but, other than that, the main guidance document available for the arboricultural profession is Arboricultural Practice Note 12 which was published in 2007 and, as products and practice have developed, it has become dated. The aim of this new good practice guidance is to draw on the past 10 years of arboricultural experience and the knowledge of the product manufacturers, to develop helpful guidance that will be useful for arboriculturists, landscape architects and building contractors.

This project is being led by Ben Rose, an Arboricultural Association Registered Consultant, on behalf of the Arboricultural Association. The initial phase of the project will be consultation with relevant product manufacturers, arboriculturists, engineers and surfacing contractors with experience in installing geocells. After this stage a draft consultation document will be produced (in 2019) and this will be made available to the whole of the arboricultural industry for comment.

Preliminary topics for inclusion in the document include the following:

  • The relevance of different types of ground conditions
  • When to use different products
  • Ground preparation
  • Use of geotextiles
  • Suitable machinery to use for installation
  • Edging options
  • Appropriate types of infill material
  • Appropriate surface finishes
  • The use of temporary load-spreading boards in conjunction with geocells during construction

During this initial phase we need to find out what information is already out there and identify gaps in our knowledge. If there are any arboriculturists that have access to independent research or who would like to comment on what they would like the document to cover at this preliminary stage of the project please contact CCSconsultation@trees.org.uk to submit relevant case studies or comments.

1 Patch, D. & Holding, B. (2007). Through the Trees to Development. Arboricultural Practice Note 12. Arboricultural Advisory and Information Service. Alice Holt Lodge, Wrecclesham, Farnham, Surrey.