Geogrids
Open grid-like meshes formed of different polymers. Usually produced with a range of strengths in either a biaxial orientation (meaning strength in both directions), or uni-axial, (meaning strength in one direction only), or tri-axial (with a honeycomb appearance and strength in all directions). The apertures within the grids may therefore be square, rectangular or triangular.
In basal and ground reinforcement applications, geogrids are typically placed underneath or within granular layers as reinforcement. They provide structural reinforcement through mechanically interlocking with the coarse particles.
By using geogrids, thinner granular layers can be built, with considerable cost savings. It is claimed that the use of geogrids in bituminous bound pavement construction can reduce cracking (from thermal stresses, reflection cracking etc.), however these claims are still being verified through trials and the use of geogrids currently requires formal approval from the Highways Agency or the Defence Estates on their schemes.
For embankment construction using reinforced soil techniques, layers of geogrid are used to reinforce the fill and connect to a soft or hard facing at the slope surface. For example the geogrids can be wrapped around the slope surface and anchored back within the soil so forming lifts of reinforced material, or can be anchored to facing structures. Sheets of geogrids are tied together or anchored to other structures using specially designed bodkins .
Geogrids can be used in soil (or rock) retention systems for vertical or near vertical faces possibly in conjunction with soil nails or anchors. Geogrids transfer loads between nail/anchor heads, thus ensuring redistribution of forces and continuous performance in case of localised soil movements or nail failures.
Geogrids can be used for erosion control at the surfaces of embankment and cutting slopes. They protect and retain the surface soil from the actions of rain and water run-off and assist in preventing debris slides.
Vegetation can readily grow through the grid openings, thus improving the erosion resistance of the slope and creating a vegetation screen which protects the grids from degrading UV rays. Geogrids can be used in conjunction with other systems, such as pre-seeded geomats or similar erosion control products specific for enhancing vegetation of the face.
Geogrids were used to build some of the landscape features within the Nottingham Science Park. The very weak soil could not support the weight of a gabion wall,which would have retained a mass of unreinforced soil. As an alternative, geogrids were used to reinforce the local arisings in the construction of a bund. A rock-filled mattress, instead of a wider traditional gabion structure, was used in conjunction with the technique for aesthetic purposes .
- BS EN 14475:2006 Execution of special geotechnical works – reinforced fill
- BS 6031:2009 Code of practice for earthworks
- BS 8006-1: 2010 Code of practice for strengthened / reinforced soils and other fills
- BS EN 15381:2008 Geotextiles and geotextile-related products - characteristics required for use in pavements and asphalt overlays
- Design Manual for Roads and Bridges Volume 2 Section 1 Part 5 (BD 70/03) Highway structures: Design (substructures and special structures), materials. Substructures. Strengthened/reinforced soils and other fills for retaining walls and bridge abutments. Use of BS 8006:1995, incorporating amendment No1
- Design Manual for Roads and Bridges Volume 4 Section 1 Part 4 (HA 68/94) Geotechnics and drainage. Earthworks. Design methods for the reinforcement of highway slopes by reinforced soil and soil nailing techniques
- Defence Estates, Design and Maintenance Guidance DMG33, Reflection cracking – a design guide for assessment, treatment selection and future minimisation, Sutton Coldfield July 2005.
- BRE Report 470 Working platforms for tracked plant: good practice guide to the design, installation, maintenance and repair of ground supported working platforms, Garston 2004
- CIRIA Publication C592 Infrastructure embankments – condition appraisal and remedial treatment, London 2003
- DEFRA, Making the best of byways - a practical guide for local authorities managing and maintaining byways which carry motor vehicles, London 2005
- TRL Report 537 Soil nailing for slopes, Crowthorne 2002
