The use of polymeric geogrids in structures with non-standard reinforced fills

Presentations were made during a workshop session co-sponsored by TC218 - Reinforced Fill Structures (Mechanically Stabilized Earth and Reinforced Soil Slopes) at the 19th ICSMGE Conference held in Seoul, Korea on September 20, 2017.  Since this was a paperless session, presenters were asked to prepare single page briefings on their subject areas.  The presentation provided in this article comes from Chaido Doulala-Rigby (Yuli) of Tensar International Ltd.

The use of polymeric geogrids in structures with non-standard reinforced fills

Prepared by: Chaido Doulala-Rigby (Yuli)

This presentation summarises the different types of reinforced fill types that can be used with stiff, monolithic, uniaxially orientated high-density polyethylene geogrids to form reinforced soil structures.

The presentation starts by giving a short historic summary of the beginning of polymeric geogrids that were invented and patented in 1979 by Dr Brian Mercer in Lancashire, UK, together with the word ‘geogrid’ itself that Dr Mercer donated to the Industry.

It then describes the very first polymeric geogrid reinforced soil wall that was constructed in 1980 in Silkstone quarry in Yorkshire, UK, only 1 year after polymeric geogrids were invented. That wall was 2.5m high and supported the railway that brought mine waste from surrounding mines in the area at the place of collection so it can then be collected and transported for safe disposal. The reinforced fill material used was mine waste too, proving at those early days how flexible, sustainable and versatile a reinforced soil structure is.

The first type of reinforced fill showcased is the ‘standard’, well graded granular fill, with which, incredible reinforced soil, near vertical, retaining wall structure heights can be reached – a case study of 3-triered step, near vertical reinforced soils, retaining wall embankments with cumulative height in excess of 60m in Fujairah in the UAE is briefly described.

The presentation carries on with listing the different types of ‘non-standard’ fills that can be used in a project depending on the project location, surrounding topography, time available, foundation type and of course type of retaining structure.

It then lists a ‘check-list of design considerations to be taken into account when dealing with ‘non-standard’ fills, like fill stockpile/site specific testing such as shear properties, crushability, chemical resistance, particle size, compactability and drainage testing.

It then presents a summary of the potential benefits when using non-standard reinforced fills.

Then a selection of case studies using non-standard follows showcasing the use of: site-won cohesive fill, coal industry waste by-product pulverised fuel ash (PFA), landfill waste fill, chalk fill, expansive polystyrene (EPS) fill and light weight aggregate (LWA) fill.

Through 2 case studies, the use of site won, cohesive reinforced fill material is described for the construction of a new 30m+ max height slope to support a new airport and a landslide repair with height in excess of 60m in the Caribbean Island of Monserrat and Malaysia respectively.

Use of PFA is showcased through its use for the construction of vertical reinforced soil wall in excess of 11m in height to support a new highway embankment. Special construction and drainage considerations when dealing with PFA are highlighted in the case study.

Use of site won landfill waste fill is showcased through its use for the construction of the repair of a landslide of a landfill slope, with 45 degree face slopes and in excess of 30m in height to support a recreation park. Special construction compaction, capping and face vegetation establishment considerations when dealing with waste fill are highlighted in the case study.

Examples of using chalk fill and EPS with polymeric geogrids are then included in the presentation.

Finally the presentation concludes with a case study showcasing the use of LWA for the construction of an approach ramp to a bridge supporting a new highway. Special placement and compaction considerations when dealing with LWA are highlighted in the case study.