Using non-standard fill in reinforced soil structures

by Craig Roberts, P.E., on 16-Jun-2020 07:24:00

Using site-won, non-standard fills is a great way to reduce the environmental impact of reinforced soil walls and slopes; plus it can save time and money.

A big advantage of using geogrids in reinforced soil structures is that they work with a huge range of materials, opening up the possibility of using marginal fill (including selected site-won fill) and industrial waste products such as pulverised fuel ash (PFA).

PFA is a by-product of coal-fired electricity generation, which, when conditioned, can be used for bulk fill in earth structures. It is not only cheaper than quarried aggregate but also has a lower bulk density, which means it can reduce bearing pressure and foundation requirements.

However, PFA commonly has a high pH value and this alkalinity limit some materials from being used to reinforce it, such as steel and polyester. Fortunately, high-density polyethylene (HDPE) geogrids are highly resistant to chemical attack, and effectively inert at in-soil temperatures, so they can be used with PFA without fear of degradation and loss of performance.

For example, the uniaxial geogrids Tensar uses in its reinforced soil walls and slope systems are HAPAS certified by the British Board of Agrément (BBA) as being fit for purpose in highways retaining walls and bridge abutments with a design life of 120 years. 

TW3 and non-standard fills at Catthorpe Interchange
1_Catthorpe Interchange

The Tensar TensarTech TW3 modular block system was used by Skanska to construct wing walls and retaining walls for new road bridges carrying new links between the M1, M6 and A14 over local roads at the Catthorpe Interchange (Junction 19 of the M1) in Leicestershire. A key reason for Skanska choosing this system was that it allowed the use of locally-sourced PFA fill, instead of more expensive imported aggregate. A total of eight walls, up to 44m long and up to 10m high, were built using the TW3 system on this highly complex junction remodelling project.

Read more about TensarTech TW3 at Catthorpe Interchange. 

GreenSlope uses low quality site-won fill at Eastwood Health and Care Centre2_Eastwood Health Centre

Tensar’s TensarTech GreenSlope system enabled the use of site-won moisture-sensitive clay in a 250m long, 3m high reinforced soil slope running along the edge of, and maximising the space for, Eastwood Health and Care Centre’s car park in Glasgow.

The clay had become saturated during extremely wet weather, which was set to continue during construction, making it difficult to handle and compact. GreenSlope, which can form vegetated slopes up to 70°, uses uniaxial geogrid connected to durable steel mesh units, covered with an erosion protection layer that, for this scheme, was hydroseeded to encourage wildflower and heathers to grow.3_Eastwood Health Centre

Additionally, Tensar’s engineers included a granular layer between the slope face units and the fill. This not only assisted with temporary and permanent drainage but also enabled saturated fill behind to be compacted to design requirements, without fear of damaging the slope face.

Read about TensarTech Greenslope System at Eastwood Health Centre

TensarTech Wall and Slope systems

With 30 years of construction knowledge, design experience and innovative geogrid products, Tensar’s TensarTech permanent and temporary retaining wall and slope systems provide a number of facing types and construction options to suit the structure’s end use, location and required design life.

Our retaining wall solutions include precast concrete, dry-laid modular block systems (with the option of adding architectural, masonry or brick finishes); precast concrete panel systems; gabion and crib walls; and robust units suitable for aggressive marine environments. Our reinforced soil slope solutions can create vegetated slopes with angles of up to 70˚.

Want to learn more about Retaining Walls?

Learn more on our Introduction to Retaining walls page here.

Topics:Walls & Slopes