Create a method for keeping soil and stones in place, such as on an embankment
'Stabilised earth' has been part of building work throughout history. Straw, sticks and branches were used to help make mud huts thousands of years ago.
A geogrid is made from synthetic material such as plastic. Its main function is to mechanically stabilise granular materials such as earth. A typical use is for a retaining wall at the base of a railway embankment to keep soil from falling onto the track.
The geogrid was invented by Brian Mercer in the 1950s. He patented the 'Netlon process' of extruding (forcing into a shape) molten plastic into a grid. The grid looked a bit like a fishing net.
Netlon geogrids were commercially successful but Mercer thought he could do better. He was sure geogrids could be used more widely in in civil engineering – he just had to make them stronger and more robust.
After years of development Mercer invented the 'Tensar process' in 1978. The new process produced stronger and longer lasting geogrids.
Nearly 40 years on Tensar geogrids are used in thousands of projects all over the world.
Chartered engineer and ICE Fellow, Yuli, talks to us from the Royal Military Academy in Sandhurst about geogrids which are used widely in civil engineering to reinforce and stabilise soil. They make pavements longer lasting, more resilient and more environmentally friendly.
Did you know …
Tensar technology was named one of Britain's 100 history changing discoveries of all time in 2013. Other discoveries included penicillin and the splitting of the atom.
Brian Mercer won the Royal Academy of Engineering's MacRobert Award for innovation in 1984. He was made a Fellow of the Royal Society the same year.
Mercer had his portrait painted by surrealist artist Salvador Dali. The portrait shows him as a saint-like figure dressed in a white robe.
Difference the geogrids have made
Tensar grids are used for a wide range of applications. They include:
- earth retaining walls
- reinforced slopes
- pavements and roads
- asphalt reinforcement
- coastal protection
- landfill construction
With a design life of up to 120 years the Tensar geogrid makes soil structures more solid and reduces settlement. It can make structures safer for longer.
The geogrids can save time and money over alternative methods.
How the Tensar grid was developed
Brian Mercer spent 20 years developing Tensar technology.
The new process aligned a polymer's long chain molecules to increase strength and durability in the net-like structure of the geogrid.
This strengthened both the ribs (the horizontal and vertical 'lines' of the net) and the junctions – the point where the ribs join. It also increased the durability of the ribs and junctions. The result was a plastic grid as strong as steel.
A trial in 1980 used Tensar geogrids to build a 2.5m high retaining wall supporting a railway at Newmarket Silkstone colliery in Yorkshire. Uniaxial geogrid was used to stabilise the embankments. Biaxial geogrid was used to stabilise aggregate in the ground beneath the railway.
The system worked. There was no discernible settlement in the structure after 3 years – despite up to 300 tonnes of waste passing over the railway every hour.