A BREAKTHROUGH in the construction of earth-retaining structures in Saudi Arabia using technology from Tensar International has provided a safe and rapid solution to building 8-m-high bridge wing walls at two major infrastructure projects in Jeddah.

The four major new bridge embankments are the first geogrid-reinforced soil modular block-retaining walls to be constructed in Saudi Arabia and the first reinforced soil structures to be constructed in Jeddah. The solution overcomes the challenge of aggressive soil chemistry in the region, which had earlier caused the Ministry of Transport (MOT) to rule out the use of reinforced soil structures.
Explains Dr Anwar El Kadi of Nile Engineering Consulting: “In the past, the normal practice in this country was to build bridge wing walls using reinforced earth techniques employing heavy poured concrete panels, backfilled with local soils that have been reinforced with layers of galvanised steel strips. However, the aggressive nature of many soils in the Arabian peninsula means that the life of the steel is compromised, which may affect long-term loadbearing performance.
“Due to poor performance of some reinforced earth structures in the Central and Eastern provinces, the use of galvanised steel strips to reinforce the soil has, therefore, been ruled out in Saudi Arabia. Tensar proposed a more durable and better performing alternative, which was approved both by Jeddah Municipality and the consultant Fluor.
“By putting forward Tensar’s Mesa earth-retaining wall technology to provide mechanical stabilisation of the soil infill material, we were able to demonstrate that the structural strength would not be affected by chemical attack. The uniaxial stiff polymer geogrids are ideal to withstand the extremely aggressive soils.
“In addition, the polymer geogrids are mechanically fastened to a facing of dry laid, split-face precast concrete blocks to create the wing walls, so that in-situ poured concrete is not needed in the construction. The minor exception is the wall levelling pad, which comprises a 60-cm-wide unreinforced concrete levelling pad placed under the facing blocks. This allows work to proceed very rapidly as there is no need to allow for curing of concrete or mortar, and the structure is load bearing as soon as it is finished.”
The embankments for the overpasses extend to 8 m in height, and are constructed from local granular soil materials, reinforced with different grades of Tensar uniaxial geogrids and fastened to the facing blocks with a unique locking connector.
The grey facing blocks for the wing walls of the bridges are finished with an attractive split face, complementing the local architecture; each bridge-retaining wing wall for the four intersections is about 2,800 sq m.