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 8m 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 Saudia 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 Saudi Ministry of Transport (MOT) to rule out the use of reinforced soil structures.
As the Saudi Arabia’s most rapidly growing city, Jeddah is undertaking significant infrastructure improvement to combat severe traffic problems, with up to 30 bridges currently in the planning stages. Congestion at the junctions of King Fahd and Quraysh Streets, Tahlyia and Prince Moutab Streets, Macarona and Heraa Streets and Prince Majid and Gharnata Streets meant that the projects needed to be completed quickly.
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 which have been reinforced with layers of galvanized 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 central and eastern provinces, the use of galvanized 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 Arabia Ltd.
“By putting forward Tensar MESA earth retaining wall technology to provide mechanical stabilization 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 pre-cast 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 leveling pad which comprises a 60cm wide unreinforced concrete leveling 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.
“Much of the construction work is manual, so heavy plant is kept to a minimum. Despite the Tensar system’s higher soil-retaining performance and longer life duration, with rapid contract completion, use of Tensar geogrid solutions is less costly than the conventional solutions so was readily accepted.”
The embankments for the overpasses extend to eight metres 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 2,800m2.
Tensar earth retaining technology offers a number of earth retaining solutions for steep slopes and embankments including vegetated slopes (Tensartech NaturalGreen and GreenSlope) and Tensartech TWI and MESA retaining wall systems. Tensar retaining wall systems offer a wide range of masonry facing materials to complement local construction materials, and are also widely used in terracing and to form containers for planting. All these systems are based on the proven mechanical stabilisation performance of Tensar stiff polymer uniaxial geogrids.
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