The retaining walls were mainly necessary due to extensive wind erosion on the side slopes and to reduce the physical footprint of the intersection ramps – the sand materials are so dry and the grading such that side slopes between 1:3 and 1:5 are not uncommon. Also, the surrounding area is pure desert: sand, rock and more sand. Says Knutton: “The three interchanges chosen for landscaping will be the busiest and Ashghal, the Public Works Authority who initiated the project, wanted to ensure they are eye catching and finally, once completed, present as colourful oasis type features on an otherwise very boring drive.” Each interchange will be irrigated from dedicated underground water tanks holding a minimum of 3 million litres of water each.
Late 2007, detailed designs were finalised and approved for all three intersections, which involved an adaptation to the wall at Interchange 17 to accommodate a series of culverts which carry the main natural gas pipelines across the desert. Also, each wall is intersected at certain points with access stairs to allow maintenance staff to move up and down the terraces easily.
The walls designs were to undergo one more revisit at a later stage of construction. Says Knutton: “Due to the four loops at each interchange being different the Client requested that each interchange design be unique. The challenge was to be creative, functional (for maintenance), have aesthetic appeal and to maintain the structural integrity required. This kind of variation could not have been achieved with the precast walls originally proposed.” As a result, the walls showcase the remarkable design flexibility that is possible with a Terraforce block, by alternating between a flush, round or rock face finish, varied setbacks for a featuresque appearance, integrated steps and good plant cover.
A total of 300 000 L16 blocks were budgeted, with the first pallets arriving in Qatar beginning 2008. As this was the first Terraforce installation in Qatar, the Client and Consultants were anxious to see early results to confirm that their decision to use Terraforce was justified. At the first interchange progress was slow, as the contracting teams and the excavator operators had to be trained by Bryan Newby of Namwall, Terraforce licensee in Namibia. Once the walls took shape, however, everybody relaxed and was well pleased with the outcome.
Knutton feels that the project was an overall success: “Considering that the labour force was made up of at least 10 different nationalities, sandstorms that endured for 6 weeks non-stop and temperatures topping 55 deg Celsius with humidity regularly in at 90% plus, the installation progressed well within a nine month time frame. This Terraforce installation has impressed and is so successful that the product is being considered for another unique project in Doha.”
Terraforce wishes to extend special thanks to Brian Newby of Namwall and Jad Sakr of AG Middle East for their hard work and dedication in ensuring the success of the project.
PROJECT: SALWA INTERNATIONAL HIGHWAY – Qatar
CLIENT: ASHGHAL Roads Authority, Qatar
PROJECT CONSULTANTS: Parsons International Limited
CONTRACTOR (Landscaping & Irrigation): AG Middle East, Qatar
TERRAFORCE WALL DESIGN: Simon Knutton of Knutton Consulting, Gauteng, South Africa
SUPERVISION OF TERRAFORCE INSTALLATION: Bryan Newby of Namwall, Namibia
SUPPLIERS OF TERRAFORCE BLOCKS: Consent L.L.C., Dubai, UAE