The daunting journey from Tawaian to Dibba, in Sharjah, through the Hajar mountains with its sheer drops and unstable cliffs, is now significantly safer.
In early 2006, Halcrow undertook an initial geological review of the highway in response to a major rockslide that closed the road for almost a year. Work began in June 2008 to stabilise 30 rock cuttings along the highway, winding up in January 2010. As well as conducting the initial review for the Ministry of Public Works, Halcrow was responsible for the design and construction supervision of this complex scheme.
The steep rock slopes that line both sides of the road have been stabilised in places using a combination of rock dowels, rock bolts, sprayed concrete, concrete buttresses, re-profiling and wire mesh protection.
Resident engineer Jamie Mackenzie explains some of these challenges: “The work was undertaken on a live, high-speed and historically dangerous road while keeping the risk to road users to an absolute minimum. Some of the rock slopes extended up to 50m above the highway, which made access very difficult.
“The geological conditions along the stretch of road are hugely diverse, with rock types ranging from weak sedimentary rocks to highly sheared metamorphic rocks,” he continued. “As such, each design had to be tailored to the specific slope.”
According to project director Julian Tyson, the team helped the client slash costs by up to 50 per cent during the design phase by identifying the slopes requiring stabilisation.
“We made a decision early on that stabilisation should only be undertaken if a potential failure could reach the road,” said Julian. “We evaluated the size of each slope, the distance from the road and the likely travel distance of a failure. We then categorised the slopes into low, medium and high hazard. High and medium hazard slopes – those that had the potential to affect one or more of the road’s carriageways – were taken forward for detailed assessment and design. Each individual slope was further assessed using the same criteria, so that only those areas that would impact the road were treated.”
With work on the £9 million scheme now complete, the danger posed to drivers on this previously perilous stretch of road has been drastically curtailed.