Work on Dubai's Fourth Interchange on the Sheikh Zayed Road is progressing on schedule with the main contractor Bin Ladin Contracting (BLC) having mobilised a large fleet of Dynapac compaction rollers and Atlas Copco portable air compressors on the $28 million project.

The second of eight interchanges is being redesigned in a bid to alleviate growing traffic congestion on one of the busiest highways in the UAE.

In a contract awarded by the Dubai Municipality, BLC is working on the Fourth Interchange, known locally as the Police Academy Interchange, which forms part of the recently-completed dual fourlane 'super highway' between Dubai and Abu Dhabi, the Sheikh Zayed Road.

The Police Academy Interchange, located 18 km from central Dubai, is being expanded to include dual feeder lanes at all exits, simplifying and speeding up traffic flow and is to be completed later this year, in a 16-month contract.

A spokesman for the BLC Group says that the company is currently in a race against time. He elaborates: "One of the biggest challenges we face is completing the project on time. The schedule is extremely tight and probably unthinkable in some countries, but Dubai is developing so fast there is a need to set these tight deadlines."

The need to carry out work on the interchanges is obvious. The old roundabouts are insufficient to cope with the growing amount of traffic along one of Dubai's busiest areas. The original interchanges were constructed in 1992 and 1993 and can no longer accommodate the enormous increase in traffic.

Work will, therefore, eventually be carried out on all the remaining six interchanges along the busy highway that links Dubai with Abu Dhabi at an estimated cost of $126 million. Most will, like the Fourth Interchange, need to be completely reconstructed.

The new Police Academy Interchange will consist of a cloverleaf design allowing unhindered flow of traffic in all directions and replacing the existing bridge 4. The new interchange will also consist of two 'curls' and directional access ramps to the new Suq Al Nakheel Mall.

The interchange will also serve the Madinat Jumeirah project, Emaar projects, Dubai Internet City, Dubai Media City and other projects in the area.

Two bridges will be constructed under the contract. The interchange is expected to provide free flow for all movements arriving to and departing from the interchange and provide proper connection to access and egress from the adjacent road network and land uses.

The project will also include the installation of signboarding and streetlighting, relocation of utilities, and the construction of utility crossings and storm drainage and irrigation systems.

Bin Ladin's scope of works also includes a diversion to the existing road in front of the Jumeirah Beach in Al Sufuoh Road. This will be part of the Madinat Jumeirah resort project. The existing roundabout will be replaced with an interchange controlled by traffic lights.

The new bridges across Sheikh Zayed Road are being built using cast-in-place posttensioned construction. Abutments and piers will be supported on piles. Reinforced soil walls will also be used to retain roadway embankment at locations of elevation difference.

Bin Ladin is utilising a large fleet of compaction equipment which includes Dynapac CA250 and CA121 vibratory rollers. The CA250 medium-size vibratory compactor is described as being ideal for compaction of sand, gravel, silt and silty soils, subbases and base courses.

Featuring a drum width of 2,130 mm, the CA250 has a capacity to compact up to 700 cu m/hr.

The CA250 and CA121 compactors are being widely used in the preparation of the new interchange feeder roads. They are currently being used on the first section of the upgraded three carriageway from the Burj Al Arab hotel, eventually linking the Sheikh Zayed Road, some 2 km away. The first 500 m section close to the Burj Al Arab features a 150 mm natural aggregate subbase, a 150 mm natural aggregate road-base, 60 mm asphalt basecourse, and a 40 mm asphalt wearing course.

Working in typically 100-m long sections, the Dynapac roller makes eight passes on both the sub-base and road base - working in vibratory mode on the second and sixth passes.

The contractor says it has been able to meet the specified compaction requirements of 95 per cent of maximum dry density for the subbase and 100 per cent for the aggregate roadbase (with macadam).

Throughout asphalting of the first 500-m section of the newly-upgraded three-carriageway road close to the Burj Al Arab, Bin Ladin Contracting is using an Atlas Copco XA146 to clean dust and sand the asphalt before laying.

A second XA146 is providing air power for rebar cutting and steelwork during construction of the elevated interchanged bridge. Working at 7 bar, the Atlas Copco Deutzpowered compressor has an actual free air delivery of 8.4 cu m/min.

Bin Ladin Contracting is also using a third XA1416 compressor to provide airpower for tools. All the compressors and Dynapac rollers were supplied by local dealer INMA.

Another difficulty faced by the contracting team is that the interchange sits within a busy urban environment and therefore the highway and its access points must remain in operation. The contractor has to work around and over traffic without disrupting the flow and maintaining original capacity while work is under way.

This has been achieved through careful planning. The roads have only been closed when there is simply no alternative, but these occasions have been rare and have only been for short periods in the early hours of the morning, according to the contractor.

The construction of the new bridges over the Sheikh Zayed Road is a major challenge for the contractor. A supporting system, however, allows traffic to pass under while the new bridges are constructed, which has meant that all eight lanes of traffic have been in constant use.

The project will also involve the demolition and removal of the existing bridges built in 1993, as well as the demolition and removal of existing ramps.