Unique formwork and shoring solutions for the taxiway tunnel project

Hamad International Airport is the sort of ambitious airport construction project that comes along every now and again and completely redefines all concept of scale in the industry.

In 2019, the airport served 38.79 million passengers, the highest number since its operations began in 2014. Construction on the airport, formerly the New Doha International Airport, in 2004, creating a construction site that is approximately a third the size of the city of Doha itself.

One key structure being built was a 1,620-metre cross taxiway tunnel, 340 metres of which was to be covered to allow the construction above of the main runway. Split between east and west sections of 810 metres, the project called for a foundation, retaining walls and the 340 metres of covered section.

Before any of this airport tunnel construction work could begin, a staggering 11 square kilometres of the airport site had to be reclaimed from the sea. The resulting operation was a feat never before undertaken on such a scale and resulted in a 13-kilometre armoured sea defence wall to prevent the sea ever reclaiming its land back.

Once the dredgers had done their work and the site was well underway, RMD Kwikform moved in to design the formwork and shoring solution to meet the needs of the taxiway tunnel construction.

A unique traveller system specially designed and built for this project was used to create the retaining walls of the tunnels; the formwork was created using Superslim Soldiers and GTX crossbeams with a plywood face to the shuttering. Incorporated into the formwork was a set of wheels, counterbalanced by concrete blocks to offset the weight of the 9-metre high formwork.

Each section of the retaining wall was poured in alternate 10 and 12-metre sections, rather inspiringly coined hit and miss respectively. Each section would be tied in using high load Rapid Bar Ties and the concrete poured. Once set, the shuttering could then be untied, released, cleaned and easily wheeled on tracks to pour the next section of the wall in a continuous cycle.

All this meant the RMD Kwikform equipment and panels only had to be craned in once, constructed once and then craned off-site when the tunnel was complete.

Once the retaining walls were in place, the 340-metre covered tunnel section became an immediate priority, this needed to be in place to allow above-ground building works to move at a pace that they would be completed on schedule. The 9-metre high reinforced concrete walls that made up either side of the tunnel had to be constructed with a covering that could be rapidly constructed to a high-quality finish.

The solution lay primarily in the incredibly versatile Alshor Plus shoring system. An Alshor Plus table complete with quick release mechanism was used to form the soffit. The lightweight aluminium design of Alshor Plus meant that once an area of the cover section had been poured and cured, it could be quickly and easily released and safely moved to pour the next section along. Any variation in height could also easily be accommodated by making millimetre adjustments to individual Alshor Plus jacks.

Another staple of this large-scale construction environment, RMD Kwikform’s heavy-duty Megashor was used to support the roof structure, while the Alshor Plus system was continually moved along the length of the tunnel. This combination of the two systems allowed the Alshor Plus tables to be moved every three days. The Megashor would then stay in place to support the slab in the final curing stages for a further eighteen days, representing a considerable time saving on this time-sensitive aspect of the build.

Ahmad Deeb, Project Engineer Civil at Consolidated Contractors Int’l Co. S.A.L., commented on the impact the traveller system had on the day-to-day running of the build. "The real benefit comes in the cycle time; on this project the cycle time has been reduced by almost a week by simply eliminating the need for a crane. On-site safety is very important to us, the traveller system we’ve used on the retaining walls shows the ability of RMD Kwikform’s designers to meet tough targets without compromising safety.

Ahmed Deeb continues: "We needed a formwork and shoring supplier that could handle the constantly changing requirements of a project on this scale and still deliver through to completion on time. Given the importance of the taxiway tunnel we are working on, any minor delays would have had a knock-on effect later in the project. The fact RMD Kwikform’s dedicated on-site engineers were quick to react to changes in both the design and programme time means we ultimately made the right choice."