Upon completion, the bridge will link two of the country’s most important highways, while helping commuters to avoid the long and often steep roads, that traverse the nearby valleys and canyons. With construction formally getting underway on 11th April 2018, the project is tipped to be delivered in 2023, providing faster access for traffic heading to and from the west of the country and to the southern districts of Port-Louis.
By presenting the best technical design solution, Doka was awarded the full scope of work to support the delivery of this highly complex piece of engineering, which included a broad range of new and used material. Designed around a two-pier structure, with the highway suspended from pylons at a height of 90 metres, Doka’s engineers had to factor in seasonal weather conditions such as cyclones, which have already tested the project’s design with winds reaching in excess of 190 km/h. Both piers were built with a step height of 4.50 metres, poured in weekly cycles during typical lifts, with the centre wall thickness of each pier increasing with height. As a consequence, a well thought out formwork system was implemented to avoid changing out panels during transitions, while considering changes to platform design, soffit formwork and safe direct climbing platform access from stair towers and access hoists. Similarly, when it came to delivering the pier table, upper pylon and abutment segment, Doka’s highly versatile solution meant it could be efficiently reconfigured to cast different structures, again, helping to save a considerable amount of time on site.
In terms of products used, Doka deployed large area formwork Top50, Climbing Formwork System MF240, DokaScaff UNI scaffolding and access stair towers, single side supporting universal frames, WS10 suspension head platforms for safe access to the massive crane braces, shoring system d3 and plywood DokaPly Birch along with all the required system anchor and connecting parts, tools, and accessories.
As a result, the project benefitted from five working platform levels for the exterior system, another three work access platforms for formwork and another two additional work levels for rebar installation along the inside.
Benefitting from safety netting and protection sheet metal enclosures for the main platforms, the system included steel access ladders, an optimised design for fast cycle repetition and the flexibility of Top50, which helped reduce the number of ties required.
To maintain efficiency, particularly considering the extensive time-constraints posed by shipping routes to Mauritius, Doka opted for formwork which had multiple uses. This also meant getting as much of the prework done on the ground as possible in order to reduce work at height. Once the groundwork was complete, the single crane was able to lift the entire inside system, which included four sides of formwork, three levels of formwork operations and support platforms and two levels of rebar installation platforms at the top. The Exterior sides also were lifted by a single crane, with unit lengths reaching up to six metres, covering Top50 formwork elements and five levels of platforms including all safety measures.
Based on free access to the top of the pier structure, the contractor was able to pre-assemble all rebar into large cages on the ground and lift into place by a few fast crane lifts which helped to drastically save time on the installation.
The design for the access stair tower, as well as the bracing connector enabled the safe anchoring of the stair towers against the pier structure by utilising the existing anchor cone system from the climbing platforms in a vertical spacing of 4.50 metres.
As one of the country’s most important and prestigious infra-projects, the contractor stated that it has been very satisfied with the overall progress made by Doka. Particular mention was made for the remote support received from its regional head offices in the Middle East, which aided the contractor to safely execute works as planned.