Hong Kong’s Civil Engineering and Development Department (CEDD) undertook an integrated and engineering study to further develop the area of Tseung Kwan O (TKO). Part of the plan was to improve the district’s accessibility and cope with the anticipated transport demand between TKO and its neighbouring areas.
This gave the foundation to the need to construct an elevated interchange over the sea to connect TKO district and Tseung Kwan O – Lam Tin Tunnel (TKO-LTT). The interchange would also be a vital part of Route 6, which is a major new link between the New Territories and Kowloon.
To bring the idea to reality, Aurecon was commissioned to deliver bridge design, geotechnical works and temporary work designs for TKO-LTT – TKO Interchange and Associated Works. The team was also tasked with carrying out the alternative design for seven bridges over the sea, following collaboration with client Chun Wo during the tender phase of the project.
Designing the interchange was not an easy feat. Challenges included designing the seven bridges over the marine zone and constructing them while being exposed to aggressive environmental conditions, such as heavy wave action and onshore wind.
Accurate assessments of exposure severity were vital to determine materials of sufficient durability. According to the Hong Kong design codes, these types of bridges should be designed to endure the highest category of typhoon with coexisting extreme sea waves action. To ensure the structure’s resilience to extreme natural events, Aurecon Project Leader Lemuel Leung explained that the piles for the bridges were founded in competent rock with some pile lengths exceeding 50 m.
With the bridges constructed over the sea, the geological longitudinal section of the rock goes as deep as 50 m below sea level requiring longer piles, while the bridge piers have piles cantilevering reaching to 20 m from the seabed. He also shared that Aurecon’s design work considered the method of erection, ensuring the geometry of the bridges met the required tolerances. This included the development of segment geometry from the casting bay to erection on the bridge, as the bridge decks were prefabricated in Mainland China and transported to Hong Kong.
Another design challenge on these bridges was the extremely tight curvature with radii as low as 44 m. Due to this curvature effect, the dynamic behaviour of the bridges became more complicated than straight bridges with inherent challenges. To make the design work, the project team avoided all external post-tensioning and used only internal tendons. This approach saved the cost of erecting a lot of deviators at close distance and resulted in better constructability during the erection stage.
Aurecon drew on its knowledge of precast segmental construction technique and collaboration from across the globe, to deliver for the client a cost-effective, robust design solution that was easily approved.
Arising from the recent transition in Hong Kong from British Design standard to European Standards and the publication of the Structures Design Manual for Highways and Railways (SDMHR) in 2013, there is limited experience using the Eurocode Standards on Precast Segmental Bridges. After a detailed review of the European Norms (EN) and SDMHR requirements, the project team closely coordinated with the Independent Checking Engineer (ICE) early in the design phase to discuss the various design approaches in the published documentation, and the approach that Aurecon’s bridge engineering team intended to follow.
Involving the ICE at an early stage ensured full transparency of Aurecon’s design approach and a platform for discussion between stakeholders. This approach facilitated a collaborative team effort and timely delivery of the bridge designs on an extremely tight schedule.
Working closely together also led to developing a construction method that not only adhered to the design requirements but was also achievable in terms of budget and timeline.
The TKO-LTT – TKO Interchange and Associated Works will alleviate traffic congestion and meet the transport demand of a growing population, as well as commercial developments in the district.
The project has been recognised with a Commended Prize at the Lighthouse Club International Design for Safety Competition 2019.