Fire protection for Hong Kong-Macao sea link 17 Jan 2019

The immersed tube tunnel of the Hong Kong-Zhuhai-Macao fixed link highway crossing in China is an important infrastructure project with 33 immersed elements submerged at depths of more than 40m below sea water. . The 6.7km long immersed tube is the longest immersed highway tunnel in the world exceeding the length of the previous record holder, the Øresund fixed link immersed tunnel between Denmark and Sweden, by about 40%. For the tunnel segment division of Promat worldwide, the Hong Kong-Zhuhai-Macao project was one of the largest fire-resistant board construction.

Route of the Hong Kong-Zhuhai-Macao sea link

Testing and material selection

When designing the fire resistance requirements for the project the designers needed to evaluate traffic type and traffic volume. Based on this information and on local standards, the designers chose the RABT (Richtlinien fuer Ausstattung und Betrieb von Strassentunneln)curve, which simulates a fast rising, high temperature fire (Fig 1). To simulate a real fire, this fire curve heats to a maximum 1,200°C within 5 minutes, causing a massive thermal shock to the concrete of the infrastructure, and stays at 1,200°C for 2 hours. This is followed by a gradual cooling phase of 110 minutes. Failure criteria is reached when the interface temperature exceeds 380°C and/or the rebar temperature exceeds 250°C at 25mm below the interface.

After the official fire test, it was determined that 25mm thick Promatect-H, a non-combustible matrix engineered mineral board, reinforced with selected fibres and fillers, was required to be fixed directly to concrete surfaces in accordance with the design and regulatory specifications. The board was fixed directly to concrete linings using anchor bolts made of 316 grade anticorrosive stainless steel. The model fire test was then repeated to show consistency of the result when using the Promat method of installation.

Fig 1. Chinese application of the German RABT fire curve

It was imperative that the fixings were tested for pull-out strength given the dynamics of the tunnel environment with positive and negative pressures constantly in force. During installation, the pull-out force tests for fixings were carried out by a supervision engineer, with a test ratio of about 0.1% of the total volume of fixings.

Board installation

Promat started supplying material in March 2016 from the Promatect-H manufacturer Eternit Guangzhou. Final shipments for the thermal linings were complete in late 2017. It was critical that the factory kept up production of the Promatect-H boards with the Promat factory in Australia also required to produce and deliver Promaseal FyreStrip in time for installation.

Board installation commenced in early April 2016. The product was shipped by truck from the factory to the Zhuhai port facility of the China Communications Construction Company JV (CCCC) where it was unloaded onto a barge

Route of the Hong Kong-Zhuhai-Macao sea link

For the 20km sea journey to the west island where it was transferred by crane onto trucks for delivery to designated areas for Shenzhen Baoying Construction Group, the installers. Some boards were taken to the onsite cutting facility where they were fabricated to the onsite requirements.

Early on it was clear that to make installation efficient, elevated working platforms would be required to get to the workface effortlessly. Through consultation with Promat, Baoying designed and manufactured six working platforms with adjustable wings that could be folded away or lowered, depending on the location of the installation. Boards were lifted onto the elevated platforms by forklift for installation.

Automatic lifters lifted the boards into position for holes to be drilled and bolts inserted with a hammer and tightened using cordless screw guns to the required torque.

At times, there were up to 60 installing staff on site, often achieving 3m² per person per hour, with a total board installation of up to 7,500m² per week.

Expansion joints

Expansion strips were located at 180m intervals at every segment joint. Designed by Promat and CCCC,the joint system comprised of 25mm Promatect-H with steel frame and a 25mm ceramic fibre was tested by CCCC in the fire test lab of Central South University. The test specimen simulated the designed structure of the element joint for 50mm ceramic fibre used on the project. The maximum temperature limit for water-tight rubber is 150°C.

Minor expansion joints were used within the segments themselves at 22.5m centres. These 10mm joints were filled with Promaseal-A acrylic sealant, a flexible fire-resistant sealant and Promaseal FyreStrip was used behind the Promatect-H to supplement the fire resistance of the joint as well as limit air leakage through the joint.

Ultimately, approximately 290,000m² of Promatect-H and 8,000 tubes of 600ml Promaseal-A acrylic sealant were used in the undersea highway immersed tube tunnel with a substantial amount of Promaseal FyreStrip used to seal various movement joints within the concrete.