Lokeren railway underpass: quick installation with ArcelorMittal sheet piles

Detailed information

Designed for a narrow time frame

The structure undercuts four railroad tracks, a service road, and a bicycle path. Two railroad tracks (no. 1 and no. 2) are for transit traffic, while the other two (no. 3 and no. 4) are siding tracks. The underpass has two lanes for cars and lorries and an elevated bicycle and foot path.

During construction of the underpass, tracks no. 1 and no. 2 could only be interrupted for two days over the weekend of 5 and 6 May 2018. To stay within this narrow time frame, a special solution was designed using the top-down method in combination with sheet piles.

• The underpass decks are supported by 46 vertical AZ® 25-800 sheet piles with lengths of 12.4 m to 12.6 m.
• The underpass entrances consist of 165 AZ® 18-800 sections in lengths between 5.6 m and 12.4 m.
• As special features, the piles have an inclination of 11° (1/5) and follow a curve with a radius of 400 m.
• The vertical piles are connected by four prefabricated special transition piles to the inclined piles.
• In addition, 18 AZ® 18-800 sections of 3.4 m length were used to create a pumping pit at the bottom of the underpass.

Quick installation

The underpass deck for railroad tracks no. 1, 2, and 3 was prefabricated next to the railroad, and 14 AZ® 25-800 sections were installed between the decks and track no. 2. On Saturday 5 May at 2:00 AM, railroad traffic was interrupted and tracks no. 1 and no. 2 were removed.

18 AZ® 25- 800 sections, two transition piles, and four inclined AZ® 18-800 piles were installed on time. The next day, the prefabricated 400-tonne underpass deck for the three tracks was pushed on rails over the sheet piles into its final position. After the connection of the deck with the sheet piles, tracks no. 1 and no. 2 were reinstalled. On Monday morning, 7 May, both tracks were opened for traffic again.

The sheet piles were installed with two 70-tonne hydraulic rigs equipped with PVE 24VM vibratory hammers with double clamps, fitting the AZ® 800 profiles. In the next phase, the AZ® 18-800 piles of the underpass entrances and the AZ® 25-800 sections underneath track no. 4 were installed. Once the sheet piles for the underpass entrance had been installed, the excavation started underneath the prefabricated underpass decks. In parallel, the decks for track no. 4, the service road, and the bicycle path were constructed in situ. After excavation to the final level was finished, the interlocks of the AZ® 18-800 piles were seal-welded to obtain a completely watertight wall. The use of ArcelorMittal’s extra wide AZ® 800 series allowed for a minimisation of the total amount of welds needed. After the pouring of the concrete floor slab, the vertical AZ® 25-800 piles were covered with an inclined concrete wall (1/15).

Just-in-time delivery for an early finish

Due to the tight planning and limited space on the job site, all sheet piles - 390 tonnes in total - were delivered just-in-time by ArcelorMittal.

The works started in November 2017. The underpass opened on 22 May 2019, and the entire project was completed in early July 2019 - two months earlier than originally planned.

Sustainability with EcoSheetPiles™

The extra wide AZ® sheet piles used for this project are part of the EcoSheetPiles™ range. Manufactured from 100% recycled steel through the Electric Arc Furnace route, they are entirely recyclable at the end of a project’s life. As such, they contributed to the reduction of environmental impacts and the carbon footprint of this infrastructure project.

Steel sheet piles used:
AZ® 18-800 / S355 GP / 3.4m – 12.4m (272 t)
AZ® 25-800 / S355 GP / 12.4m – 12.6m (118 t)