The formwork and scaffolding solution used in building the new subway station in Seattle was the result of a project-specific construction kit system. In addition to the widest possible use of rentable PERI system components, the construction method saved time and money.

The length of Seattle’s metropolitan railway system (Light Rail) is being extended 3 miles. Two stations are also being added. Capitol Hill, one of the two new subway stations is 330 feet long and is at a depth of 60 feet. Huge steel-composite tubes with 40-inch and 60-inch diameters brace the underground structure on two levels.

A team of PERI engineers from the U.S. and Germany developed a cost-effective solution. It was economical because the walls and reinforced concrete beams could be monolithically constructed (concreted in one pour), thus avoiding the need for construction joints and resulting in assembly cost savings. The solution is largely based on the Variokit engineering construction kit with rentable system components which are available at very short notice. For Turner Construction’s site management team this meant tremendous time and cost savings.

One formwork carriage for three tunnel levels

The Variokit formwork carriage construction for the nine deepest sections, each 40 feet long and 26 feet high, has been designed with two parts. It has also been possible to use the top half of the carriage for the remaining two levels completing the lower level. These were constructed using six concreting cycles with heights of 16 feet and 13 feet.

The formwork carriage is fully hydraulically operated, and moved on the reinforced concrete edge beams of the respective lower level with heavy-duty rollers. HD 200 heavy-duty props were used as temporary supports for the edge beams to safely transfer the additional loads from the formwork carriage and the respective concreting cycle. The Variokit unit supported the huge steel tubes so it was also possible to fill these with concrete while the walls were being concreted.

To transfer the high loads resulting from the concreting operations for the 48-inch-thick reinforced concrete slab of the subway station into the longitudinal edge beams, the formwork carriage was adapted to suit the changed load situation. However, the Variokit system components as well as the hydraulic handling and easy movability of the complete formwork carriage unit continued to be used.

Comprehensive: system and detailed solutions

The PERI project team developed detailed solutions for all stages of construction, including designing the widened areas along the bottom level and positioning the steel tubes below a temporary bridge. Here, the Variokit formwork carriage served as a transport vehicle. Also, the PERI systems Trio, Vario GT 24, SB Brace Frames, Multiflex, Multiprop shoring towers, and PERI UP stair access proved valuable.

Variokit engineering construction kit

With its standardized, rentable system components and site-compliant connecting system, the Variokit engineering construction kit, bridges, and tunnels can be adapted to suit construction requirements. The modular design allows customized, load-optimized supporting formwork solutions for virtually all geometries.