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The length of Seattle´s metropolitan railway system (Light Rail) is currently being extended by 5 km and includes increasing the number of stations from 18 to 20 – as part of the rapid transit project for the Greater Seattle region. Capitol Hill, one of the two new subway stations is around 100 m long and is being realized at a depth of 18 m. Huge steel-composite tubes with 1.00 m and 1.50 m diameters respectively brace the underground structure on two levels.
Engineering with system
A very experienced team of PERI engineers from PERI USA and PERI Germany developed a cost-effective solution for this project. Economical due to the fact that, on the one hand, the walls and reinforced concrete beams could be monolithically constructed, i.e. concreted in one pour, thus avoiding the need for construction joints as well as resulting in assembly cost savings. On the other, the PERI 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 has meant tremendous time and cost savings for the realization of the ambitious building project.
One formwork carriage for three tunnel levels
The VARIOKIT formwork carriage construction for the nine deepest sections, each 12 m long and 8 m high, has been designed with two parts. As a result, it has also been possible to use the top half of the carriage for the remaining two levels after completion of the lower level. These were realized using 6 concreting cycles each time with heights of 5 m and 4 m respectively.
The PERI formwork carriage is fully hydraulically operated, and moved along on the reinforced concrete edge beams of the respective lower level by means of heavy duty rollers. HD 200 heavy-duty props were used here as temporary supports for the edge beams in order to safely transfer the additional loads from the formwork carriage and the respective concreting cycle. Furthermore, the VARIOKIT unit served to support the huge steel tubes so that it was also possible to fill these with concrete at the same time as the walls were being concreted.
In order to transfer the high loads resulting from the concreting operations for the 1.22 m 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
Contributing positively to ensure the project was successfully realized was the fact that the PERI project team were also able to develop, in particular, detailed solutions for all stages of construction: for example, the design of the widened areas along the bottom level and the positioning of the steel tubes below a temporary bridge. Here, the VARIOKIT formwork carriage likewise served as a transport vehicle. In addition, the PERI systems TRIO, VARIO GT 24, SB Brace Frames, MULTIFLEX, MULTIPROP shoring towers and PERI UP stair access complemented the comprehensive project solution.
VARIOKIT engineering construction kit
With standardized, rentable system components and site-compliant connecting means of the VARIOKIT engineering construction kit, bridge and tunnel structures can be cost-effectively realized and optimally adapted to suit the respective construction requirements. Furthermore, the modular design allows customized, load-optimized supporting formwork solutions for virtually all geometries.
Seattle
Seattle is the largest city in the north-west of the USA, and home to such well-known companies as Microsoft, Amazon, Boeing and Starbucks. For movie and television audiences, the city is known for films like "Sleepless in Seattle" or the TV series "Grey's Anatomy".