Trelleborg Designs Bespoke Seal to Help Immersed Tunnel Building

Dalian Bay Immersed Tunnel Construction

Trelleborg’s marine and infrastructure operation has been awarded a contract to supply all the closure joints, comprising a bespoke seal, to CCCC (China Communications Construction Company) First Harbor Engineering Co’s Dalian Bay immersed tunnel in Dalian, Liaoning, China.

The immersed tunnel covers 5.1km and includes 18 large tunnel elements, with some weighing about 60,000t. once completed by 2024, it is going to be the longest immersed tunnel in northern China.

For the 18 tunnel elements and 219 segment joints, Trelleborg will supply a mixture of its Gina gaskets, water stop seals, Omega seals, and a new closure joint seal.

Besides the 18 immersed elements, there are going to be 14,000m of water stop and 7,000m of Omega seals supplied for the cut and a cover section at the north and south shores of the tunnel, which is going to seal the building joints and expansion joints. Also, the seals for the cut and cover sections will assist to speed up the building time of the project.

Trelleborg argued that in traditional construction, bulkhead and concrete pouring would take two to three months longer underwater. However, it described that its solution allows all the works to be prepared on the drydock, which saves great amounts of time.

Zhang Haiying, China Communications Construction Company First Harbor Engineering Co-chief engineer of the Dalian project stated: “This exciting and large-scale project aims to help relieve local traffic pressure in the area by connecting the two banks of the Dalian Bay. The highly technical aspects of such a project required a sealing specialist, as these seals must be able to withstand a maximum of 1,700mm movement under a 35m water head. Trelleborg was the ideal choice as its seals are designed with long-life expectancy, have the ability to handle the immense weight, and demonstrate strength against extreme environmental factors.”

He added: “Additionally, we required the company’s expertise to develop an entirely new closure joint structure for the immersed tunnel. Although this closure joint structure will consist of many units, a section of this joint will be an entirely new M seal design, made especially for this project and the first of its kind. This new seal passed a performance test to an extremely high standard and will also help speed up construction work by allowing us to prepare works on the drydock. Also due to its high sliding capacity, we could measure seal tolerances throughout construction instead of at the last minute.”

Eddy Chen, Trelleborg’s marine and infrastructure operation in China sales director mentioned: “The Dalian Bay immersed tunnel is an exciting project for Trelleborg. Our specialist expertise was not only selected to supply seals for the entire project but to also invent an entirely new type of membrane seal for the closure joint structure. This new joint is made up of various units and once in use, the new membrane seal will be the widest seal ever used in an immersed tunneling project.”

He also asserted: “One of the main challenges for the development of this seal was ensuring that it not only had a wide movement of 1,700mm but that it could simultaneously handle the challenge of high-water pressure. As the original seal design has a capacity to withstand a wide movement of 1,000mm, the seal had to be redesigned and tested for 1,700mm. The seal passed the design requirements with a high-performance and high safety rate. As well as the benefits the seal provides in terms of decreasing construction time, as it’s already watertight, its installation will also save time and allow for final tunnel completion with minimal effort.”

Trelleborg’s Gina gaskets and Omega seals are used among the sectional elements of immersed tunnels to stop water ingress as a result of the external water pressure. Trelleborg claimed that its sealing systems promise a product life expectancy of up to 120 years with little-to-no maintenance. They are designed to handle the intense transfer of hydrostatic loads and movements among tunnel ends caused by environmental pressures like seismic activity, soil settlement, and temperature effects.

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