China's longest and watertight underwater highway tunnel – A new Instagram-worthy spot in Taihu

Source:CCCCTime:2022-05-05

A new Instagram-worthy spot – Taihu Tunnel, has attracted a lot of people with endlessly changing LED landscape belts inside the tunnel and the Jasper-snail shaped pavillon on the surface.

A new Instagram-worthy spot – Taihu Tunnel, has attracted a lot of people with endlessly changing LED landscape belts inside the tunnel and the Jasper-snail shaped pavillon on the surface.
LED landscape belts inside Taihu Tunnel
Taihu Tunnel is the second expressway between Shanghai and Nanjing, and increases the number of tourists by 50% for Lingshan and Nianhua Bay Scenic Spots. It is a veritable "special tourist line".
The Jasper-snail shaped pavillon on Taihua 
As a key control project of the Suzhou-Wuxi-Changnan Expressway, Taihu Tunnel has a total length of 10.79 kilometers. Undertaken by CCCC's subsidiary CCCC Third Harbor Engineering Co., Ltd. AndChina Highway Engineering Consulting Corporation, the tunnel officially opened to traffic on December 30, 2021. It is the longest underwater tunnel in China.
Let's take a look at the innovative measures in the construction of Taihu Tunnel.
Cofferdam Building Method
Taihu Lake is the third largest freshwater lake in China, with more than 50 main inflow and outflow rivers, and a large amount of muddy silty clay has been formed on the bottom of the lake due to long-term geological evolution. This made it impossible to use conventional tunnel excavation methods such as shield tunneling to excavate rock mass in the construction of Taihu Tunnel. After careful inspection, the project team decided to adopt the cofferdam building method. That is to enclose a piece of land in Taihu Lake to create the conditions for "onshore construction".
In order to ensure the tunnel construction without affecting the navigation of the Taihu Lake waters, the project adopts a "sectioned cofferdam" to divide the 10-kilometer-long tunnel into 9 sections. Each time the construction of the main project of a section is completed, the project team would backfill soil and water to gradually restore the lake surface.
Build a watertight tunnel with scientific and technological innovations
About one million cubic meters of concrete are poured for the main body of the Mashan section of the tunnel, and the deepest part of this section is 20 meters down blow Taihu Lake. In order to build a "watertight" tunnel, the project team started with technological innovation and made great efforts.
The first thing to address is the key issue of the durability of mass concrete. The project team had set up a technical research team. Combining with scientific research and on-site practice, the research team proposed a set of methods to solve concrete cracks and internal defects in hot climates and improve the appearance of fair-faced concrete.
The project team also introduced a high-tech ice-making unit to reduce the hydration heat of concrete by physical cooling, and strictly control the concrete temperature within the standard range. In the pouring process, the team introduced the distributed optical fiber sensing technology, pre-burieddistributed optical fiber cablesin the concrete construction process, and collected the temperature and vibration data in real time to control the concrete pouring quality. With such gestures, the project team overcame the problems emerging from mass concrete pouring and ensured that the tunnel floor was cast and formed at one time.
In addition, the project department had also established a distribution center for rebar processing and component prefabrication, and adopted automatic rebar processing equipment such as intelligent sorting robots, which not only reduced the labor input, but also ensured the quality of the project. At the same time, the project had set up a fully enclosed concrete supply center integrating modernization, intelligence, informatization and mechanization, and trained a group of scientific research personnel and industrialized professional construction teams.
Ecological Protection
Near the construction waters of the Taihu Tunnel project, there are 15 kinds of fish resources, zooplankton and phytoplankton gather, which is the traditional farming operation area of fishermen in Taihu lake; and near the land area of the project is the Wuxi Taihu National Tourist Resort, which is known as a natural oxygen bar. The resort area has 42 kilometers of scenic lake shoreline, with forest coverage rate of about 70%, and there are two 5A-level tourist attractions around. In order to ensure that the tunnel construction does not affect the beauty of Taihu Lake, the project department had always adhered to the concept of environmental protection during construction.
The project department built a "V-shaped" aerial belt conveyor with a height of about 6 meters and a total length of more than 700 meters above the temporary dock of Taihu Lake to transport sand and gravel required for the construction to the concrete supply center 200 meters away from the temporary dock. Then through two belt conveyors with a length of about 200 meters, all the sand and gravel materials were accurately placed in the designated positions of the 12 silos. After that, four high-altitude fog cannons sprayed water mist continuously to drown the dust in the silo. This method not only solved the problem of transporting dust, but also reduced the time cost and distance cost of land transportation of raw materials.
In terms of noise reduction and sewage prevention, the piling was carried out in the steel casing to reduce the noise radiation surface and the construction volume. The project department established a zero tolerance for sewage system, and collected and sent the oily engine room water and machine repair sewage to designated locations, to protecct Taihu Lake from pollution.
Moreover, the project department voluntarily organized volunteers to remove the white garbage in the Taihu Lake waters and surrounding communities to minimize the impact of the construction on the local ecological environment and fishery resources.
After the Taihu Tunnel is opened to traffic, the Suzhou-Wuxi-Changnan Expressway will realize direct communication with the expressway loops in the cities of Suzhou, Wuxi and Changnan, which will help enhance the function of the Shanghai-Nanjing Corridor as a national comprehensive transportation channel and become a new driving force for the economic development of the Yangtze River Delta.
 

Editor: Highway Engineering Consultants