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HZMB Project: Completion of the Offshore Works of Immersed Tunnel

On July 2, 2017, with the last rock backfill filled in the closure joint, it marks a successful completion of the offshore works of Hong Kong-Zhuhai-Macao Bridge Island & Tunnel Project undertaken by China Communications Construction Company Ltd.(CCCC) over the past seven years.

As the core one of the HZMB Project, the island & tunnel project includes two artificial islands covering 100,000 square meters and a 6.7-kilometer immersed tunnel. In this project, some crucial parts belong to the offshore works, such as the construction of artificial islands, the trench excavation, the foundation treatment, elements towing and immersion, the placement of closure joint, and the backfill of immersed tunnel. Due to the special working environment, CCCC builders must overcome many difficulties, such as the hostile offshore environment, and long construction period.

Under the guidance of the HZMB project office since January 2011, nearly a thousand builders from five construction divisions of CCCC have stood the test of long time, endured lonely when working on the vessels and artificial islands, overcome challenges caused by the complex offshore environment, and operated various working vessels in Lingding Sea. As a result, they accomplished the historic mission of building the artificial islands and immersed tunnel.

On May 15, 2011, it marked a milestone for the HZMB island & tunnel project that eight-hammers simultaneously vibrate to install the first cylinder. In the following seven months, CCCC builders prevented typhoons, safeguarded security, overcome difficulties caused by high temperature, and increased productivity, making the records of " installing three cylinders within one day and eight cylinders within four days ". Finally, CCCC builders completed the installment of all the 120 cylinders on December 7, 2011, which is two years earlier than that time taken by the traditional method. Then it creates a project miracle of "beginning and finishing the construction of the artificial islands at the same year", showing the “rapid speed" of CCCC.

From August 14, 2011 to August 4, 2013, various units of CCCC made joint efforts to overcome the challenges from typhoon, hydrology, geology and other aspects in the East and West artificial island. They completed the placement of sand compaction pile(SCP) around the sloping dike and the section where the artificial island connects with immersed tunnel through the technology optimization, setting a number of records in the domestic application of that technology.

Within nearly five years’ efforts in trench desilting and dredging, CCCC builders made full use of trailing suction hopper dredgers, fixed-drop grab dredger Jin Xiong and some other important equipment to complete the trench excavation and desilting.

When it comes to the foundation construction of the immersed tunnel, CCCC builders designed and built rock dumping and tamping barges, platform gravel placing barges and other equipment to tamp the foundation of the immersed tunnel with flatness, laying a good foundation for the following construction of the immersed tunnel. After 1,423 days of hard work, the work team for gravel beds overcame various difficulties, including the complex geological conditions, serious back silting and ship wave, and laid the gravel beds for all the 33 immersed tunnel elements, making a miracle with an elevation error of only 2.5cm, and a 100% qualification rate.

On May 2, 2013, the CCCC builders finished the towing and immersion of the first immersed tunnel element; and on May 2, 2017, they accomplished the placement of closure joint. Over this past four years, in line with rigorous scientific attitudes, the builders overcame world-class difficulties and placed each immersed tunnel elements seriously, keeping a Chinese speed of "finishing the placement of ten immersed tunnel elements within one year", and making some shocking world records, such as "placing two elements within half a month" and "placing the closure joint with millimeter-level deviation". Finally, they completed the placement of 33 immersed tunnel elements and the closure joint, constructing an offshore immersed tunnel with perfect waterproof effect.

From May 7, 2013 to July 2, 2017, the team responsible for backfilling finished rock backfill of 3.6 million cubic meters from 33 immersed tunnel elements and the closure joint.

Through the great efforts of the past seven years, CCCC builders make a new record in the history of engineering construction in China, highlighting the Chinese people's abilities in engineering construction and technological innovation.

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