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Successful Placement of the Closure Joint in HZMB immersed Tunnel Project

On May 2, 2017, Mr. Chen Fenjian, president of China Communications Construction Company (CCCC), proudly announced at the job-site: "The closure joint of the immersed tunnel in HZMB project has been successfully placed." So far, the placement of all the 33 tunel elements, to which CCCC builders devoted great efforts, has successfully come to an end!

The closure joint is located between the Element 29th and Element 30th with a depth of nearly 30 meters. CCCC builders of Island Tunnel project adopted new techniques like water proofing through multipoint hydraulic pushing as well as hoisting and sunken placement in whole one assembling unit. The closure joint weighs 6,120 tons and has a 9.6-meter base slab and a 12-meter roof slab. It was the first time in China to use a "sandwich" steel structure filled with tremie concrete, and to employ a new technique named "high-flowability concrete". It was also the first time to approach the "M-gasket + LIP seal + GINA gasket" water proofing system in immersed tunnel project around the world. Thus, CCCC has received more than ten patents in this regard. Yet it has met sorts of challenges. This project faced dual pressure from "gear phenomenon" in deep trench and "gap effect" in estuary of final closure as the final construction field of the joint was in offshore open waters. The construction is challenging, with strong winds and typhoons, extremely complex current, abnormal back silting, large runoff, and harsh weather. Besides, the giant closure joint must be placed to a 30-meter-deep trench through a mere 15-centimeter gap, which was a daunting challenge like "threading a needle in great waves." Also, the safety of temporary water stop is the "lifeline" of the closure weld since the small-size GINA gasket, supported by a "giant piston" of 54 jacks and pushing beams, was supposed to connect seamlessly with steel cap of the immersed tunnel. It can be said that each step is the first attempt with a huge risk, but it could not fail. Therefore, with strong support of the CCCC, builders of Island Tunnel project have introduced a lot of researchers, who devoted themselves to technology research and carried out more than 50 studies, test exercises and many job-site marine environmental monitoring work. Finally, the research and design process of the closure joint, which took 3 years and beyond, finally came to an end with its successful placement.

Just before placing the closure joint, president Chen specifically organized an international expert consultation to solve problems that may occur in this mega project. In April this year, an expert group composed of six domestic authoritative academicians and more than 30 well-known experts at home and abroad offered consultations on the placement of closure joint and made more than 100 pieces of advice and suggestions. Just as the traditional Chinese saying goes, "Good medicine always tastes bitter", builders of the Island Tunnel project deliberated over all these advice and suggestions one by one with a scientific and rigorous attitude. By drawing inferences about other cases from one instance, they found out more than 100 new risk points, developed plans and effectively controlled these risks one by one. On the day of the placement, president Chen released the order to commence the placement of the closure joint on site and remained there during the whole process to secure its success. Also, other leaders are always concerned about the construction of this mega project. At every critical moment, H.E. Feng Zhenglin, vice minister of the Ministry of Transport and head of HZMB Technical Experts Group, would go to the job-site in person. While placing E10, he went there to coordinate solutions to difficulties. He made a phone call in the first place to inquire about the abnormal back silting during the placement of E15 and made arrangement for resolving difficulties. Placing immersed tunnel sits at the top of his agenda, so he specially gathered together with the CCCC builders prior to the final placement. He encouraged them to be courageous to win this final battle and then he witnessed this great process.

Lin Ming, the general manager of HZMB Project, gave the start command "Lift the boom and rotate it to 90 degrees" at 5:53 a.m. on May 2, after which the huge boom and the red sun rose simultaneously. With bright red national flag, red boom and red slings silhouetted against the blue sea, the scenery was quite magnificent.

The hoisting of the 6000-ton closure joint is the largest hoisting construction in the transport industry in China, and the 90-degree rotation of a 6000-ton hoist is another progress in conquest of gravity for humanity. To achieve this, Lin stood on the top of the closure joint in the whole process. Through carefully observing different movements, including hoisting, rotating and lowering, he kept communicating with all monitoring and security teams and constantly gave all sorts of instructions to directed the staff to cooperate closely. With hoisting force gradually increasing from 1000 tons, 2000 tons ... 6,000 tons, to 6,120 tons, the closure joint was slowly hoisted from the transport deck and then rotated, which was the first 6,000-ton rotation around the world. From hoisting to lowering into the water, the whole process went quite smoothly with steady hoist, balanced rotation, and relative placid sea. This process is carried out by Zhenhua 30, a 12,000-ton crane ship, and it is its debut, perfectly interpreting the extraordinary power of "The Pillars of a Great Power".

The placement of closure joint is a systematical engineering which not only is highly complex but also must be closely integrated. On the Zhenbo 28, a stone laying and compacting barge, the operators are seizing their time to winch away; in the command cabin, a variety of monitoring data are constantly updated on a dozen of screens; on the diving boat, groups of divers dived in the sea in procession to check the immersed closure joint; in the operating room, the builders carefully handled the equipment and cables. Different monitoring teams who are responsible for foundation, structure, measurement, weather, position and others worked closely and the atmosphere of the construction field was tensed but orderly.

With the gradual sinking of the closure joint, the area of water resistance further increased and the "gap effect" became increasingly obvious, which made it more and more challenging to control the placement. Since placing the closure joint is completely different from that of an immersed tunnel element, the placement experience of 33 elements cannot be borrowed. To overcome arduous conditions such as waves, wind, current in the open sea and buoyancy effect, the height difference of underwater hoist must be controlled within 1.5 centimeters in the process of placing the closure joint through a gap of only 15 centimeters atop specially designed gravel beds. Builders dared not to have the slightest slack. Everyone in the command cabin, security command cabin and on crane ship, diving ship was absorbed and constantly recorded and analyzed each set of data on screens to secure the placement process. At 11:55, the closure joint was placed atop the grave bed smoothly.

Fine tuning and water stop are key factors to the placement of closure joint. For four hours and more, builders adhered to the spirit of craftsman, operated carefully and adjusted repeatedly regardless of the fatigue of continuous working. Finally, they placeed the closure joint successfully with millimeter precision through fine tuning system. At the same time, the incremental launching system was working, with small-size GINA gasket crimping tightly with the steel cap of the immersed tunnel. This successful placement represents the first watertight placement of a joint under a complex environment in deep water in the world.

After witnessing this placement process, top experts from Hong Kong, Japan, the Netherlands as well as other experts in immersed tunnel from home and abroad spoke highly of the innovative capacity of Chinese engineers, the rapid development of China's construction industry and the great power of "The Pillars of a Great Power". They praised CCCC builders for completing a six-month project of closure joint placement within just one day and it is nothing short of a miracle.

On May 2, 2017, Mr. Chen Fenjian, president of China Communications Construction Company (CCCC), proudly announced at the job-site: "The closure joint of the immersed tunnel in HZMB project has been successfully placed." So far, the placement of all the 33 tunel elements, to which CCCC builders devoted great efforts, has successfully come to an end!

The closure joint is located between the Element 29th and Element 30th with a depth of nearly 30 meters. CCCC builders of Island Tunnel project adopted new techniques like water proofing through multipoint hydraulic pushing as well as hoisting and sunken placement in whole one assembling unit. The closure joint weighs 6,120 tons and has a 9.6-meter base slab and a 12-meter roof slab. It was the first time in China to use a "sandwich" steel structure filled with tremie concrete, and to employ a new technique named "high-flowability concrete". It was also the first time to approach the "M-gasket + LIP seal + GINA gasket" water proofing system in immersed tunnel project around the world. Thus, CCCC has received more than ten patents in this regard. Yet it has met sorts of challenges. This project faced dual pressure from "gear phenomenon" in deep trench and "gap effect" in estuary of final closure as the final construction field of the joint was in offshore open waters. The construction is challenging, with strong winds and typhoons, extremely complex current, abnormal back silting, large runoff, and harsh weather. Besides, the giant closure joint must be placed to a 30-meter-deep trench through a mere 15-centimeter gap, which was a daunting challenge like "threading a needle in great waves." Also, the safety of temporary water stop is the "lifeline" of the closure weld since the small-size GINA gasket, supported by a "giant piston" of 54 jacks and pushing beams, was supposed to connect seamlessly with steel cap of the immersed tunnel. It can be said that each step is the first attempt with a huge risk, but it could not fail. Therefore, with strong support of the CCCC, builders of Island Tunnel project have introduced a lot of researchers, who devoted themselves to technology research and carried out more than 50 studies, test exercises and many job-site marine environmental monitoring work. Finally, the research and design process of the closure joint, which took 3 years and beyond, finally came to an end with its successful placement.

Just before placing the closure joint, president Chen specifically organized an international expert consultation to solve problems that may occur in this mega project. In April this year, an expert group composed of six domestic authoritative academicians and more than 30 well-known experts at home and abroad offered consultations on the placement of closure joint and made more than 100 pieces of advice and suggestions. Just as the traditional Chinese saying goes, "Good medicine always tastes bitter", builders of the Island Tunnel project deliberated over all these advice and suggestions one by one with a scientific and rigorous attitude. By drawing inferences about other cases from one instance, they found out more than 100 new risk points, developed plans and effectively controlled these risks one by one. On the day of the placement, president Chen released the order to commence the placement of the closure joint on site and remained there during the whole process to secure its success. Also, other leaders are always concerned about the construction of this mega project. At every critical moment, H.E. Feng Zhenglin, vice minister of the Ministry of Transport and head of HZMB Technical Experts Group, would go to the job-site in person. While placing E10, he went there to coordinate solutions to difficulties. He made a phone call in the first place to inquire about the abnormal back silting during the placement of E15 and made arrangement for resolving difficulties. Placing immersed tunnel sits at the top of his agenda, so he specially gathered together with the CCCC builders prior to the final placement. He encouraged them to be courageous to win this final battle and then he witnessed this great process.

Lin Ming, the general manager of HZMB Project, gave the start command "Lift the boom and rotate it to 90 degrees" at 5:53 a.m. on May 2, after which the huge boom and the red sun rose simultaneously. With bright red national flag, red boom and red slings silhouetted against the blue sea, the scenery was quite magnificent.

The hoisting of the 6000-ton closure joint is the largest hoisting construction in the transport industry in China, and the 90-degree rotation of a 6000-ton hoist is another progress in conquest of gravity for humanity. To achieve this, Lin stood on the top of the closure joint in the whole process. Through carefully observing different movements, including hoisting, rotating and lowering, he kept communicating with all monitoring and security teams and constantly gave all sorts of instructions to directed the staff to cooperate closely. With hoisting force gradually increasing from 1000 tons, 2000 tons ... 6,000 tons, to 6,120 tons, the closure joint was slowly hoisted from the transport deck and then rotated, which was the first 6,000-ton rotation around the world. From hoisting to lowering into the water, the whole process went quite smoothly with steady hoist, balanced rotation, and relative placid sea. This process is carried out by Zhenhua 30, a 12,000-ton crane ship, and it is its debut, perfectly interpreting the extraordinary power of "The Pillars of a Great Power".

The placement of closure joint is a systematical engineering which not only is highly complex but also must be closely integrated. On the Zhenbo 28, a stone laying and compacting barge, the operators are seizing their time to winch away; in the command cabin, a variety of monitoring data are constantly updated on a dozen of screens; on the diving boat, groups of divers dived in the sea in procession to check the immersed closure joint; in the operating room, the builders carefully handled the equipment and cables. Different monitoring teams who are responsible for foundation, structure, measurement, weather, position and others worked closely and the atmosphere of the construction field was tensed but orderly.

With the gradual sinking of the closure joint, the area of water resistance further increased and the "gap effect" became increasingly obvious, which made it more and more challenging to control the placement. Since placing the closure joint is completely different from that of an immersed tunnel element, the placement experience of 33 elements cannot be borrowed. To overcome arduous conditions such as waves, wind, current in the open sea and buoyancy effect, the height difference of underwater hoist must be controlled within 1.5 centimeters in the process of placing the closure joint through a gap of only 15 centimeters atop specially designed gravel beds. Builders dared not to have the slightest slack. Everyone in the command cabin, security command cabin and on crane ship, diving ship was absorbed and constantly recorded and analyzed each set of data on screens to secure the placement process. At 11:55, the closure joint was placed atop the grave bed smoothly.

Fine tuning and water stop are key factors to the placement of closure joint. For four hours and more, builders adhered to the spirit of craftsman, operated carefully and adjusted repeatedly regardless of the fatigue of continuous working. Finally, they placeed the closure joint successfully with millimeter precision through fine tuning system. At the same time, the incremental launching system was working, with small-size GINA gasket crimping tightly with the steel cap of the immersed tunnel. This successful placement represents the first watertight placement of a joint under a complex environment in deep water in the world.

After witnessing this placement process, top experts from Hong Kong, Japan, the Netherlands as well as other experts in immersed tunnel from home and abroad spoke highly of the innovative capacity of Chinese engineers, the rapid development of China's construction industry and the great power of "The Pillars of a Great Power". They praised CCCC builders for completing a six-month project of closure joint placement within just one day and it is nothing short of a miracle.


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