On December 29, Guangdong communications group reported another good news that the E28 pipe joint of the immersed tunnel of Shenzhen middle channel was sunk and installed. So far, the deep and medium channel has completed the docking of 20 immersed pipe joints, and the installation length of pipe joints has reached 3052.8m, accounting for about 61% of the total length of immersed pipe sections. The deep middle channel is a cross sea cluster project integrating "bridge, island, tunnel and underwater interconnection". The subsea tunnel is 6845m long, including 5035m long immersed pipe section, which is composed of 32 pipe joints and one final joint. It is the world's first two-way eight Lane steel shell concrete immersed pipe tunnel. The E28 pipe joint sunk this time is an ultra wide and variable width non-standard pipe joint, which is undertaken by the S08 contract section of the deep and medium channel project of poly Changda Guangzhou Salvage Bureau consortium. In the early morning of December 28, led by a tugboat formation with a total horse power of more than 44000, E28 pipe joint set out from Longxue port pool in Nansha, Guangzhou to the tunnel site. Under the dual influence of recent typhoon "Ray" and strong cold air, the wind, waves and temperature in the construction sea area have changed sharply, which has brought many adverse factors to the floating transportation and installation of immersed pipes. To this end, the construction team carefully planned and integrated resources. After the removal of outfitting parts of E29 pipe joint, the construction team intensively carried out the secondary outfitting of E28 pipe joint and the foundation construction of tunnel site, and grabbed the construction window period; The gravel leveling ship was used for all-weather gravel foundation laying. With the leveling accuracy of no more than 2.5cm, the technical difficulties of laying very fine and flat gravel foundation in the coastal Strong Silting environment were overcome, and the foundation was tamped for the smooth docking of E28 pipe joints. In addition, the construction team adopted the self-developed visual immersed pipe docking system to dynamically capture the fine and micro measurement errors caused by the deformation of the pipe joint under the action of water pressure, and further improve the absolute accuracy of the measurement system and control the installation accuracy of the pipe joint at the millimeter level by using the independent analysis and deviation correction functions of the anchor block tension sensor and the system. "E28 pipe joint is the fifth pipe joint connected to the east side of the immersed tunnel of the project. We overfulfilled the annual construction task with millimeter level docking accuracy. The sinking pipe floating transportation and installation technology of the construction team of Guangzhou Salvage Bureau also provides a solution for the fine control construction of multi tugboat formation on the towing of curved special-shaped pipe joints under long-distance and complex routes in the open sea." Li Wangbiao, chief engineer of Shenzhen China channel project of Guangzhou Salvage Bureau, introduced. At 14:00 on December 29, after nearly 7.5 hours of fine adjustment, sinking, pulling and hydraulic crimping, E28 pipe joint was butt jointed and installed about 25m underwater. At 17:30, through the joint penetration measurement of the three parties, the installation absolute deviation and relative deviation met the requirements of the design and inspection and evaluation standards. In order to adapt to the technical problems such as super width, buried depth, widening and large back silting of deep and medium channel immersed tunnel, the deep and medium channel construction team applied the new structural form of steel shell concrete immersed tunnel for the first time in China. "In order to overcome the problem of filling compactness of non vibrated concrete in closed compartment, we have developed high flow self compacting concrete, independently developed intelligent pouring equipment and system, summarized the three-dimensional numerical simulation technology of stress in the pouring process of condensed pipe joint, and realized the filling compactness of concrete up to 100% by intelligent pouring." Introduced by Su Zongxian, chief engineer of poly Shenzhen China channel project. At present, the construction of Shenzhen China corridor is advancing steadily. The sinking and docking of 14 pipe joints of immersed tunnel has been completed this year, and the docking installation of 20 of the 32 pipe joints of the whole line has been completed in total; The construction of East and West man-made islands has been promoted in an orderly manner; The construction of the main tower, anchorage and anchor body of Lingdingyang bridge has been completed, and the hoisting of the main cable saddle has been completed. The box girder erection of Zhongshan Bridge is under way. (Xinhua News Agency)