At around 12:00 noon on the 11th, aboard the drilling vessel “Rongyang 288,” as the last casing was slowly pulled out from the Hangzhou Bay waters, it marked the successful completion of the offshore exploration work for the Jiaxing section of the Hangzhou Bay Sea-Crossing Bridge of the Nantong-Suzhou-Jiaxing-Ningbo Railway, two and a half months ahead of the original plan.

The Nantong-Suzhou-Jiaxing-Ningbo Railway is located in the central area of the Yangtze River Delta urban agglomeration. It is part of the coastal railway passenger transport corridor, one of the main frameworks of the national high-speed railway network's “eight vertical and eight horizontal” lines, and also a backbone line of the Yangtze River Delta intercity railway network. The Hangzhou Bay Sea-Crossing Bridge project is an important part of the Nantong-Suzhou-Jiaxing-Ningbo Railway, located upstream of the existing Hangzhou Bay Highway Bridge. Once completed, it will be the world's longest and highest-standard sea-crossing high-speed railway, becoming another landmark project in the Hangzhou Bay Greater Bay Area.

Geological exploration is the most critical technical step in survey and design. On November 12 last year, offshore drilling for the Hangzhou Bay Sea-Crossing Bridge of the Nantong-Suzhou-Jiaxing-Ningbo Railway began, with plans to drill 579 boreholes in the Hangzhou Bay waters. Among them, 171 boreholes are in the Jiaxing waters of Hangzhou Bay, jointly implemented by China Railway Design Corporation and CCCC Third Harbor Engineering Co., Ltd., both with advanced technology and rich experience.

The Hangzhou Bay Sea-Crossing Bridge of the Nantong-Suzhou-Jiaxing-Ningbo Railway is situated in the Hangzhou Bay waters. “The natural environment in these waters is harsh, with the largest tides, tidal currents, and tidal ranges along the national coast. The sea conditions are very poor, with wind speeds up to 39 m/s, wave heights up to 6.87 m, maximum tidal range of nearly 9 m, and maximum flow velocity of 4.72 m/s. The upper marine silt layer on the seabed is 20 to 40 meters thick, posing great challenges to offshore exploration operations,” introduced Zhang Peng, project manager of the Hangzhou Bay Sea-Crossing Bridge section of the Nantong-Suzhou-Jiaxing-Ningbo Railway at China Railway Design Corporation. Meanwhile, Wang Nianxi, senior engineer and assistant general manager of CCCC Third Harbor Engineering Co., Ltd., said: “The geological conditions in Hangzhou Bay are complex. Shallow gas in nest-like distributions often occurs at the interface of silty sand layers. The eruption of flammable shallow gas poses extremely high safety risks, further increasing the difficulty of exploration.”

Conventional drilling methods are not only difficult but also have a low success rate. The reporter learned during interviews that to overcome the difficulties of offshore drilling, the geological exploration team of China Railway Design Corporation adopted, for the first time in the world, a needle-shaped hard alloy rib-type simultaneous casing drilling technique. This can improve the borehole completion rate, overcome the effects of swell and thick silt layers on exploration, and effectively avoid seabed collapse and borehole collapse accidents caused by shallow gas eruptions. It can be regarded as a model of using innovative means to improve quality and efficiency in the field of railway engineering geological survey.

“After adopting this technique, the success rate of one-time drilling increased from 60% to over 90%, while saving up to 24 hours per borehole, reducing total survey costs by more than 8.6 million yuan,” introduced Sun Quansheng, on-site technical engineer for geological exploration at China Railway Design Corporation.

Despite tight schedules and heavy tasks, the offshore exploration work was completed two and a half months ahead of the original plan, embodying the tremendous efforts and hard work of all exploration staff. “To ensure the exploration work was completed on schedule, we did not stop work during the Spring Festival and maintained 24-hour operations. At the same time, the development of a new drilling technique was indispensable, saving exploration time,” said Zhang Peng.

Xu Yang, a technician at China Railway Design Corporation, introduced that during this year's Spring Festival, all workers on the offshore geological exploration project not only “celebrated the New Year in place” but also “worked in place,” sacrificing their family time for the sake of completing the exploration work on time. Gao Zhibo, a surveyor from the Second Institute of the Survey and Mapping Institute of China Railway Design Corporation, was responsible for precisely positioning each borehole. Since before the Spring Festival, he had been stationed offshore, constantly moving between several drilling vessels. “Because each vessel needs positioning, and each vessel's progress is different, I need to stay at sea all the time,” Gao Zhibo said.

To avoid delaying the project, Sun Quansheng had not been home for more than half a year. “I am from Tianjin. I left home on October 17 last year and haven't been back since. My name is 'Quansheng' (meaning 'complete victory'), so I must nail myself here like a nail. I will never retreat without complete victory,” Sun Quansheng told the reporter with a smile.

On the 11th, the offshore exploration work for the Jiaxing section of the Hangzhou Bay Sea-Crossing Bridge of the Nantong-Suzhou-Jiaxing-Ningbo Railway was completed ahead of schedule. This will provide detailed geotechnical design parameters and basis for the next step of design and construction, and also buy time for the project to start construction as soon as possible.

Once the Nantong-Suzhou-Jiaxing-Ningbo Railway is completed, it will greatly shorten the travel time and distance from Jiaxing to Ningbo, Shanghai, Suzhou, Beijing, and other places, reducing travel time and costs. At the same time, once this coastal corridor is opened, it will help Jiaxing better integrate into the Yangtze River Delta, boost Zhejiang's construction of “Greater Bay Area, Greater Garden, Greater Corridor, and Greater Metropolitan Area” and its development as a strong transportation province, and accelerate the formation of a world-class urban agglomeration in the Yangtze River Delta.