Hubei Daily, August 13

At the construction site of the No. 5 main tower pier of the Xihoumen Road-Railway Bridge on the under-construction Ningbo-Zhoushan Railway in Zhejiang, the final concrete was poured into the 6.3-meter-diameter steel casing, marking a new world record for the diameter of a deep-water bored single pile for bridges in China. According to China Railway Major Bridge Engineering Group, this bored single pile broke the previous world record for the largest single pile (4.9 meters) set by the same company at the Fujian Pingtan Road-Railway Bridge, meaning that the Chinese have achieved another major breakthrough in the construction of bridge main piers.

The design and construction were respectively completed by the Wuhan-based central SOEs China Railway Major Bridge Reconnaissance & Design Institute and China Railway Major Bridge Engineering Group. The 6.3-meter pile foundation of the No. 5 main tower pier of the Xihoumen Road-Railway Bridge is currently the world's largest-diameter bored pile for bridges, with a single pile area of 31.2 square meters, a concrete pouring volume of 2,928 cubic meters, and a single-pile vertical bearing capacity of more than 30,000 tonnes, equivalent to a single pile supporting the weight of 20,000 cars. Li Yongqi, deputy general manager of the Xihoumen Road-Railway Bridge project of China Railway Major Bridge Engineering Group on the Ningbo-Zhoushan Railway, said that increasing the single pile size is not merely an increment, but also means progress in related supporting drilling and hoisting equipment, and is an important reflection of a country's comprehensive bridge construction capability.

Lowering the reinforcement cage for the 6.3-meter super-large-diameter pile foundation

The Xihoumen waterway, where the Xihoumen Road-Railway Bridge is located, is a golden maritime channel for ships entering and leaving the Port of Ningbo-Zhoushan, with more than 200 30,000-tonne container ships and bulk carriers passing through every day. The maximum water depth in the waterway reaches 93 meters, and the width where the water depth exceeds 60 meters reaches 1 kilometer. The bridge is designed as a cable-stayed and suspension cooperative system bridge with a main span of 1,488 meters, adopting a same-level arrangement of a double-track railway (design speed 250 km/h) and a six-lane expressway (design speed 100 km/h), and is currently the world's largest-span road-railway bridge under construction.

"This is the first time in the world that a bridge pile foundation has been built in water deeper than 60 meters," said Xiao Haizhu, chief engineer of China Railway Major Bridge Reconnaissance & Design Institute and chief designer of the Xihoumen Road-Railway Bridge on the Zhejiang Ningbo-Zhoushan Railway. The sea conditions in the construction area are complex, with more than 100 days of Force 6 strong winds a year, and there are also many unfavorable factors such as deep water, rapid currents, and bare rock on the seabed. Therefore, while taking into account construction risks, project cost, and the capacity of drilling and hoisting equipment, the builders decided to support the bridge's main tower with 18 piles of 6.3 meters in diameter. The successful pouring of the first pile this time provides valuable experience for the subsequent pouring of the remaining 17 piles.

Xiao Haizhu said that this attempt has driven the industry chain to achieve six innovations: for the first time, the process of "hammering for initial stability + staged and repeated drilling + staged hammering follow-up" was adopted in the embedding of steel casings; together with the construction unit and XCMG Group and others, a super rotary drilling rig and a super rotary drill matched to the "6.3-meter super-large-diameter bored pile" were developed for the first time; and for the first time, a multi-tremie synchronous pouring process for pile concrete was adopted, successfully solving problems such as concrete pouring for super-large-diameter bored piles.

Zhejiang Online, August 15

The 3,118-meter-long Xihoumen Road-Railway Bridge is a sea-crossing bridge on the under-construction Ningbo-Zhoushan Railway and the Ningbo-Zhoushan Expressway duplicate line, crossing the Xihoumen waterway and connecting Jintang Island and Cezi Island in Zhoushan. The middle of the bridge carries a double-track railway passenger dedicated line with a design speed of 250 km/h; both sides carry a two-way six-lane expressway with a design speed of 100 km/h. The bridge is managed for construction by Shanghai-Hangzhou Passenger Dedicated Line Co., Ltd., and constructed by the project departments of China Railway Major Bridge Engineering Group and China Railway No. 4 Engineering Group.

The Xihoumen waterway, where the Xihoumen Road-Railway Bridge is located, is a golden maritime channel for ships entering and leaving the Port of Ningbo-Zhoushan, with more than 200 30,000-tonne container ships and various bulk carriers passing through every day. To meet the needs of the waterway while avoiding deep-water foundation operations as much as possible and reducing construction safety risks, the Xihoumen Road-Railway Bridge is designed as a cable-stayed and suspension cooperative system bridge with a main span of 1,488 meters, and is currently the world's largest-span road-railway bridge.

In the complex marine environment of strong winds, rapid currents, bare rock, and deep water, in order to make this long-span, heavy-load bridge more stable, for the No. 5 main tower pier, the only one located in 60-meter-deep water and 294 meters high, the design adopts 18 bored piles each 84 meters long and 6.3 meters in diameter, the world's largest diameter, as the foundation, so that the main tower can take root in the riverbed rock layer and stand firmly above the sea.

It is reported that the first pile in this construction is No. 15 pile of the No. 5 main tower pier, with a pile diameter of 6.3 meters and a pile length of 84 meters. It is an end-bearing pile and was formed by staged drilling with an SWDM1280 rotary drilling rig. The geological conditions at this pile are relatively hard, with 22.9 meters of slightly weathered rhyolite and 7.5 meters of micro-weathered rhyolite, making drilling difficult. From the completion of drilling to the smooth completion of underwater concrete pouring, this first pile provides reliable technical parameters for the construction of large-diameter pile foundations and also sets a benchmark for the pile foundation construction of the project.

To ensure the smooth pouring of the world's largest-diameter first pile foundation, the construction management unit Shanghai-Hangzhou Passenger Dedicated Line Co., Ltd. and the project department of the construction unit China Railway Major Bridge Engineering Group formulated emergency plans and construction plans based on the actual situation of frequent strong winds and unpredictable and frequent rainfall at the site, organized special technical seminars many times, and invited domestic bridge engineering experts to provide on-site guidance. Before the pouring of the first pile, the project department of China Railway Major Bridge Engineering Group made overall plans in advance, conducted technical and safety briefings, and strictly controlled the construction specifications and operating procedures of each process during pouring to ensure compliance with design requirements.

The Ningbo-Zhoushan Railway starts from Ningbo East Station in the west, passes through Yinzhou District and Beilun District of Ningbo, Jintang Island, Cezi Island, and Zhoushan Main Island of Zhoushan, and ends at Baiquan Town, Dinghai District in the east. The line is about 77 kilometers long with a design speed of 250 km/h. It is intended to build Zhejiang Province's "one-hour transportation circle" and form a convenient passenger transport corridor between the mainland and Zhoushan Island. After the project is completed, it will fill the gap that the last prefecture-level city in Zhejiang Province has no railway. It is of great significance for improving the railway network layout, promoting tourism development along the line, realizing the integrated and same-city development of Ningbo and Zhoushan, and accelerating the integration of Zhoushan and Ningbo into the "Belt and Road" and the Yangtze River Economic Belt.