Mr. Sun Jun is a senior academician of the Chinese Academy of Sciences (Division of Technological Sciences) and a First-Class Lifetime Honorary Professor at Tongji University. He has long been engaged in academic and technological research in the fields of geotechnical mechanics and underground engineering, and has profound attainments in sub-disciplines such as rheological mechanics of geotechnical media, structural viscoelastic-plastic theory, and anti-blast dynamics of protective engineering. He is a major founder and pioneer of the discipline branch "Underground Structural Engineering Mechanics" (1962) both domestically and internationally. Over the past two decades, he has also been committed to pioneering the application of urban environmental geotechnology and soft science theories and methods in geotechnical mechanics and engineering, as well as scientific research in emerging technological disciplines such as the renewal and transformation of traditional civil engineering disciplines using high-tech means, and has already achieved considerable creative progress.

　　Professor Sun Jun attended the Second International Summit on Piles and Deep Foundations and delivered an excellent speech. This time he mainly discussed with everyone the durability issues of underwater pile foundation engineering in marine environments. In his speech, Professor Sun Jun pointed out that the durability issue of piles originated in the early 1990s. Research on structural durability must begin at the design stage, and prevention and treatment must be carried out across all links including materials, design, fabrication, construction, curing, and maintenance and repair. At present, the development of "high-performance marine concrete," the selection of "anti-corrosion coatings for steel structures," and various "anti-corrosion additive materials in concrete mixing" are the top priorities in research.

　　Professor Sun Jun introduced a new pile type to the guests. The prestressed concrete pile sleeve and steel pipe pile composite pile type adopts the process of pre-tensioning longitudinal reinforcement and centrifugal forming of concrete to produce a hollow cylindrical concrete precast sleeve-type structural member pile. Inside the PHC pile sleeve, a TSC (Thin-wall Steel-tube Concrete) pipe pile is then inserted and driven—that is, a precast thin-wall steel pipe centrifugal concrete pipe pile, which is a composite section with a thin-wall steel pipe wrapping an inner lining of hollow concrete. The upper section of the pile body is then combined with the outer PHC pile sleeve (from below the pile cap, inserted and driven through seawater to a certain depth below the scour depth of the seabed) to form a new type of composite pile. This new type of pipe pile integrates the advantages of several previously existing pile types, such as steel pipe piles, steel pipe concrete piles, centrifugal concrete pipe piles, and centrifugal steel fiber concrete pipe piles, and features strong hammering resistance, high soil penetration capacity, fast pile sinking speed, good durability, excellent pile formation quality, and low material cost.

　　This pile type has three main application scenarios in construction: 1. Long and large pile bodies subjected to large horizontal static and dynamic actions, especially in high seismic intensity areas with large ship impact forces and high horizontal seismic forces; 2. Where the driven foundation soil is firm and hard soil layers, such as iron-plate sand and fully to strongly weathered rock formations; 3. High pile cap scenarios where the water depth above the river (sea) bed surface is large and the pile cap position is high.

　　Main technical measures to improve the durability of PHC-TSC composite piles: increase the thickness of the concrete cover; apply coating protection on the structural surface; adopt multiple layers of other protective measures (such as steel rust inhibitors and other anti-corrosion coatings); use high-quality waterproof materials and corrosion-resistant structural concrete; establish inspection, monitoring, and maintenance systems; strictly control material quality and strengthen the control of structural quality inspection.

　　Basic requirements for ensuring the durability of pile structures: prevent the reduction of concrete strength, prevent steel reinforcement corrosion, ensure that the concrete cover does not corrode, spall, and pay attention to the surrounding humid environment; and corrosion of thin-wall steel pipes in the splash zone, etc.; through refined design, curing, construction, and operation management, maximizing the structure's own resistance to chloride ion diffusion and permeability and delaying the neutralization (carbonation) of concrete materials, thereby preventing steel reinforcement corrosion, is the most fundamental measure requiring attention to enhance the durability of concrete structures; according to different environmental conditions in the region where the structure is located, adopt corresponding commonly used protective measures such as anti-corrosion, anti-corrosion deterioration, anti-salt, resistance to alkali-aggregate reaction of concrete, wear resistance, and resistance to spalling of the concrete cover, etc.; adopting concrete "double permeability" technology to prevent seawater corrosion, mixing high-quality concrete, and preventing improper steam curing from causing initial microcracks in concrete can be considered an effective solution for the anti-sea corrosion and crack resistance of the prestressed concrete pile sleeve structure here.