This project belongs to the field of transportation engineering. With the rapid development of traffic infrastructure construction, a large number of road and rail transit projects need to pass underground through existing high-speed railway mainlines. High-speed railways have extremely high requirements for the smoothness of the track surface, which necessitates that the deformation during construction under the railway be minimized; traditional technologies are difficult to achieve this. Especially in the Yangtze River Delta region, where geological conditions are extremely weak, high-speed rail networks are densest, and railway transportation is most busy, conducting construction under the railway presents a major challenge to the international engineering community. Therefore, it is urgent to overcome the scientific and technological difficulties of predicting, controlling, and accurately monitoring millimeter-level track deformation during construction under complex environments and with rapid train operation. On this basis, a new set of construction technology and safety assurance system for railway underpasses that minimally interfere with the railway and do not affect train safety and punctuality should be established. Through multiple national and provincial-level research programs, after more than a decade of efforts, And fully participated in the scientific research and practice of underpass railway projects in the Yangtze River Delta region, achieving the following innovative results: 1. Pioneered the construction of a theoretical framework and computational methods for the dynamic design of underpass railway engineering systems. In response to the lack of design methods targeting train operation safety for underpass railways, a 'four-element' coupling system dynamics analysis theory was proposed for the vehicle-rail-road (bridge)-underpass engineering system. A design control method that meets the common safety requirements of train operation, underpass construction, and structural service life was established, and a high-precision calculation method for the key quantity of deformation during underpass construction was obtained. This achieved a leap from single structure analysis to systematic safety analysis, and from quasi-static to system dynamic design methods in underpass railway engineering design, enriching the theory of vehicle-rail coupling dynamics. 2. Developed methods for controlling small deformations during underpass railway construction and intelligent, refined construction techniques. In response to the large deformation issues in traditional underpass railway construction, The 'Shelter Box Method' for small deformation shallow burial under railway was proposed, and the intelligent guidance and positioning device system for long tube shed crossing railway was developed for the first time, along with the research and development of small deformation construction technology; the segmented reinforcement and rigid-flexible composite deformation isolation techniques for shield tunneling under railway were proposed, an intelligent balance control system for shield construction was developed, forming small deformation tunneling technology. The breakthrough from centimeter-level to millimeter-level deformation reduction in railway construction underpass was achieved, overcoming the defects of traditional methods that require restrictions on train speed, as well as tunnel burial depth, span, and crossing distance. 3. Research and development of high-precision measurement and real-time monitoring and early warning technology for rail under the influence of wheel-rail action environment were carried out. In response to the reliability of rail deformation monitoring results affected by wheel-rail action environment, principles for establishing a high-precision monitoring network and error control methods for track deformation underpass construction were proposed, and the first establishment of wheel-rail vibration, Temperature and humidity interference filtering methods have been developed, along with software that achieves sub-millimeter level high-precision monitoring; an information management platform for remote transmission of deformation during underpass construction, real-time monitoring and early warning, and multi-party linkage response has also been created. This has enabled immediate responses to early warnings. The achievements include 16 authorized invention patents, 19 utility model patents, 3 software copyright registrations, 2 national-level construction methods, and 3 provincial/ministerial-level construction methods. A monograph has been published, and more than 20 master's and doctoral students have been trained. Over 50 papers have been published, with one paper selected as a "Top Academic Paper in China's Top Quality Science Journals." The overall achievements reach the international advanced level, with several key technologies leading internationally. They have been applied to more than a hundred projects nationwide, creating multiple records in the international engineering field. This has enabled rapid and busy railway trunk lines underpasses that are not limited by speed, over long distances, with large spans, and at ultra-shallow depths. Several academicians believe that "numerous breakthroughs have been made in the field of underpasses for railways, which are of great practical significance for ensuring the safe and punctual operation of trains." They have been entrusted by the State Railway Administration to preside over the compilation of the national "Technical Regulations for Engineering Projects of Highway and Municipal Facilities Underpassing High-speed Railways." In the past three years, cumulative added value has reached 5.68 billion yuan, with an additional profit of 570 million yuan and an increased tax revenue of 220 million yuan, achieving significant social and economic benefits.