Intelligent construction technology of ballastless track for high-speed railway

With the continuous development of high-speed railway construction technology, intelligent construction technology supported by new generation information technology has gradually become one of the important development directions of high-speed railway technology. As an important infrastructure of high-speed railway, the construction quality of the track is directly related to the operation quality and driving safety, so it is necessary to study the intelligent construction technology of the track. The intelligent construction of the track includes three aspects, namely intelligent design, integration of design and construction, and intelligent control. Design, as the source and foundation, must first achieve intelligence. Through digital, dynamic, and visual design technology of the track, traditional blueprint delivery is transformed into digital design delivery of the track, providing a data foundation for intelligent manufacturing, construction, and operation. Based on this data foundation, for the construction process of the track panel, the digital design results are connected with the various intelligent equipment through the digital channel, realizing the automation and operation of measurement robots, track geometric position detection instruments, portable measurement and control terminals, and related tools. Establish a real-time data acquisition channel for ballastless track and construct a big data resource pool for ballastless track to form intelligent construction and control technology for the track of "quality monitoring, data access, and closed-loop management". At the same time, track intelligent construction equipment and software have been developed, which reduces the labor intensity of workers, improves the precision level of ballastless track control, and effectively improves construction efficiency.


INTRODUCTION
In the construction of ballastless track, high precision, smoothness and stability are required. Ballastless track construction is a key control project. In the time dimension, track construction generally takes place near the opening of traffic, with a short construction period. Once a construction defect occurs, there is almost no time for rectification. In terms of quality, the level and quality of track construction are the core key points of railway construction. As the most precise sub-project in civil engineering, balancing millimeter-level control with construction duration has always been a challenge to improve the level of ballastless track construction [1][2].
At present, traditional construction management mode dominates the rail construction industry. The design results are delivered in the form of construction drawings, and construction units construct according to the drawings. The level of information technology and intelligent design, manufacturing, and construction is relatively low, and research on intelligent construction is still in its infancy [3][4]. With the development of new technologies such as artificial intelligence and the Internet of Things, research on intelligent construction technology can help improve the quality of track construction, enhance operational efficiency, ensure project progress, and control construction costs. The current construction mode depends mainly on manual work cooperating with machinery and has not realized automated and intelligent construction. Millimeter-level concrete precision control is difficult, and construction measurement and finetuning are mainly carried out manually, leaving significant room for improvement in efficiency, especially considering the frequent nighttime operations which are very labor-intensive [5][6][7][8].
Against the background of "Intelligent High-Speed Rail," driven by the rapid development of emerging technologies, high-speed rail construction has entered a new stage of intelligent construction [9][10]. The development of high-speed railway construction technology, intelligent railways, smart railways, and green railways have become the focus of railway construction. Higher requirements have been put forward for process monitoring of construction quality and measurement data management. This article focuses on the intelligent construction technology of ballastless track for high-speed railways. It combines emerging information technologies such as artificial intelligence, cloud computing, and data warehousing with traditional railway construction techniques, mainly forming real-time dynamic adaptive design technology for ballastless track, data-driven less-man construction measurement and control technology, and visual intelligent management and control technology based on numerical and physical integration,as follow Figure 1..

REAL-TIME DYNAMIC ADAPTIVE DESIGN TECHNOLOGY FOR TRACKLESS RAILWAYS
The track is installed on the foundation of the substructure under the roadbed, bridge, and tunnel. Due to the asynchronous construction schedules, the substructure foundation is often built earlier than the ballastless track. The construction deviation of the substructure will directly affect the accuracy of the track laying. In order to eliminate the construction deviation of the substructure foundation before the track construction, it is necessary to carry out a dynamic real-time adaptive design of the track based on the actual working conditions. By using automated data sensing methods, the actual measured data of the completed substructure foundation can be obtained to dynamically design the concrete base, prefabricated track panels, adjustable track gauges, rail pads, steel rails, etc., in terms of plane and elevation.
Dynamic design can effectively solve the dual control problem of the distance between rail pads at the end of the largespan continuous beam being too large, the overhanging structure of the track structure, and the elevation and thickness of the layered track structure. At the same time, it also overcomes the dynamic design problems of following such as line changes caused by loads during the installation of ballastless tracks on large-span bridges, deformation joints at tunnels, and substructure stiffness matching., as follow Figure 2.   Based on a unified coding system, a seamless track unit model is constructed to superimpose the three-dimensional structure, terrain, and underground foundation models to form a three-dimensional panoramic model. The data-driven integration of component models such as rails, sleepers, and fasteners is realized by reading the track digital model, calling and modifying the instantiation parameters of the component model, and carrying out coordinate and directional positioning and assembly of different track components along the line, as shown in Figure 4.

BASED ON DATA-DRIVEN TECHNOLOGY, LESS LABOR-INTENSIVE CONSTRUCTION MEASUREMENT AND CONTROL TECHNIQUES
Connect digital interfaces with construction equipment such as measuring robots, track geometric position detection devices, etc., driven by design data, to achieve intelligent measurement and control of key processes such as basic elevation retesting, automatic layout measurement of the base/support layer, rough rail laying measurement, precise adjustment and control of rail/track slab, as shown in Figure 5. (1) The portable intelligent measurement and control terminal A portable intelligent measuring and control terminal has been developed, using GeoCom communication technology to communicate in real-time with the measuring robot through instructions, achieving remote automatic control of the measuring robot. It also calculates the current spatial geometric position deviation and three-dimensional adjustment amount of the track laying in real-time, achieving automated measurement and control. At the same time, the data from the refined process is uploaded in real-time to the "intelligent management platform" to connect the data interface throughout the design and construction process, achieving automated measurement and control of key processes such as track laying positioning, track plate refinement, track alignment refinement, steel rail refinement, etc., improving efficiency and reducing manual input. The interaction and flow of construction information "design, measurement, feedback" are realized.
(2) Fine adjustment of track slab based on data drive( Figure 6) The fine-tuning process of adjusting the position of the track slabusually involves precise measurement during the installation phase, by measuring the key points of the track board or using a setting out tool to locate the design theoretical position. During the fine-tuning preparation period, basic data such as curve elements, slope information, chain length, and dynamic calculation modules are used to calculate the three-dimensional coordinates of the track support platform. Then, place a measurement frame that accurately matches the bolt holes on the track support platform, and install a prism in the center for the robot to recognize. The intelligent measurement robot will collect the prism 3D coordinates of each point and send them to the mobile terminal. The measurement and adjustment software automatically analyzes, compares, and calculates the differences between the measurement coordinates and the design coordinates in real-time, thereby determining the geometric position deviation of the track support platform track plate in threedimensional space. Finally, the fine-tuning robot will automatically adjust according to the deviation control to complete the fine-tuning process.  The automatic fine-tuning robot shown in Figure 7, combined with the electrical control system and servo motor, can receive real-time feedback of measurement deviations and automatically execute fine-tuning instructions without manual intervention. This automated adjustment method reduces fine-tuning errors and adjustment time while maintaining finetuning accuracy. Compared with manual fine-tuning, the overall efficiency is increased by more than three times.

VISUALIZATION INTELLIGENT MANAGEMENT AND CONTROL TECHNOLOGY BASED ON NUMERICAL MODEL INTEGRATION
The management and control platform of ballastless track needs to provide services such as design data, construction process progress and precision data, visual model, process approval management and control for the construction unit, design unit, construction unit, supervision unit, etc. according to departments and positions, so as to ensure the monitoring and tracing of ballastless track progress and quality. Integrating data warehouse, cloud computing and other information technologies, building a data warehouse for the whole process of design and construction, studying 3D model lightweight processing technology, interactive rendering technology of open source 3D engine based on WebGL, integrating track model and ballastless track integrated information flow, taking 3D track model as the information carrier, forming a visual model display of invisible information flow, and associating different construction information with the model, Form a cloud platform based on 3D models, forming a digital and analog fusion of "one model, multiple information, and comprehensive control". Realize track construction progress, accuracy and error monitoring, reporting and statistics during the construction process, and realize dynamic evaluation of ballastless track quality, defect early warning and comprehensive state control,, as follow Figure 8. The main functions include: 1) Unified data warehouse docking, realizing the unified management of structured and unstructured data during the design and construction process of ballastless track, eliminating the information fragmentation management between various stages that causes poor circulation and information island effect.
2) Based on role-based access control technology, allocate different functions and permissions according to users' units, departments, responsibilities, and job levels to achieve resource authorization management.
3) For the construction process of track engineering, develop project plans, personnel allocation, production material configuration, real-time progress statistics, lagging progress reminders, etc. on a daily, weekly, and monthly basis.
4) According to relevant track engineering quality acceptance standards and regulations, the system analyzes the construction quality of each process. Based on the over-limit level, real-time grading warning and auxiliary decisionmaking suggestions are given for abnormal values. For example, based on different track gauge over-limit values, different methods such as color rendering, sending emails, and sending text messages are used for grading warning, and auxiliary decision-making suggestions are proposed. 5) Implement visual management based on BIM model. Based on web-end model lightweight technology, the construction information of ballastless track is associated with twin models to more clearly, accurately, intuitively, and efficiently reflect the construction progress and accuracy of ballastless track and improve the efficiency of collaborative work among all participating units.
6) Implement cloud filling and cloud review of inspection batches of raw materials, processes, and other items in the ballastless track construction process, solving problems such as low efficiency of traditional offline approval information circulation, difficult traceability of approval traces, and inconvenient paper document retrieval.

CONCLUSION
This article introduces the intelligent construction technology of ballastless track for high-speed railway. Advanced sensors and monitoring systems are used to monitor and analyze changes in real-time during the construction process, so as to adjust the construction parameters in a timely manner and ensure the accuracy and quality of construction. Modern measuring instruments and software are used to accurately measure and analyze various data during the construction process to achieve sub-millimeter precision control. Through big data analysis and artificial intelligence algorithms, various data during the construction process are processed and predicted to achieve automated control and intelligent decision-making.
The application of these technological measures has replaced traditional manual calculation, measurement, adjustment, and control, forming a new intelligent mode. Currently, this technology has developed into a complete technical system and has been applied in several high-speed railway projects such as Nanchang-Ganzhou High-Speed Railway and Shangqiu-Hefei-Hangzhou High-Speed Railway. Through the application of these technologies, sub-millimeter precision control of ballastless track has been achieved, improving construction efficiency and the level of intelligence, and achieving significant social and economic benefits.