Perspective Chapter: Intelligent Construction Technology of Ballastless Track for High-Speed Railway

Abstract

Intelligent construction technology is the only way to realize the construction and upgrading of high-speed railways, and strongly supports the construction of smart railways. In terms of intelligent track design technology, the digital, dynamic and visual design of track is realized, which changes the way the traditional design unit provides only construction drawings. The design unit then provides digital track design results in addition to construction drawings, facilitating intelligent manufacturing, construction, operation and maintenance, etc. In terms of the intelligent construction of track slabs, the traditional track construction technology is upgraded by using the results of track intelligent design, and data from the total station, rail inspection trolley, note books and related tooling are automatically collected, controlled and adjusted. Data collection, analysis, statistics and prediction mechanism of the plate ballastless track are established to form a track intelligent construction technology of “data collection, data penetration, data sharing and openness, data tracking and tracing”. In terms of complete sets of software for track intelligent construction, a series of intelligent design, manufacturing, construction software and complete sets of intelligent construction equipment are proposed, which greatly improves the level of intelligent construction.

1. Introduction

Ballastless track is one of the core technologies of high-speed railways. The track structure directly acts on the substructure, the deformation of the substructure will directly affect the track smoothness and stability, and the construction quality and accuracy will directly affect the safety and comfort of high-speed train operation. Track engineering has the following characteristics (Figure 1) [1, 2].

1. High precision requirement: The required accuracy of rail laying is ±1 mm, the manufacturing accuracy of track slab is ±0.5 to −1 mm; the accuracy of the molds is 0.3 to 0.5 mm; The thickness accuracy of cast-in-situ concrete is 0 to 10 mm.

2. The short period of construction, and the time of completion is quite close to the opening of operation: After the completion of the track engineering construction, it will enter the joint trial and test period. The track quality needs to be strictly controled, and there is no time for mending and repair [3, 4].

3. There are abundant sources of construction data for track engineering. The measurement mainly adopts total station and rail inspection trolley; with the development of new technologies such as the Internet of Things, the integration of data interfaces has become possible [5, 6, 7, 8]. Research on the conversion of data to information and intelligence for track construction and laying can be carried out to realize real-time data uploading and intelligent control, which can greatly improve construction quality and accuracy.

Figure 1.

Construction site laying of ballastless track for high-speed railway.

A new round of scientific and technological revolution and industrial transformation is emerging; artificial intelligence (AI), big data, cloud computing, Internet of Things (IoT), building information modeling (BIM), Beidou Navigation satellite system (BDS) and other new technologies are accelerating breakthrough applications, and human society will quickly enter the era of intelligence [9, 10].

With the rapid development of high-speed railways and artificial intelligence and other high-tech higher requirements have been put forward for the supervision ability, intelligence and recording of information for high-speed railway construction on site. At the same time, the development of high-speed railways is turning to pay more attention to delicacy management, the development quality, the service level, and solving the deep-seated and overall problems, further improving the modernization of construction and the management level of the high-speed railway.

The design realization of the traditional construction management mode of high-speed railway track engineering shall be delivered in the form of construction drawings, and the construction organization constructs according to the drawings. The construction level of information gathering and intelligence is too low. Research on intelligent construction technology is helpful to improve the quality of track construction, enhance the efficiency of operation, ensure project progress and control construction cost.

This chapter introduces the intelligent technology of ballastless track construction for high-speed railways, and intellisense, mobile internet intelligent transmission technology, intelligent analysis and control technology introduced to the track construction process. This mainly forms the dynamic design technology of the ballastless track construction process, the measurement and control technology of high-speed railway ballastless track construction based on data driven and the intelligent control technology which realize the high precision control and automatic measurement and control of ballastless track construction processes, lays the foundation for intelligent railways, and promotes the development of railway construction to an intelligent approach (Figure 2).

Figure 2.

The overall technical scheme of ballastless track intelligent construction.

2. Process dynamic design technology for ballastless track construction in high-speed railway

Ballastless track is greatly affected by changes in the substructure, such as subgrade, bridges and tunnels. Realizing the intelligent update of design results and complete intelligent operation with dynamic data driven construction equipment is the key to promoting the efficiency of ballastless track construction and controling quality. Based on the collected data of the whole construction process, taking into account the changes of the substructure such as subgrade, bridge and tunnel as the input conditions, the plane and elevation dynamic design of the concrete base and track slab is realized. Problems such as the fastener at beam end exceeding the standard requirement, the control of the concrete base plate hanging out, and the precise control of the geometric size of the ballastless track are solved. The dynamic updating of the design results in the construction process is realized, and dynamic design problems such as alignment changes at long-span Bridges, deformation joints and transition section position updating are all overcome.

Take the extremely long span bridge such as Ganjiang bridge of Chang-Gan Railway (main span 300 m), Yuxihe bridge of Shang-He-Hang Railway (main span 324 m) as an example, which were affected by bridge creep, temperature deformation, load on the bridge and wind speed and other factors, as a result of which the ballastless track line is difficult to control. The dynamic design technology was adopted to obtain the exact correspondence between bridge loads and cable force and design model (main beam line type) after the main bridge design was finally closed and preloaded. The main bridge line type was systematically adjusted and the digitized track results have been corrected in real time (Figure 3).

Figure 3.

Process dynamic design technology of ballastless track construction process.

This mainly includes the layout algorithm of ballastless track, the coordinate cluster calculation method of ballastless track under the condition of complex line and the virtual preassembly technology of ballastless track.

2.1 The layout algorithm of ballastless track

During the construction period, due to the great difference between the actual working conditions of the substructure such as the subgrade, bridge and tunnel and the assumed design working conditions, the ballastless track needs to be dynamically adjusted according to the actual working conditions. The layout of the track is as follows:

1. By configuring different lengths of track slab and adjusting the gap of the track slab to meet the layout requirements, the layout of track slab is disconnected at the bridge joint, settlement joint, deformation joint of subgrade and bridge, subgrade and tunnel, bridge and tunnel boundary, etc.

2. The track slab lays on such as a 24, 32 m beam, and commonly used continuous beam and other areas of standardized layout, the track layout should consider the sleeper spacing uniformity and the maximum spacing of fastener at the beam end and other restrictions.

According to the above track slab layout principles, the track slab layout in the track slab design software is implemented as follows:

1. The left line and right line are arranged separately.

   Due to the different lengths of the left line and right line, the different beam joints at the center line of the track in curved sections, and the different beam lengths at the center line of the track when the bridge is designed into a curved beam in a small radius curve section, the layout of the track slab should be arranged separately on the left line and right line. According to the way that the left line and right line is laid separately, the more accurate data file of the track slab can be obtained.

2. The track layout mode of “the whole is zero and set zero for the whole” will adopted.

   The line is composed of straight line, front easing curve, round curve and back easing curve, etc. which is composed of subgrade, bridge and tunnel. The line of track layout design can be decomposed into different sections, each section is composed of many small sections with the same length, that is one line can be divided into several blocks. Each block is composed of a lot of simply supported beam and continuous beam bridge, for example: there are a lot of same span 32.6 m beam, the track layout on the 32.6 m beam takes the same parameters. Therefore, the detailed idea of the track layout design is: the parameters of the same length that compose the line are first laid out, for example, the 32.6 m simply supported beams are arranged first, and all the later simply supported beams of the same type are arranged in the same way.

Therefore, the layout design of track slab is designed to find the optimal layout scheme under the constraints of slab length, slab gap, sleeper spacing, etc., to achieve uniform layout of fastener spacing, the fastener spacing at beam end that meets the design requirements, and the optimal control of curve vector distance deviation on small radius curve (Figure 4).

Figure 4.

Schematic diagram of track layout algorithm.

2.2 Calculation method for ballastless track coordinate cluster under complex line conditions

Accurate measurement is the most important and difficult process to control in the construction of ballastless track. The whole measurement technology requires high precision and is influenced by many factors. The azimuth of the track slab centerline and the three-dimensional coordinates of the rail top center at the rail support platform used in the measurement process need to be accurately calculated, and digital results are automatically generated to guide the construction and laying of the base, track slab, etc.

According to the plane data of the route, the tangent offset method (i.e. rectangular coordinate method) is used to calculate the coordinate values of each point on the route. As shown in the figure, take the calculation of any point coordinates. The mileage of the starting and ending points (HZ/ZH) of the curve and the coordinates of the intersection point (JD) are known. The azimuth of the line conductor is expressed in A, the radius of the circular curve is expressed in R, and the length of the transition curve is expressed in l₀. The coordinates of the straight-line segment, the transition curve segment (front/back), and the circular curve segment are calculated section by section to form the track design data file.

The horizontal and vertical relative coordinates of each calculation point within the straight line are fixed, and the longitudinal coordinates are the cumulative value of the fastener spacings. The coordinates and azimuth of the main point and control point of the plane curve are calculated through the plane design data of the line, including the coordinates of the intersection point, the curve radius and the length of the transition curve. The elevation of the main point and control point of the vertical curve is calculated through the design data of the line profile, including the elevation of gradient change point, slope, grade length and radius of the vertical curve. At the same time, the coordinates of track slab rough laying position point and base corner point are calculated.

Each point of the transition curve is a gradually changing three-dimensional coordinate, the plane takes the starting point of the plate as the coordinate origin, and the vertical takes the midpoint of the rail top line of the starting point of the plate as the coordinate origin.

The horizontal coordinate of each point within the circle curve has an offset value, the vertical coordinate is fixed, and the longitudinal coordinate is the cumulative value of fastener spacings.

After calculation, the system will automatically generate the digital results guiding the construction survey, as shown in the Figure 5.

Figure 5.

Generated digital results.

Description of relevant figures of track slab data file

1. Line 1: Slab number; Coordinates of the starting point of the slab, X coordinate perpendicular to the line direction; Y coordinate along the line direction; Elevation Z coordinate; Type of track slab; Mileage; Radius of plane circular curve; Vertical curve radius; Superelevation;

2. Line 2: Slab number and control point; X coordinate perpendicular to the line direction; Y coordinate along the line direction; Elevation Z coordinate; Type of fastener;

3. …

4. The last line: Slab number; Coordinates of the ending point of the slab, X coordinate perpendicular to the line direction; Y coordinate along the line direction; Elevation Z coordinate; Type of track slab; Mileage; Radius of plane circular curve; Vertical curve radius; Superelevation.

2.3 Three dimensional model building and updating technology of ballastless track

Based on the results of (2.1) and (2.2) in this section, the 3D visualization building technology of ballastless track is developed, and the real-time dynamic updating of 3D model during construction is realized.

The track structure is composed of steel rails, fasteners, track slab, etc. There are many types of track components. To avoid repeated creation of models, a component library was developed. Unified standards and formats were used for creating component models, such as component classification, naming, material standards, modeling accuracy, etc.; Developing parametric modules to build models of the same type but with different sizes, such as track slabs and bases; Realizing the unified management of component models to facilitate the reuse of components at all stages. Based on the unified coding system, the detailed design model of track unit was constructed. Create component models with fixed dimensions such as rails, fasteners and sleepers, by inputting design parameters, parameterized design of different types of track slabs and different plane section bases can be achieved. For example, ballastless track structures (track slabs, etc.) can be rapidly designed according to the information of non-standard slabs and curve superelevation value generated by layout design. The creation of composite model is realized by inputting elevation, layout design, etc. Combined with the component model and the track engineering design data, the track model can be quickly created and updated according to the change of relevant professional information. By means of human-computer interaction, track components creation, data model generation, 3D digital model layout, etc. are all completed through the system interface (Figure 6).

Figure 6.

3D model building and updating technology of ballastless track.

3. Data driven construction measurement and control technology for ballastless track of high-speed railway

Using new generation information technologies such as big data, mobile Internet, edge computing, etc., based on the digital design results of track engineering, and data driven mode, the intelligent construction measurement and control mode of “data perception, real-time transmission, dynamic analysis” was established by using the data automatic acquisition and measurement of total station, track inspection trolley, measurement and control terminal, etc.

The portable intelligent measurement and control terminal, fine tuning robot and rail geometry and position information acquisition device were developed. The data interface of the whole process of design and construction has been opened up, and the automatic measurement and control of key processes of ballastless track, such as base laying and positioning, track slab fine adjustment, track panel fine adjustment and rail fine adjustment, has been realized, which improves efficiency and reduces manual inputs. It realizes the interaction and flow of “design, measurement and control, feedback” of construction information flow. The GeoCom communication technology is used to open the control interface with the measuring robot, realize the wireless communication and automatic control with the measuring robot, realize the automatic calculation of fine adjustment deviation, and complete the wireless upload of fine adjustment results to the management and control platform (Figure 7).

Figure 7.

Intelligent measurement and control scheme based on data drive.

3.1 Base laying and positioning based on data drive

Through the CP III control network and digital design results, the station setting of the measuring robot is completed. The terminal is used to control the measuring robot wirelessly to realize automatic measurement of base plate lofting. At the same time, the elevation measurement data of the subgrade surface, beam surface and other offline foundations are obtained, and the elevation deviation is obtained through real-time comparison with the digital design results. This determines the influence of beam surface elevation before the construction of the base, the base thickness adjustment scheme, automatically generates the formwork height of the base, and realizes the accurate control of the plane position, elevation and thickness of the base (Figure 8).

Figure 8.

Schematic diagram of base laying and positioning process based on data drive.

3.2 Fine adjustment of track slab based on data drive

The fine adjustment of track slab is basically a precise measurement in the installation stage, that is, the key point measurement or setting out of the track slab under to acheive the design theoretical position. During the preparation for fine adjustment, the process uses curve elements, slope information, long and short chains, other basic information and dynamic calculation modules to calculate the three-dimensional coordinates of the rail support platform based on the positional mileage of the track slab. A measuring frame accurately matched with a bolt hole is placed on the rail support platform. A prism for the identification by the measuring robot is installed in the center of the frame. The intelligent measuring robot is used to collect the three-dimensional coordinates of the prism at the corresponding point and send them to the mobile terminal. The measurement and adjustment software automatically analyzes, compares and calculates between the measured coordinates and the design coordinates in real time to form the geometric position deviation under the three-dimensional space of the track slab at the rail support platform. The fine adjustment robot is controlled according to the deviation to complete automatic adjustment (Figure 9).

Figure 9.

Schematic diagram of track slab fine adjustment scheme based on data drive.

The measurement and control is mainly realized by a GeoCom interface, and a communication unit is composed of the request of the mobile terminal and the response of the measuring robot. The GeoCom interface is a dynamic link library that encapsulates multiple secondary development functions. When developing the software, the above encapsulation functions can be used to realize the calibration, rotation control, automatic target recognition, accurate ranging, angle measurement, etc. of the measuring robot. It is developed based on an Android platform and uses ASCII protocol to realize control communication with the measuring robot. The Bluetooth communication module of the mobile terminal is used to establish the information channel with the measuring robot and send ASCII commands through GeoCom interface technology. The measuring robot receives ASCII character commands, and returns a response string after protocol analysis. It can then realize the basic measurement and control operations such as equipment initialization, instrument connection, station setting, parameter configuration, verification, measurement, upload, port release, etc.

With the SQLite database as the data organization and storage carrier, the wireless control of the measuring robot is realized through ASCII command mode, and the automatic measurement of track slab fine adjustment is realized. The main functions of the software include the following functions: engineering information configuration of track slab fine adjustment operation, parameter setting of track slab fine adjustment operation system, layout data interface configuration, calibration of fine adjustment standard frame, track slab overlapping orientation, track slab fine adjustment measurement, fine adjustment result data upload, etc. (Figure 10).

Figure 10.

Functional structure of wireless intelligent fine adjustment software for track slab.

The measured deviation is fed back to the developed automatic fine track slab adjustment robot in real time, and the electric control system is combined with the servo motor to automatically execute the fine adjustment command without manual adjustment. The fine adjustment deviation and adjustment time are reduced, and the precision of fine adjustment is guaranteed. Compared with manual fine adjustment, the comprehensive efficiency is increased by more than 3 times (Figure 11).

Figure 11.

Schematic diagram of track slab fine adjustment robot scheme.

3.3 Track panel and rail fine adjustment based on data drive

Based on the geometric dimension data of the track in the design results, the automatic measurement of the track centerline, the three-dimensional coordinates of the left and right rails, and the calculation of the lateral and vertical deviations of the track is determined. Based on the developed track inspection trolley information equipment, the automatic collection of track geometry and position data is determined. The thickness distribution of track bed slab is analyzed in real time by measuring the rail top elevation information and combining the elevation data of base slab/bearing layer; determine the year-on-year analysis of the fine adjustment data of the rail panel, the retest data after pouring, and the fine adjustment data of the rail, so as to provide support for obtaining the variation law of the construction deviation of the rail panel, improving the construction control process, and also provide a pre-foundation for the subsequent fine adjustment of the rail (Figure 12).

Figure 12.

Data driven rail panel and rail fine adjustment.

4. High speed railway ballastless track construction intelligent management and control technology

The intelligent construction control technology of ballastless track is composed of four parts: automatic data collection, intelligent transmission, big data storage, and the whole process supervision of the control platform. The information equipment interconnected with the management and control platform, such as the intelligent measurement and control terminal for base positioning and track slab fine adjustment, and the collection device for track geometry and position, are used to realize the automatic upload of relevant information such as construction process measurement and laying. Using big data storage technology, a distributed data warehouse is built on the server to realize the orderly, regular and structured storage of massive amounts of data. Through the construction intelligent management and control platform, the massive amount of data in the data warehouse are screened, extracted, analyzed and processed. In combination with the relevant requirements of the slab track construction acceptance standards, the data is judged to exceed the limit. Through the early warning cloud system, various ways of early warning and prediction are realized, so as to realize the interconnection between the construction site and the remote platform, the interconnection between the construction workers and the management personnel, and the control of the process flow, as well as realize the whole process management of quality (Figure 13).

Figure 13.

Control platform for ballastless track construction.

The intelligent management and control technology takes the intelligent management and control platform as the core, and takes “design data achievements” and “dynamic data files of the whole construction process” as the data basis. The core of management and control is the progress and accuracy of the whole process of ballastless track construction. Analyze, judge and count the progress and quality of track construction according to the set tolerance requirements by quickly analyzing the on-site construction survey data. It will provide detailed and convenient statistical information for project construction managers, achieve the dynamic management of track construction process on site, improve management efficiency and promote construction quality.

The main functions are as follows:

1. Construction precision control: elevation deviation of the offline foundation surface, plane linetype of the base slab/bearing layer, elevation and thickness control, concrete thickness and elevation control of the track bed slab, precision control of the rail panel and long steel rail laying, etc.

2. Track progress management: Combined with the track 3D visualization design model, the visualization progress management is achieved.

3. Report statistics management: Automatically generate a progress report and precision quality report.

4. Early warning and forecasting: Limit management, early warning value setting, automatic early warning of construction deviation, etc.

5. Online approval and management of inspection batch for concrete, reinforcement and testing.

6. Digital asset management such as full-line 3D model and construction real-time information model.

7. Organization and structure management: Assign authority functions to the management personnel of construction units, supervision units and construction units.

4.1 Schedule management

Prior to the construction of ballastless track, engineering plans are made for the upcoming process, such as track slab rough laying plan, track slab fine adjustment plan, track slab retest plan, etc. Generating a progress Report to display detailed progress information of each process (Figure 14).

Figure 14.

Project schedule management.

4.2 Construction quality control

According to the fine adjustment result data uploaded at the construction site, the control platform automatically calculates the qualified rate and the percentage by which the limit of each indicator parameter is exceeded according to the allowable limit set by the user for the fine adjustment of the track board. For example, the platform will display the statistical results in the form of charts and provide the function of querying detailed data of fine adjustment. The fine adjustment data which exceeds the limit will be marked in red in the table for processing. Statistical indicators and parameters include:

1. The deviation between the actual elevation of the rail seat and the designed elevation after the fine adjustment of the track slab;

2. The deviation between the center line position and the design center line position of the rail seat after the fine adjustment of the track slab;

3. Elevation deviation of adjacent track slab rail seat after fine adjustment of track slab;

4. Center line deviation of adjacent track slab rail seat after fine adjustment of track slab.

After the track plate is perfused with self-compacting concrete, the rail seat is measured again. According to the acceptance standard, the deviation of the height and center line of the rail seat is controlled, and the qualified quantity is counted automatically in the platform and fed back to the management personnel along with with the early warning mechanism.

Track slab retest progress and accuracy pass rate statistics, including elevation of rail seat, center line of rail seat, elevation of adjacent slab rail seat, center line deviation of adjacent center line of rail seat deviation are produced (Figure 15).

Figure 15.

Construction quality control.

4.3 Early warning and forecast function

The platform automatically calculates the percentage of qualified rate and limit exceeded for each indicator parameter. Data exceeding the limit will be warned in real time. The administrator of each unit conducts on-site treatment in time according to the over-limit situations and eliminates the alarm information. This can achieve real-time control of construction quality (Figure 16).

Figure 16.

Early warning and forecasting.

4.4 Progress and accuracy report

According to the data upload status of each Construction section of the whole line, the platform will conduct statistical work according to the set fixed time and a final statistical statement is presented. Reports can be divided into daily reports, weekly reports and monthly reports according to different time segments. They can also be divided into base, track plate and other different procedures according to the statistical content of the report. Reports can also be produced for the precision statistics of all processes (Figure 17).

Figure 17.

Progress and accuracy report.

5. Conclusion

This chapter mainly describes the intelligent construction technology for ballastless track of high-speed railways from three aspects: construction dynamic adjustment technology, construction measurement, and control technology based on data driven and intelligent construction control technology. Through the application of the above technical measures, the traditional manual calculation, measurement, adjustment and control is replaced by a new intelligent mode. At present, after more than 10 years of research, this technology has advanced to form a complete technical system, which has been applied in more than 11 high-speed railway projects such as Zheng-Xu, Chang-Gan, Shang-He-Hang and Fu-Xia. The submillimeter precision control of ballastless track is realized, the efficiency and intelligence level of construction are improved, and significant social and economic benefits are achieved.