The National Railway Group's Engineering and Electric Department issued the "Guiding Opinions on Precise Measurement and Tamping of Operating Conventional Speed Railway Tracks" (Engineering and Electric Line Letter [2021] No. 4) and the "Opinions on Further Standardizing the Construction and Management of Control Networks for Operating Conventional Speed Railways" (Engineering and Electric Line Letter [2021] No. 62). These documents propose the requirement to "comprehensively apply precise track measurement technology, primarily through the establishment of control networks for operating conventional speed railway tracks, to promote digital precision tamping operations using large-scale track maintenance machinery. This will effectively improve the efficiency and quality of track measurement and large machinery tamping operations, thereby enhancing the operational quality of conventional speed railway lines."

This article mainly shares the experience of using a "Beidou + inertial guidance" cart, relying on benchmark plane control points, to achieve rapid measurement of the track alignment for conventional speed railways.

Figure 1: "Beidou + Inertial Guidance" Measurement of Track Alignment for Conventional Speed Railways

1. Project Background

1.1. Control Stake Layout Method

A certain line, in accordance with the requirements of the "Interim Technical Conditions for the Setting and Measurement of Control Stakes in Conventional Speed Railways" (TJ/GW159-2019), has laid out control stakes in pairs along both sides of the line with a spacing of 100 meters in the direction of the line. On bridges and embankment sections, the stakes are laid out using clamps on the catenary poles, while in tunnel sections, they are pre-embedded in the tunnel walls using embedded parts and drilling.

1.2. Benchmark Plane Control Points

A benchmark plane control point is laid out every 1000 meters along the direction of the line.

1.3. Leveling Benchmark Point

Leveling benchmark points are laid out every 1000 meters along the direction of the line, coinciding with the benchmark plane control points.

2. Necessary Conditions for Operations

To achieve rapid measurement of track alignment for conventional speed railways using "Beidou + inertial guidance" technology, the following basic conditions must be met:

(1) The line ledger data is complete, and the basic technical briefing has been completed.

(2) The benchmark plane control points and leveling benchmark points coincide, and the measurement results meet the specification requirements.

(3) Good satellite signal reception is required.

(4) The work is carried out during the maintenance window period.

Note: For ease of description, the benchmark plane control points and leveling benchmark points will be collectively referred to as reference points in the following text.

3. Field Data Collection

Step One: Setting up the Reference Station. The reference station is set up on the reference point. According to the standards of static measurement, the station is centered, leveled, and the instrument height is measured. The reference station should be turned on at least 15 minutes before the Beidou inertial guidance cart.

Figure 2: Setting Up the Reference Station

Step Two: Complete the assembly of the Beidou inertial guidance cart, push it to the starting point of the measurement, and complete the equipment initialization.

Step Three: Begin the measurement. Mark special locations such as curve characteristic points (ZH/HY/YH/HZ), bridges, culverts, signal machines, and switch positions (before switch, after switch, switch center) when encountered.

Step Four: Push the Beidou inertial guidance cart to the end point of the measurement, conclude the measurement, and the task is completed.

Figure 3: Pushing the Inertial Guidance Cart

4. Data Processing in the Office

The internal data processing for the "Beidou + Inertial Guidance" conventional railway track alignment measurement is convenient. By importing the original measurement data, one can achieve "one-click" data processing to obtain the three-dimensional coordinate sequence of the track centerline.

(1) Route ledger data (information on horizontal curves, gradients, broken chains, etc.).

(2) Benchmark point result data;

(3) Original measurement data from the Beidou inertial guidance cart;

(4) Field marking data;

(5) Reference station data.

5. Curve Fitting

5.1. Technical Requirements for Horizontal Curve Fitting

The input data for planar alignment fitting are the northeast coordinates of the track centerline and the starting point mileage. Special points should be configured with attributes. The fitted planar curve should be as close as possible to the existing line to minimize the total realignment amount. During planar alignment fitting, checks should be conducted on bridge eccentricity, building clearance, and track spacing until the requirements are met. (Due to article length limitations, specific technical requirements can be found in relevant specifications.)

Figure 4: Process of Horizontal Curve Fitting

Figure 5: Results of Horizontal Curve Fitting

5.2. Technical Requirements for Longitudinal Profile Fitting

Vertical curves should not overlap with horizontal circular curves, and they should not be placed within the range of transition curves, mainline turnouts, or rail expansion regulators. During the data fitting process, the points of gradient change are generally selected at whole 10-meter mileages. In sections where the gradient changes significantly, the mileage of the points of gradient change can be selected at whole meters. For curve sections, the elevation of the lower rail is taken. For straight sections, the elevation is determined by the lower rail of the curve in the direction of increasing mileage. If there is no curve (or a mileage break) in the direction of increasing mileage, then the elevation is determined by the lower rail of the curve in the direction of decreasing mileage. (Due to article length limitations, specific technical requirements can be found in relevant specifications.)