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The line construction survey mainly includes: the measurement of the center line of the restoration line, the measurement and design of construction control piles, the lofting of subgrade side piles, the lofting of subgrade slopes, the lofting of pavement construction and the measurement and design of vertical curves.
1. Line control measurement
1. Coordinate system
The coordinate system of the line control measurement should meet the projection length deformation of no more than 25cm km:
1) Adopt a unified Gaussian projection 3° with plane Cartesian coordinate system.
2) The Gaussian projection 3° zone is used to project the plane Cartesian coordinate system on the offset elevation surface or the average elevation surface of the survey areaor a planar Cartesian coordinate system with an arbitrary band projection surface of the 1985 National Elevation Datum.
3) For small areas or control networks with special accuracy requirements, independent coordinate systems can be adopted.
4) In the area where there is a plane control network, the original coordinate system can be used.
5) The building coordinate system can be used in the factory area.
2. Elevation system
The elevation system for line measurements should be based on the 1985 National Elevation Datum. The original elevation system can be used for measurements in areas where there is an existing elevation control network;When joint surveying of small areas is difficult, a hypothetical elevation system can also be used.
3. Control point measurement and setting
1) The point of the control point.
The location of the plane control point should be selected in a place where the soil is solid, easy to observe, and easy to preserve. The point of the elevation control point should be selected on the periphery of the construction disturbance area. The points of the plane and elevation control points should be buried with permanent markers as needed.
2) Measurement method.
The plane control of the line should be based on the traverse or GNSS measurement method, and should be laid close to the line through-line. For the elevation control of the line, it is advisable to adopt the leveling measurement or electromagnetic wave ranging triangulation elevation measurement method, and lay it close to the line.