4.2　Surveying

4.2.1　Prior to survey，following stake handover and shift work shall be properly conducted:

1　Construction contractor shall protect the coordination controlling piles and turning point stakes with necessary measures after handover by design contractor.

2　Detailed review and on site verification shall be conducted for route survey data，route layout and profile.

3　Proper identification shall be marked on fixed reference object.Pile number shall be indicated and the direction shall be pointed out.

4　The equidistance method of moving stakes along paralleling pipeline centerline may be used for plain areas and the traverse method of positioning pipeline may be used for mountain areas with difficulties to move stakes.

4.2.2　Pile coordinate data shall be reviewed based on permanent benchmarks and pipeline centerline shall be surveyed.The stakes of one-hundred-meter spacing pile，longitudinal slope change pile，wall thickness change pile，crossings makers pile，and curve additional pile between turning point piles shall be set up and identified information such as the pile type，number，milestone etc..

4.2.3　Survey of pipeline centerline shall include handover point survey，deflection angle survey，centerline milestone pile survey and round curve survey.

4.2.4　The curve additional piles shall be set up for larger pipeline horizontal defection angle and spacing between curve additional piles shall be not more than 10 meters.

4.2.5　Survey personnel shall check the quantity and angle of flexible laying pipe section，cold bending section and hot bending section in design drawings.

4.2.6　For flexible laying section or cold bending section，their horizontal turning point shall be set out with a curve on ground according to the parameters such as length of tangent line，and external vector moment.For the pipe section adopted with prefabricated bend pipe，the curve shall be laid out according to curvature radius and angle.

4.2.7　For the pipeline located in mountainous area and the pipeline with comparatively large topographic areas，the slope change point location，angle and curvature radius of longitudinal deflection angle change point shall be defined on the basis of construction drawings and or measurement data.

4.2.8　Radius for curvature with horizontal flexible laying shall not be less than 1000 times steel pipe diameter.Radius for curvature of elastic laying pipeline on vertical surface shall be more than curvature radius of deflection curve generated for pipe under self-gravity effect.Radius for pipeline elastic bending curvature shall be calculated as below:

Where　R——pipe elastic curvature radius（m）

D——steel pipe OD（m）

α——pipe deflection angle（°）

4.2.9　Pipeline horizontal angle and longitudinal angle should be adopted with round curve with the same curvature radius for control.

4.2.10　In order to ensure that pipeline flexible laying is attached to trench bottom，surveying shall be conducted as required by design and pipeline trench depth shall be in compliance with design requirements.