GB/T 12897-2006Specifications for first and second order levelling (English PDF)

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m) or scale stand (mass not less than 5 kg) based on the soil materials of the line, the number of turning-point pins shall be not less than

4.It may use cloud nails as the turning-point pin for special sections.

4.3 Layout principles

4.3.1 The first order leveling line shall be laid along the road as far as possible, the leveling line shall be closed into a loop and form a mesh. The perimeter of the first order leveling loop shall not be greater than 1600 km in the eastern region and not greater than 2000 km in the western region, such perimeter can be appropriately widened in mountain and difficult areas.

4.4 Benchmark layout density Along the leveling line, it shall lay benchmarks at certain interval. The benchmarks are divided into three types. bedrock benchmarks, basic benchmarks, and ordinary benchmarks. The requirements for the spacing and layout of various benchmarks shall be implemented in accordance with Table 2.

4.6 Connect leveling of new line and surveyed line

4.6.1 The starting point and the end point of the newly established first and second order leveling lines shall be the bedrock benchmark or basic benchmark of the surveyed higher and same order lines. When the end point cannot be subject to connect leveling with the surveyed line, it shall predict the future connect leveling line.

4.6.2 When the newly established leveling line will pass or be close to the surveyed first and second order benchmarks within 4 km, within 1 km from the surveyed third or fourth order benchmarks, in case of new line surveying, it shall include the surveyed benchmarks into the plan for connect leveling or adjoining leveling. In case of connect leveling, it shall check the surveyed benchmarks in accordance with the provisions of 7.10.

4.7 Gravity survey on leveling lines

4.7.1 Gravity shall be measured at each benchmark on the first order leveling line. For the second order leveling line with an elevation greater than 4000 m or an average height difference between the benchmarks of 150 m ~ 250 m, gravity shall also be determined for each benchmark. In the first and second order leveling observation where the height difference is greater than 250 m, gravity shall be measured at the ground inclination change.

4.8 Technical design of leveling network

4.8.1 Prior to the deployment of the first and second order leveling network, it shall make surveys to collect the leveling, geological, hydrological, meteorological, and road data.

5.1.1 Selection of leveling line

5.1.2 Selection of benchmark position The benchmark points shall be selected to be at location with stable ground and representative ground elevation, be conducive to the long-term preservation and elevation connect leveling, facilitate the satellite positioning technology to determine the coordinates.

5.1.3 Selection of bedrock benchmark The bedrock benchmarks should be selected on the outcrop of the bedrock or bedrock not deeper than 5 m above the ground. The selection of bedrock benchmarks shall be attended by geologists, to collect and analyze existing data, to make field survey to understand the geological structure, the nature of rocks and soils, adverse geological phenomena and groundwater.

5.2 Buried stone

5.2.1 Type of mark stone The leveling mark stones are divided into 14 types as listed in Table 3, depending on the burial location, fabrication materials, and the specifications of buried stone. The road leveling mark stone is the ordinary benchmark stone which is buried on the shoulder of the road.

5.2.4.5 Burial of road leveling mark stone When mechanical drilling is used, underground installations such as tap water, gas pipelines, optical cables and cables shall be avoided.

5.2.5 External finishing of mark stone After the leveling mark stone is laid, external finishing shall be carried out, which will not only help to protect the mark stone, but also does not affect the appearance of the environment.

5.2.8 Stabilization time limit for leveling mark stones After the leveling stone is buried, the general area shall go through a rainy season, and the permafrost area with a permafrost depth greater than

0.8 m shall also go through a freezing and thawing period. The mark stones laid on the rock formations shall be stabilized for one month, before they can be subject to leveling observation.

5.2.9 Data to be submitted at the end of stone burial

5.2.10 Inspection and maintenance of leveling mark stone The national first order and second order benchmarks shall be regularly inspected and maintained, to ensure the benchmark integrity and elevation effectiveness. Every five years and before resurvey of the leveling line, it shall perform a field inspection and maintenance against the benchmarks. During field inspection, it shall request the local government administrative departments to provide assistance, to record the current situation of the mark stone one by one, and deal with the following issues.

6.2 Instrument calibration

6.2.1 Instruments used for leveling shall be sent to the statutory metrological verification organization for verification and calibration, it shall be used within the validity period of the verification and calibration.

6.2.2 For the new exit-factory instrument calibration, the calibration of instrument before work, and the calibration of instrument used for cross-river leveling, the items shall be in accordance with the provisions of Table 5, the inspection methods and technical requirements shall follow Appendix B.

6.3 Instrument technical indicators Leveling instrument technical indicators are performed in accordance with Table 6.

7.1 Observation method

7.1.1 The first and second order leveling uses a single line round-trip observation. The round-trip observation for the same section shall use the same type of instrument and turn-point pin along the same road.

7.2 Observation time and weather conditions Leveling observations shall be performed when the scale division line imaging is clear and stable. The observations shall not be made under the following conditions.

7.3 Setting up survey stations

7.3.1 Leveling observations in the first and second orders shall select turning- point pin (pin mass not less than

1.5 kg and length not less than

7.6 Observation tolerance and settings for survey station

7.6.1 Observation tolerance of survey station The survey station observation tolerance shall not exceed the requirements of Table 8.

7.11 Round-trip observation height difference discrepancy and loop closure error

7.12.5 When the time interval between the repeated leveling of the leveling section and the original leveling exceeds three months, and the difference between the repeated leveling height difference and the original leveling height difference exceeds the checking tolerance, it shall perform reliability checking of the both ends of this leveling section in accordance with the provisions of 7.10.

8.8 Theodolite inclination method

8.8.1 Preparation The same preparation as in 8.7.1.The theodolite used, in addition to the visual inspection of general performance, shall also be inspected in accordance with the provisions of 6.2.2.

8.10.7.2 Quality checking of GPS baseline solution The quality check of the GPS baseline solution shall meet the following requirements.

9.1 Recording methods and requirements

9.1.1 Recording method The field results measured in the first and second order leveling are divided into electronic records and handbook records in accordance with record carriers, and electronic records shall be given priority. Handbook records can also be used in special areas that are not suitable for electronic records. Electronic records are implemented with reference to C/T 2004 and CH/T 2006.

9.1.2 Record items

9.2.2 The compilation and calculation of the height difference and the approximate elevation table shall be compiled by the two persons independently and checked errorless. When calculating the benchmark elevation of the state leveling network, the following corrections are performed for the height difference used (see D.2 and D.3 for the calculation method).

9.2.3 After finishing the measurement of each leveling line, it shall calculate the round-trip observation height difference discrepancy and the accident mean square error MDelta per kilometer of leveling (for the line less than 100 km or number of leveling sections less than 20, it can be included into the adjacent line for joint calculation), it shall also comply with the requirements of

9.3.3 Submission of information

9.3.3.1 Sorting and submission of data The leveling results passing inspection and acceptance shall be counted and sorted based on lines, bound into a book, cataloged, listed, and submitted to the data management department.