What are regulations on choosing national gravity points in Vietnam? What are regulations on establishing of national gravity benchmark in Vietnam?

What are regulations on choosing national gravity points in Vietnam?

Clause 2 Article 6 of Circular 11/2020/TT-BTNMT stipulates the following:

2. Selection of gravity points

a) Gravity benchmarks must be placed in areas with stable, solid geological and soil conditions, free from human and natural impacts, ensuring the accurate determination of the acceleration of gravity and long-term use.

b) Basic gravity benchmarks must be placed in solid buildings. The room for the benchmark must have a minimum useful area of 8 m2, the distance from the top of the benchmark to the ceiling must be greater than 3 m, and it must meet the technical conditions for gravity measurement. The building for the benchmark must have been built and stabilized for over 5 years from the time of burial of the gravity benchmark. In special cases, if a gravity point cannot be selected in a solid building, it is allowed to be placed outdoors, but must meet the conditions specified in point a of Clause 2 of this Article. Class I and Class II gravity benchmarks are placed outdoors.

What are regulations on choosing national gravity points in Vietnam? What are regulations on establishing of national gravity benchmark in Vietnam? - Source: Internet

What are regulations on establishing of national gravity benchmark in Vietnam?

Article 7 of Circular 11/2020/TT-BTNMT stipulates the following:

1. Construction of gravity benchmarks

a) Gravity benchmarks must be made of reinforced concrete with a grade of M25 (39TCVN 6025:1995) or higher. The top of the benchmark must be at least level with the ground and must be fitted with a brass marker.

b) The specifications for basic gravity benchmarks are specified in Sample 1 attached to this Circular. The specifications for Class I gravity benchmarks are specified in Samples 2a and 2b attached to this Circular. The specifications for Class II gravity benchmarks are specified in Samples 3a and 3b attached to this Circular.

2. The construction and handover of gravity benchmarks shall be carried out in accordance with the provisions of Clause 2 and Clause 3 of Article 12 of Decree No. 27/2019/NĐ-CP dated March 13, 2019 of the Government detailing some articles of the Law on Surveying and Mapping.

What are regulations on national gravity measurement instrument in Vietnam?

Based on Article 8 of Circular 11/2020/TT-BTNMT, the following regulations apply to gravity measurement instruments:

1. Gravity measurement instruments are specialized instruments used to determine the acceleration of gravity. The national gravity network consists of three groups: the group for measuring the acceleration of gravity using the absolute gravity method, the group for measuring the acceleration of gravity using the relative gravity method, and the group for measuring the vertical gradient of the acceleration of gravity.

2. Gravity measurement instruments using the absolute gravity method are instruments that directly measure the value of the acceleration of gravity. They are divided into two groups: the group with an accuracy of ≤ ± 0.005 mGal for building the basic gravity network; the group with an accuracy of ≤ ± 0.015 mGal for building the Class I gravity network.

3. Gravity measurement instruments using the relative gravity method are instruments that measure the difference in the acceleration of gravity between two points. They are divided into two groups: the group with an accuracy of ≤ ± 0.020 mGal for building the Class I gravity network; the group with an accuracy of ≤ ± 0.035 mGal for building the Class II gravity network.

4. Gravity measurement instruments for measuring the vertical gradient of the acceleration of gravity are instruments that directly measure the value of the vertical gradient at the measurement point. Vertical gradient measurement instruments have pairs of accelerometers. In each pair, the accelerometers are placed at a specific distance and direction to obtain the difference in the acceleration of gravity in that direction and display the result as the gradient.

Best regards!