5.2　Ground surface control survey

5.2.1　The coordinate and the elevation reference points shall be determined according to status quo of the existing control network in the project site，the coordinate and elevation systems，the network layout method，and the network hierarchy and the accuracy.When a construction control network is set up，the horizontal and elevation control networks should be used together with the local control network.

5.2.2　The horizontal control network may be based on the methods such as the satellite positioning survey method or the traverse survey method.On the premise of meeting the accuracy requirements given in Table 5.2.3-1 and Table 5.2.3-2 in this code，the horizontal control network may also be based on other network layout methods.

5.2.3　The horizontal control network survey technology shall comply with the following requirements:

1　The technical requirements for horizontal control network survey based on satellite positioning are shown in Table 5.2.3-1.

2　The technical requirements for traverse control network survey are shown in Table 5.2.3-2.

5.2.4　The elevation control network may be laid out once for all using the leveling survey method，or it may be laid out using the triangular elevation survey method of the same accuracy.The technical requirements for the elevation control network（leveling）survey are shown in Table 5.2.4.

5.2.5　A unified construction control survey system shall be established for the storage cavern construction section.The horizontal control coordinate system shall meet the requirements that the projection length in the entire storage cavern survey area shall not be greater than 25mm/km，and each tunnel portal shall be provided with at least three horizontal control points and two elevation control points. 2TwBAiIS6B1vK/2oTU7Ra6tG5q/CPuK2H2qDc09E4AdkhIu2q0LfbM9cAprFMfXN