5.3　Underground control survey

5.3.1　The underground control survey shall comply with the following requirements:

1　The angular mean error of the underground traverse control survey shall be determined in accordance with Table 5.3.1-1，depending on the length of the control line.

2　The 1000m-elevation difference total mean error of the underground elevation control survey shall be determined in accordance with Table 5.3.1-2，depending on the control line.

5.3.2　The establishing of the underground horizontal control network shall comply with the following requirements:

1　The underground horizontal control network should be of traverses，and long-side traverses or narrow and long multi-loop traverses shall be set up along the centerline or both sides of the storage cavern，with the application point of the portal（inserting point）as the starting point.

2　The traverses should have equal side lengths.In the straight sections，the side length of the traverses should not be shorter than 150m；in curved sections，the side length of the traverses should not be shorter than 50m.The clear distance between the traverse side and the underground facilities should not be shorter than 0.5m.If the side length of the traverses in the straight sections is shorter than 150m or that in the curved sections are is shorter than 50m，the number of the survey cycles or the accuracy of the instruments shall be increased.

3　When the cavern is excavated to 2 times to 3 times the designed traverse side length，one traverse extension survey shall be performed.

5.3.3　The underground elevation control survey shall comply with the following requirements:

1　The leveling points should be set up at intervals of 200m；

2　The leveling points may be based on the traverse points or may be laid independently；

3　The underground elevation control survey should be based on the leveling survey method.It may also be based on the triangular elevation survey method.

5.3.4　The underground construction survey shall comply with the following requirements:

1　The cavern construction centerline should be set up using the polar coordinate method according to the underground control points.When the excavation distance extends to one or two times the traverse side length，new centerline points should be set according to the extended traverse points.

2　When the centerline method is used，the interval of the centerline points should not be shorter than 100m. URIkA7dhBL6AeklZHyhmZnGXXNQLZ4gVVIEQ0CZHun4Yuaqu+y+ahSUnEVzmMXCQ