2 Terms and Symbols
2.1 Terms
2.1.1 Large crossing
Tension sections of lines crossing wide navigable rivers，lakes or straits with large span lengths（above 1000m）or high towers（higher than 100m），where special consideration shall be given to conductor selection or tower design and a fault may severely influence the navigation or is extremely difficult to repair.
2.1.2 Straight line location survey
A method of survey with which positions of stakes of straight line are set up in the direction of the line between two angles to facilitate plan and section survey，crossing-over survey and location survey.
2.1.3 Linearity
The description of straight-line stakes deviating from the theoretical line formed by two angle stakes，with the straight-line stakes and the theoretical line formed by two angle stakes all projecting in the same plane.
2.1.4 The stake of straight line
Control stakes arranged on the line between two angle stakes to facilitate subsequent surveying work such as plan and section survey，crossing-over survey and location survey.Also known as straight-line stake.
2.1.5 Directional stake
A stake arranged close to the turning angle on the straight line in front of or behind the angle in determining route or location.A directional stake is used to indicate the direction of line.
2.1.6 Distance between two stakes
The horizontal distance between two adjacent straight-line stakes or a straight-line stake and its adjacent angle stake.
2.1.7 Difference of elevation between two stakes
The difference of elevation between two adjacent straight-line stakes or a straight-line stake and its adjacent angle stake.
2.1.8 Central section
The section line formed by the vertical plane in which the line between two angle stakes lies intersecting the ground surface.
2.1.9 Side line The section line at which the vertical plane formed by side conductors between two towers intersecting the landform or surface features.
2.1.10 Wind slanting point
Points of the landform（such as ridge，ramp and steep rock）and buildings（structures）which need to be surveyed as they may be approached by the side conductor under the effect of the largest wind force.
2.1.11 Crossed point of two lines
The point at which the central plane of central conductor or side conductor intersects the crossed line.
2.1.12 Cross section
The landform section lines perpendicular to the central section.
2.1.13 Height line of the trees The section line formed by connecting the intersecting points of vertical plane of the conductor（or side conductor）between two towers and the tree tops.
2.1.14 Location survey A method of survey with which a tower location is determined and the cumulative distance or coordinates and elevation of a tower location stake is measured.
2.1.15 Distance between two poles
The horizontal distance between two adjacent tower location stakes.
2.1.16 Geotechnical investigation
Activities of ascertaining，analyzing，and assessing the geological and environmental features and geotechnical properties of the construction site according to the project requirements，and compiling investigation documents.
2.1.17 Geotechnical exploration
The means of geotechnical engineering investigations，including drilling，welling，trenching，pitting，geophysical exploration and cone penetration testing.
2.1.18 Investigation of subgrade for each individual tower
Activities carried out during the geotechnical investigation at the detailed design stage to explore the subgrade of each pole or tower.
2.1.19 Investigation during construction
Activities carried out during construction，which are used to ascertain the engineering geological conditions which cannot be ascertained at the detailed design stage or satisfy certain special requirements，including exploration，monitoring，analysis，evaluation and preparation of exploration documents.
2.1.20 Prototype test
A kind of solid engineering test carried out within a typical site on the ground rock and soil under the engineering conditions equivalent to the proposed project.
2.1.21 Result of geotechnical investigation
Systematic investigation documents which are obtained by means of organization，statistics，summary，calculation，analysis，evaluation and proposition of engineering suggestions based on raw data.These documents are to be used for the proposed construction project.
2.1.22 Design flood
The flood satisfying the requirements of design standards，which are represented by characteristics such as peak flood flow，flood level，total flood volume，and flow hydrograph.
2.1.23 Standard of design flood
Flood frequency or flood standard adopted in the engineering for different classes of buildings.
2.1.24 Flood control standard Standards for flood control determined by the state based on the importance of protected objects and economic rationality.
2.1.25 Flood control planning
The general planning developed to prevent or control flood.
2.1.26 Fluvial process
The changes in erosion and deposition of a river channel under the interaction of water flow and riverbed，which occurs naturally or due to human interference.
2.1.27 Seabed evolvement The changes in erosion and deposition of seabed，beach or shore under the interaction of water flow and seabed，which occurs naturally or due to human interference.
2.1.28 Hydrological computation Organization，analysis and computation of hydrological data for a specific purpose，so as to provide hydrological data required for the planning，design，construction and management of a project.
2.1.29 Maximum stage of waterway
The maximum stage of waterway permitted for the normal navigation of vessels carrying standard loading.
2.1.30 Navigation standard
The basic technical provisions specified by the state which must be observed in waterway planning and construction.
2.1.31 Grade of waterway
The grade of waterway designated according to national waterway grading criteria.
2.1.32 Navigation clearance
The height and span of space which must be provided under river-crossed buildings for safe and free access of vessels.
2.1.33 Design wind speed
The wind speed at design frequency required by engineering standards.
2.1.34 Wire ice covering
A meteorological phenomenon when glaze，rime，freezing mixture of glaze and rime，and wet snow congeal and stick to the conductors.
2.1.35 Standard ice thickness
The ice thickness obtained by converting the thicknesses of ice with different densities and shapes to snow having a density of 0.9g/cm3 and evenly wrapping the conductors.
2.1.36 Design ice thickness
The ice thickness obtained by means of a series of analysis and computation，including correction in terms of conductor height，diameter，landform，distance between two poles，and line direction，and the conversion of re-occurrence period.