道路工程专业英语-(第二版) 相关资料

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Traditionally, rural highway location practice has been field oriented, that is, the bulk of thelocation party's time and effort went to measurement and observation　" on the ground. "Reconnaissance of the area was the first step; the locator, using available topographic maps andsometimes an airplane, explored the area. The aim was to search out feasible routes and determinesuch primary control points as mountain passes or suitable river crossings and to locate majorobstacles such as steep slopes. Reconnaissance of feasible routes came second; each of these wascovered on foot and rough measures of relative length, difficulty, and cost were taken. Where rate ofclimb was critical, slopes were measured with an Abney hand level or some comparable instrument.Often the locator "flagged" out the line as he went to establish control points for more detailedsurveys that might follow. The third step was for the survey party to run in the preliminary or P line,or, where necessary, two or more alternate lines. Distances and angles commonly were measured bytransit and taping methods; a profile was taken by differential leveling. Topographic features andcontours often were "hung onto" the P line. In the office, after the P line data plotted, the engineerlaid out the final location or alternate locations by studying the maps and profiles. Finally this L linewas staked on the ground and profiles, cross sections, and drainage were taken for it.
Modern location practice is usually based on photogrammetric techniques.　The parallel totraditional methods as outlined above is striking; each contains the succeeding steps of area androute reconnaissance, preliminary-line survey, and final location. The difference is that the newmethod is "office" oriented. Field work before the final location is ready for staking is primarilydevoted to the aerial survey and ground control for it, to checking out obscure or incomplete data

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