Engineering Geodesy

a subdivision of geodesy that studies the methods of measuring and the instruments used during the surveying and construction of engineering structures. Engineering geodesy is broken down into topographic-geodetic surveying, geodetic-engineering planning, marking out of areas, verification of structures, and observation of the deformations of structures.

When surveying construction sites the terrain is mapped on a scale of from 1:5,000 to 1:500. Geodetic substantiation is constructed in the form of triangulation, traverse, and leveling grids. Preliminary surveys of the routes of linear structures are made using topographical maps and materials from aerial photography. The final survey is done by laying the route out in the field. Optimal alternatives for routes and sites are chosen by means of computers, using numerical models of the terrain. Geodetic-engineering planning consists of preparing the topographical base for the project (plans, profiles), analytic data (coordinates and markers for points and lengths and azimuths of lines), vertical layout of the sites, analytic preparation for the project, and so on.

To transfer the project layout to the terrain a layout network of geodetic control points is set up in the form of tunnel, hydro-engineering, or bridge triangulation, in the form of a construction grid (at industrial sites), traverse grids (in cities), or precise trilateration (for high-rise and unique structures). Using the layout network, one transfers the principal axes of the structures to the physical site and all the construction axes and transverse lines are marked off in detail. A check survey is made on completed structures. Installing structural elements and equipment in the project position includes verifying axes in the plan, by elevation and on the vertical. Eye-and-string and optical methods are used for plan verifying. The height of structural elements is controlled using geometric and hydrostatic leveling or microleveling. The verticality of the axes is tested by precision theodolites (slant sighting) or special zenith instruments. When observing the deformation of structures, one determines sag and planar displacement of fixed points (marks). Sag is measured by high-precision leveling that is done periodically according to a strictly established program. Electronic hydrostatic systems with automatic recording of readings are also used. Planar displacements of rectilinear structures are determined by the method of thwart marks, and displacements of curved structures are determined by triangulation or traverse surveying. It is reasonable to measure spatial deformations by the ground stereo-photogrammetric survey method. During this work special attention is paid to the stability of the planar and elevation geodetic base.