engleski

Monitoring and Analysis of Vertical Movements at the Test Geodetic Base Network

The test network of geodetic base is located at the territory of the park Jelenovac in Zagreb. The test area is rather unstable and suspected of ground subsidence. The geodetic base has therefore been renewed and established for the purpose of monitoring and analysing vertical movements of the geodetic control network. The state of the existing geodetic control points has been recorded and damaged points have been renewed, and destroyed points stabilized anew. The stabilization of points has been made on concrete stakes with the size of 0.13 x 0.13 x 0.70 m, having iron bolt fixed with concrete in it in the shape of a hemisphere. For the purpose of stability and because of possible external damages the upper surface of the stake was set up in the level of the terrain. The stabilization of newly established control points network was made in October 2007, and it consists of 10 points. In order to achieve the stability of points, a longer period of six months has been left till the measurement. Since highly precise method of height determination was demanded, the method of precise geometric levelling was chosen. The following equipment has been used in the measurement: precise optical level Leica NA2 with plan parallel plate, two invar centimetre staves with double scale (GPLE3), two levelling plate feet, staff frames, tripod and sunshade. Before, and also after the measurements performed, the level has been tested, especially its main condition. Invar levelling staves have been adjusted on the comparator in the Laboratory for Measurement and Measuring Technique at the Faculty of Geodesy, University of Zagreb. The zero measurement epoch was made in June 2008, and the first measurement epoch was made in April 2010. In both epochs the measurements were made in two directions, forwards and backwards. The levelling section was about 1300 m long, and it was attached to high bench mark R462. The heights of the points were determined in the closed levelling section with the bench mark R462 being its initial and end point. At the end of the work the numeric and graphic presentation of vertical movements between the zero and the first measurement epoch (vector presentation) was given, as well as their analysis with regard to terrain configuration.

bench mark; height difference; geometric levelling; measurement epoch; vertical movement

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