MONITORING AND ANALYSIS OF VERTICAL MOVEMENTS AT THE TEST GEODETIC BASE NETWORK

10th International Multidisciplinary Scientific GeoConference - SGEM2010, www.sgem.org, SGEM2010 Conference Proceedings/ ISBN 10: 954-91818-1-2, June 20-26, 2010, Vol. 1, 893-900 pp

ABSTRACT

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.

Keywords: bench mark, height difference, geometric levelling, measurement epoch, vertical movement.