Monitoring for horizontal movement in an earth dam using differential GPS

Abstract

In the past, Geodetic survey techniques were traditionally used to determine horizontal movement in Dams and other structures. Geodetic methods are however difficult to arrange and labour intensive. Additionally, the displacements obtained may be relative, with respect to some known points whose coordinates are referenced to a relative datum. Global positioning system is less labour intensive and offers the advantage of giving three dimensional absolute displacement of the deformable body. In this paper, the use of differential GPS for monitoring for horizontal movements in an earth dam is discussed. Measurement carried out at the Ikpoba Dam using one reference receiver and three rovers present case study scenario. Four units of Leica 500 GPS receivers were deployed for the survey. Twenty GPS stations consisting of eleven control points and nine reference points along the Dam crest were observed with data collected for at least 1 hour in each case. On completion of the data collection the data were post processed using the LEICA SKI PRO- 2 software for processing and adjustment in each of the measurement epoch for 2008, 2009 and 2010 field seasons. Point’s displacements were computed between the three measurement epoch. Post adjustment analysis was then carried out to determine if the difference in coordinates was as a result of point displacement or errors of measurement. The results obtained revealed that all the points in the network have moved. Maximum movement of 136 mm