APPLICATION OF LEAST ABSOLUTE SUM (LAS) DEFORMATION DETECTION METHOD USING COORDINATE DIFFERENCES FROM DIFFERENT OBSERVATIONAL CAMPAIGNS

Omogunloye O.G., Shittu O.G., Ipadeola A.O. and Ojegbile B.M

Department of Surveying and Geoinformatics Engineering

University of Lagos, Akoka-Lagos, Nigeria

E-mail:- gabolushohan@yahoo.com,

Abstract: Deformation study is one of the main research fields in geodesy. Deformation study comprises measurement, processing and analysis phases, Measurement techniques can be divided into geotechnical, structural and geodetic methods. Geotechnical and structural methods uses equipment such as tiltmeters, Pseodolites, Laser scanners e.t.c to measure changes in length, inclination, relative height, strains e.t.c.  The geodetic methods are of two basic types, the reference and relative methods. This study focuses on the deformation analysis using the geodetic method known as the Least Absolute Sum Method. The method consists mainly of the independent adjustment of each of two epoch data, compatibility test on their a posteriori variances, followed by determination of Trend of movements for all the common points in the monitoring network. A triangulation network was designed (carefully selected) consisting of  45  YTT series second order control  points within the study area (Lagos State) resulting in  a total of  63 triangles,189 observations and 90 unknown parameters with 99 degrees of freedom. The network adjustment was done using the method of least squares observation equations. The estimated variance factors for the 2D (horizontal) network were 7.82989325645394e-08 and 7.7207636996395e-08 while 0.03944 and 0.052339 represent the estimated variance factors for the 1D (height) for the first and second epochs networks respectively. The compatibility of the two epoch data was tested with the variance ratio and compatibility test criteria. Actual displacement vectors were computed and transformed into the same computational base using S-transformation by Least Absolute Sum (LAS), stable and unstable points within the monitoring network were determined using Single Point displacement test, the displacement vector magnitude was computed for the two methods, represented graphically to indicate possible trend of movements that might have occurred. This study finds applications in studying the deformation of large engineering structures such as high rise buildings, bridges, dams, oil exploration zones, mining sites and land slide monitoring.