No. NJSG/07/16 APPLICATION OF LEAST ABSOLUTE SUM (LAS) TECHNIQUE FOR DETECTING DEFORMATION OF STRUCTURES *Omogunloye O.G., *Shittu O.A., Ipadeola A.O. and Ojegbile B.M.* *Department of Surveying and Geoinformatics Engineering Faculty of Engineering, University of Lagos, Akoka - Lagos, Nigeria. Corresponding E-mail:-gabolushohan@yahoo.com,07026385672. Abstract This study focuses on the deformation analysis using a geodetic method known as the Least Absolute Sum. The method consists mainly of independent adjustment of each epoch data, compatibility test on their a posteriori variances, followed by determination of trend of movements for all the common points in the network. A triangulation network was designed consisting of 45 Ytt series Second Order control points within the study area 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 respectively. The compatibility of the two epoch data was tested with the variance ratio and compatibility test passed. Actual displacement vectors were computed and transformed into the same computational base using S-transformation by Least Absolute Sum (LAS), stable and unstable points were determined using Single Point displacement test, the displacement vector magnitude was computed, represented graphically to indicate possible trend of movements that might have occurred. This study finds Least Absolute Sum (LAS) Technique useful in studying the deformation of large engineering structures such as high rise buildings, bridges, dams, oil exploration zones, mining sites and land slide monitoring. KEYWORDS: Epoch, Coordinates, Least Square Adjustment, Compatibility Test, Deformation analysis, Least Absolute Sum (LAS). 1.0 Introduction Any object, when acted upon by external forces, deforms, or exhibits changes in its size or shape. These observable changes are manifestations of internal stresses or pressures produced by the physical interaction of the external forces and the material itself. Materials either fail or tear when stresses exceed certain critical values [7]. It is this risk of failure which practically necessitates deformation monitoring surveys, which allow the implementation of mitigating constructive procedures or evacuations to take place early enough, to prevent loss of life and material. Generally, the deformation measurement techniques can be divided into geotechnical, structural and geodetic methods. Geotechnical and structural methods are direct measurement