DEFORMATION MONITORING OF AMAKOHIA FLYOVER IN OWERRI NORTH LOCAL GOVERNMENT AREA, IMO STATE NIGERIA.

This research focused on the deformation monitoring of the Amakohia flyover along Orlu Road in Owerri North, Imo State, utilizing geodetic techniques. A reconnaissance survey, including steel tape measurements, was conducted to assess the site conditions. Three control stations were established: IMSU/2024/C1 on Egbeada Road, IMSU/2024/C2 on Akwakuma Road, and IMSU/2024/C3 towards Orji Flyover. Additionally, nine reference points (IMSU/2024/R1 to IMSU/2024/R9) were marked on the flyover. The 3 control stations were made of concrete pillars measuring 150 cm in length and 40 cm in width, while the 9 reference points were marked with white oil paint and concrete nails driven into the ground. Monitoring points were also set up along both sides and the centerline of the flyover at 10-meter intervals. Differential Global Positioning System (DGPS) observations were performed using the control extension method with CHCNAV i50 and Trimble DGPS to determine the coordinates of the control and reference points, with the base instrument located at the Nigerian Institution of Surveyors Secretariat (NIS) in Owerri. Control observations was observed at one hour each, while reference stations were observed at 30-minute intervals. The data from the control stations and reference points was analyzed using Trimble Business Center software. Precise leveling (Leica Wide Heerbrugg NA24 and Accessories ) operations were conducted to obtain the leveling data for 93 monitoring stations, further refined using the Height of Collimation (HOC) method to determine their reduced levels. GPS and leveling observations at the reference and monitoring stations were conducted over three epochs: November 16, 2024; December 18, 2024; and January 25, 2025, and analyzed using Trimble Business Center. The leveling data was also examined using the HOC method. To assess the deformation of the flyover, two methods were applied: mathematical and statistical analysis. The mathematical approach involved comparing and subtracting the data from the three epochs. The difference in coordinates for the first and second epochs showed a maximum difference of (EASTINGS = 0.434, NORTHINGS = 0.437) and a minimum difference of (EASTINGS = -0.003, NORTHINGS = -0.010). The difference in coordinates for the second and third epochs showed a maximum difference of (EASTINGS = 0.009, NORTHINGS = -0.003) and a minimum difference of (EASTINGS = -0.004, NORTHINGS = -0.019). The statistical analysis used the correlation coefficient in Microsoft Excel, the correlation coefficient for the first and second Easting Coordinates for the first and second epoch was r= 0.998157395 while that for the second and third epochs was r=0.998157395. For the first and second Northings Coordinates, the first and second epoch was r= 0.999997446 while that for the second and third epochs was r=0.999999995. The above results showed that there was no notable deformation on the flyover during the period of observation but however, the study recommends continuous monitoring of the flyover to ensure its safety and to prevent potential hazards.