Establishment of a reference framework for topometric auscultation of the third Cotonou Bridge in Southern Bénin

Abstract

Geodetic monitoring of engineering structures is not often promoted in developing countries. However, its usefulness is increasingly perceived at a time when the first bridges of the colonial period are approaching their centenary. The main objective of the process was to set up a network of target points for the auscultation of the third Cotonou Bridge, a strategic structure for urban mobility and economic development in Bénin, built twenty years ago. Faced with the continuous dynamic and environmental stresses, a methodology has been developed to ensure three-dimensional monitoring of any deformations of the structure, thus guaranteeing its integrity and the safety of traffic in the long term. The approach adopted was based on the following three major axes: the selection of reference bollards outside the bridge's area of influence by ensuring their stability and the materialization of the auscultation points by guaranteeing their visibility and durability; the combined use of advanced geodetic techniques, including static GNSS and precision levelling, to obtain millimeter measurements; the establishment of a protocol of periodic measurements allowing early detection of structural anomalies. The results highlighted the effectiveness of the proposed methods for the monitoring of deformities. The 36 geodetic points, materialized by durable landmarks and validated by repeated measurement campaigns, constitute a reliable reference for the future auscultation of the bridge. Future directions include the adoption of innovative technologies that will increase the accuracy and frequency of measurements, reduce the duration of campaigns, and extend the reach of the monitoring network to other critical infrastructure.