Study of the Behavior of Deep Foundation Piles of a Bridge, Adapted to the Environment on Compressible Soils: The Case of the Bridge (420 ml) from the Porto-Novo Lagoon in Benin

Abstract

Bridge design has long been guided by purely economic criteria. However, today, given the potential impacts of climate change, it is imperative to adopt an approach that incorporates sustainable criteria at every stage of a bridge’s life cycle, in order to protect the environment without compromising safety, functionality, and sustainable development. Adding to these concerns is the major challenge posed by the construction of bridges on compressible soils for socio-economic development. This study highlights the behavior of deep foundations on compressible soils subjected to axial loads from an environmentally adapted bridge on the Porto-Novo lagoon in Benin. It addresses the problems posed by climate change and, in particular, compressible soils. To achieve this, a multi-criteria analysis was conducted using a Matlab program for the ELECTRE I multi-criteria method, in order to determine the type of bridge suitable for our project, based on the principles of sustainable development. This analysis revealed that composite steel-concrete bridges of the twin-girder type with cantilevered sections are much more suitable. Furthermore, the soils (intended to support this bridge), identified as compressible, present risks of settlement and liquefaction, as revealed by geotechnical tests. Unable to improve the situation, we adopted a method using a group of piles, specifically driven cast-in-place piles. To determine the optimal dimensions, piles with diameters of 0.8 m, 0.9 m, and 1 m, ranging from 30 to 48 m in depth, were modeled using GEOFOND software. The results of this design allowed us to select piles with a diameter of 1 meter and a depth of 45 m, providing a bearing capacity of 3.19 MN. These dimensions, combined with a center-to-center spacing of 4.5 m between piles, demonstrate that the group of 6 piles is suitable, with an efficiency coefficient of 83%. Finally, the PLAXIS 3D software allowed us to understand the behavior of the group under axial load. Based on settlements, it was observed that the soil exhibits horizontal and vertical displacements, the largest values of which, 27 mm, are obtained in the underconsolidated surface layers.