TITLE:
Assessment of the Liquefaction Risk of a Sandy Soil in a Coastal Environment Using the Direct PMT Method and the PMT-SPT Correlation: Case of Cotonou (Bénin)
AUTHORS:
Kassa Issifou Mounou Sambieni, Euphorie Gamavo, François de Paule Codo
KEYWORDS:
Earthquake, Floods, Magnitude, Liquefaction, Coastal, PMT-SPT
JOURNAL NAME:
Open Journal of Civil Engineering,
Vol.16 No.3,
September
16,
2026
ABSTRACT: West African coastal cities experiencing rapid urban growth are (prone) facing to flooding and seismic tremors, which expose infrastructure to structural damage during seismic events. This study aims to assess the liquefaction risk of sandy soil in the coastal environment of Cotonou. Geotechnical characterization reveals loose sand with an average permeability of 0.00002429 m/s, high friction angles ranging from 37.41˚ to 38.93˚, and low cohesion values ranging from 0.39 kPa to 6.17 kPa. The calculation of liquefaction potential by layer, derived from the cyclic stress ratio, is based on the direct PMT method and the PMT-SPT correlation. For a seismic coefficient of 0.108 g in loose sandy soils and earthquake magnitudes below 7 on the Richter scale, all layers exhibit a liquefaction potential factor greater than the value 1. This threshold is exceeded at depths between 22 and 25 m for a magnitude of 9.1, triggering localized liquefaction that does not pose a significant risk. A moderate risk is indicated starting at from a magnitude of 10.8. Mitigating this risk would require localized improvement measures, such as cement grout injection to consolidate the soil and reduce flow, or vibroflottation and stone columns to densify the sand and dissipate excess pore water pressure. This study enhances the understanding of natural phenomena, facilitating the design and construction of durable structures that ensure the safety of people and property while minimizing economic losses.