Finite Element Modelling of Transient Seepage and Sediment Transport in Diaphragm Walls for Coastal Protection Works in the Niger Delta

Abstract

In this research, a two-dimensional analysis of transient seepage and sediment transport in diaphragm walls for coastal protection projects was conducted using the finite element method. One of the key factors influencing the stability of diaphragm walls in coastal protection works is transient seepage and sediment transport (flow boundary conditions). The reduction of passive soil resistance due to seepage and sediment movement can lead to stability issues through piping and scour effects. A representative soil profile from the Niger Delta region was subjected to transient seepage (long-term steady-state seepage with a gradual drawdown over a 24-hour period) and modeled using the finite element method with the Geostudio 2018R2V9.1 (SEEP/W) software. The movement of sediments (soil particles) through advective processes (water alone) was simulated and monitored based on the seepage flow velocities. Calculations were performed to determine the velocities of sediment transport and the total distances traveled due to seepage forces for each case study. The finite element solutions employed the Galerkin’s weighted residual method along with Lagrange isoparametric triangular or quadrilateral elements. Results from the seepage and sediment transport analyses indicated significantly higher rates of water and particle transport for diaphragm walls embedded in sandy layers compared to those in clay or in a sand-clay mixture. Thus, it is advisable to incorporate seepage and sediment transport considerations in the analysis and design of diaphragm walls for coastal protection in the Niger Delta region.