Journal of Earth Sciences and Geotechnical Engineering

Analysis of Foundation Options for the marine segment of the Greater Port Harcourt Ring Road, in the Niger Delta

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• Abstract

  The greater PHC ring road was conceived as the remedy for the growing congestion of roads in Port Harcourt city, Nigeria the proposed road traverses some 40km of marine section over which are a decision is needed for a suitable pavement foundation design. The sub-soils, which are diurnally inundated by up to 2.5m of water, comprise a top very soft to soft silty and peaty clay (5 to 30m thick) overlying a predominantly medium dense sandy formation. The foundation options included the placement of 6m of sand fill, the removal of 3m of top softsoil and replacement with sand, supplemented with vertical sand drains and combinations of micro-piles. Settlement analysis based on a surcharge of roughly 120kN/m² representing maximum expected axle road, indicated values of up to 3m, reducing only to 1.2m after removal of 3m of the top soft soil. The option maximizes the benefits from improved bearing capacity of top layers, settlement minimization, partial improvement in navigation through a thoughtful dredging layout, and the potential for development of new coastal settlements. Although the cost of implementing the micro-piles option was considered exorbitant, the option exerted minimum impact on the environment with a capacity to conserve the hydro ecology. The balance of functionality, cast and the environment were critical in the final choice of the option for implementation.