Ground Improvement by Controlled Modulus Columns

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The San Pedro dry-bulk terminal expansion in Abidjan, Côte d’Ivoire, required ground improvement after post-award investigations revealed soft clay and peat layers missed by the tender-stage surveys. These weak, compressible soils posed risks to reclamation stability and caused predicted settlements to exceed the project’s 50 mm limit.<br /><br />The project used several improvement methods according to soil conditions: vibro-rollers and shallow or deep compaction for fills and loose sands, and Controlled Modulus Columns (CMCs) beneath areas with soft compressible soils. CMCs are semi-rigid, grouted inclusions that work together with surrounding soil. A compacted granular load-transfer platform distributes structural loads to the columns and soil, reducing total and differential settlement without treating the columns as conventional piles that carry the entire structure load.<br /><br />At Zone 3A, 400 mm diameter CMCs were installed through the soft layers and terminated within dense sand. Finite-element analyses informed their layout and predicted residual settlements of approximately 25 mm, within the 50 mm criterion. Construction monitoring recorded drilling and grouting parameters, and static load tests across several zones verified column performance. Test columns sustained their maximum design test loads without ground or concrete failure; measured performance supported the design.<br /><br />The case study concludes that CMCs can provide effective settlement control on stratified weak ground, enabling construction to proceed after column strength and capacity are confirmed. The method offered rapid installation and detailed construction monitoring. However, the authors caution that automated rig records should not replace physical checks of column cut-off levels: inaccurate termination records led to unnecessary excavation and concrete work, adding cost and delaying handover.

Keywords

San Pedro dry-bulk terminal

Abidjan

Côte d’Ivoire

ground improvement

soft clay

peat layers

Controlled Modulus Columns

settlement control

static load tests

construction monitoring