Utilizing Ground Improvement for Support of Large Retaining Walls Adjacent to Wetlands-PPT Presentation

PPT Presentation

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This case study describes ground improvement used to support a large MSE retaining wall beside wetlands in Fuquay-Varina, North Carolina. Very soft and loose soils under the wall footprint, combined with high groundwater, made settlement a concern and ruled out practical undercut-and-replacement. Initial analysis estimated up to 5 inches of settlement and raised global stability concerns. Additional CPT testing refined the analysis and showed a global stability factor of safety of 1.5, resolving that concern.<br /><br />The selected solution was Geopier Impact Piers, installed using a displacement method that does not typically generate spoils. The design treated the reinforced zone of the wall as a large footing and used the piers to limit settlement—not as a specifically designed global-stability measure. The target was no more than 2 inches of total settlement and 1 inch of differential settlement. Wall designer-provided bearing pressures, which varied with wall height, helped tailor the design and avoid unnecessary cost.<br /><br />The reinforced zone covered approximately 12,200 square feet. The project used 715 piers averaging about 31 feet deep and roughly 4 feet apart. Installation required a flat, stable working platform and sufficient equipment access; recycled concrete stabilized the upper 3 feet of the work area, and a coordinated benching plan accommodated site and equipment constraints.<br /><br />The wall was constructed as planned, with only modest schedule and cost increases. Ground improvement provided a viable alternative to an extremely expensive deep-foundation solution, and may also have improved global stability.

Keywords

ground improvement

MSE retaining wall

settlement control

Geopier Impact Piers

soft soils

high groundwater

global stability

North Carolina

wetlands construction

foundation support