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Engineers say failing granite retaining wall needs full replacement; recommend precast modular option at ~$2.8M
Summary
Staff and a Du Bois and King consultant reported that safety factors on a 100-foot section of an aging granite retaining wall fall below code; after scoring five alternatives they recommended a precast modular wall, estimated about $2.8 million, and requested direction to prepare design and pricing.
City engineering staff and a Du Bois and King consultant told the Infrastructure Committee that a historic granite stacked-block retaining wall on the Hannibal Hanlon Parkway is deteriorating and that safety factors fall below standards. The consultant said engineering analysis—including ground-penetrating radar and geotechnical review—found voids behind the wall and loose soils, and concluded that “the full wall replacement is the only engineering solution that addresses our stability requirements,” a point presented during the evaluation.
The consultants presented five conceptual alternatives (repair in place; remove and cast-in-place concrete; remove and rebuild stone masonry; precast modular units; vinyl sheet piles) and said staff and consultants selected the precast modular system because it balances constructability, aesthetics and long-term stability. The recommended scope covers roughly the worst 100 linear feet; the consultant and staff estimated construction cost at about $2,800,000. Staff asked the committee for direction to proceed with design and pricing; a member moved and a second was recorded and staff said they will return with design documents and cost estimates.
