Chesapeake Bay Bridge Tunnel Duct Bank Compaction Grouting

The Job

CJGeo was contracted to provide ground improvement services on one of the islands of the Chesapeake Bay Bridge Tunnel (CBBT). The work supported the Thimble Shoals parallel tunnel installation project. The objective was to stabilize an adjacent, critical electrical duct bank that supplies power to the island’s essential ventilation and utility systems.

Compaction grouting operation by CJGeo on a Chesapeake Bay Bridge Tunnel (CBBT) islandk.

The Challenge

During the installation of sheet pile walls for a slurry separation pit, the contractor observed settlement of the adjacent electrical duct bank. The vibratory nature of the sheet pile installation was the source of soil consolidation. Given the critical function of the duct bank, the contractor and their geotechnical consultant required an immediate, non-disruptive measure to consolidate the subgrade soils. This measure had to mitigate the risk of further settlement caused by continued construction vibrations and minimize the likelihood of future long-term consolidation.

The Solution

CJGeo mobilized a single crew to perform polyurethane compaction grouting beneath the settling duct bank. Utilizing CJGrout 35NHV high-density geotechnical polyurethane, we injected the material directly into the bearing soils. The expansion of the polyurethane compacted the granular material, effectively increasing the soil density and filling any subsurface voids. The ground improvement work required two shifts for completion. Following the grouting operation, sheet pile installation was successfully resumed. Monitoring confirmed that no further movement of the duct bank occurred after the compaction grouting process.

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