Supported Excavation Movement Causing Lateral Displacement and Cracks in Drilled Shafts - Lessons Learned from a Case Study in Chicago-Paper

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A Chicago hotel project experienced excessive movement of a cantilevered sheet-pile excavation support system, causing lateral displacement and cracking in six nearby drilled shafts. The shafts were only 1–2 feet from the wall; the sheet-pile tops moved inward by as much as 9 inches, while shaft tops shifted up to 8 inches. Integrity testing, coring, and video inspections identified cracks approximately 19–21 feet below the shaft tops.<br /><br />The movement resulted from several factors that increased forces on the wall or reduced its resistance. Soil near the southern end of the site was softer than the average values used in design. Field conditions also differed from design assumptions: the slope behind the wall was steeper, excavation extended about 2 feet deeper than anticipated, and over-excavation in front of the sheet piles was wider and left unfilled longer than specified. Pumping lowered water levels inside the excavation, creating unbalanced groundwater pressures; rainy-season perched water added further pressure. Together, these conditions reduced the wall’s stability.<br /><br />Additional sheet piles, walers, and rakers were installed to prevent further movement. Five damaged shafts were repaired by splicing in reinforcing bars with high-strength grout; one was replaced. The completed repairs have performed successfully.<br /><br />The case highlights the need to account for localized soil variability rather than relying uncritically on average properties, and to ensure construction follows the assumptions underlying the design. Any changes in excavation depth, slope, groundwater conditions, or work sequence should be promptly communicated to the designer so the design can be reviewed and adjusted. Close coordination among designers and contractors can help prevent costly movement and damage.

Keywords

Chicago hotel project

cantilevered sheet-pile wall

lateral displacement

drilled shaft cracking

soil variability

excavation overrun

groundwater pressure

sheet-pile movement

structural repair

design assumptions