Managing SOE Construction Risk through Design-Build Systems-Paper

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The paper describes how design-build contracting can manage support-of-excavation (SOE) risk on complex urban projects, using San Francisco’s Block 9 as a case study. The project involved a six-level basement excavation, 63–77 feet deep, on a constrained site with variable soil and bedrock, groundwater, abandoned foundations, and sensitive neighboring buildings and freeway structures.<br /><br />Specialty contractors contributed feasibility advice, budgets, and risk assessments during early project development. This input helped the Owner and General Contractor compare excavation depths, wall systems, underpinning, tiebacks, and internal bracing. The selected scheme combined a low-permeability shoring wall, tieback anchors, and contingency options for secant piles and internal bracing. Contract qualifications clarified responsibility for risks such as unknown obstructions and potential impacts beyond the contractor’s control.<br /><br />Construction required additional measures to secure easements near freeway foundations, remove unexpected historic foundations, coordinate intersecting anchors with a neighboring development, and adapt wall construction to difficult rock. Three-dimensional modeling, testing, monitoring, and field adjustments helped manage these challenges.<br /><br />Excavation was completed in April 2017. Measured wall movement was less than 0.75 inch—well below the geotechnical estimate of 1–2 inches—and groundwater cut-off performance was effective. The principal cost and schedule impact came from removing unforeseen obstructions.<br /><br />The case demonstrates that successful design-build SOE depends on early risk identification, realistic scope and cost development, assigning risks to the parties best able to manage them, and clear contractual definitions. Specialty contractors can materially improve project decisions even before formal appointment.

Keywords

design-build contracting

support-of-excavation

urban excavation

geotechnical risk

Block 9 San Francisco

tieback anchors

shoring wall

groundwater control

specialty contractors

contract risk allocation