Risk-Based Approach in Drilled Shaft Design for Infrastructure Projects-Paper

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The paper proposes applying risk-based decision-making early in the design of drilled shafts for infrastructure projects. Conventional design uses geotechnical data, analytical models, safety factors, and sometimes monitoring, but uncertainty in subsurface conditions, assumptions, and construction can still lead to shafts that do not perform as intended. This is especially important for non-redundant foundations, where a single shaft may carry critical loads.<br /><br />The proposed approach treats risk as the probability of an adverse event multiplied by its consequences. It adds two elements to conventional design: event trees, which map possible failure-triggering events and their probabilities, and explicit evaluation of consequences. Designers can use these assessments to compare actions such as proceeding with available data, conducting more investigation, changing the design, or selecting another site.<br /><br />For example, uncertainty about bedrock depth may lead to longer or overdesigned shafts. Additional borings cost money but can reduce uncertainty and potentially avoid unnecessary construction costs. Similar risk assessments can address lateral movement, soil response, and other design factors.<br /><br />The paper highlights a collapse during construction of Tampa’s Crosstown Expressway, where a drilled shaft failed into a limestone cavity in karst terrain. The incident caused damage, injuries, extensive redesign, and major cost escalation. The author argues that additional shaft-location borings—though costly—could have been justified by the risks and potential consequences.<br /><br />Risk-based design is presented as a developing method rather than a complete replacement for established procedures. The paper encourages integrating structured “what if?” analysis into drilled-shaft design so that investigation, design, and mitigation choices are made with clearer consideration of uncertainty, cost, safety, and performance.

Keywords

risk-based design

drilled shafts

geotechnical uncertainty

event trees

probability of failure

consequence analysis

subsurface conditions

foundation risk

karst terrain

construction safety