Drilled Shaft Risk Mitigation through Pre-Emptive Collaboration and Strategy-PPT Presentation

PPT Presentation

Pdf Summary

The presentation emphasizes that large drilled-shaft foundations carry risks including unstable excavations, casing and concrete-placement problems, defective shafts, inadequate load-test performance, environmental impacts, and damage to nearby structures. Effective mitigation begins with understanding site geology and uncertainty, investigating a range of conditions, assessing constructability, and preparing flexible installation plans with backup options.<br /><br />Case histories show the value of adapting designs and methods to actual conditions. At the Hurricane Deck Bridge, a concealed cavity in limestone disrupted one shaft; the owner, contractor, and designer collaborated on a casing-and-reinforcement redesign. At Lake Barkley, a pier was changed from three shafts to four to avoid a cavity. For the Bond Bridge, polymer fluid, sidewall scaling, and careful base cleaning addressed risks associated with shale.<br /><br />Load tests at the St. Croix Bridge illustrated how construction practices influence performance: improved excavation support, base cleaning and inspection, tremie placement, and concrete-quality testing accompanied substantially higher measured resistance in the later test. At the Sellwood Bridge, segmental casing and multiple acceptance pathways provided flexibility in highly variable ground.<br /><br />The central lesson is that foundation performance depends not only on design, but also on installation methods and field conditions. Owners, engineers, and contractors should identify and manage risks together, allocate costs and responsibilities fairly, and respond collaboratively when conditions differ from expectations. Overloading contractors with risks is both ineffective and likely to lead to disputes.

Keywords

drilled-shaft foundations

foundation risks

construction mitigation

site geology

constructability

casing problems

concrete placement

load testing

collaborative design

field conditions