Final Report: Workshop on Quality Assurance for Post-Grouted Drilled Shafts-PDF

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The 2015 FHWA/Caltrans workshop, organized by the Deep Foundations Institute, examined quality assurance and acceptance practices for post-grouted drilled shafts. Participants reviewed industry experience and discussed design, construction, inspection, verification, and research needs.<br /><br />Post-grouting can improve a shaft’s base resistance, stiffness, and settlement performance, particularly in granular soils, but it is not a substitute for a full load test or for proper shaft construction. The main field measurements are grout pressure, shaft uplift, and grout volume. Pressure is generally the most important indicator, followed by uplift and then volume; monitoring trends should be stable. Pressure targets should reflect site conditions and shaft resistance, while minimum grout volume should verify that grout reaches the base, not serve as a measure of capacity. Some uplift is useful evidence of load transfer, although high side resistance may prevent movement at the shaft top. Telltales can help measure movement at depth.<br /><br />Participants supported using qualified, experienced specialists, reviewing contractor installation plans, maintaining detailed records, and applying the same shaft-bottom cleanliness standards used for conventional shafts. Contractors should generally select the grouting method, while owners and designers set performance and acceptance criteria. Test shafts and load tests are important for verifying design assumptions and establishing production targets. Staged grouting may be allowed but should not be routine.<br /><br />The workshop also identified unresolved issues: how reliably grout pressure predicts load and performance; the influence of delivery systems, grout volume, and staged grouting; possible long-term creep; and appropriate design resistance factors. Further research and standardized guidance are needed to improve predictability and consistency across projects.

Keywords

post-grouting

drilled shafts

quality assurance

acceptance criteria

grout pressure

shaft uplift

load testing

base resistance

construction monitoring

foundation research