Construction QA/QC Methods for Postgrouting Drilled Shafts

The design and anticipated end-bearing capacity of postgrouted drilled shafts hinge on achieving sufficient grout pressure applied to the soils beneath the shaft tip. Implied, however, is that the grout is distributed reasonably well across the entire tip area. To this end, minimum grout pressure and volume thresholds are usually prescribed in an effort to address both concerns. Unfortunately, it is difficult to practically ascertain the actual area of the grout bulb during production grouting when manually-recorded values of pressure, volume, and uplift are the only available information. Therein, artificially-high grout pressure can be recorded, resulting from a blocked grout-distribution system that goes undetected and the shaft is accepted as both the minimum pressure and volume criteria were satisfied. This article outlines minimum monitoring practices and field quality-assurance/quality-control (QA/QC) measures that can and should be used to better ensure tip grouting is performed in conformance with the designer's expectations and intended outcome. The value of the proposed standard of care is highlighted through case studies where drilled shafts for bridge foundations were constructed, grouted, and met all acceptance criteria but where they were not grouted satisfactorily. (C) 2015 American Society of Civil Engineers.