FEATURE ARTICLE In partnership with the California Department of Transportation (Caltrans), Federal Highway Administration (FHWA), and with support from the International Association of Foundation Drilling (ADSC), Deep Foundations Institute (DFI) organized a workshop drilled shafts in conjunction with DFI’s 40 Annual Conference on Deep Foundations. The 1.5 day workshop was held on October 15- 16, 2015, at the Oakland Marriott City Center in Oakland, Calif. Post-grouting, in the context of the workshop and report, refers to the alternative design and construction of base-grouted drilled shafts wherein a grout distribution system is installed during construction and used to grout the base under pressure. This occurs after the drilled shaft concrete has gained adequate strength, resulting in a stiffer axial-compression load-displacement relationship and additional possible ground improvement effects. Workshop Goals Post-grouted drilled shafts have seen increased interest in the U.S. in the last decade. To address issues with consistency and control of post-grouting, and to develop appropriate and effective guidance, FHWA initiated a significant effort in 2012 focused on the following objectives: • Bound current state of knowledge on use of post-grouting (what industry knows and does not know). • Quantify improvement mechanism(s) for post-grouting. • Establish design methodology(ies) for appropriate use. • Define control/assurance/verification measures and acceptance criteria. This workshop was organized to assist Caltrans in better understanding issues related to acceptance of post-grouted drilled shafts on highway projects. The goals of the workshop were to: • Identify and summarize the state of the practice for design, construction, inspection, verification, acceptance criteria, reliability and performance of post-grouting. • Identify gaps and needs in quality assurance that should be addressed for successful use of post-grouting. Several state DOTs have expressed strong interest in better understanding the mechanisms of improvement due to post- grouting, and in implementing appropriate provisions for quality assurance and acceptance of post-grouted drilled shafts. FHWA will use the results of this workshop in conjunction with the on- going study to formalize guidance on design, construction and acceptance of these foundation elements. 86 • DEEP FOUNDATIONS • SEPT/OCT 2016 Mary Ellen Large, P.E., D.GE, Deep Foundations Institute; Silas C. Nichols, P.E., and Benjamin S. Rivers, P.E., FHWA AUTHORS Figure 1. Typical grouting setup and measurements (Muchard, 2015) Detailed discussions following the presentations were attended by a small invited group of participants. Discussions focused on identifying areas of agreement and disagreement on post-grouting best practices, acceptance criteria, design and verification procedures, and inspection requirements. on quality assurance practices for acceptance of post-grouted th Workshop on Quality Assurance for Post-Grouted Drilled Shafts Workshop Program The workshop program included the following presentations that outlined the state of practice and views from owners, engineers and contractors on acceptance of post-grouting methods for drilled shafts: • Introduction and Workshop Purpose (Benjamin Rivers, P.E., FHWA) • U.S. State of Practice for Post-Grouting Methods (Mike Muchard, P.E., Applied Foundation Testing) • Owner Perspective on Use and Acceptance of Post-Grouted Drilled Shafts (Ray Castelli, P.E., WSP | Parsons Brinckerhoff) • Engineering Perspective on Use and Acceptance of Post-Grouted Drilled Shafts ( Dan Brown, Ph.D., P.E., Dan Brown and Associates) • Research Needs and Ongoing Studies (Professor Erik Loehr, P.E., University of Missouri-Columbia) • Post-Grouting Effectiveness (Professor Gray Mullins, University of South Florida) • Quality Assurance Measures and Acceptance (Silas Nichols, P.E., FHWA) • Caltrans General Practices for Foundation Acceptance and Specific Requirements for Post-Grouted Drilled Shafts (Tom Shantz, P.E., G.E., Caltrans)
