Settlement of a slab on grade foundation: a case history

Speaker: Dr. Graham Elliott, CEng MICE, Golder Associates, Inc., Atlanta.

Date and Time: Tuesday, October 13 at 11:00 am. Location: SEB 122

Abstract: Vibro replacement stone columns are gaining popularity in the US foundations market for use in a variety of geotechnical applications. They have the potential to offer significant schedule and cost savings when compared to traditional deep foundation systems, but they should not be viewed as a panacea for all geologic conditions, and much depends on empiricism and the experience of the specialty contractor. This presentation will review the investigation of significant settlement of a slab on grade foundation for a portal framed warehouse structure. The lightly reinforced slab was founded on a sub grade treated with vibro replacement stone columns. The serviceability of the building was impaired to such an extent that it was ultimately demolished and re-constructed on piles. In this example, the use of ‘vibro’ was ineffective, with the treated ground acting as a ‘pseudo raft’, forcing the stresses deeper into the ground profile. Beneath the sub-grade, a heterogeneous assemblage of landfill material was found to overlie by-product lagoon waste from a former industrial process. Instrumentation data proved that the seat of the settlement was distributed throughout this ground profile. Geotechnical and mineralogical testing revealed that the lagoon sediments were made of gypsum particles. These deposits exhibited high angles of shearing resistance, and yet were prone to creep settlement. The lessons to be learned from this case history will be shared, including those relevant to engineering desk study, sub- surface geotechnical exploration, laboratory testing of by-product materials, and vibro ground treatment.

Speaker Bio: Graham Elliott joined Golder Associates Inc. in 2009, with 12 years in practice as a consulting geotechnical engineer. He was previously an Associate Director at the global consulting engineering firm Arup, where he led a business unit in the Geotechnics and Tunneling Group in London, providing advice to clients in the building, infrastructure, and water sectors. He has worked on major design projects as Lead Geotechnical Engineer, including the Heathrow Airport East Terminal, and a venue for the London 2012 Olympic and Paralympic Games. He has acted as an expert in litigation, and has advised the international insurance market on major infrastructure project risks. Prior to this, Graham gained experience with Ardaman & Associates, Inc. in Florida where he was involved in the design, monitoring and oversight of several gypsum stack expansions in the phosphate mining and industrial chemical sector. Graham has a Masters degree in Soil Mechanics and Environmental Geotechnics from Imperial College London and before that, he was awarded a PhD in the fields of sedimentology and quaternary geology from the University of Reading for his work on solifluction sediments in Norway and Iceland. He is registered as a Chartered Civil Engineer, and is a Member of the Institution of Civil Engineers. Graham has taught geotechnical engineering topics on public courses for Thomas Telford Training, the commercial arm of the ICE, and he currently sits on the Editorial Panel of the Proceedings of the ICE: Geotechnical Engineering Journal.