Construction Methods and Quality Outcomes for Bored Cast-in-Situ Piles – A Review of Current Practice

"It is well known that the adoption of an appropriate construction methodology is critical to quality outcomes for bored piles (drilled shafts). Many case studies have been published documenting quality issues that have arisen due to a range of causes involving ground conditions, ground support, drilling and cleaning techniques, groundwater, concrete properties and concreting methods, amongst other things. Despite the body of published information, pile defects remain common in practice. The authors share over 40 years’ experience in the Australian piling industry and have participated in many hundreds of projects involving bored piles in design, construction and testing roles. It is the authors’ experience that many defects are caused by conditions or practices that are known to be problematic, but that are often not recognised or addressed at the time of the works. This paper provides an overview of industry practices and key factors relevant to quality outcomes. The authors draw upon their own construction experience, published case studies and guidelines, and observations from independent pile testing activities they have been involved in across the Australian piling industry. The intent of the paper is to provide a consolidated review of typical industry practices and to highlight key areas in which construction quality can be enhanced.INTRODUCTIONThere are many published studies of cases where bored piles have been constructed and found to have concrete defects. The authors have had personal involvement in many cases where the outcomes and learnings are not publically available. The nature and cause of defects is always dependent on site and project specific factors, and therefore methodologies and materials that produce satisfactory outcomes in certain circumstances may be problematic elsewhere. The process of bored pile construction encompasses the following key areas:??excavation and ground support;??pile preparation and cleaning;??pile reinforcement and fitments.??concrete supply and mix performance;??concrete placement methodology;Each of these elements is equally important and can influence construction quality in completed piles. In the authors’ experience, it is often a combination of seemingly minor issues that leads to significant defects in piles. Conversely, attention to detail in all aspects of bored pile construction is required to produce outcomes of a consistently high standard."