Continuous Flight Auger (CFA) Pile Retaining Walls Boundary Settlements During Pile Installation

It is incumbent on developers, designers and contractors to ensure the safety of buildings and occupants on adjacent sites during construction. The critical period on most sites is prior to and during the excavation of the site. This is particularly true on sites where the strata are mainly sands. The use of contiguous and secant pile walls using the continuous flight auger (CFA) method is commonly adopted to provide support to the excavation on such sites. This method can be an economical and, in most cases, effective method. However, there seems to be little cognisance given to the damage caused during installation of the piles by the process sometimes known as “sand mining”. There have been several instances of severe damage to adjacent buildings due to this process not being recognized during the investigation, design and early construction phases. This paper discusses the main causes of settlement during construction and proposes a method to estimate them during the investigation so that the structural engineer can assess their effect on adjacent buildings and services.