Rammed Aggregate Pier (RAP) Ground Improvement at Darlington New Nuclear Project (DNNP)

Abstract

Overburden soil conditions play an important factor in determining design demands such as seismic hazard and choice of foundation systems for nuclear power plant (NPP) structures. Due to the high seismic loads considered in the design of NPPs, soil liquefaction can become of particular concern. This is even more significant for certain Small Modular Reactor (SMR) technologies that rely on deep embedment in the ground. The embedment, along with a smaller footprint, causes their response during a seismic event be more influenced by the response of the surrounding soil. The most commonly used method to treat poor soils on NPP construction projects to date is to excavate and replace with engineered backfill. This method can be costly, and associated with high environmental impact due to the potential requirement of dewatering, disposal of potentially contaminated soils, and import of backfill material. It would be beneficial to be able to identify suitable alternatives for such projects. Ontario Power Generation (OPG) has conducted a trial program using Rammed Aggregate Pier® elements (RAP) with the intent to remediate soft and potentially liquefiable soils at the Darlington New Nuclear Project (DNNP) site. This paper describes the work performed, summarizes the results, and presents conclusions drawn.