In the nuclear power industry large pile groups are used world-wide at soil sites with soft and weak near-surface soil layers as foundations for both safety and non-safety related structures. Entire nuclear power plant (NPP) facilities are founded on piles in areas of low to moderate seismicity, as for example in Belgium (Doel 3), Brazil (Angra 2), Canada (Pickering 1, 2, 3 & 4), Germany (e.g. Unterweser, Brunsbüttel, Brokdorf), the Netherlands (Borssele), and United States (Fort Calhoun 1, Point Beach 1 & 2, Robinson 2). Foundations of these NPPs can consist of groups of hundreds of piles. One advantage of NPP structures supported by piles is to indirectly achieve the purpose of a seismic isolation by tuning the natural fundamental frequency of the coupled soil-pile-foundation-structure system in horizontal directions to relatively low frequency values, where spectral accelerations (i.e. seismic demand) of typical ground motion response spectra are usually low. In addition, the response amplification of the NPP structure is further decreased due the inherent radiation damping effects present in pile foundations.
Current nuclear standards and codes (e.g. ASCE 4-16, KTA 2201.3) allow the use of pile-supported foundations for NPP structures, yet do not provide guidance on their seismic analysis. Their regulatory technical review is on a case-by-case basis, as e.g. stated in the US-NRC Seismic Review Plan (SRP). Therefore, the evaluation of pile foundations requires a good understanding of: (a) individual sub-systems: piles, soil, structure, loads; and (b) interaction between sub-systems, under both operational and extreme loading conditions. Because the dynamic behavior of large pile foundations is complex and its mathematical characterization is a challenging task, former as well as current soil-structure interaction (SSI) analyses of pile foundations are most often performed using simplified methods. Rigorous analysis approaches are computationally expensive but allow for a realistic assessment of the complex pile foundation structure interaction, especially under extreme loading.
The main goal of this paper is to present representative results from the extensive verification benchmark performed by Framatome GmbH (former Areva GmbH) with a new pile element implemented in the software package SC-SASSI, cf. SC Solutions (2018). Quality assurance of computational software used as a design or evaluation tool as well as its correct application play a crucial role in the safety of NPPs. A companion paper introduces in detail the theoretical background and implementation of the pile element in SC-SASSI, García et al (2019).