Dynamic geotechnical properties evaluation of a candidate nuclear power plant site (NPP): P- and S-waves seismic refraction technique, North Western Coast, Egypt

Determination of the dynamic geotechnical properties and Vs30 of soil and rocks from seismic wave velocities serves as essential inputs for a foundation design cognizant of seismic site response and rock strength. This study evaluates a site which was suggested for a Nuclear Power Plant (NPP) in El-Dabaa area, north western coast of Egypt. On the near subsurface geology is made up of a thick succession of limestone overlain by a thin layer of soft soil. Assessment of geotechnical materials and Vs30 of the near sub-surface lithological layers are required for design of the foundation of critical structures like turbo-generator and reactor buildings. Interpretation of ninety one shallow P-waves and S-waves seismic refraction profiles distributed within the study area in conjunction with data of 76 boreholes were undertaken to delineate the dynamic properties of shallow soil for construction NPP. The velocity of the P- and S-waves were acquired and interpreted using SeisImager Software Package, then the results were used to build a velocity-depth model to estimate the depth to the bedrock and the thicknesses of overburden layers. This model was verified using boreholes data dissected the seismic profiles to improve the final velocity depth model. The depth to bedrock was determined from both shallow seismic refraction profiles and boreholes. Vs30, elastic moduli and dynamic geotechnical parameters were calculated and the site was classified as a National Earthquake Hazard Reduction Program (NEHRP) class “B”. The values of seismic velocities, the engineering consolidations, and the strength parameters showed that the bedrock in the study area is characterized by more competent rock quality.