In the present research, SPT results were adopted to establish relationships for estimating of the relative density in a sandy soil. SPTs were performed in 20 boreholes in Astaneh-ye Ashrafiyeh city in Iran. Laboratory tests including mineralogy, relative density, soil gradation, Atterberg limits, and unit weight were performed on the soil samples. The SPT numbers were then properly corrected. In particular, the correct procedure for correction of the SPT number against the existing overburden effective stress was discussed when the SPT is performed in the vadose zone where the soil may be unsaturated. The soil in the study area was dominantly classified as SP-SM. The relationship between the relative density as one of the most important parameters for dominantly granular soils, with the corrected SPT number (N1(60)) and fines content was then investigated and discussed using artificial neural network and statistical analysis. Results showed that for the soil of interest, the developed relationship performs better than those established in the literature, hence demonstrating the value of developing locally tuned relationships for important projects.
