GIS-Based Estimation of Corrected Standard Penetration Number Using the Best Semi-Variogram Model for Naogaon Sadar

Abstract

The objective of this study is to calculate the corrected standard penetration number (SPT-Nc) and generate SPT-Nc thematic maps using the best-fitting semi-variogram model. The study is based on 79 standard penetration tests (SPTs) carried out at five SPT measurements per test on each borehole, at depths of 3 m, 6 m, 9 m, 12 m, and ~15 m from the ground surface. A number of factors, such as density, GW table, and overburden pressure, in addition to other correction factors, were introduced to obtain SPT-Nc values. The SPT-Nc at each depth was then computed with Microsoft Excel. Maps obtained as a result of this procedure were subjected to GIS-based thematic maps; for each map a different color was used to indicate the value of SPT-Nc. Maps were generated using ordinary kriging interpolation and tested with six semi-variogram models to find the best-fitting model. Among the six models, the stable, k-bessel and Gaussian semi-variogram models were selected for having the least nugget-to-sill ratio. Since underground consists of clay soil at shallow depths, SPT-Nc was less than 24 and 32 at 3 m and 6 m, respectively. At a depth of 9 m, SPT-Nc ranged from 21 to 35, covering 70.23% of the area measured. At a depth of 12 m, SPTNc reached a maximum of 47 due to the decrease in clay content. The greatest values were recorded at 15 m, with 82.6% of the area with SPT-Nc between 38 and 51.