Investigation of spatial variability of SPT data in Mashhad City (NE Iran) using a geostatistical approach

Precisely investigating subsurface conditions is a major concern for both geotechnical and geological engineers. In recent years, growing urbanization and construction of high-rise buildings in Mashhad City, Iran, have increased the demand for 3D models as a basis for subsurface characterization. In this regard, this study deals with the development of a 3D geological engineering model for standard penetration test (SPT) results on Mashhad City sedimentary deposits using sequential indicator simulation (SIS) and sequential Gaussian simulation (SGS) approaches. Reliable estimation of SPT values can be helpful in prediction of other geotechnical properties such as soil strength parameters and bearing capacity. The intense variability of the Mashhad sedimentary basin gives rise to complex and challenging ground conditions for civil engineering work. A better understanding of these deposits is crucial for many current and future civil engineering projects. Since design parameters in the study area are usually determined based on SPT results, 12,440 SPT data collected from 1380 boreholes were employed as the input data. After variability analysis, the SIS procedure was applied to coded data to determine areas with very dense sediments (areas with SPT > 50). Then, data with SPT values < 50 were transformed into normal scores in order for them to be applicable as input data in SGS. Finally, coupled maps showing the results of these two approaches were provided for different depths.