Geospatial and statistical interpolation of geotechnical data for modeling zonation maps of Islamabad, Pakistan

This study aims to create soil zonation maps (SZM) using a spatial interpolation approach relying on vast geotechnical subsoil data gathered through field and laboratory analysis. Islamabad, a rapidly growing city and capital of Pakistan, is used as a case study. The sub-soil data were evaluated from 210 geotechnical investigation reports in terms of soil type, standard penetration (SPT-N value), undrained shear strength, and consolidation parameters. The data were digitally analyzed in ArcGIS using the ordinary kriging interpolation technique, and SZM were developed based on SPT-N and soil type. For the developed SZM, settlement and allowable bearing capacity (ABC) are evaluated for shallow foundations. The results showed that the study area was divided into three main zones based on SPT-N [i.e., zone-1(4-15), zone-2(16-30), and zone-3(> 30)], and six sub-zones based on lithology. The lean/silty clay is predominant up to 15 m, underlain by gravel and shale/sandstone up to 50 m. Correlations were presented based on linear regression analysis with R-2 = 0.98 to predict the SPT-N with depth for expeditious appraisal of stiffness and strength of sub-soils throughout preliminary planning and feasibility studies of several construction projects. The ABC for the shallow foundation in Islamabad found to be above 100 kPa, indicating an excellent safe ABC to support foundations of lightly loaded structures. Moreover, the correlation coefficient to predict SPT-N values is around 85%, while about 94% for soil type. Furthermore, reliable information on geotechnical properties of the subsoil's layers will work as a complement for the site characterization and identification of hazard for upcoming projects.

Automated summary

This study focuses on creating soil zonation maps using geotechnical subsoil data in Islamabad, Pakistan. The results show that the study area can be divided into three main zones based on SPT-N values and six sub-zones based on soil lithology. The correlation coefficient for predicting SPT-N values is around 85%, indicating reliable prediction capability. The ABC for shallow foundations in Islamabad is above 100 kPa, indicating a high level of safety for lightly loaded structures.