Geostatistical modelling of spatial and depth variability of SPT data for Bangalore

Abstract

The purpose of this study is to develop a geostatistical model to evaluate the spatial and depth variability of Standard Penetration Test (SPT) data from Bangalore, India. The database consists of 766 boreholes spread over a 220 km² area, with several SPT values (N) in each of them. The geostatistical analysis is done for N corrected (N _corrected) values. The N _corrected value has been corrected for different parameters such as overburden stress, size of the bore hole, type of sampler, hammer energy and length of the connecting rod. The knowledge of the semivariogram of the SPT data is used with kriging theory to estimate the values at points in the subsurface of Bangalore where field measurements are not available. The model is used to compute the variance of estimated data. The model predicts reasonably well the SPT data. The geostatistical model provides valuable results that can be used for seismic hazard analysis, site response and liquefaction studies for the development of microzonation maps. The predicted N values from the developed model can also be used to estimate the subsurface information, allowable bearing pressure of soils and elastic modulus of soils.

Keywords:

• Geostatistics
• Kriging
• Semivariogram
• SPT data

Acknowledgements

The authors thank the Seismology Division, Department of Science and Technology, Government of India, for funding the project titled ‘Geotechnical site characterization of greater Bangalore region’. Ref no. DST/23(315)/SU/2001, dated October 2003.