Maximum shear modulus estimative from SPT for some Brazilian tropical soils

Abstract

Maximum shear modulus (G₀) has been used in various geotechnical jobs (e.g., seismic site assessment, machine vibration and pile driven). Laboratory and in situ determination of G₀ is not a current practice in Brazil. G₀ can be estimated from empirical correlations based on in situ tests like Standard Penetration Test (SPT) and Cone Penetration Test (CPT) in the preliminary design phase. Several empirical correlations to estimate G₀ from SPT N value have been developed and are available in the literature. However, most of these correlations were established based on experience with well-behaved soils formed in temperate and glacial zones, which may not always be used for tropical soils. This paper assessed and discussed the applicability of some correlations for G₀ estimative from SPT data in lateritic and saprolitic soils. The classical correlations for sedimentary soils underestimated G₀ of tropical soils. After updating the database, the tropical soils correlations reasonably estimated G₀ for the lateritic ones, which was not the case for the saprolitic soils. It was observed that differentiating the soils only as lateritic or saprolitic was not adequate for a good G₀ estimate for the saprolitic sandy soils. It was found that only the lateritic soils correlation can be used with caution as a preliminary attempt to estimate G₀ from SPT N value in soils with similar characteristics to the ones presented in this paper.

Keywords:
Maximum shear modulus; SPT N value; Tropical soils; Correlations