Go/N ratio in tropical soils from Brazil

Abstract

The geotechnical behavior of tropical soils is complex and cannot be supported only by the classical soil mechanics. The Standard Penetration Test (SPT) is broadly used for geotechnical site characterization. However, it provides a single index to estimate several parameters. The seismic SPT is a test that associates the up-hole technique to the SPT. It allows determining the maximum shear modulus (Go) together with the N value. The ratio between Go determined from seismic tests (cross-hole, down-hole, and SCPT) and the N value from SPT was used to identify unusual compressibility of soils from three well studied sites from São Paulo State, Brazil. It was observed that all studied soils presented a higher Go/N ratio than sedimentary uncemented sandy soils. It was also observed that the lateritic soils tend to achieve a higher Go/N ratio than the saprolitic soils. S-SPT tests were also carried out at the same studied sites and the use of the up-hole seismic data and N value in the same test is an interesting approach to help characterize unusual and different soil behavior based on Go/N ratio. Relating an elastic modulus to a penetration resistance can help identifying different tropical soils since the low strain modulus determined by seismic tests reflects the cemented structure of these soils.