Routine and advanced analysis of mechanical in situ tests : results on saprolitic soils from granites more or less mixed in Portugal

Abstract

This paper covers the more recent findings in the interpretation of different in-situ tests, such as SPT, CPT, PMT, SBPT, DMT and PLT to obtain geotechnical parameters of significant use in engineering practice. It concerns mainly shearing resistance properties and stiffness properties with special emphasis on the importance of stress and strain dependency. In this context some practical rules are presented for using parameters at two levels of design: routine and advanced levels. These practical rules concern transported soils (unaged and uncemented) are compared with those established in this paper for residual saprolitic soils from granite from different regions of Portugal.

lt was noticed that the bonded structure and fabric of residual saprolitic soils from granite have a significant influence on their geomechanical behaviour. Consequently, the structural peculiarities of these residual soils influence the pattern of their non-linear constitutive behaviour. Deformability modulus derived from robust but relatively crude tests, such as SPT, CPT, DPT or even PMT, are compared with reference values taken from seismic survey (CH) and load tests, such as PLT. They can be situated on stress-strain levels defined from laboratory triaxial tests over high quality undisturbed samples. Several parametric correlations were established, which agree well with other correlations proposed for residual soils of the same nature. Significant differences are apparent between those correlations and the ones established for transported soils with identical grading curves, which may be explained by the weak bonded structure, inherited from the parent rock.