Small strain stiffness of natural granitic saprolite in Hong Kong

Nonlinear stress-strain characteristics and shear stiffness-shear strain relationships of sedimentary soils and recompacted sands at small strains have been reported by many researchers. However, research work on the behavior of granitic soils at small strains has not attracted much attention, despite the fact that many countries around the world are underlain by granitic saprolites. In the study reported in this paper, shear stiffness of a natural granitic saprolite from Hong Kong has been investigated in the field, using the self-boring pressuremeter and geophysical techniques such as the suspension P-wave and S-wave logging method, and in the laboratory, using a triaxial apparatus equipped with internal displacement measuring devices. The observed stiffness-strain relationships of the natural granitic saprolite are highly nonlinear at small strains. Shear stiffness decreases significantly as shear strain increases. At very small shear strains (in the order of 0.001%), the elastic shear moduli deduced from the suspension S-wave logging method are generally consistent with the predictions made using an empirical correlation based on standard penetration test N values and also with the results of triaxial tests incorporating local displacement measurements. For shear strains larger than 0.01%, reasonable consistency can be found between the normalized shear stiffness-shear strain relationships obtained using the self-boring pressuremeter and from the triaxial apparatus.