G-γ decay curves in granitic residual soils by seismic dilatometer

Due to stiffness non-linearity direct application of small-strain shear modulus to evaluate deformations in most practical problems is not possible, which gave rise to the development of modulus (E0 or G0) degradation curves. This has been applied with success to sedimentary soils, but in residual soils the experience and available information in the international community is still scarce. Those soils are considered as structured soils, often classified as problematic soils as they do not fit into the behaviour that of remoulded or unstructured soils. In reality the role of bonding and fabric enhances the strength and stiffness of the soil. In this paper, the use of the seismic dilatometer test (SDMT) for the determination of in situ decay curves of stiffness with strain level (G-gamma curves or similar) in a granitic residual soil, located in NE region of Portugal (Guarda) is illustrated, revealing its adequacy to solve this kind of problems. In situ tests and laboratory tests were performed in those granitic residual soils. The results were used for this investigation. The approach adopted relies on the ability of SDMT to provide a small strain modulus G0 (from the shear wave velocity Vs) and a “working strain” modulus GDMT (from the constrained modulus MDMT by elasticity theory). Thus in situ G-gamma decay curves are tentatively constructed by fitting curves through these two points. At this site the working strain modulus and the operational strain modulus are compared with same depth reference stiffness decay curves obtained by triaxial tests.