The Validity Assessment of Laboratory Shear Modulus Using In-Situ Seismic Piezocone Test Results

Abstract

Seismic piezocone device (SCPTu) together with Resonant Column and Cyclic Triaxial test apparatus are employed to measure small strain shear modulus (G₀) of carbonate sandy and clayey soils of southern coasts of Iran. A large area of southern regions of Iran is formed from clay, silt and sand. In this study, maximum shear modulus that is derived from both field (by seismic piezocone) and laboratory (by Resonant Column and Cyclic Triaxial) tests on soil samples from the southern region, indicated a meaningful effect of sample disturbance. Results show that in laboratory tests, loose samples tend to become denser and therefore exhibit greater stiffness whereas dense samples tend to become looser, showing a reduction in stiffness. According to the results of the present study, there are narrow limits of soils shear moduli for which the laboratory tests and the field measurements yield approximately the same amounts. This limit of shear moduli is about 30-50(MPa) for clay deposits and 70-100 (MPa) for sandy deposits. Since the shear moduli of soils in small strains can also be computed from the shear wave velocity, also correlations based on parameters derived from SCPTu test for shear wave velocity determination of sandy and clayey soils of the studied area are presented. This study shows that shear wave velocity can be related to both corrected tip resistance and total normal stress. Regarding the shear moduli and the damping ratio, due to the disturbances of the stiff deposits in the sampling process and great deviations of laboratory results from field results, the laboratory measurements of these parameters out of the above limits are not recommended.