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Showing 3 results for Shear Wave Velocity

S.m. Mir Mohammad Hosseini, A.a. Hajimohammadi, A. R. Hajimohammadi,
Volume 8, Issue 2 (6-2010)

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. The measurements of the damping ratio and shear module, because of a great disturbance of stiff

deposits during the sampling process and also due to considerable differences between the laboratory and field

results, by the laboratory approaches are not reliable and advised.

Rouzbeh Dabiri, Faradjollah Askari, Ali Shafiee, Mohammad Kazem Jafari,
Volume 9, Issue 2 (6-2011)

Laboratory data, which relate the liquefaction resistance of Firoozkooh sand and non-plastic silt mixtures to shear wave velocity are

presented and compared to liquefaction criteria derived from seismic field measurements by Andrus and Stokoe [1]. In the work

described herein, cyclic triaxial and resonant column tests were conducted on specimens of clean sand and sand-silt mixtures with silt

content up to 60%, prepared at different densities. Cyclic undrained strength and small strain shear wave velocity were determined

for identical specimens formed by undercompaction method. It was found that silt content affects cyclic resistance and shear wave

velocity. In addition, the laboratory results indicated that using the existing field-based correlations will overestimate the cyclic

resistance of the Firoozkooh sand-silt mixtures when silt content is 60%. For clean sand and the specimens containing up to 30% fines,

results of this study on cyclic resistance are fairly consistent with Andrus and Stokoe correlations. These findings suggest the need for

further evaluation of the effects of non-plastic fines content upon liquefaction criteria derived from seismic field measurements.

M. Fazlavi, E. Haghshenas,
Volume 13, Issue 1 (3-2015)

In this paper we are going to show the importance of mode identification in microtremor array analysis. The idea come from four concentric ambient noise array recordings with aperture 100 to 1000 meters, performed in southern urban area of Tehran near the shrine of Imam Khomeini. These measurements were part of a comprehensive research project with the aim of determination of deep shear wave velocity model of Tehran alluvial deposits. Using appropriate signal processing techniques, including array processing methods as well as classical and time-frequency horizontal/vertical spectral ratio, the dispersion curves of surface waves, fundamental resonance frequency and Ellipticity of Rayleigh waves, were extracted. In the final step, the shear wave velocity profile of the site was determined by joint inversion of all of these attributes. The results show 2 different energetic trends in dispersion curves, for arrays of aperture 200 and 400 meters that one of them is coincide with 100m aperture array. For array with aperture 1000m any clear trend of energy could be observed because of deficiency of energy in low frequency. The inversion of data obtained by 100m aperture array alone, assuming the dispersion curve as fundamental mode (a common procedure in urban area) result in shear wave velocity that is not match with existing geological information. Performing the inversion, assuming 2 energetic trends, observed for larger arrays one as fundamental mode and another as mode 1 of Rayleigh waves, can modify significantly the shear wave velocity profile in accordance with existing geological and geotechnical information. This study show the importance of extracting of correct dispersion curves with detecting fundamental and higher modes, using array measurement with various aperture at one place to obtain more realistic shear wave velocity profile.

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