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- 2009 (2) (remove)
Granular soils can amplify earthquake shaking at small strains without reaching the level of pore pressure generation. The hysteretic constitutive behaviour of sands and gravels under this specific consideration has been described in the thesis using the total stress based simplified model, SimSoil (Pestana and Salvati, 2006). SimSoil retains the basic features of the hysteretic constitutive behaviour described in the generalized effective stress model, MIT-S1 (Pestana 1994). It uses only four parameters (n, Gb, ws, and wa) which are readily determined from laboratory tests. Model parameters in the SimSoil execute independent control of nonlinearity of the soil behaviour under cyclic loading which is a unique feature of this model. ...
The initial shear modulus, Gmax, of soil is an important parameter for a variety of geotechnical design applications. This modulus is typically associated with shear strain levels about 5*10^-3% and below. The critical role of soil stiffness at small-strains in the design and analysis of geotechnical infrastructure is now widely accepted.
Gmax is a key parameter in small-strain dynamic analyses such as those to predict soil behavior or soil-structure interaction during earthquake, explosions, machine or traffic vibration where it is necessary to know how the shear modulus degrades from its small-strain value as the level of shear strain increases. Gmax can be equally important for small-strain cyclic situations such as those caused by wind or wave loading and for small-strain static situations as well. Gmax may also be used as an indirect indication of various soil parameters, as it, in many cases, correlates well to other soil properties such as density and sample disturbance. In recent years, a technique using bender elements was developed to investigate the small-strain shear modulus Gmax.
The objective of this thesis is to study the initial shear stiffness for various sands with different void ratios, densities, grain size distribution under dry and saturated conditions, then to compare empirical equations to predict Gmax and results from other testing devices with results of bender elements from this study.