Fardin Jafarzadeh

Effect of Direction of Principal Stress on Cyclic Behavior of Dense Sands

Soils have an anisotropic response and changing the inclination and magnitude of the major principal stress will affect the collapse potential and brittleness as well as the shear strength and shear stiffness. A series of undrained cyclic tests on dense Babolsar and Toyoura sands with induced anisotropy were conducted using automatic hollow cylinder apparatus. Special attention was paid to the significant role of the principal stress direction (α). Results show that changes in α has significant effect on the type and the quantity of strains that directly affect the excess pore water pressure generation. Changes in α would change the deformation mode as well as soil stiffness. Stiffness reduction has led lower transient pore water pressure and higher residual pore water pressure in sands. It was shown that Booker et al. model is applicable for predicting the pore pressure generation of dense soils. Results reveal that principal stress direction had no effect on internal friction angel at steady state or phase transformation in dense sands.

Application of Base-Line Correction Methods to Obtain Permanent Displacements of a Near-Source Ground Motion: The 2003 Bam Earthquake

In this article, two base-line correction methods for correcting the near-source strong motions were studied on the near-source recording of the 2003, Bam earthquake. To obtain permanent ground displacements at Bam station, two methods were applied with some modifications and without using any kind of filtering. Even though it is difficult to calculate true permanent displacements from data attained by present accelerograms, the results of this study show that the rational limit of permanent ground displacements can be successfully achieved by rational choosing of effective parameters. In addition, it is observed that some pre-processing steps suggested in literature have no considerable influences on the final results. For more rationally choosing the parameters influencing calculation of permanent displacement, the velocity trace must be paid more attention, and consideration of Specific Energy Density may be useful for better estimating the effective parameters. Finally, using suggested methods, a good agreement between results of base-line correction process and real reported permanent displacements of Bam earthquake is observed.

Seepage through Rockfill Dams in Narrow Valleys

Seepage analysis serves as one of the most significant stages in the design process of an embankment dam. In two-dimensional (2D) seepage analysis of embankment dams, little or no attention is paid to the seepage through side abutments. Moreover the role of grout curtain extensions into the side abutments and abutment material properties are inevitably neglected when performing a 2D seepage analysis. In this paper, two and three-dimensional. (3D) models of a rockfill dam during operation state are generated and several unsteady and steady state seepage analyses are performed using finite element method (FEM). The results obtained from 2D and 3D seepage analyses were compared with measurements from the instrumentation system installed in the dam body and foundation during construction. It is concluded that for embankment dams to be constructed in narrow valleys, 2D seepage analysis results are far from reality and considering 3D modeling of such dam sites is vital. Several design graphs were developed to calculate 3D discharge rates and hydraulic gradients from those obtained from 2D seepage analysis.