Determination of Anisotropy of Granular Materials and Its Relation to Liquefaction Resistance Under Cyclic Loading

Granular materials such as sand deposits have anisotropic characteristics due to the gravitational forces during depositional process and various stress histories. These anisotropic characteristics make evaluation of liquefaction resistance of soil very complex. Since obtaining undisturbed soil specimens for laboratory tests from discrete elements like sandy soils is very laborious, the soil specimens are reconstituted in laboratory with regards to the in-situ density of soil. Reconstituting the soil changes the soil fabric or anisotropic characteristics in comparison with field conditions. Many researchers have pointed out that liquefaction resistance is highly influenced by differences in the structure of the soil (or soil fabric) produced by different sample preparation techniques. Liquefaction resistance could vary with different soil fabrics even for the same soil with a specific density. The objective of this research is to investigate the anisotropy of granular materials and to establish its relation to the liquefaction resistance. Anisotropy can be expressed by the directional mechanical properties of the soil. In order to investigate the effects of the anisotropy on the liquefaction resistance in a quantitative way, uniform medium dense sand specimens were prepared using three different techniques to create the different initial soil fabrics. Undrained cyclic triaxial tests were performed to determine the liquefaction resistance of each soil specimen. A relationship between liquefaction resistance and the number of cyclic loads was established for three types of specimens with different soil fabrics. The results clearly demonstrate that the preparation methods significantly affect the liquefaction behavior. After preparation of the soil specimens, vertical and horizontal compression (P) wave velocity and vertical shear (S) wave velocity were measured, and the soil fabric effects on elastic properties of the soil were investigated under dry and saturated conditions. P-wave velocities in both directions showed small difference for all sample preparation techniques except for air pluviated (AP) specimens. AP specimens reflected cross anisotropy. However, S-wave velocities turned out to be very affected by soil-fabric. S-wave promised to distinguish nature of inherent anisotropy with regard to liquefaction resistance. Anisotropic elastic constants of soil specimens were recovered quantitatively from elastic wave measurements and consolidation test data. Induced anisotropy due to different preparation techniques was identified by recovered anisotropic constants. The recovered elastic constants were found sufficient to express anisotropy of specimens. Accordingly, by using directional variation of elastic constants, three anisotropy indices were created. The anisotropy indices were then used to create pseudo cyclic stress ratio. Liquefaction cyclic stress ratios of the specimens were normalized with corresponding pseudo cyclic stress ratios. It was observed that the anisotropy effects on liquefaction resistance can be eliminated with those anisotropy indices. It was found that under cyclic loading, anisotropy indices obtained from experimental S-wave measurements were able to express anisotropy of granular materials and a relation to the liquefaction resistance

Recovery of Elastic Parameters for Cross-Anisotropic Sandy Soil via Elastic Wave Measurements

In this study, the elastic properties of loose to medium dense (Dr=50%) sandy soil were obtained from elastic wave propagation techniques in the laboratory. The soil specimens were assumed cross anisotropic medium. Two bender elements are embedded in the top cap and the pedestal of the triaxial device as receivers and transmitters in the vertical direction for P- and S-waves. In addition, two bender elements are attached to the membrane surrounding the soil specimen to measure horizontal P-wave velocities. After the preparation of the specimens, vertical and horizontal P-wave velocities and a vertical shear wave velocity were measured under different effective confining pressures. Numerically 5 independent elastic parameters of cross anisotropic soil samples were recovered. In terms of the anisotropy parameter (α), modified Young’s modulus (E*) and Poisson ratio (ν*)

Elastic foundation effects on arch dams

Earthquake response of an arch dam should be calculated under ground motion effects. This study presents three-dimensional linear earthquake response of an arch dam. Thereby, we considered different ground motion effects and also foundation conditions in the finite element analyses. For this purpose, the Type 3 double curvature arch dam was selected for application. All numerical analyses are carried out by SAP2000 program for empty reservoir cases. In the scope of this study, linear modal time-history analyses are performed using three dimensional finite element model of the arch dam and arch dam-foundation interaction systems. According to numerical analyses, maximum horizontal displacements and maximum normal stresses are presented by dam height in the largest section. These results are evaluated for rigid and various elastic foundation conditions. Furthermore, near-fault and far-field ground motion effects on the selected arch dam are taken into account by different accelerograms obtained from the Loma Prieta earthquake at various distances

Allowable bearing capacity based on Schmertmann method for sandy soils

WOS: 000287940100015In this study, since the city of Bartin in Northwest Turkey on the Black Sea is in the first-degree seismic zone and its residential area only occupies 7% of the total acreage that is expected to expand with newly flourishing urbanization, soil samples were obtained from a total of five different locations where there are open areas for the construction of dwellings. Engineering properties of the soils were assessed by laboratory experiments and the allowable bearing capacity and elastic settlement (Schmertmann method) values of the soils were calculated. The results showed that calculated settlement values are very high and can damage the foundation systems of any building constructed in future; therefore, allowable settlement value was fixed at 50 mm and allowable bearing capacities of the soils were obtained from back calculations by using the Schmertmann method. The aim of calculating allowable bearing capacity modified by settlement analysis is to propose a procedure about the foundation designs of the building laying on compressible sandy soils.Zonguldak Karaelmas University Scientific Research Projects UnitBulent Ecevit University [2007/2-45-05-06]; Zonguldak Karaelmas UniversityBulent Ecevit UniversityThis study was funded by Zonguldak Karaelmas University Scientific Research Projects Unit (2007/2-45-05-06). The authors would like to express their gratitude to Zonguldak Karaelmas University for their financial support