m. hazeghian

A great deal of research has been conducted on the performance of granular columns under vertical loads. However, in some situations, the movement of the soil mass can lead to lateral deformations and, as a result, shear stresses in the soil and columns. The primary objective of the present study is to numerically investigate the shear performance of soft clay soil improved with a single Ordinary Granular Column (OGC) in the direct shear test using a hybrid Discrete Element-Finite Difference Method (DEM-FDM). The numerical modeling method was first validated by simulating a direct shear test conducted previously on a soft clay-OGC composite in the laboratory. Afterward, an extensive parametric study was conducted to determine how various factors affect the shear strength of clay-OGC composites. According to the results, increasing the area replacement ratio from 15 to 35% can increase the peak shear strength of clay-OGC composites in the direct shear test by up to two times, depending on the level of applied normal stress. The micro-scale results also indicated that the surface roughness of soil particles in OGC has a greater effect on the shear strength of clay-OGC composites than their angularity. Furthermore, the results showed that the equivalent friction angle of clay-OGC composites should be calculated based on the residual friction angle of granular soil used in OGC.

It is the objective of the present study to present a methodology for determining the horizontal seismic coefficient for soil-nailed walls based on numerical non-linear dynamic analysis. As a first step, two verification tests were simulated in order to validate the numerical modeling methodology and assumptions both in static and dynamic modes. The static validation phase involved simulating the soil-nailed wall in the Clouterre project and comparing numerical and measured profiles of horizontal displacement after excavation. The dynamic validation phase included a shaking table test on a soil-nailed wall, followed by a comparison of numerical and experimental profiles of the horizontal displacement of the wall at the end of the seismic loading. Afterwards, an in-depth explanation of the numerical modeling methodology used to calculate the seismic coefficient for soil-nailed walls was provided. Thereafter, an extensive parametric study was conducted to examine the effects of various factors on the horizontal seismic coefficient, including the wall height, soil relative density, soil cohesion, earthquake frequency content, ground surface acceleration, and altering the soil nailing design. In the parametric study, three earthquake acceleration records were used: Kocaeli, Avaj and Chi-Chi. The results of the parametric study showed that the ratio of the maximum horizontal seismic coefficient to the maximum ground surface acceleration (khmax/PGA) decreased on average with the increase in the wall height, the predominant frequency of earthquake motion and the maximum ground surface acceleration. Furthermore, the results indicated that the khmax/PGA ratio increased with an increase in soil relative density. Moreover, the ratio increased slightly as soil cohesion increased. Additionally, it was found that modifying the soil nailing design by increasing the diameter, reducing the horizontal spacing, and increasing the length of nails did not significantly alter the khmax/PGA ratio. The calculated horizontal seismic coefficients (khdesign) resulted from the parametric study ranged from 0.18 to 0.46 of the maximum ground acceleration (PGA), which is less than the commonly used range of 0.33 to 0.5 PGA.