سعيد حسيني

The performance of large grid walls and discrete columns is generally weak against liquefaction; however, smaller walls, despite their higher construction costs, exhibit better performance. Therefore, combining grid walls of economical dimensions with discrete columns to mitigate liquefaction is a logical approach. This method not only improves the design economically by optimizing the dimensions of the wall but also controls the increase in shear stress in confined soil caused by the enlargement of the wall through the addition of columns. Parametric studies are conducted separately on the grid wall and the combined system of grid walls and discrete columns to compare their performance. In the grid wall study, the effects of parameters such as grid wall dimensions, grid wall shear modulus ratio, grid wall depth, grid wall thickness, and the thickness of the liquefiable soil layer are examined with respect to outcomes including excess pore pressure ratio, peak surface acceleration, lateral soil deformation, and average settlement of the structure. Subsequently, the performance of the combined system is eva‎luated by considering parameters such as area replacement ratio, depth of improvement, type of discrete columns, type of pile head connection, site response effects, and shear strain compatibility effects, alongside performance-based design principles, using 3D nonlinear, solid-fluid, fully-coupled, effective stress, dynamic finite-element (FE) analyses in OpenSees. Based on the results of the grid wall parametric study, since the shear stress reduction factor does not decrease with changing parameters, liquefaction in grid wall designs with L/H> 1.31 is not controlled. However, changing parameters to achieve better performance (such as reducing grid wall dimensions) results in reduced lateral deformation and settlement. Yet, increasing the stiffness of the soil environment leads to higher ground surface acceleration and increased inertial forces acting on the structures. Additionally, the safety factor in combined designs is greater than in designs with discrete columns or grid walls (L/H=1.85) with near area replacement ratios across different designs. However, in designs with discrete columns and combined systems where the structure is directly influenced by the columns, settlement is better controlled compared to grid wall designs. Furthermore, it was determined that comparing the performance of different designs solely based on the area replacement ratio is not appropriate. In addition, the performance of piles is generally better than that of soil-cement columns, and a fixed pile head has a negligible impact on the results. However, the site response effect significantly reduces the safety factor, and the unconservative assumption of shear strain compatibility, along with the consistency of this study's results with the modified method by Nguyen et al. (2013), has been observed.

كاهش پتانسيل روانگرايي , ديوار شبكه اي , سيستم تركيبي ديوار شبكه اي و ستون هاي مجزا , اثر پاسخ ساختگاه , سازگاري كرنش برشي , اپنسيس

liquefaction potential reduction , grid wall , combined system of grid wall and discrete columns , site response effects , shear strain compatibility , OpenSees

Saeed Hosseini

Dr. Mohsen Sabermahani