Numerical estimation of the fundamental frequency of improved sites with stone columns

Abstract

Background/Objectives: Installation of stone columns is one of the appropriate techniques for the improvement of soft soils. However, the seismic behavior of this reinforcing elements has been limitedly studied. Methods/Statistical Analysis: In this paper, effects of stone column construction on the fundamental frequency of the sites are studied numerically. Finite element analysis was performed using ABAQUS. The performed analysis was a modal analysis through the calculation of eigenvalues to determine of the fundamental frequency of improved sites with stone columns. The analyses was carried out in 3D and 2D in some cases. Findings: The results demonstrated that constructing the stone columns can increase the fundamental frequency of the site up to three times. Based on the performed analyses, the fundamental frequency amplification factor of the site (a) can be defined according to the dimensionless parameters including stone column to soil shear wave velocity, stone column height to its diameter, stone column distance to its diameter, and stone column arrangements. The results indicated that a decreased with a rise in the ratio of the stone column height to its diameter. A comparison of the stone column arrangements demonstrated that, in a triangle arrangement, the value of a was greater than the corresponding value in square arrangement. The results indicate that, in floating stone columns the effects of stone columns on the soil mass due to the absence of the bottom of the column with respect to the condition where the stone column was end bearing was considerably insignificant. Application/Improvements: Based on the results, a was presented for the square and triangle arrangements according to the dimensionless parameters and finally a 2D equivalent method was presented for the simplification of the 3D actual problem.