Determination of stress concentration factor in stone columns by numerical modelling

Yıldız, Melis
The behaviour of stone columns in soft cohesive soil is investigated by finite element analyses. Conventional design methods and settlement calculations of improved ground require the knowledge of stress concentration factor which is in stone column design practice either determined by field tests or estimated from recommendations given in literature. The former is not economical for small to medium scale projects. This study focuses on the determination of stress concentration factor in stone columns by numerical modelling. Numerical analyses are carried out by using Plaxis 2D software. The stress concentration factor is defined to represent the load sharing between the column and the surrounding soil. A parametric study is carried out to define the change of stress concentration factor with modulus of elasticity of clay, the column length and applied foundation pressure. The study includes assessment of settlement reduction ratio with the same parameters. The rigid foundation analyses show that the stress concentration factor changes between 2.5 and 5.0. The ratio decreases by the increasing rigid foundation pressure and linearly decreases with increasing modulus of elasticity of soil. The floating columns give values close to each other while end bearing columns give higher stress concentration ratios. The flexible foundation analyses are carried out to compare the stress concentration factors with those of the rigid foundations. The ratio is found to change between 1.8 and 3.0. The behaviour of change of the ratio with modulus of elasticity of soil in floating and end bearing columns is similar to the rigid foundations. The stress concentration factors are almost constant at different flexible foundation pressures. The stress concentration factor in flexible foundation analyses is determined to be approximately 30% smaller than in rigid foundation analyses.


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Citation Formats
M. Yıldız, “Determination of stress concentration factor in stone columns by numerical modelling,” M.S. - Master of Science, Middle East Technical University, 2013.