Experimental study on stress concentration factors in single and groups of end bearing and floating stone columns

Çekinmez, Zeynep
In this study, small scale model tests were performed in order to observe effects of column length and undrained shear strength on settlement reduction ratios at different zones, as well as the stress concentration factor. In these tests different loading conditions, i.e. single stone column loading, unit cell loading and group loading, were studied. Stress carried by stone columns under various foundation pressures were directly measured by soil pressure transducers. Surface and subsurface settlements were measured by dial gauge and potentiometric rulers. Variation of stress concentration factor with time is assessed. Unit cell and group behavior with floating and end-bearing columns are compared. An empirical equation to obtain the group settlements from the unit cell settlements, as a function of normalized column length and normalized foundation pressure is proposed. For infinite pattern of column groups, emipirical relationships between total settlement reduction ratio and undrained shear strength and; stress concentration factor and undrained shear strength are proposed.