INTERFERENCE OF STRIP FOOTINGS RESTING ON LEVEL AND SLOPING GROUNDS

Abstract

The structures are quite often constructed close to each other due to lack of space, which results in the close placement of the footings. The close placement of footings causes them to interfere with each other. The stress distribution below interfering footings will be different from a single individual footing. The interference phenomenon may be due to large loads on closely-spaced footings of the same structure or of different structures. The interference of footings causes variations in engineering parameters such as bearing capacity, load-settlement curve, failure patterns etc. Hence, the present study is on studying and analysing the behaviour of closely-placed strip footings on flat and sloping grounds keeping the bearing capacity in focus. This is a comprehensive parametric study wherein both geometric and materialistic parameters such as angle of internal friction of soil, slope inclination, spacing between the footings, setback distance from the crest of slopes, etc have been varied within certain ranges to understand the nature and mechanism of interference by performing numerical simulations using finite element limit analysis (FELA) software-Optum G2. The numerical results are also verified by performing small-scale model laboratory tests. The interference effect is determined by calculating the efficiency factor (ξ) corresponding to each unique set of parameters adopted in the study. For flat grounds, no interference effect is observed for closely placed two strip footings, but there is significant interference effect for the centre footing if it receives confinement on both the sides by other footings. For sloping grounds, interference effect primarily depends upon the placement of study footing with respect to critical setback distance and the spacing between the footings. The interference of strip footings on sloping grounds will occur if the footing is confined either on the sloping side or on both its sides by other footings. For both flat and sloping grounds, the ultimate bearing capacity decreases with the increase in spacing between the footings, and the effect of interference is significant only up to S/B≤2, above which there is no considerable effect of interference