Collapse of a Model Strip Footing on Dense Sand Under Vertical Eccentric Loads |
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Authors: | Antonino Musso Settimio Ferlisi |
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Institution: | (1) Department of Civil Engineering, University of Rome “Tor Vergata”, Via del Politecnico, 1, 00133 Rome, Italy;(2) Department of Civil Engineering, University of Salerno, Via Ponte don Melillo, 84084 Fisciano (SA), Italy |
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Abstract: | The paper focuses on the behaviour of a model strip footing, resting on a saturated dense sandy soil, subjected to centred
or eccentric vertical loading. Experimental tests, carried out on a small-scale physical model, are able to reproduce effective
stress levels equivalent to those prevailing in prototype problems, thanks to the maintenance of a downward steady-state seepage
in the soil. The test program consists of three series of tests, each corresponding to an imposed value of hydraulic gradient,
and each involving five load eccentricities; one series, in particular, is carried out with still water. Relevant points of
load–settlement curves are related to the evolution of soil-footing collapse mechanism, evidenced by the distortion of some
vertical coloured sand strips. The collapse mechanism is formed either by one or two sliding surfaces, depending on both load
eccentricities and hydraulic gradient values. Significant differences are shown to occur between centred and eccentric loading
footing response. Shear strength parameters obtained from back-analyses carried out on load values recorded at the appearance
of each sliding surface on the free soil surface, in both hypotheses of associated and non-associated flow rule validity,
are adopted to draw, for each test, a theoretical collapse mechanism consisting, in plane strain, of a log-spiral line with
adjacent-end tangents; the obtained theoretical sliding surfaces, in turn, are compared to the experimental ones, showing
that these latter are either stress characteristic or zero-extension lines depending mainly on cumulative footing displacements
and current effective stress level in the soil. |
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Keywords: | Footing Sand Model tests Eccentric loading Hydraulic gradient Collapse mechanism |
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