Abstract
Tests on small-scale physical models of a strip footing resting on a dense sand bed containing a thin horizontal weak soil layer were carried out at normal gravity (1 g ). The results, reported in a companion paper, point out that the weak layer plays an important role in the failure mechanism and the ultimate bearing capacity of the footing if it falls within the ground volume relevant to the behaviour of the sand–footing system. The same problem was also investigated by means of centrifuge tests on reduced-scale models at 25 g and 40 g . The results of these tests, reported and discussed in this paper, confirm that failure mechanisms are governed substantially by the presence of the weak layer if its depth does not exceed a critical value and highlight marked scale effects involving the ultimate bearing capacity related essentially to the mean equivalent stress level in the soil beneath and around the footing. Equivalent bearing capacity factors, [Formula: see text], for footings on a dense sand bed containing a thin weak layer are derived from experimental results and are proposed in the paper.
Highlights
Minor geological and geotechnical details can have great relevance for seepage and consolidation processes as well as for the movements and stability of natural and manmade geotechnical systems (Leonards, 1982; Rowe, 1972; Terzaghi, 1929)
Bm = 40 mm, footing model width; zi, depth of the top surface of the weak layer; t0, thickness of the weak layer; qlim, ultimate bearing capacity; qlim,0 = 3869·7 kPa, ultimate bearing capacity for the homogeneous sand case; rm,lim, settlement of footing model corresponding to ultimate bearing capacity; lm, maximum lateral extent of failure mechanism; zm, maximum depth of failure mechanism; qL and qR, emersion angles of the failure surface on the left and right sides of the footing, respectively
Bm = 40 mm, footing model width; zi, depth of the top surface of the weak layer; t0, thickness of the weak layer; qlim, ultimate bearing capacity; qlim,0 = 4937·2 kPa, ultimate bearing capacity for the homogeneous sand case; rm,lim, settlement of footing model corresponding to ultimate bearing capacity; lm, maximum lateral extent of failure mechanism; zm, maximum depth of failure mechanism; qL and qR, emersion angles of the failure surface on the left and right sides of the footing, respectively
Summary
Full Professor, Dipartimento di Ingegneria, Università degli Studi di Ferrara, Ferrara, Italy. Tests on small-scale physical models of a strip footing resting on a dense sand bed containing a thin horizontal weak soil layer were carried out at normal gravity (1g). The same problem was investigated by means of centrifuge tests on reduced-scale models at 25g and 40g. The results of these tests, reported and discussed in this paper, confirm that failure mechanisms are governed substantially by the presence of the weak layer if its depth does not exceed a critical value and highlight marked scale effects involving the ultimate bearing capacity related essentially to the mean equivalent stress level in the soil beneath and around the footing. F10 p peak angle of shearing resistance of sand f01Ãp mean equivalent angle of shearing strength f20 p angle of shearing resistance of the weak layer y10p peak dilation angle of sand
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