BEARING CAPACITY OF CIRCULAR FOUNDATIONS ON SOFT CLAY OF STRENGTH INCREASING WITH DEPTH

ABSTRACT Huge offshore gravity structures such as deep-sea oil platforms are often equipped with a skirt system underneath their bases. When such foundations of substantial size with deep skirts are to be placed on soft clay deposits, it becomes important to take account of the influence of a non-homogeneous strength profile in bearing capacity calculations. In this study, plasticity theory was used to evaluate the influence of linearly increasing undrained shear strength with depth on the bearing capacity of shallow foundations, under both plane strain and axisymmetric conditions. Based on the results of computations, a simple method is proposed to calculate bearing capacity using a set of charts, which introduces the effect of increasing strength consistently into the framework of conventional bearing capacity theory. A series of centrifuge experiments was also conducted for circular models founded on clay beds. With a limited number of test cases, the experimental results have proved the validity of the proposed method. Furthermore, the failure observed in the model clay beds was due to punching shear; the mechanism of which was confined to shallow depths to avoid shearing of the clay quickly strengthening with depth.

[1]  Guy T. Houlsby,et al.  Calculation of Stresses on Shallow Penetrometers and Footings , 1984 .

[2]  G. G. Meyerhof.  The Ultimate Bearing Capacity of Foudations , 1951 .

[3]  G. Raymond.  The Bearing Capacity of large footings and Embankments on clays , 1967 .

[4]  Alec Westley Skempton,et al.  The bearing capacity of clays , 1951 .

[5]  EH Davis,et al.  The Effect of Increasing Strength with Depth on the Bearing Capacity of Clays , 1973 .

[6]  J. B. Hansen,et al.  A general formula for bearing capacity , 1961 .

[7]  J. Salençon.  Discussion: The effect of increasing strength with depth on the bearing capacity of clays , 1974 .

[8]  Keizo Ugai.  Bearing Capacity of Square and Rectangular Footings on Nonhomogeneous Clays , 1985 .

[9]  A. Zelikson.  Geotechnical Models Using the Hydraulic Gradient Similarity Method , 1969 .

[10]  A. Nakase.  BEARING CAPACITY OF RECTANGULAR FOOTINGS ON CLAYS OF STRENGTH INCREASING LINEARLY WITH DEPTH , 1981 .

[11]  George Geoffrey Meyerhof,et al.  Some recent research on the bearing capacity of foundations , 1963 .

[12]  Jiro Takemura,et al.  A STUDY ON THE DEFORMATIONS AND BEARING CAPACITIES OF NORMALLY CONSOLIDATED CLAY LAYERS UNDER STRIP LOADING , 1987 .

[13]  A New Admissible Velocity Field for Bearing Capacity Caluculations of Strip Footings , 1986 .

[14]  Kazuo Tani,et al.  DEVELOPMENT OF CENTRIFUGE CONE PENETRATION TEST TO EVALUATE THE UNDRAINED SHEAR STRENGTH PROFILE OF A MODEL CLAY BED , 1995 .

[15]  E. H. Davis,et al.  Theories of plasticity and the failure of soil masses , 1968 .

[16]  P. W. Rowe,et al.  A New Consolidation Cell , 1966 .

[17]  Christian Madshus,et al.  MODEL TESTS OF GRAVITY PLATFORMS I: DESCRIPTION , 1989 .

[18]  Osamu Kusakabe,et al.  An upper bound calculation on bearing capacity of a circular footing on a non-homogeneous clay. , 1986 .

[19]  J. Brinch Hansen.  AKADEMIET FOR DE TEKNISKE VIDENSKABER , 2008 .

[20]  G. Houlsby,et al.  Direct solution of plasticity problems in soils by the method of characteristics , 1982 .

[21]  E. Beer,et al.  Experimental Determination of the Shape Factors and the Bearing Capacity Factors of Sand , 1970 .