Abstract
Progressive failure is common in many natural clays of strain-softening behavior and may affect the bearing capacity of foundations placed on such soils. The progressive failure might be insignificant for small structures where the mobilized strains are generally uniform within the failed soil mass. This places a demerit to the applications of knowledge obtained from physical model tests to prototype. The study aims to understand and quantify this scale effect on bearing capacity of shallow foundations on strain-softening clays, with a numerical investigation using a large deformation finite element analysis. The progressive failure is numerically replicated and the controlling parameters for the bearing capacity have been discussed. A correction factor is introduced which is inversely proportional to the foundation size normalized by the proposed characteristic length. An empirical relationship of the correction factor and the normalized foundation size has been obtained via the numerical data, which may improve the design of shallow foundations on strain-softening clays.
Highlights
IntroductionThe calculation of bearing capacity is one of core tasks in foundation design, and its vertical component for saturated clays, q, is usually given by q
The calculation of bearing capacity is one of core tasks in foundation design, and its vertical component for saturated clays, q, is usually given by q = Nc su FS + p (1)where Nc is the bearing capacity factor, su the undrained shear strength, FS the factor of safety, and p the overburden pressure at the foundation depth
The first term of the vertical bearing capacity, i.e., equation (1), needs a factor, α, which can be interpreted as a correction either for the bearing capacity factor or the operational strength upon foundation collapse in natural clay deposits
Summary
The calculation of bearing capacity is one of core tasks in foundation design, and its vertical component for saturated clays, q, is usually given by q. The load transferred from a superstructure is non-uniformly distributed through the non-rigid soil ground as illustrated, with the soil strength reaching the post-peak stage near the tip of the foundation while remaining pre-peak at the end of the rupture surface (Griffiths, 1989; Conte et al, 2013). This type of progressive failure might be insignificant for small structures, such as a cone device, where the mobilized strains are quasi- uniform within the failed soil mass. Lc Nc Nc,ref p q s St su su,p su,r α ν δp δpr γpr width of foundation displacement of foundation Young’s modulus vertical load factor of safety characteristic length bearing capacity factor reference bearing capacity factor overburden pressure vertical bearing capacity shear band thickness soil sensitivity undrained shear strength of clay peak undrained shear strength residual undrained shear strength reduction factor Poisson’s ratio plastic shear displacement the value of δp to soften the shear strength to the residual plastic shear strain to soften the shear strength to the residual
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