Undrained lower bound solutions for end bearing capacity of shallow circular piles in non‐homogeneous and anisotropic clays

Abstract

SUMMARY The undrained bearing capacity of shallow circular piles in non‐homogeneous and anisotropic clay is investigated by the lower bound (LB) finite element limit analysis (FELA) under two‐dimensional (2D) axisymmetric condition using second‐order cone programming, and the new solution of the problem is presented. Modified from the isotropic von Mises yield criterion, a cross‐anisotropic undrained strength criterion of clays under the axisymmetric state of stress requiring three input shear strengths in triaxial compression, direct simple shear, and triaxial extension is employed in the 2D axisymmetric LB FELA. Parametric studies on the effects of pile embedment ratio, dimensionless strength gradient, anisotropic strength ratio, and pile roughness are investigated extensively, while the predicted failure mechanisms associated with these parameters are discussed and compared. Numerical results of undrained end bearing capacity of shallow circular piles are summarized in the form of design tables that are useful for design practice and represent a new contribution to the field of pile capacity considering the combined effects of undrained strength non‐homogeneity and anisotropy.

Lower bound limit analysis for an axisymmetric problem in rock mass using power cone programming

“…Rather than making this assumption, the authors have satisfied the equilibrium only at the centroids of each element. A number of studies studies 4,22,23,26,33,35,37,40 are available in literature at present which confirm that this assumption provides quite acceptable (accurate) solutions if not the true lower bound. Therefore, in the present study the equilibrium conditions were satisfied only at the centroid of each element.…”

“…At present, amongst all the existing mathematical programming techniques for solving the optimization problems with the usage of the FELA, the conic‐based optimization procedures are reported as the most robust ones both in terms of accuracy as well as computational efficiency 29–31,34–36 . The robustness of the second order cone programming (SOCP) technique in analyzing different plane strain problems, in terms of accuracy as well as computational efficiency, was demonstrated by Makrodimopoulos and Martin 29,34 .…”

Application of Artificial Neural Networks for Predicting the Stability of Rectangular Tunnels in Hoek–Brown Rock Masses

“…The finite element limit analysis (FELA), which is the computational method based on a perfectly plastic material with an associated flow rule, employs the plastic bound theorems, finite element discretization, and mathematical optimization (Sloan, 2013;Keawsawasvong and Ukritchon, 2017;Ukritchon and Keawsawasvong, 2017;Krishnan et al, 2019;Ukritchon et al, 2019;Ukritchon and Keawsawasvong, 2020a;Ukritchon and Keawsawasvong, 2020b;Ukritchon et al, 2020;Keawsawasvong and Ukritchon, 2021). This FELA technique is carried out to derive the bracket of the true limit load from the targeted upper Bound (UB) and lower Bound (LB) solutions.…”

Response of vertically-loaded pile in spatially-variable cement-treated soil

“…For piles in cohesive soil, the undrained shear strength of the surrounding soil plays as an important role for the pile foundation design. Ukritchon and Keawsawasvong [ 1 – 5 ] investigated the undrained end bearing capacity of piles in clays involving with anisotropic strengths and the undrained lateral capacity of circular piles, I-shaped concrete piles and rectangular piles.…”