Modelling the Response of Deep Foundations under Oblique Loading

Deep foundations are slender pile elements used to transfer loads from structures into deeper soil strata below the ground. Deep foundations have a variety of loads including axial, lateral and moments. Often these loads will act together to form a combination of loads, such as oblique forces that have a component of axial and lateral forces. Due to the pile’s length, which can extend past 30 m, it is difficult and expensive to carry out full scale testing. Any full-scale test data is limited to the area conditions and soil properties at the testing site. Small scale testing can be used as an alternative to full scale testing, although scaling effects will influence the conclusions from this type of study greatly. Computer simulations of finite element modelling allow for indepth studies into the complex pile-soil interaction under combination loading in deep foundation structures. This work used 3D finite element modelling to explore the effect of pile shape, sand properties, pile length and loading conditions on the capacity of a pile. Using trends discovered by these simulations design charts were developed to aid consultants when determining the bearing capacity for oblique interaction for square piles. It was found through a carefully planned sensitivity analysis that sand properties and pile shape can influence the capacity of a pile extensively. The mesh density, boundary and initial stress conditions imposed on the simulation will ultimately determine the accuracy and reliability of the model results. To gain a good understanding of a model’s capability and accuracy the simulation output must be tested and verified against case studies. The trends obtained from modelling the complex mechanisms such as the pile-soil interaction allows for greater understanding of failure mechanisms, which could otherwise not be observed.