Mathematical modelling of the mechanical response of geosynthetic-reinforced and pile-supported embankments

Abstract

Piled foundations are commonly employed to reduce settlements in artificial earth embankments founded on soft soil strata. To limit the number of piles and, consequently, construction costs, popular is the use of geosynthetic reinforcements laid at the embankment base. Nowadays, the complex interaction between geosynthetics, piles and soil is not yet fully understood and, in the scientific literature, simplified displacement-based approaches to choose reinforcements, pile diameter and spacing are missing. In this paper, the authors, starting from the critical analysis and theoretical interpretation of finite difference numerical results, introduce a new mathematical model to rapidly assess both (i) differential/average settlements at the top of the embankment and (ii) maximum tensile forces in the basal reinforcement. The model, conceived to reproduce the response of a pile belonging to the central part of the embankment, is the result of an upscaling procedure based on a suitable sub-structuring of the spatial domain (an axisymmetric unit cell) and on the concept of plane of equal settlements. For the foundation soil, drained conditions are considered, the pile skin roughness is disregarded, and piles are assumed to get the rigid bedrock. As generalised kinematic variables average and differential settlements are employed, whereas as generalized static ones the embankment height and the geosynthetic axial force. The model is validated against field measurements (where layered foundation soil and pile caps are included) and an application example of the model, used as a preliminary design tool in a displacement-based perspective, is finally provided.