A Numerical Model to Study the Response of Piles under Lateral Loading in Unsaturated Soils

The interaction between a laterally loaded pile and the surrounding soil is typically limited to the shallower soil layer. Often, this zone is above the water table and therefore the interaction takes place under unsaturated conditions. The available evidence is scarce but suggests that unsaturated conditions play a major role on the pile’s response. The actual mechanisms governing the soil–pile interaction under unsaturated soil conditions are not understood entirely, and this paper provides a useful insight on this topic. The analysis is carried out with a fully coupled three-dimensional numerical model, the soil behaviour is simulated with a Modified Cam Clay Model extended to unsaturated conditions. The model accounts for the increase in stiffness and strength of unsaturated soils as well as the volumetric collapse upon wetting. The constitutive model is calibrated on the laboratory data and validated against centrifuge data with satisfying agreement. The results highlight the substantial differences in the soil reaction against the pile depending on different water saturation profiles. The study also shows that the influence of unsaturated conditions on the pile response increases as the pile’s flexibility increases. Comparing the findings with currently available design methods such as the p–y curves, it is found that these do not adequately describe the unsaturated soil reaction against the pile, which opens the door for new research in the field. The proposed numerical model is a promising tool to further investigate the mechanisms underlying the soil–pile interaction under unsaturated soils.

Analysis of the pile skin resistance formation

This paper introduces a method based on a static load test which is aimed to verify the mechanism of the piles soil–skin interaction. The authors base their analysis on detailed data from static load test with extensometers on CFA piles. The main goal of the research is to determine the proper method of examining how the skin of the pile and soil interacts and apply it to practical engineering practice. As the first stage of the research is limited to the available set of piles, the authors make assumptions that will be verified on later stages of research as more data become available. The authors attempt to formulate the boundary conditions for the formation of pile skin resistance formation using mathematical physics equations to describe the phenomena. Current research proves that it is possible, with the suitable for practical engineering calculations, to describe soil–pile interaction mechanism based on static load test results. Experimental research indicated that there is possibility, for practical engineering calculations purposes, to assume that skin resistance of the pile due to depth can be presented with linear graph. The description is made upon extensometer results, but is meant to be appropriate with the standard static load test results, which provide load–settlement curve of the pile.

Pseudo-static Simplified Analysis Method of the Pile-liquefiable Soil Interaction Considering Rate-dependent Characteristics

The lateral pressure generated by liquefied soil on pile is a critical parameter in the analysis of soil-pile interaction in liquefaction-susceptible sites. Previous studies have shown that liquefied sand behaves like a non-Newton fluid, and its effect on piles has rate-dependent properties. In this study, a simplified pseudo-static method for liquefiable soil-pile interaction analysis is proposed by treating the liquefied soil as a thixotropic fluid, which considers the rate-dependent behavior. The viscous shear force generated by the relative movement between the viscous fluid (whose viscosity coefficient varies with excess pore pressure and shear strain rate) and the pile was assumed to be the lateral load on the pile. The results from the simplified analysis show that the distribution of bending moment is in good agreement with experiments data. Besides, the effects of various parameters, including relative density, thickness ratio of non-liquefiable layer to liquefiable layer, and frequency of input ground motion, on the pile-soil rate-dependent interaction were discussed in detail.

Serviceability analysis of piled foundations supporting tall structures

Pile foundations supporting tall structures, such as wind turbines, chimneys, silos, elevated water tanks or bridge piers, are subjected during their life span to remarkably eccentric loads. These may lead to significant rotations which, however, cannot exceed the limiting values corresponding to the safe operation of the structure. A physically motivated mathematical framework aimed at the prediction of the serviceability performance of such kind of structures is herein presented and discussed. Piles are idealized as uniaxial nonlinear elements characterized by two yielding loads, one in compression and one in uplift, while pile-to-pile interaction effects are modeled by means of superposition, through an approximate solution. The axial load–moment capacity of the pile group is preliminary determined from a recent closed form, exact solution based on upper and lower bound theorems, allowing the analysis to be performed under load control. The model is capable of accounting for the dependence of the moment–rotation response from the dead load of the structure and the ‘coupling effect’ between generalized loads and displacements. The prediction performance of the proposed calculation method is validated against both numerical and experimental benchmarks. Finally, a parametric study allowed to assess the importance of pile-to-pile interaction on the foundation response under eccentric loads.