Neutral plane of single pile in clay subjected to surcharge loading using the “critical state soil mechanics” (CSSM)

Abstract

ABSTRACT Piles are designed to support direct loads, however, floating piles in clay are often subjected to indirect loading (surcharge). In this case, the pile’s shaft will be subjected to negative skin friction on part or on its full length, depending on the value of the surcharge, soil condition and pile’s length. The total negative skin friction acting on the pile’s shaft is known as the drag-load, which will reduce the pile capacity and perhaps pull the pile out of its cap, leading to catastrophic failure of the structure. A numerical model was developed using the finite element technique to simulate the case of a single pile floating in clay subjected to surcharge. The model utilizes the concept of the Critical State Soil Mechanics (CSSM) and the constitutive law of the Modified Cam Clay (MCC). The MCC is capable of incorporating the effect of soil deformation and the stress history into the stresses acting on the pile’s shaft. It is widely used in modelling geomechanics problems. The objective of this study is to determine the location of the neutral plane on the pile’s shaft for a given surcharge, soil condition and pile’s length. Thus, the positive and negative skin frictions acting on the pile’s shaft can be determined and accordingly the pile capacity. After validating the numerical models with the data available in the literature, the model was used to generate a wide range of data, which commonly used in practice, to examine the effect of the parameters which govern the location of the neutral plane for these piles. Design charts and design example are presented.