The development of negative skin friction (NSF) on single piles is investigated based on an uncoupled method of analysis with the Mikasa (1963) generalized nonlinear consolidation theory in terms of finite strain and the nonlinear load-transfer method. Predicted results are compared with results based on the conventional linear consolidation theory with infinitesimal strains. It is found that predicted development of dragload using the conventional consolidation theory is slightly greater and conservative compared to that using the nonlinear consolidation theory based on effective stress (β method). Effective stress predictions using the conventional theory are larger due to the faster dissipation of excess pore pressures, with the assumption of constant coefficient of consolidation and permeability. However, since the relative displacements required to mobilize the ultimate skin friction are small, and piles are usually installed near the final stages of soil consolidation, the differences in the predictions for the development of dragload on piles between the two consolidation theories are overshadowed. Using the uncoupled model for pile NSF, it is therefore found that the most significant factor for the estimation of dragload and downdrag is the proper selection of the β value rather than the consolidation theory used.

In planning and designing geotextile tubes, predicting the consolidation characteristics is very important to ensure that the capacity and deformation of the tubes are well regulated during construction. Design and construction parameters, such as dewatering time and permeability, must be evaluated considering the interaction of the soil and geotextile during filling and consolidation. In this study, field scale tests, such as the hanging bag test and geotextile tube demonstration tests, were performed as a geotechnical design approach in determining the equivalent soil-geotextile consolidation parameters. In the hanging bag test, seepage pressure was applied to simulate the effect of filling pressure in the actual construction site. Procedures to determine the required slurry volume, soil-geotextile consolidation parameters, tube geometry, and consolidation characteristics were introduced in this study. The procedures were proposed on the basis of the areal method, which considers the vertical and lateral movement of the tube, and the large strain consolidation theory, which considers finite strain and the change of the coefficient of consolidation. Finally, using the proposed procedures and obtained consolidation parameters, a parametric study was performed to show the applicability of the areal method and large strain consolidation theory.

A modified analytical model is proposed in this study for the analysis of pile axial load capacity with the load transfer method using nonlinear T-z and Q-z curves to model soil-pile behavior in skin friction or side shear and end bearing respectively. The method uses a three-dimensional (3D) pile model using solid finite elements with nonlinear load transfer curves resolved into components and mobilized around the pile perimeter. The use of multiple T-z component springs is demonstrated to accurately capture the total side resistance of the pile. The 3D pile method produces results of predicted pile axial load capacities from the load-settlement curves comparable to the one-dimensional analysis (1D) method. For a combined vertical and lateral loading on the pile, the proposed 3D pile method can address the limitation of the 1D pile method having vertical and lateral springs only acting at the pile center without rotational springs, which neglects the contribution of the side shear in the computation of pile bending moments. In the case of 3D pile model the moment or couple developed by the side shear around the perimeter can be taken into account, where this moment can be significant especially in strong soil material or in the case of large diameter pile/shafts.