Improvement of soft clay deposits by the installation of stone columns is one of the most popular techniques followed worldwide. The stone columns not only act as reinforcing material increasing the overall strength and stiffness of the compressible soft soil, but they also promote consolidation through effective drainage. The analytical and numerical solutions available for ascertaining the response of column-reinforced soil have been developed on the basis of the equal strain hypothesis. For typical surcharge (embankment) loading, the free strain analysis appears to give more realistic results comparable to field data. The paper presents a novel numerical model (finite-difference method) to analyze the response of stone column–reinforced soft soil under embankment loading, adopting the free strain approach and considering both arching and clogging effects. Apart from predicting the dissipation of excess pore water pressure and the resulting consolidation settlement with time, the load transfer m...

Among various ground-improvement techniques, soft-soil reinforcement by stone columns is one of the most common and convenient methods with numerous benefits including increased bearing capacity and consolidation, reduced postconstruction settlement and lateral movement, and improved slope stability and liquefaction control, among others. Because of the limited confinement offered by the surrounding soft soil especially at shallow depths, lateral deformation of stone columns is not uncommon. Although several analytical and numerical solutions are available to predict the load-settlement performance and consolidation characteristics of stone-column-improved soft ground, most existing models do not accurately capture the lateral deformation of stone columns. In view of this, the authors have developed in-house a novel numerical model based on the Fast Lagrangian Finite-Difference technique with associated subroutines to analyze the behavior of a stone column including its lateral deformation. In particular, the displacement compatibility and the barreling effect are considered in the model. Soft-soil consolidation under imposed loading is considered by adopting the modified Cam-clay theory. The proposed solutions are validated using available field observations and existing numerical solutions. The model was successfully applied to a selected case study at the Pacific Highway near the town of Ballina, New South Wales, Australia. It is demonstrated that both the deformation pattern and bulging depth of stone columns are dependent on several factors including the particle interlock, imposed load-intensity, soil-column stress concentration ratio, soil shear strength, and column geometry.

Major offshore and onshore structures, including transport corridors and high-rise buildings, resting on soft compressible clays are often supported by pile foundations. Apart from the usual vertical loading from the superstructures, these piles are usually subjected to large cyclic loads arising from the actions of waves, ship impacts, or moving vehicles. Under such circumstances, vertical and lateral modes of cyclic loading are predominant and affect overall stability. Such repetitive loading on piles leads to reversal of axial stresses in the adjacent soft clay, initiating progressive degradation in soil strength and stiffness that deteriorates the pile capacity with unacceptable displacements. Although several studies have been carried out to investigate the response of a single pile, a detailed investigation on a pile group in soft soil subjected to cyclic lateral loading, which is of immense practical interest to field engineers, had yet to be conducted. In this paper, extensive laboratory model tests with steel-pipe-pile groups in soft cohesive soil were conducted followed by the development of a numerical model that was based on a two-dimensional (2D) dynamic finite-element (FE) approach. The degradation of both axial and lateral capacities of the pile group and the pattern of the degradation with variations in the cyclic-loading parameters were studied. Comparisons of the experimental data with the computed results validated the numerical analysis. The study indicates that both the axial and lateral pile capacities and displacements were significantly influenced by the cyclic-loading parameters (number of cycles, frequency, and amplitude). Relevant design recommendations are presented.

Installing stone columns is a convenient method of soft ground improvement. Although several analytical and numerical solutions are available to predict the performance of stone column–improved soft ground, these models are incapable of capturing the influence of cyclic loading on transport corridors, such as highways and railways. The authors developed a novel finite-difference model adopting modified Cam clay theory to analyze the response of stone column–reinforced soft soil under static and cyclic loadings. Apart from predicting excess pore water pressure dissipation and the resulting settlement, the model also captures the effect of cyclic loading by considering yield surface contraction. The solutions developed were validated using available field observations and laboratory test results. The model was successfully applied to a selected case study at the Australian National Field Testing Facility at Ballina, New South Wales, Australia. The limitations of the proposed model are highlighted as...