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A method for the estimation of the non-linear, time-dependent settlement of piled raft foundations (PRFs) embedded in saturated clayey soils subjected to uniformly distributed load under the single-drainage condition was developed. A total of 20 different rectangular PRFs resting on four different types of normally consolidated to moderately overconsolidated clays (overconsolidation ratios of 1, 2 and 5) were analysed to quantify their short- and long-term settlements. Rigorous three-dimensional, elasto-plastic finite-element (FE) analyses were performed with the critical-state-based modified Cam Clay soil constitutive model. Biot's coupled consolidation theory was used to model the time-dependent dissipation of excess pore pressure under the single-drainage condition. The FE analysis results were used to investigate systematically the influence of time and various soil and PRF parameters on the settlement responses of piled rafts. Fitted equations correlating PRF settlements and the degree of consolidation with various influencing parameters were developed. The proposed equations predicted the immediate and primary consolidation settlements and the degree of consolidation with reasonable accuracy and can be used in initial design stages. [ABSTRACT FROM AUTHOR]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

Time-dependent settlements of piled raft foundations embedded in consolidating clays were studied using three-dimensional (3D) finite-element analysis and critical state-based soil constitutive modified Cam-Clay (MCC) model. In this study, different small to large rectangular rafts connected to circular bored cast-in-situ piles resting on four different types of clays and with varying overconsolidation ratios (OCRs) (1, 2, and 5) for each clay under a single drainage condition were analyzed. The influence of various piled raft parameters (pile length, pile spacing, pile diameter, raft thickness) and soil parameters (Poisson's ratio of soil, soil critical state parameters, stress history of soil or OCR) on immediate and consolidation settlements of piled rafts were investigated. The detailed parametric study shows that critical state parameters and soil elastic properties have important roles in piled raft immediate and consolidation settlements. However, the pattern of parametric influence on immediate settlement and consolidation settlement is different. To capture the total settlement at the end of primary consolidation, a simple and quick calculation method for estimating the average soil subgrade modulus below the piled raft in consolidating clays is proposed through regression analysis and defining a combined influence parameter based on soil parameters, area ratio, and normalized loading. The results of the proposed method were compared with five case studies of piled raft foundations in various normally or overconsolidated clays showing satisfactory matches. It is believed that the proposed method will be very useful for design practitioners to get a quick estimate for the overall settlement of piled raft at the initial design stage. [ABSTRACT FROM AUTHOR]

Installation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay. The gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtained between the shaft resistance values calculated with the proposed equations and the data available in the literature. [ABSTRACT FROM AUTHOR]

The current study examines and quantifies the limit shaft resistance of drilled shafts installed in clay through finite-element analyses that use an advanced two-surface-plasticity constitutive model for clay. The clay constitutive model used in this study reproduces the mechanical response of clays under multiaxial loading conditions, predicts both drained and undrained behavior at small and large strains, and captures the drop in strength toward a residual value at very large shear strains. One-dimensional finite-element analyses are performed to simulate the essential stages of the installation and loading of drilled shafts in clay for different initial stresses, different overconsolidation ratios, and different values of the difference between the critical-state and the minimum residual friction angles. On the basis of these simulations, equations for the shaft friction coefficient are proposed that can be used in the calculation of the shaft resistance of drilled shafts in clay. Predictions using the proposed equations compare well with the data derived from different field pile load tests on drilled shafts. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a two-surface plasticity constitutive model for clays based on critical-state soil mechanics. The model reproduces the mechanical response of clays under multi-axial loading conditions and predicts both drained and undrained behavior at small and large strains. The constitutive model also captures both the strain-rate-dependent behavior of clays and the drop in strength towards a residual value at very large shear strains using novel approaches. The paper also describes a hierarchical process for the determination of the model parameters relying more on simple curve fitting of model equations to experimental data points corresponding to specific soil states instead of trial-and-error simulations of entire experiments. Model parameter values are determined for London Clay, San Francisco Bay Mud, Boston Blue Clay and Lower Cromer Till, and the performance of the model in simulating mechanical response of clays is demonstrated for a variety of initial states and loading conditions. [Copyright &y& Elsevier]

The authors respond to a commentary on their paper "Shaft Resistance of Drilled Shafts in Clay." They thank the commentary for appreciating their research on the drilled shaft design on clay. They note that the paper captured the dependence of shaft resistance on stress history of the clay deposit through the normalized shear strength ratio.