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This paper presents an analytical approach for predicting the nonlinear load-displacement behaviour of pile groups consisting of displacement piles in normally consolidated and lightly overconsolidated clayey soils. The effects of squeezing and remolding on the soil around the piles caused by pile installation are reflected by the soil strength and shear modulus. The nonlinear load-displacement behaviour at the pile-soil interface is modeled by the load-transfer method with exponential load-transfer functions and the pile-pile interaction effects are reflected by the shear displacement method. A hybrid analytical method, incorporating the developed soil parameters and combining the load transfer method and the shear displacement method, is proposed for the problem considered. Four sets of centrifuge model tests, involving pile groups with different pile diameters, pile lengths and pile spacings, were conducted to verify the proposed analytical framework. The validity of the proposed method, the significance of the installation effects as well as the nonlinear behaviour of the pile groups are demonstrated by comparing the load-displacement curves from the centrifuge model tests with those from the proposed method and other relevant methods. Parametric studies are conducted to investigate the pile diameter, pile length, pile spacing and pile number on the stiffness efficiency of pile groups. The results indicate that increasing the pile diameter and length can effectively improve the stiffness efficiency and the load carrying behaviour of displacement pile groups.

In this paper, a simple but feasible approach is proposed to predict the time-dependent load carrying behaviours of jacked piles from CPTu measurements. The corrected cone resistance, which considers the unequal area of the cone rod and the cone, is used to determine the soil parameters used in the proposed approach. The pile installation effects on the changes in the stress state of the surrounding soil are assessed by an analytical solution to undrained expansion of a cylindrical cavity in K0-consolidated anisotropic clayey soil. Considering the similarity and scale effects between the piezocone and the pile, the CPTu measurements are properly incorporated in the shaft and end resistance factors as well as in the load-transfer curves to predict the time-dependent load carrying behaviours of the pile. Centrifuge model tests are conducted and the measured load carrying behaviours of the model piles are compared with the predictions to validate the proposed approach. The proposed approach not only greatly saves the time of conducting time-consuming pile load tests, but also effectively avoids solving the complex partial differential equations involved in the consolidation analysis, and hence is feasible enough to determine the time-dependent load carrying behaviours of jacked piles in clay.

Reusing existing displacement piles is economical, time-saving, and environment-friendly. This paper presents an analytical approach for predicting the load carrying behavior of pile groups consisting of new and existing displacement piles. The evolutions of the undrained shear strength and shear modulus of clay adjacent to the piles from installation through consolidation to long-term ageing are investigated to determine the load carrying behavior of displacement piles. The nonlinear load-settlement behavior of an individual pile is modelled by load-transfer method, where the exponential function-based load-transfer models integrating the two developed soil parameters are employed to represent the nonlinear behavior at the pile-soil interface. The pile-pile interaction in the pile group is explored based on the shear displacement method. Combining the load-transfer method and the shear displacement method, an analytical framework is proposed for predicting the load-settlement behavior of pile groups consisting of new and existing piles. The proposed framework is validated by predicting the vertical settlement of a high-rise apartment built on a pile group consisting of 74 new displacement piles and 22 existing displacement piles during construction. Good agreement is achieved between the predicted and measured results. A parametric study is performed to explore the stiffness efficiency and the load-settlement behavior of pile groups with different layouts of new and existing piles. The results indicate that the pile group with larger ratio of the number of existing piles to the number of total piles shows both stronger stiffness and a higher load carrying capacity.

This paper develops an analytical solution for the settlement of jacked piles induced by reconsolidation of the surrounding soil. The Terzaghi’s radial consolidation theory is utilised to model the...

Mechanical behaviour of the soil around a jacked pile changes significantly during pile installation and subsequent consolidation. Hence, an axially loaded jacked pile exhibits apparent time-dependent bearing performance after pile installation. This paper presents a semi-analytical approach to predict the time-dependent bearing performance of an axially loaded jacked pile in saturated clay strata. The effects of pile installation and subsequent consolidation on the changes in mechanical properties of the surrounding soil are modeled by the cavity expansion theory and the radial consolidation theory, respectively. An exponential function–based load-transfer (t–z) curve is employed to describe the nonlinear behaviour of the pile–soil interface during pile loading. The evolutions of the three-dimensional strength and shear modulus of the surrounding soil are subsequently incorporated into the two model parameters of the proposed t–z curve to capture the time-dependent pile–soil interaction behaviour. The time-dependent elastic response of the soil outside the pile–soil interface is also considered in the proposed approach. With the proposed load-transfer curve, an incremental algorithm and a corresponding computational code are developed for assessing the time-dependent load–settlement response of a jacked pile. To verify the proposed semi-analytical approach, predictions of the time-dependent load–settlement curves are compared with the measured values from pile tests at two sites. The good agreement shows that the time-dependent bearing performance can be reasonably predicted by the proposed approach.

This study employs the limit analysis method to evaluate the seismic stability of anisotropic and nonhomogeneous slopes stabilized with anti-slide piles. The pseudo-static approach is used to simplify the earthquake load. The yield seismic acceleration factor is obtained from the optimization procedure and the results are verified with the published data. Then, the seismically-unstable slope is reinforced with anti-slide piles, and the seismic stability of the reinforced slope is explored. The results show that the anisotropy and nonhomogeneity of soils have significant effects on the stabilizing force required from the anti-slide piles and the optimal location of the pile is near the toe of the slope.

The mechanical properties of soils adjacent to a jacked pile significantly affect the bearing capacity and settlement of the pile. This paper investigates the evolution of the mechanical properties of the remolded soil surrounding a jacked pile by considering in-situ properties of natural clays, pile installation effects and variable coefficient of consolidation. The pile installation process is modeled by the undrained cylindrical cavity expansion. The distribution of excess pore pressures around the pile is derived by adopting the K 0 -based anisotropic modified Cam-clay ( K 0 -AMCC) model, which can incorporate the initial stress anisotropy and the initial stress-induced anisotropy of natural clays. The Terzaghi's radial consolidation theory is further developed by introducing a variable coefficient of consolidation to the governing equation, which is solved by the variable separation method. The predicted results are in good agreement with the published test data. The variations of the mechanical properties of the remolded soil are studied with different variable coefficients of consolidation and the in-situ properties. The calculated results show that the variable coefficient of consolidation plays a significant role in the dissipation rate of excess pore pressures. The undrained shear strength considering thixotropic effect and the shear modulus of the remolded soil increase more rapidly with larger values of the introduced parameter α (related to the variable coefficient of consolidation). Moreover, the overconsolidation ratio has a pronounced effect on the undrained shear strength and the shear modulus of the remolded soil after pile installation.

Prestressed high-strength concrete (PHC) piles have advantages of light weight and high load carrying capacity, which have been widely applied in coastal and offshore engineering. However, PHC piles serving in the coastal or offshore regions have already undergone severe durability problem. This paper presents a comprehensive method for predicting the service life of PHC piles in the marine environment, which reasonably takes the temperature effects and the concrete stratification caused by centrifugation of PHC piles into account. The pile service life is divided into the diffusion and corrosion periods. The service life of the diffusion period is predicted by solving the diffusion equation formulated for chloride ion diffusion in a two-layer ring medium, the results of which are compared with the data obtained from the elaborate experimental tests to examine the validity. The service life of the corrosion period is determined based on the ultimate corrosion expansion pressure produced by the accumulated corrosion products of steel bar. Various possible key factors, like protective cover thickness, initial chloride ion concentration, mortar layer thickness, etc., are considered to investigate how these parameters critically affect the pile service life. The results suggest that increasing mortar layer thickness can lead to a significant decrease of the service life in both diffusion and corrosion periods; and increasing protective cover thickness and sealing pile end are two effective ways to extend the service life of PHC piles.

This paper proposes an analytical approach to evaluate the time-dependent bearing capacity of a driven pile in clayey soils by taking the pile installation and subsequent reconsolidation effects into consideration. The process of pile installation is modeled by undrained expansion of a spherical cavity at the pile tip and a cylindrical cavity around the pile shaft. The cavity expansion solution, which is based on a K0-consolidated anisotropic modified Cam-clay model (K0-AMCC), is used to capture the pile installation effects. After pile installation, the dissipation of the excess pore water and the increase of the effective stress in the surrounding soil are evaluated by the radial consolidation theory. Based on the effective stress, the strength of the remolded soil is quantified by the modified Cam-clay (MCC) model and the spatially mobilized plane (SMP) criterion. With the three-dimensional strength of the surrounding soil, the time-dependent bearing capacity of the driven pile is evaluated by ...