A reliable assessment and design of engineering structures requires appropriate estimation and consideration of different sources of uncertainty. The randomness of seismic ground motion is one major uncertainty that needs to be considered from the perspective of performance-based earthquake engineering. To properly account for this uncertainty and its corresponding effect on pile foundations, a stochastic seismic response analytical framework based on a probability density evolution method and a stochastic ground motion model is proposed for the nonlinear stochastic seismic response analysis of pile foundations. A three-dimensional finite element model of a reinforced concrete pile with a large diameter embedded in the soil foundation is firstly established and calibrated using the full-scale lateral load test results from the literature, in which the nonlinear behavior of soil, the soil–pile interaction, the concrete damaged plasticity, and the steel yielding of the pile are properly modeled. Then, the calibrated three-dimensional numerical model is employed as an illustrative example for the stochastic seismic response analysis using the proposed framework. The mean, standard deviation, and probability density function of pile settlement and the dynamic reliabilities of the pile concerning various performance requirements are obtained in the present study. The settlements of the pile show great variability under the excitation of various stochastic ground motions, and the maximum mean value of the pile settlements is about 8 mm. The changing shape of the settlement probability density functions in every moment demonstrates that it is unreasonable to use assumed probabilistic distribution models to characterize the seismic responses of pile foundations during a seismic reliability analysis. Based on the proposed method, it is found that the dynamic reliabilities of the selected reinforced concrete pile concerning four different performance levels are 0, 0.1293, 0.8247, and 1, respectively. The proposed stochastic seismic response analytical method in the present study can provide a proper and comprehensive way to quantify various uncertainties and their corresponding effects on the seismic performance of pile foundations. It can also be used to estimate the actual reliability level of pile foundations that are designed by the current codes when they are subjected to seismic loads.

Peridynamics (PD) is a novel nonlocal theory of continuum mechanics capable of describing crack formation and propagation without defining any fracture rules in advance. In this study, a multi-grid bond-based dual-horizon peridynamics (DH-PD) model is presented, which includes varying horizon sizes and can avoid spurious wave reflections. This model incorporates the volume correction, surface correction, and a technique of nonuniformity discretization to improve calculation accuracy and efficiency. Two benchmark problems are simulated to verify the reliability of the proposed model with the effect of the volume correction and surface correction on the computational accuracy confirmed. Two numerical examples, the fracture of an L-shaped concrete specimen and the mixed damage of a double-edged notched specimen, are simulated and analyzed. The simulation results are compared against experimental data, the numerical solution of a traditional PD model, and the output from a finite element model. The comparisons verify the calculation accuracy of the corrected DH-PD model and its advantages over some other models like the traditional PD model.

Antiliquefaction performance improvement for developed sites beneath existing structures has drawn increasing public attention to meet stricter requirements of seismic protection. Liquefaction mitigation using nanoparticles is a novel countermeasure because of its low environmental disturbance and greater environmental friendliness. This paper reports a centrifuge test to evaluate the effectiveness of laponite (the representative nanoparticle) for liquefaction mitigation. A constructed reservoir embankment foundation was selected as the prototype and the laponite-treated model was carried out with a centrifugal acceleration of $45g$ . Additionally, the viscosity of laponite suspensions was measured to determine the appropriate concentration range and curing time. A similar test with an untreated model was conducted beforehand as a comparison. The subsequent research results showed that the generation of excess porewater pressure was suppressed and both lateral displacements and settlement were reduced in the laponite-treated model versus the untreated model. This paper provides experimental data beyond the elemental scale to support the beneficial effects of laponite on the antiliquefaction performance improvement of the developed sites.

This study presents an experimental investigation of the penetration process in marine soft clay in the Shanghai coastal area using three types (non standard Ball (N), standard Ball(S) and T bar) of full-flow penetrometers. Three main factors (the penetration resistance, strength degradation, and strength factor) are evaluated and discussed in the comparative analysis of the penetration process. The results reveal that there is a model to predict the soil strength degradation in the range of low soil sensitivities (ST < 8). In particular, for the Ball(N) penetrometer, which is a non-standard penetrometer, the degradation process is more readily affected by the soil properties. For the Ball(S) and T bar penetrometers, the test results indicate a certain relationship between the soil sensitivity (ST) and the strength factors of undisturbed and remoulded soils with low sensitivity (ST < 8). however, this relationship is not observed with the Ball(N) penetrometer. These tests can enrich the application of conventional full-flow penetrometers in marine soft soils while facilitating the adaptation of non-standard penetrometers for in-situ tests in various soft soils.