Recently, behavior of large-diameter mono-pile foundations for offshore wind turbines under long-term cyclic wave loading has attracted great attentions from coastal engineers. In this study, a ...three-dimensional integrated numerical model is developed to investigate the wave-induced seabed response around a monopile foundation. In the model, the Reynolds-Averaged Navier-Stokes (RANS) equations are used for the mean fluid flow, while the Biots consolidation equations are used for the solid-pore fluid interaction in a porous seabed. The monopile is considered as a single phase medium and behaves under a linear elastic law. To reproduce the residual soil behavior under cyclic shearing induced by ocean waves as well as structural rocking motions, a poro-elastoplastic model is adopted, in which the consolidation analysis of seabed foundation under gravitational forces including the body force of structure is pre-assessed and incorporated. The present numerical framework was first validated against several laboratory experiments and obtaining fairly good agreements. Based on the proposed model, failure of monopile foundation caused by liquefaction due to the buildup of pore water pressure under cyclic shearing is investigated. Numerical results indicate that the potential areas for residual pore pressure development and the resulting liquefaction are most pronounced in the vicinity of the monopile following the wave propagation direction, which is caused by waves as well as the rocking motion of the structure induced by the wave impact. Parametric studies indicate that there is no possibility of generating soil liquefaction below the pile bottom in the vicinity of the mono-pile even under large waves.
•Integrated model for wave-induced residual liquefaction around mono-piled foundation.•The rocking of the pile is the main reason for inducing residual liquefaction around a monopile foundation.•The potential areas in the vicinity of the monopile for soil liquefaction can be reduced by increasing the pile diameter.
Substructure method is widely used to evaluate the seismic performance of caisson foundations supporting bridge piers subjected to strong ground motions, mainly because of its simplicity. However, ...the strongly‐simplifying assumption of linear viscous‐elastic behaviour for the foundation soil limits its applicability to flexible systems subjected to low‐intensity earthquakes, for which irreversible strains and pore water pressure build‐up are not anticipated. Furthermore, lumped‐parameter models are typically adopted in calculations in which soil‐foundation compliance is reproduced via dynamic impedance functions, whose dependency on frequency of excitation is often neglected. Modification of free‐field motion leading to foundation input motion (FIM), due to the presence of caisson embedment, is also mostly ignored. The influence of these simplifying assumptions on the seismic performance of bridge piers on caisson foundations is assessed in this paper through a parametric study, where soil‐caisson‐bridge pier‐deck systems differing in geometric and mechanical properties are subjected to real seismic records. Dynamic analyses were carried out in the time domain with the finite element method, using a 3D continuum and a lumped‐parameter model for the foundation soil. In the 3D model both the linear viscous‐elastic and the nonlinear soil behaviour were assumed, while linear viscous‐elastic behaviour was assumed in the lumped‐parameter model. The influence of inelastic soil behaviour was assessed by comparing the seismic performance of the systems obtained with the 3D model, while the role of FIM was evaluated by comparing the results of the dynamic analyses computed assimilating the soil to a linear elastic medium.
In this paper, the results of snapback, cyclic and forced-vibration tests performed by laboratory and full-scale facilities are collected and analysed to investigate the nonlinear response of shallow ...foundations. The outcomes of tests on a full-scale soil-foundation-structure prototype, performed during the EU-research project SISIFO, were exploited to fill the lack of data on foundation damping and stiffness associated with the translation motion and enrich the database relevant to low-amplitude rocking motion. Predictive equations are calibrated to estimate the nonlinear variation of the foundation stiffness and damping ratio with the increasing amplitude of the foundation translation and rocking motions. In the latter case, the availability of numerous experimental data allows differentiating the predictive damping equation according to the so-called ‘critical foundation-soil contact area’, which is the most influencing factor on the energy dissipation capacity of the foundation. To prove the reliability of the proposed approach, two different applications with an increasing level of complexity are discussed. First, simplified analytical formulas are employed to calculate the fundamental period and damping ratio of the prototype tested during the SISIFO project. Then, a flexible-base model of the same structure is calibrated to simulate the experimental forced-vibration tests. The outcomes of both applications successfully match the experimental measurements.
•Experimentally based evaluation of soil-foundation stiffness and damping ratio.•Normalization procedure for the experimental data on foundation damping ratio.•Correlation between soil-foundation stiffness or damping ratio and rocking motion.•Application to simulate real-scale tests on a soil-foundation-structure system.
Abstract
This paper numerically examines the effect of foundation shape on the subgrade reaction coefficient. The distribution of the subgrade reaction coefficient on the foundation area and the ...values of this coefficient in different regions are studied. A method is also introduced to determine the subgrade reaction coefficient of unusually shaped foundations sometimes encountered in practice. It has been shown that it is possible to divide the foundation area into several regions, and the subgrade reaction coefficient of each part is a multiplier of the central point reaction coefficient. The reaction coefficient of a trapezoidal foundation is equal to the reaction coefficient of a rectangular foundation with a similar area, and the length of the rectangle is the same as the height of the trapezoid. Also, the settlements of two foundations are equal. An L-shaped foundation’s reaction coefficient is a product of multiplying the reaction coefficient of a rectangular foundation to a ratio of the rectangular area by an L-shaped area if the settlements of the two foundations are equal. Besides, the reaction coefficient of a ring-shaped foundation is a product of multiplying the reaction coefficient of a circular foundation with the same outside diameter by the ratio of the circular area to the ring area if the settlements of both foundations are the same.
Foundation pit engineering has been developing rapidly with the challenges associated with modern urbanization. As a result, deep excavations can now be performed at the heart of coastal metropolises ...with dense existing structures and adverse soil and hydraulic conditions. On the other hand, foundation engineering is challenged with sustainability and economic viability such that cost-effectiveness is a key factor provided that the robustness and safety requirements are fully satisfied. This paper presents the design of the retaining system for a deep foundation excavation that is located in a second-tier inland city with less crowed existing structures and good soil and hydraulic conditions. This is representative of the current trend of the suburban development of major cities and the development of below first-tier cities, as a response to the saturating of the major cities. Different designs are reviewed for this case in order to strike the balance between structural capability and cost-effectiveness. The analysis indicates that a hybrid solution is particularly suitable for such type of construction. Specifically, results show that the maximum displacement, bending moment, and shear force in the pit can be reduced by over 50%, 40%, and 30%, respectively, by the combination of soil nailing wall and pile anchor compared with a single support solution. And for the combination of non-prestressed anchor bolts and prestressed anchor cables can effectively save the cost while improving the safety factor of foundation pit during excavation. The findings are instructive to similar projects with cost-effectiveness as a major factor.
A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs has focused on the load ...transfer mechanism, foundation and soil settlement, bearing capacity, load distribution, and bending moment of the piles. DPR piles can act to increase the bearing capacity of the ground, and DPRs can reduce settlement while securing the bearing capacity. In this study, centrifuge model tests are performed to simulate the static behavior of DPRs under actual stress conditions. The behaviors of the DPR foundation for axial load, axial load distribution among the piles, and bending moment are compared to those of the connected piled raft foundation to understand the complex behaviors of DPRs. The centrifuge test results show that DPRs help reduce the pile axial load and bending moment during vertical loading. In addition, DPRs show smaller vertical settlement than shallow foundations. Therefore, we confirm that DPRs can be applied in foundation design as settlement reducers.
Traditionally seismic design of structures supported on piled raft foundation is performed by considering fixed base conditions, while the pile head is also considered to be fixed for the design of ...the pile foundation. Major drawback of this assumption is that it cannot capture soil-foundation-structure interaction due to flexibility of soil or the inertial interaction involving heavy foundation masses. Previous studies on this subject addressed mainly the intricacy in modelling of dynamic soil structure interaction(DSSI) but not the implication of such interaction on the distribution of forces at various elements of the pile foundation and supported structure. A recent numerical study by the authors showed significant change in response at different elements of the piled raft supported structure when DSSI effects are considered. The present study is a limited attempt in this direction, and it examines such observations through shake table tests. The effect of DSSI is examined by comparing dynamic responses from fixed base scaled down model structures and the overall systems. This study indicates the possibility of significant underestimation in design forces for both the column and pile if designed under fixed base assumption. Such underestimation in the design forces may have serious implication in the design of a foundation or structural element.
The paper analyses in detail and compares different interpretation procedures of snap-back and forced-vibration tests on a full-scale prototype founded on soft-soil, in order to assess their ...effectiveness for measuring the stiffness and damping of a shallow foundation under dynamic loads. Both properties were back-calculated through three alternative methods, i.e. through impedance functions computed in the frequency domain, or by interpreting force-displacement loops in terms of peak-to-peak amplitudes or of phase-shift. The damping was further calculated from the logarithmic decrement of free-vibration records. The resulting foundation stiffness and damping were observed to vary with the number of cycles and with the load frequency and amplitude. The comparison among the interpretation techniques revealed that the peak-to-peak approach fails when damping is high, because it neglects the delay between force and displacement.
This paper exposes buckling solutions of a plane, quasi-static Timoshenko beam with small transformation subjected to a longitudinal force and surrounded by an elastic wall modeled by two-parameter ...elastic foundations. A non-dimensional analysis of associated Haringx and Engesser model is performed and buckling stress and shape are exposed analytically. Relations for rigidity of the wall and buckling solutions were made for different regimes and for both models using asymptotic approach. Introducing the yield limit gives a simple criterion in terms of stiffness foundation and slenderness ratio for which buckling or irreversible transformation occur.
The vertical factor of safety (FSv) of shallow foundations has been widely used for static design and seismic design. The FSv is a function of the bearing capacity of the system and the vertically ...applied load from the structure and foundation loads to the soil and foundation interface. However, the structure-to-foundation mass ratio (MR) can be different for the systems presenting the same FSv. The dynamic responses of the structure and foundation system depend on the MR as it develops dissimilar inertial behaviors from the structure and foundation. In this study, the effect of MR on the structure and foundation responses was evaluated using an analytical model that enables influence of the nonlinearity of the soil on the modeled foundation base and structure. For systems with the same FSv under identical input loading conditions, the inertial behavior of heavy foundations had a larger acceleration response than the lighter foundations. Consequently, MR should be considered for evaluating dynamic soil-foundation-structure interaction problems.
•The effect of the structure-to-foundation mass ratio was evaluated using the three-degree-of-freedom analytical model.•The methodology to reflect nonlinearity of soil into the analytical solution was developed, and validated with centrifuge tests.•The heavier foundation manifested its swaying frequency during the strong earthquakes.•The heavier foundation resulted in the permanent deformation by the foundation inertial response.
