Stiffness and load sharing characteristics of piled raft foundations subjected to dynamic loads
TL;DR: A substructuring method-based soil structure interaction (SSI) analysis model is employed to study vertical and horizontal dynamic impedances of piled rafts (PR) in homogeneous and layered soil conditions.
About: This article is published in Soil Dynamics and Earthquake Engineering.The article was published on 2020-06-01. It has received 22 citations till now. The article focuses on the topics: Dynamic load testing & Pile cap.
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TL;DR: In this article, system identification analyses are used to evaluate soil-structure interaction effects for 77 strong motion data sets at 57 building sites that encompass a wide range of structural and geotechnical conditions.
Abstract: System identification analyses are used to evaluate soil-structure interaction effects for 77 strong motion data sets at 57 building sites that encompass a wide range of structural and geotechnical conditions. Kinematic interaction effects on the \"input\" motion at the bases of structures are found to be relatively modest in many cases, whereas inertial interaction effects on the structural response to these motions can be significant. To quantify inertial interaction effects, fixed- and flexible-base modal vibration parameters are used to evaluate first-mode period lengthening
148 citations
TL;DR: In this article, a novel approach is presented to describe the dynamic interaction system of a large-diameter floating pipe pile and surrounding soils, taking the three-dimensional wave effects into account.
92 citations
TL;DR: In this paper , an experimental study on vibration velocities of piled raft supported embankment and foundations is presented in soft soil with different underground water levels, showing that the change in water level has slight impaction on the peak spectrum of vibration velocity at harmonic frequencies.
Abstract: In recent years, the high development of high-speed railway lines cross through areas with poor geological conditions, such as soft soil, offshore and low-lying marsh areas, resulting geotechnical problems, such as large settlements and reduction of bearing capacity. As a new soil reinforcement method in high speed railway lines, the piled raft structure has been used to improve soil conditions and control excess settlement. In order to study the dynamic behavior of piled raft supported ballastless track system in soft soil, an experimental study on vibration velocities of piled raft supported embankment and foundations is presented in soft soil with different underground water levels. Vibration velocities at specified positions of the piled raft supported embankment and foundations are obtained and discussed. The vibration velocity curves on various testing locations of piled raft foundations are clearly visible and have sharp impulse and relaxation pattern, corresponding to loading from train wheels, bogies, and passages. Vibration velocity distribution in the horizontal direction at three train speeds clearly follows an exponential curves. Most of the power spectrums of vibration velocity at various locations are mainly concentrated at harmonic frequencies. The change in water level has slight impaction on the peak spectrum of vibration velocity at harmonic frequencies. The vibration power induced by train loads are transmitted, absorbed, and weakened to a certain extent through embankment and piled raft structure. The dynamic response character of embankments are affected by their self-vibration characteristics and the dynamic bearing capacity of the piled raft structure.
20 citations
TL;DR: In this paper , a three-dimensional water-pile-soil model was developed to investigate the dynamic responses of end-bearing pile under vertical P-waves, where the soil and pile were modelled as linear viscoelastic media with hysteretic material damping, and the water was modelled by linear acoustic medium.
8 citations
TL;DR: Wang et al. as mentioned in this paper examined the settlement mechanisms of piled-raft foundation (PRF) constructed in different grounds subjected train loads, and showed that the load sharing ratio between pile and raft also changed significantly during vibration loading, implying that extensive precaution should be taken in design and construction of PRFs for high-speed railway constructed in soft ground.
7 citations
References
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TL;DR: In this paper, the authors discuss the philosophy of using piles as settlement reducers and the conditions under which such an approach may be successful and some of the characteristics of piled raft behavior are described.
Abstract: In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of the raft by the addition of piles. The use of a limited number of piles, strategically located, may improve both the ultimate load capacity and the settlement and differential settlement performance of the raft. This paper discusses the philosophy of using piles as settlement reducers and the conditions under which such an approach may be successful. Some of the characteristics of piled raft behaviour are described. The design process for a piled raft can be considered as a three-stage process. The first is a preliminary stage in which the effects of the number of piles on load capacity and settlement are assessed via an approximate analysis. The second is a more detailed examination to assess where piles are required and to obtain some indication of the piling requirements. The third is a detailed design phase in which a more refined analysis is employed to confirm the op...
379 citations
TL;DR: In this article, a simple analytical solution is developed for computing the dynamic impedances of floating rigidly-capped pile groups with due consideration to pile-soil-pile interaction.
Abstract: A simple analytical solution is developed for computing the dynamic impedances of floating rigidly-capped pile groups with due consideration to pile-soil-pile interaction. The method introduces some sound physical approximations and considers the interference of cylindrical wave fields originating along each pile shaft and spreading radially outward. Axial, lateral, and rocking oscillations of rigidly-capped pile groups are studied parametri-cally. Results are presented for the dynamic stiffness and damping of the whole group, and for the distribution of dynamic loads amongst the individual piles. The predictions of the simple method for vertical and rocking oscillations compare extremely well with rigorous numerical solutions, thereby offering a valuable insight into the nature of pile-soil-pile interaction. It is demonstrated and explained how the dynamic efficiency may far exceed unity at certain resonant frequencies due to destructive wave interference. The proposed method can be readily applied by en...
264 citations
TL;DR: In this paper, system identification analyses are used to evaluate soil-structure interaction effects for 77 strong motion data sets at 57 building sites that encompass a wide range of structural and geotechnical conditions.
Abstract: System identification analyses are used to evaluate soil-structure interaction effects for 77 strong motion data sets at 57 building sites that encompass a wide range of structural and geotechnical conditions. Kinematic interaction effects on the "input" motion at the bases of structures are found to be relatively modest in many cases, whereas inertial interaction effects on the structural response to these motions can be significant. To quantify inertial interaction effects, fixed- and flexible-base modal vibration parameters are used to evaluate first-mode period lengthening
211 citations
TL;DR: In this paper, a hybrid approach for the analysis of piled raft foundations, based on a load transfer treatment of individual piles, together with elastic interaction between different piles and with the raft, is described.
Abstract: A piled raft foundation comprises both piles and a pile cap that itself transmits load directly to the ground. The aim of such a foundation is to reduce the number of piles compared with a more conventional piled foundation where the bearing effect of the pile cap, or raft, is ignored. This paper describes a ‘hybrid’ approach for the analysis of piled raft foundations, based on a load transfer treatment of individual piles, together with elastic interaction between different piles and with the raft. The numerical analysis is used to evaluate a simple approximate method of estimating the overall response of the foundation from the response of the component parts. The method leads to estimates of the overall foundation stiffness, the proportion of load carried by the pile group and the raft, and an initial assessment of differential settlements. Parametric studies are presented showing the effect of factors such as raft stiffness and pile spacing, length and stiffness, and a worked example is included demonstrating the accuracy of the approximate design approach.
194 citations
TL;DR: A series of parametric studies have been presented investigating the effects of internal soil damping, Poisson's ratio, layer depth, and embedment on the stiffness functions of circular footings subjected to dynamic forces as mentioned in this paper.
Abstract: A series of parametric studies have been presented investigating the effects of internal soil damping, Poisson's ratio, layer depth, and embedment on the stiffness functions of circular footings subjected to dynamic forces. The effect of having a finite layer of soil on rigid rock is to introduce valleys in the stiffnesses at the resonant frequencies of the stratum. These valleys are smoothed by the presence of internal damping and their position depends on the value of Poisson's ratio. Embedded foundations have an increased static stiffness, but the frequency variations of the stiffness coefficients is not very different from the corresponding curve for surface footings. The most important factor in reproducing adequately the effect of embedment is the evaluation of the static stiffnesses. They are, however, very sensitive to the assumed conditions at the vertical edges (sidewalls welded to the surrounding soil, degree of disturbance of the backfill, etc.). Experimental work to assess these conditions is necessary.
155 citations