Abstract
As a cross-sea or river deep-water foundation, it is clear that the caisson foundation will be subjected to significant lateral dynamic loads due to winds or waves and suffer from scouring under its long-term effect. In order to obtain the scour effect on the dynamic response of the foundation, an analytical model describing the scour-hole effect in terms of scour depth, scour width, and slope angle was constructed. Combined with the nonlinear Winkler theory, a method for the dynamic response of the caisson foundation considering the scour-hole dimensions was proposed. Comparisons against the results from the dynamic FEM demonstrate the reliability of this method. The effects of the scour width, slope angle, and scour depth on the dynamic response of the caisson were discussed. The results show that the scour depth affects the dynamic displacement and resonant frequency of the foundation most, whereas the scour width does less and the slope angle does the least; the dynamic response of caisson can be approximated as the case of the slope angle 5° and the scour width 5B when the slope angle is less than 5° and the scour width is greater than 5B, respectively; the effects of scour width and slope angle on the dynamic response of caisson have the similar change pattern in the displacement and resonant frequency when the scour depth is different. However, the effect of amplitude on dynamic response shows a nonlinear increase trend when the scour depth is relatively large.
Highlights
Caisson is a common foundation type which is suitable for bridge engineering
Once the soil parameters, such as the effective unit weight of soil c0′ and void ratio e0, are determined, the stiffness coefficients kxi, kri and the damping coefficients cxi, cri at a certain scour state with scour depth Sd, scour width Sw, and scour slope angle θ can be re-examined by equation (13). en, the dynamic response of a caisson subjected to the lateral load can be calculated based on the proposed model
Considering the effect of scour depth on the resonant frequency, the value of resonant frequency gradually decreases with the increase in the scour depth around the caisson, which is different from the effect of the scour width and scour slope angle on the resonant frequency of the foundation; and the percentage increases in the peak value of the displacement compared with the no scouring condition are 14.4%, 70.1%, and 242.1% when scour depth varied from 0.15d to 0.45d
Summary
Caisson is a common foundation type which is suitable for bridge engineering. It is widely used in cross-river and crosssea bridges because of its strong integrity and large bearing capacity, such as the Shanghai-Nantong Yangtze River Bridge in China, the Brooklyn Bridge in the United States, and the Akashi Strait Bridge in Japan [1]. Shock and Vibration taken into account [3, 4] Such a huge scour depth value will inevitably cause significant changes in the bearing performance and dynamic characteristics of the foundation and may even cause the damage of bridge foundation. Zhang et al [7] conducted a laboratory test to investigate the lateral response of the caisson and its dependence on the characteristics of the applied cyclic load and scouring These methods for analyzing the scour effect mentioned above focused on the static behavior of the foundation, and the dynamic behavior of the foundation was not involved. E objective of this paper is to propose a simplified model for the analysis of laterally loaded caisson foundations under scouring, which can account for the effects of scourhole dimensions on the dynamic performance of foundations. To provide a reference for engineering application, the influence of the scour depth, scour width, and scour slope angle of scour holes on the dynamic characteristics of the caisson foundation are studied based on the proposed model
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