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Seismic performance of group pile foundation with ground improvement during liquefaction
Soils and Foundations ( IF 3.7 ) Pub Date : 2021-07-13 , DOI: 10.1016/j.sandf.2021.06.010
Yasuo Sawamura 1 , Keita Inagami 2 , Tomohiko Nishihara 3 , Takashi Kosaka 3 , Masahiro Hattori 4 , Makoto Kimura 5
Affiliation  

A pile foundation with ground improvement under the footing is a composite foundation with the objectives of enhancing the seismic performance and rationalizing the substructure by combining the pile foundation with ground improvement. Although the effectiveness of this method has been confirmed in previous studies for application to soft grounds, the applicability of this method to liquefiable grounds has yet to be fully investigated. In this study, therefore, centrifuge model tests and finite element analyses were conducted to clarify the effectiveness of this method and to ascertain the improvement in strength (stiffness) when the method is applied to a liquefiable ground. Firstly, in order to investigate the effect of an improved ground on the behavior of the pile foundation during liquefaction, dynamic centrifuge model tests were conducted for three cases with different strengths of the improved ground. Then, three-dimensional soil–water coupled finite element analyses of the centrifuge model experiments were performed to validate the applicability of the analytical method. After that, parametric studies, in which the strength of the improved ground and the input ground motion were changed, were conducted using the same analytical model. The results confirmed that the horizontal displacement of the pile heads was reduced by the improved ground even in the liquefiable ground, and that the effect of this reduction was more remarkable in cases of high stiffness of the improved ground. Furthermore, it was possible to reduce the bending moments at the pile heads by applying the ground improvement. However, since the bending moment at the boundary between the improved ground and the natural ground became the local maximum, there was an optimum stiffness of the ground improvement at which the maximum bending moment of the piles was reduced. This is because improving the ground around the pile heads has the same effect as extending the footing. It was thus concluded that the behavior of the pile foundation is similar to that of a composite foundation comprised of a caisson and group piles.



中文翻译:

液化过程中地基改良群桩基础的抗震性能

地基下地基改良桩基是一种复合地基,其目的是通过桩基与地基改良相结合,提高抗震性能和合理化下部结构。虽然该方法的有效性在先前的研究中已被证实适用于软土地,但该方法对可液化土地的适用性尚未得到充分研究。因此,在本研究中,进行了离心机模型试验和有限元分析,以阐明该方法的有效性,并确定将该方法应用于可液化地面时强度(刚度)的改进。首先,为了研究改良地基对液化过程中桩基行为的影响,对三种不同强度的改良地基进行了动态离心模型试验。然后,对离心机模型实验进行三维土水耦合有限元分析,以验证分析方法的适用性。之后,使用相同的分析模型进行参数研究,其中改进的地面强度和输入的地面运动发生了变化。结果证实,即使在可液化的地基中,改良地基也减少了桩头的水平位移,并且在改良地基刚度较高的情况下,这种减少的效果更显着。此外,可以通过应用地面改进来减少桩头处的弯矩。然而,由于改良地基与自然地基交界处的弯矩为局部最大值,因此存在桩基最大弯矩减小的最佳改良地基刚度。这是因为改善桩头周围的地面与延长基础具有相同的效果。因此得出结论,桩基础的行为类似于由沉箱和群桩组成的复合基础的行为。

更新日期:2021-08-01
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