不同承台形式斜直交替群桩-土-结构地震相互作用特性分析

Analysis on Seismic Interaction Characteristics of Pile-soil-structure of Obliquely Pile Groups with Different Pile Caps

为研究不同承台形式斜直交替群桩-土-结构在地震互相作用,利用FLAC3D有限差分软件作为研究工具,采用El Centro地震波作为动荷载。分别建立了斜直交替群桩-土-结构的低承台、高承台数值模型。并对地震作用下可液化土体的孔压比变化、桩基的受力与位移、桥墩顶部的位移进行分析研究。研究结果表明:在地震作用下,土层中孔隙水压力分布是自上而下逐渐增大。振动加速度峰值时部分土体由于发生剪胀孔压出现瞬时负值。砂土层中桩基中部区域容易产生液化现象。同一模型中,直桩的最大弯矩小于斜桩的最大弯矩。在低承台模型中,直桩和斜桩的最大水平位移均发生在桩基顶端,直桩的竖向位移沿埋深是一恒值,而斜桩的竖向位移沿埋深是变化的。在高承台模型中,斜桩的水平位移沿埋深不再是单调变化,最大值发生在砂土层中。高承台模型中斜桩和直桩的竖向位移和水平位移均明显大于低承台模型桩体。两个模型的桥墩顶部最大水平位移出现的时刻基本相同。

In order to study the interaction between piles,soil and structure with different caps,the FLAC3D finite difference software was used as the research tool,and the El Centro seismic wave was used as the dynamic load. The numerical models of pile-soil-structure of obliquely pile groups with low cap and high cap were established respectively. The change of pore water pressure ratio,the stress and displacement of the piles and the displacement at the top of the pier were analyzed. The results show that the distribution of pore water pressure in the soil layer under earthquake action increases gradually from top to bottom. Instantaneous negative pore pressure occurs in parts of soil due to shear dilation at peak vibration acceleration. The middle part of the pile foundation in sandy soil is prone to liquefaction. In the same model,the maximum bending moment of the vertical piles is smaller than that of the inclined piles. The maximum horizontal displacement of both vertical piles and inclined piles occurs at the top of piles. The vertical displacement is constant along the depth for vertical piles,while it varies along the buried depth for inclined piles. In the high cap model,the horizontal displacement of the inclined piles no longer changes monotonously with the buried depth. The maximum value occurs in the sand soil layer. The vertical and horizontal displacement of the inclined piles and vertical piles in the high cap model is obviously greater than that of the low cap model. The time corresponding to the maximum horizontal displacement of the two models is basically the same.