作为一种新型完全挤土桩,螺旋桩在各类工程建设中已得到广泛应用。基于离散单元法,以钙质砂为模拟对象,对螺旋桩在沉桩过程中土体颗粒破碎情况进行数值模拟。颗粒破碎采用碎片替换法,破碎应力判定选取八面体剪应力准则。分析了螺旋桩在不同初始应力、不同贯入转速比条件下桩周土体位移场、速度场、应力场分布及土体颗粒破碎演化规律。数值模拟结果表明:在螺旋桩贯入地基土过程中,土颗粒在高应力诱发下发生破碎,桩端土体破碎严重,桩侧颗粒破碎稍弱;随着贯入深度增加,破碎颗粒数量增加,桩侧土体级配发生演化,发生破碎的地基土中桩尖应力略低于不破碎地基土体;提高初始应力,会导致更剧烈的颗粒破碎,破碎颗粒的散布范围更广,桩尖应力明显减小;提高贯入转速比会增加颗粒破碎的程度,在高转速比条件下,破碎颗粒均匀散布在桩侧,螺纹附近的颗粒速度、位移较大;而低转速比工况下,土颗粒的速度、位移峰值主要集中在桩尖下部。开展可破碎颗粒材料中螺旋桩贯入特性的研究,对分析较脆弱砂土场地上的桩基稳定、保障工程建设的安全具有指导意义。
Abstract
As a fully displacing pile, screw piles have been widely used in various engineering construction projects. The particle breakage behavior induced by screw pile drilling in crushable sands such as calcareous sand was simulated using discrete element method. Fragment replacement method and octahedral shear stress breakage criterion were adopted for the simulations. The distributions of soil displacement, velocity, stress, and particle fragmentation evolution during pile penetration were numerically analyzed in consideration of different initial stress levels and different penetration velocity ratios. The simulations revealed that in the process of pile drilling, soil particles crushed due to high stress; in particular, particles at the end of pile crushed more severe than those at pile side. As the pile drilled deeper, the number of crushed particles increased, and the particle gradation at pile side changed. The pile tip stress in the simulation case of breakable sand was slightly lower than that of non-broken sand. The increase of initial stress level led to more severe particle breakage, wider particle dispersion range and also significantly smaller pile tip stress. Higher penetration velocity ratio helped increasing the degree of particle crushing. Under high penetration velocity ratio, particle fragments evenly distributed surrounding the pile side, and the particle velocity and displacement near the screw threads were large; under low velocity ratio, the peak particle velocity and displacement mainly concentrated at the bottom of pile tip. The research on drilling characteristics of screw piles in crushing granular materials is of guiding significance for the study of pile foundation stability and construction safety in fragile sandy soil.
关键词
螺旋桩 /
颗粒破碎 /
离散元模拟 /
钙质砂 /
贯入特性
Key words
screw pile /
particle breakage /
DEM simulation /
calcareous sand /
drilling characteristics
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