桩承式路堤中土拱效应产生过程可视化分析

"土拱效应"在提高桩承式路堤承载能力方面发挥着重要的作用。现今关于"土拱效应"的研究主要采用现场原型试验和数值模拟及其在此基础上的理论计算。借助于传统的光弹试验技术,研制出一种直径3 mm、透明度较高的聚碳酸酯光弹颗粒,用于近似模拟桩承式路堤中的土颗粒,通过自制的加载装置和光测力学图像处理系统,实现多种条件下路基内部应力分布的可视化,重点观测模型内部力链网格的产生、分布及变化规律,试验结果表明:填土高度会对土拱的形成及形状产生极大影响,填土高度太小,斜向力链会因缺乏扩展空间无法闭合而不能形成拱结构,随填土高度增加,土拱由三角拱向半圆拱或梯形拱过渡;荷载的大小变化不会影响土拱效应的出现,但会对土拱的结构形状产生较大影响;随桩距比的增大,土拱由三角拱向半圆拱或多拱演化,当桩距比大于3∶1时,土拱效应开始减弱直至消失,路堤承载能力大幅下降。

Visual analysis of initiation of soil arching effect in piled embankments

“Soil arching effect” is known to improve the bearing capacity of piled embankments. The studies reported in literature on “soil arching effect” mainly focus on the numerical simulation methods, theoretical analysis and field application of prototype tests. In this study by using the traditional photoelastic testing procedures, the particulates 3 mm in diameter similar to those of polycarbonates are developed. The developed loading device and optical measurement mechanics image processing system are employed for visualization and obtaining the internal stress distribution in the embankments under various conditions. This is achieved by observing the rules of generation, distribution and changes in the internal force network of the model. The experimental results show that the height of fill significantly influences the formation and shape of soil arch. The oblique for chain is not able to close or even form the arch structure due to inadequate expansion space if the height of fill is too low. The soil arch transforms from triangular to semicircular or trapezoidal arch with the increasing height of fill. The load fluctuation has no influence on the emergence of the soil arching effect but significant influence on its structure and shape. The soil arch changes from triangular arch to semicircular arch or multiple arches with the increasing pile spacing ratio, and when the pile spacing ratio is greater than 3∶1, the soil arching effect starts to weaken and finally totally vanish. At this point, the bearing capacity of embankment substantially decreases.