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.