The purpose of this paper is to study and compare arching in reinforced and unreinforced piled embankments for different fill materials and pile spacings. Toyoura sand, silica sand no.7, silica sand no.8 and dry powder clay are used as fill materials. In this study, X-ray CT method is used as a non-destructive technique to examine the load distribution mechanism quantitatively. Vertical cross sectional images are constructed by the data obtained from CT scanning. It is seen that low density areas represent the shear planes and dilatancy in the arch within the piled embankment. The angle of density change is defined as the angle formed by the arch-shaped shear plane and the horizontal plane within the inter-pile soil. While Toyoura sand has the smallest angle of density change due to the largest peak internal friction angle and the effective particle size, dry powder clay has the largest angle of density change. The earth reinforcement is found to be effective with the use of pile elements for the purpose of stress redistribution in the fill. Furthermore, the amount of the embankment loading is visualized by three dimensional extraction images. The effectiveness of the proposed method is verified by conducting a comparative study with the current Japanese design model. It is shown that, using X-ray CT method and visualization techniques provide a better understanding of soil arching in a reinforced embankment with rigid pile foundation system. (C) 2011 Elsevier Ltd. All rights reserved.