Effects of water content and dry density on the passive soil arching effect in unsaturated compacted clay

In this study, a series of trapdoor tests were conducted on compacted clay at various water contents and dry densities, to investigate the evolution of the passive soil arching effect with the upward movement of the trapdoor. During the test, the displacement field, the shear strain, and the soil stress were monitored. The testing results indicate that as the trapdoor displacement increases, the fill with a lower water content or a higher dry density shows a larger loading zone and a wider influencing range. Moreover, in such cases, a larger inclination angle of the shear band is developed, which remains constant during the increase of the trapdoor displacement. At the same time, a larger stress ratio appears above the trapdoor under such cases, along with a smaller normalized displacement corresponding to the maximum stress ratio. Totally three failure patterns of samples can be identified： tensile-shear failure pattern, shear failure pattern and continuous deformation pattern. Finally, by comparing the testing results among the present study, the passive soil arching effect in sand and the active soil arching effect in unsaturated compacted clay, the deformation and failure mechanism of the passive soil arching effect in unsaturated compacted clay are further unravelled