Arching effect in fine sand due to base yielding

This paper presents results of an experimental work on the arching effect in loose and dense sand. The apparatus comprises concentric circular trapdoors with different diameters that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to yield, the whole mass of soil deforms elastically. However, after a specified displacement that depends on the trapdoor diameter and soil relative density, the soil mass behaves plastically. This behavior, which is due to flow phenomenon, continues until the stress applied onto the trapdoor decreases to a minimum value. Then the stress carried by the trapdoor shows an ascending trend. This indicates the gradual separation of the yielding mass from the whole soil body. Finally, the flow process creates a stable arch of sand. This process is called the arching mechanism. Depending on the trapdoor diameter, there is a critical relative density at and beyond which the test leads to the formation of a stable arch. The results are also compared with Terzaghi’s theory and the assumption of an upper boundary solution is discussed.