An Experimental Investigation into the Arching Effect in Fine Sand

In the current paper results of a well instrumented experimental procedure for studying the arching effect in loose and dense sand are presented. 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 soil mass deforms elastically. However, after an immediate specified displacement, depending on the diameter of the trapdoor and relative density of the soil, the soil mass behaves plastically. This behavior of sand occurs due to flow phenomenon and continues until the stress on trapdoor is minimized. Then the failure process develops in sand and the measured stress on the trapdoor shows an ascending trend. This indicates gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to establish a stable vault of sand called arching mechanism. Depending on the trapdoor diameter there is a critical relative density at/above which the test leads to form a stable arch. A mathematical method to establish the shape of the sand vault is introduced and the results obtained from experimental investigations are compared to this method. The results are also, compared to Terzaghi's theory and the assumption of upper boundary solution is discussed.