Study of Stress Paths in Arching Effect Using Frictional Strain Hardening and Softening in Fine Sand

Arching is one of the most common phenomena that occur in most geotechnical structures. To determine the properties and quality of this phenomenon, a physical model has been designed and constructed. The apparatus comprises rectangular trapdoors with different widths that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to fail, the whole soil mass deforms elastically. However, after an immediately specified displacement, depending on the width of the trapdoor, the soil mass behaves plastically. This behavior of sand occurs due to the flow phenomenon and continues until the stress on the trapdoor is minimized. Then the failure process develops in the sand, and the measured stress on the trapdoor shows an ascending trend. This indicates a gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to the establishment of a stable vault of sand called the arching mechanism or progressive collapse of the soil body. To simulate this phenomenon with continuum mechanics, the experimental procedure is modeled in ABAQUS software using stress- dependent hardening in an elastic state and plastic strain-dependent frictional hardening-softening with Mohr Coulomb failure criterion applying user sub-routine. The results show that the experimental data have an acceptable corresponding to the numerical analysis data. So the selected soil behavior could indicate the main aspects of the arching effect, such as the flow that occurs in specific periods of strains. In the following, the stress path in p, q, and p, ν space was extracted from numerical analysis, and the results have been discussed.