No abstract

In the area of civil engineering and especially hydraulic structures, we find multiple anomalies that weakens mechanical characteristics of dikes, one of the most common anomalies is erosion phenomenon specifically pipe flow erosion which causes major damage to dam structures. This phenomenon is caused by a hole which is the result of the high pressure of water that facilitate the soil migration between the two sides of the dam. It becomes only a question of time until the diameter of the hole expands and causes destruction of the dam structure. This problem pushed physicist to perform many tests to quantify erosion kinetics, one of the most used tests to have logical and trusted results is the HET (hole erosion test). Meanwhile there is not much research regarding the models that govern these types of tests. Objectives: In this paper we modeled the HET using modeling software based on the Navier Stokes equations, this model tackles also the singularity of the interface structure/water using wall laws for a flow turbulence. Methods/Analysis: The studied soil in this paper is a clay soil, clay soil has the property of containing water more than most other soils. Three wall laws were applied on the soil / water interface to calculate the erosion rate in order to avoid the rupture of such a structure. The modlisitation was made on the ANSYS software. Findings: In this work, two-dimensional modeling was carried of the soil.in contrast of the early models which is one-dimensional model, the first one had shown that the wall-shear stress which is not uniform along the whole wall. Then using the linear erosion law to predict the non-uniform erosion along the whole length. The previous study found that the wall laws have a significant impact on the wall-shear stress, which affects the erosion interface in the fluid/soil, particularly at the hole's extremes. Our experiment revealed that the degraded profile is not uniform. Doi: 10.28991/cej-2021-03091742 Full Text: PDF

Problem statement: Internal soil erosion is a real threat for hydraulic infrastructures. In its final stage it develops in piping involving the formation and progression of a continuous void inside the soil between the upstream and downstream sides. The hole erosion test was introduced to characterize kinematics of piping in terms of the time left to rupture. Actual modeling approaches of this test are essentially one dimensional. The wall shear stress generated by the flow is assumed to be uniform, so that erosion rate is also uniform along the hole length. Experimental observations show however an irregular profile of the eroded hole. Approach: In this study an axisymmetric extension representation of the hole erosion test was performed. The biphasic flow at the origin of surface erosion occurring in the porous soil sample was modeled by means of the renormalization group based k-ε turbulence equations. Fluent software package was used to perform the numerical modeling. Results: This had enabled to estimate the wall shear stress which was found to be non uniform along the hole length. Erosion rate was then estimated by using a classical law. Its variations as affected by the applied gradient pressure, fluid density as well as the actual fluid/soil interface roughness were analyzed. In particular, wall roughness and clay concentration were found to increase noticeably the erosion rate. Conclusion/Recommendations: Predicting erosion rate at the start of piping formation can be done by the proposed model. Flow features are however very complex in the real HET configuration. In particular, clay concentration does not vary equally along the hole length. The erosion law coefficients are variable. Transport phenomenon of some soils particles that detach is present in the problem. Further investigations including these aspects should be performed in order to render more profoundly the complex physics involved in this experiment