Laboratory Study and Statistical Analysis on the Hydraulic Failure of Sandy Soils

The sand boiling phenomenon occurs downstream of hydraulic structures, and the continuation of this phenomenon could lead to a structural failure. In this paper, by developing a device to simulate sand boiling, experimental tests have been performed to determine the critical hydraulic gradient on various sandy soil. The effect of different parameters was evaluated such as four relative densities (0, 20, 50 and 80%), uniformity coefficient, woven and non-woven geotextiles in both single and double-layer states and the particle size distribution. Based on the results, with increasing the relative density and uniformity coefficient, the sand resistance against the hydraulic failure improved and also in soils with C u = 1, coarser sands have indicated more resistance to the boiling. In improvement by geotextile, reinforced sands beard more water load than natural sands, and the type and layer number of reinforcements have affected the test results. In addition, a statistical comparison has been performed between the experimental results and the proposed equation by Terzaghi to calculate the critical hydraulic gradient. Finally, by using experimental results, a linear and nonlinear regression model is presented to predict the required seepage force for the hydraulic failure of the specimens.