Analysis of the dispersivity in soils by applying a modified test based on the pinhole method

Abstract

The Pinhole test is an empirical probe with a qualitative classification foundation that identifies fine-grained soils with dispersive potential using hydraulic heads. However, the original technique was designed to identify dispersive clays. In some cases, it is misused as a quantitative test for measuring subsurface erosion rates. This paper presents a physicochemical modification to the exact test, based on adding a dispersant in the sample compaction water. For the quantitative evaluation of the susceptibility of the soil to generate internal tubification or piping, the effects of hydraulic load, flow, and orifice diameter before and after the execution of the test are explored—both for the samples treated with deflocculant and for those compacted using distilled water. Additionally, to complete the identification results, physical and chemical approaches were applied as methods of comparison. The results obtained from the altered soils indicate a significant increase in the clay fraction among the samples at the end of the test and gains of 3.7 and 6.2 times the initial diameter. The study demonstrates that the modified test is suitable for identifying non-dispersive soils before raising the percolation pressure. This modification is helpful for the improvement of the test because it helps to understand the procedure better and allows to calibrate the apparatus used.