Investigation on the effects of modified gradation on consolidation behavior of the coarse grained clayey soils

The determination of consolidation properties of the clayey soils is one of the most important steps in designing and constructing the civil engineering projects; especially, irrigation and drainage projects. It is mainly important due to the fact that the settlement of these soils may cause a significant damage to the structures. Generally, the consolidation behavior of the soils is being evaluated by Oedometer in the form of one-dimensional consolidation. However, some modified gradation techniques should be employed in order to prepare samples of coarse grained clayey soils due to the smaller size of the test mold, which causes an alteration in the soil gradation. The hydraulic consolidation cell provides controlling drainage pathways and recording the pore pressure of the specimens during the test. The main objective of this study is to investigate the alterations made on coarse grained soils due to modified gradation. In this regard, the coarse grained clayey soils were grade modified by using scalped and replacement methods. Then, the consolidation behavior of the graded and modified specimens was tested by oedometer test. Moreover, the base soil specimens were tested by using hydraulic consolidation test. The results showed that by performing modified gradation techniques, the values of compression index and coefficient of consolidation, respectively, increases 1.5 to 2.5 time and decreases 30% to 80%. These alterations are more intense in grade modified specimens with sculpted method. Thus, the replacement method is a better approach for evaluating the consolidation behavior of coarse grained clayey soils, by providing closer values.