Iranian Journal of Earth Sciences Evaluation of the ability of rock (soft) dispersion at the basement of the Darbandikhan Dam’s reservoir, NE Iraq, with a new investigation and Crumb test Volume 16 (2024) Issue 2, April 2024 2024 08 07 Evaluation of the ability of rock (soft) dispersion at the basement of the Darbandikhan Dam’s reservoir, NE Iraq, with a new investigation and Crumb test 10.57647/j.ijes.2024.1602.12 EN Mohammad Fathollahy Department of Earth sciences, Faculty of sciences, university of Kurdistan, Sanandaj, Iran 0000-0002-8787-2658 Hossein Azizi Department of Mining, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran 0000-0001-5686-4340 Baktiyar Mohammed Abdulrahman Al-Taeshi Department of Earth sciences, Faculty of sciences, university of Kurdistan, Sanandaj, Iran 0009-0009-0078-6297 Journal Article 2024 08 07 The Darbandikhan Dam reservoir in NE Iraq is located on soft sedimentary rocks which sporadically were affected by erosion. The basement rocks include sandstone, siltstone, and claystone, and mineralogically comprise quartz, and feldspar with some lithic fragments that are distributed in a soft matrix. The scanning electron microscope (SEM) images show sheet layers with clay structures for the matrix which is confirm by Semi-quantitative analyses of the EDAX data. The results demonstrate that samples categorize as dispersive soil based on the crumb test (ASTM D 6572–21). The Crumb tests were done in six hours, and the short duration can be considered as a defect. In this research the test time was extended and the behavior of the samples was investigated up to 7 days in intervals of two minutes, one hour, 6, 24, 72 hours, and 7 days. The results indicated that some samples which didn’t show any sign of dispersion in standard duration underwent some kind of egg-shaped erosion after 72 hours, which completely were separated in 7 days, so it would perhaps be better to make modifications to the crumb test. Correspondingly, the Sodium Absorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) results of soft grain units demonstrated that these units are mainly dispersive.