Laboratory study on leaching to investigate hydro-mechanical properties of gypsiferous soil

The present work aims to investigate the effects of leaching on the hydro-mechanical properties of gypsiferous soil taken randomly from the banks of the Euphrates River in the Al-Kifl district in Iraq. The gypsiferous soil samples were prepared by weight replacement method of gypsum with 20%, 25%, and 35% of the weight of the fine portion in the natural soil samples. A set of laboratory tests were carried out to measure the saturated permeability of the soil samples. The strength parameters were measured for the soil samples before and after the leaching process. The results of measured parameters show that the initial gypsum content affects adversely on the saturated permeability; hence, when approaching the end of the leaching process, the permeability of soil was increased because of the increase and development of voids space in the soil mass to seep more infiltrated water as a result of gypsum salts dissolution. The findings of the present work, about 32% as a relative difference, had increased the cohesion of soil in the wet state with 25% gypsum content after the end of the leaching process. In contrast, the soils with 35% gypsum content had lost a significant amount of cohesion. On the other hand, before the leaching process, the gypsiferous sample with 20% initial gypsum content decreased roughly the internal friction angle for the natural soil in dry and wet states, respectively. The gypsiferous samples with 35% gypsum content show development in values of internal friction angles for leaching and moisture conditions.