Lack of knowledge of soil geotechnical properties can cause many problems associated with the construction and maintenance of irrigation and drainage networks. In general, all of unconventional soils can cause some problems in irrigation canals. Two of unconventional or problematic soils are gypsiferous and unstable sandy soil. Some studies have been conducted with a variety of problematic soils, but still there is a need of more research activities and field studies. This research conducted to study the impact of adding perlite and pumice (5%, 10%, 15%) and micro silica (1%, 5%, 10%) and polypropylene fibers (6 and 12 mm in length) with different percentages (%0.05, %0.1, %0.15, %.25) on some mechanical properties of soil including shear strss, bearing capacity and Atterberg limits. Statistical analysis was done to compare their averages (P 0.01). Results showed that micro silica had the best effect on shear, bearing and condensation parameters and Atterberg limits of gypsiferous and sandy soils and it improved these parameters of both soil types. Pumice improved shear, bearing and condensation properties of gypsiferous soil and it only improved bearing property of sandy soil. Polypropylene fibers improved the shear, bearing and condensation properties of gypsiferous soil howere it only improved bearing and shear properties of sandy soil. Perlite reduced the shear, bearing and condensation properties of both soil types gypsiferous and sandy.
