عنوان مقاله [English]
Problematic soils are sometimes needed to be used in dam construction. This usually happens when appropriate materials are far located from the dam site and cannot be used due to economic reasons. In this case, available problematic soils (for example dispersive soils) can be utilized after amendment. The amended soil is supposed to not show its problematic behavior before treatment. It is conventional to treat dispersive soils by additives the most used one being lime. But, adding lime may cause a considerable reduction in plasticity index of the mixture which in turn, can result in other problems. An important consequence, caused by low plasticity index of the amended soil used in earth dams is arching phenomenon which can finally lead to failure of the dam. In this research lime and bentonite is used to amend dispersive soil samples taken from Mirzakhanloo-Dam site located in Zanjan Provience. The aim was to treat dispersivity of samples and also to avoid arching problem. For this reason, a set of laboratory test were conducted on the prepared samples. Lime was used in samples with amount of 0.6, 1, 1.5, 3, 5 percent of dry weight of the soil. Also bentonite was used with amount of 3, 5, 10, 15 and 20 percent. Pinhole test, double hydrometer test, crumb test, and chemical test were performed on the pure soil and additive-soil samples to evaluate dispersivity of soil samples. Also Atterberg limits, particle size, and hydraulic conductivity of samples were examined. The result showed that the combination of 5% lime and 15% bentonite can solve the problem such that, in one hand, the dispersivity of soil is treated and on the other hand arching problem is controlled. Almost all previous researches have recommended the lime and other additives for dispersive soils amendment without any attention to arching problem. This paper is strongly recommend to pay attention to this problem. Since the creation of a small crack in dams can lead to failure with regard to piping problem, it is important to carefully assess the outcome of soil improvement programs and control the plastic index of the amended soil.