Investigation of the behavior of modified bentonite clay with basalt fiber and polyvinyl-acetate resin in wet and dry cycles Afsaneh Haghshenas Afsaneh.Haghshenas@cv.iut.ac.ir September 19, 2020 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M. Sc Language: Farsi M. Abtahi, Prof. Email address: mabtahi@iut.ac.ir H. Share Isfahani, Prof. Email address: hajarshare@iut.ac.ir In recent decades، one of the most important issues in societies is burial of wastes and prevention of the spread of its pollution in the environment. One of the most dangerous wastes for the environment and human life is the waste of radioactive materials، which has become very important in industry، medicine، agriculture، etc. Because low-level radioactive wastes contain radioactive material، it can remain active in the environment for thousands of years، causing severe damage to the environment and alive beings. Therefore، in order to protect the environment and against the pollution caused by these wastes، it is necessary to use appropriate methods to repel them. These wastes are treated as much as possible and then their remains are buried in surface reservoir. It is essential to create an impermeable and protective cover to prevent diffusion of radiation and gas from the reservoir into the environment or the entrance of rainwater into the reservoir that leading to contamination of groundwater and surrounding soil. Due to the characteristics required to landfill cover، bentonite clay is one of the best options for use in low-level radioactive waste storage. This cover is exposed to wet and dry cycles in different seasons of year، and this causes the cover to crack. These cracks affect the performance of the clay as landfill cover. Previous studies have examined the effect of adding basalt fiber to bentonite clay on the linear attenuation coefficient. The results show that the addition of basalt fiber has reduced the linear attenuation coefficient. But at the same time، due to the creation of cavities in the soil، the water permeability coefficient has also increased، which is not desirable. Therefore، in this study، with the aim of reducing cavities and more adhesion of fibers to the soil، basalt fiber with polyvinyl acetate resin have been used and its effect on linear attenuation coefficient، water permeability coefficient and gas permeability coefficient has been investigated. Another purpose of adding fibers is to reduce the growth of cracks in the wet and dry cycle. Basalt fibers and polyvinyl acetate resins were added to bentonite clay at the same percentages of 0.25-0.5-1-2 and water and gas permeability tests were performed on the sample in wet and dry cycles. Also، the linear attenuation coefficient for the samples was obtained using Na(TI) detector، simulation method with MCNP code and through Xcom database. The results show that the linear attenuation coefficient has increased somewhat with increasing percentage of fibers and resin. The water permeability coefficient in the sample containing 0.25% fiber and resin decreased slightly and increased for other samples. However، in the 0.5 and 1% samples، this coefficient is still within the allowable range. The results of the gas permeability test show that with increasing percentage of fibers and resins، the absolute permeability coefficient decreases. In wet and dry cycles، the water permeability coefficient decreases because of the process of saturation of the samples. Due to cracking of the samples in the wet and dry cycle، the gas permeability coefficient increases and it can be said that adding fibers had not much effect on reducing the growth of crack. Key Words Bentonit Clay, Basalt Fiber, PVA Resin, Water Permeability, Gas Permeability, Linear attenuation coefficient, Wet and dry cycles.