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In recent decades, with the growth of population and the development of metropolitans around the world, the issue of landfill and waste management has become more and more critical. Due to development of radioactive material applications, disposing these radioactive waste material became an important geo-environmental concern. Bentonite clay as an eco-friendly and natural shielding material is used as the main material for landfill barriers. The radiation shielding performance of bentonite clay modified by different percentages of basalt fiber and Polyvinyl alcohol (PVA) resin additives is investigated using experimental measurement, Monte Carlo N-Particle (MCNP) simulation, and XCOM database methods, in Gamma-ray energy levels of 60Co (1173.2 and 1332.5 keV). The employed sample mixtures include 0.25, 0.5, 1, and 2 percent of basalt fiber and PVA resin additive. The obtained results for Gamma-ray shielding measurement from these three methods have a good agreement, depicting an increasing trend in the linear attenuation coefficient for higher percentages of additives. The maximum increment is observed at 0.5 percent of additive, from 7.85 to 9.69 m-1, and 9.3 to 11.23 m-1, in energy levels of 1132.5 and 1173.2 keV, respectively. This improvement may decrease the bentonite clay Gamma-ray barrier thickness (half-value layers (HVL), tenth value layers (TVL)), up to 20 and 23 percent for 1173.2 and 1332.5 keV, correspondingly. Moreover, the hydraulic and gas permeability of the mixtures are controlled to find the standard and optimum mixture. In which the 0.5 to 1.0 percent of additives will keep the permeability requirement in an allowable and preferable range.