Design Factors Affecting the Flow of Water through Below-Ground Concrete Vaults

Underground concrete vaults have been and are planned to be used to store contaminated materials, such as hazardous materials and radioactive waste, over long periods of time. To protect humans from exposure to the contamination, the key to this long-term storage is immobilization achieved through designing concrete vaults with enhanced hydraulic performance. This paper evaluates concrete vault design parameters including properties of soil layers surrounding the vault, vault size, slope of the vault roof, and the amount of concrete degradation under various infiltration rates. A numerical model that estimates the flow of water through the vault is used as the computer simulation tool. Conclusions from the modeling simulations are that clay layers, including sand and loam layers forming a capillary barrier and placed adjacent to the vault concrete, were found to have a better hydraulic performance. Smaller vault sizes result in lower seepage through the vault and suggest a scale effect. Roof slope has a relatively small influence on hydraulic performance.