Structural analysis of underground gunite storage tanks. Environmental Restoration Program

This report documents the structural analysis of the 50-ft diameter underground gunite storage tanks constructed in 1943 and located in the Oak Ridge National Laboratory (ORNL) South Tank Farm, known as Facility 3507 in the 3500-3999 area. The six gunite tanks (W-5 through W-10) are spaced in a 2 {times} 3 matrix at 60 ft on centers with 6 ft of soil cover. Each tank (Figures 1, 2, and 3) has an inside diameter of 50 ft, a 12-ft vertical sidewall having a thickness of 6 in. (there is an additional 1.5-in. inner liner for much of the height), and a spherical domed roof (nominal thickness is 10 in.) rising another 6 ft, 3 in. at the center of the tank. The thickness of both the sidewall and the domed roof increases to 30 in. near their juncture. The tank floor is nominally 3-in. thick, except at the juncture with the wall where the thickness increases to 9 in. The tanks are constructed of gunite (a mixture of Portland cement, sand, and water in the form of a mortar) sprayed from the nozzle of a cement gun against a form or a solid surface. The floor and the dome are reinforced with one layer of welded wire mesh and reinforcing rods placed in the radial direction. The sidewall is reinforced with three layers of welded wire mesh, vertical {1/2}-in. rods, and 21 horizontal rebar hoops (attached to the vertical rods) post-tensioned to 35,000 psi stress. The haunch at the sidewall/roof junction is reinforced with 17 horizontal rebar hoops post-tensioned with 35,000 to 40,000 psi stress. The yield strength of the post-tensioning steel rods is specified to be 60,000 psi, and all other steel is 40,000 psi steel. The specified 28-day design strength of the gunite is 5,000 psi