The Mechanical Behavior of Safety Plugs for Underground Petroleum Stockpiling

The concrete plugs installed in underground petroleum stockpiling bases must be strong enough to support the hydraulic pressure of the stored crude oil and fairly impermeable against both of oil and gas. In order to test and confirm the mechanical competence of the concrete plugs, in-situ tests were carried out in three underground petroleum stockpiling bases; Kuji, Kikuma and Kushikino. In each case, an lm thick concrete plug was installed in a 2m wide by 2m high test adit and pressed as high as 10kg/cm2by four 200 ton hydraulic jacks. Deformations of the concrete plug and stresses induced in reinforcing rods as well as displacements of the surrounding rock were measured continuously while loading and unloading. Following results were obtained and discussed in details. (1) None of visible damages such as cracks was found on the surfaces of the tested plugs and the pressure durability of the plugs was certified. (2) Careful and scrupulous construction rather than geological condition affected the performance of the concrete plug more favorably. (3) Although due to the time-dependent behavior of the surrounding rock applied pressure-displacement relations of the tested plugs showed slight non-lineality and creep deformation while holding constant pressure, the elastic deformations of the plugs showed fairly good coincidence with the results of FEM calculations.