This case study presents the successful application of the formal observational method for constructing eighteen 2000 m³ steel storage tanks on soft, problematic soil in a port in southwestern Iran. The site investigation revealed soft clayey soils with an allowable bearing capacity of only 36 kN/m², far less than the 170 kN/m² imposed by the proposed structures. To avoid costly deep foundations, a geotechnical solution was implemented using engineered soil filling (2 m thick multi‑layered fill of sand, gravel, and silty gravel) placed and compacted in the tank area. Finite Element Modeling (FEM) with the Hardening Soil Model predicted a long‑term consolidation settlement of 209 mm. A four‑month-controlled hydro‑test was conducted to preload the ground and accelerate primary consolidation, during which tanks were interconnected with flexible polyethylene pipes to accommodate differential movements. Settlement was meticulously monitored throughout and after the hydro‑test, with predefined alert, action, and alarm trigger levels as required by the observational method. Field results showed acceptable agreement with FEM predictions (average final settlement 234 mm). Long‑term average creep after hydro‑test was estimated at 30–50 mm over fifty years, well within the tolerance of flexible connections. The study concludes that the formal observational method, combined with soil replacement, is a viable and cost‑effective strategy for such challenging ground conditions. Key practical recommendations include the use of flexible hoses for all pipe connections and sliding restraints for access ladders.