Publish and Present
This paper presents a summary of structural design challenges experienced, and resolved, during the construction of a Train Unloading Station at a key coal export terminal in Colombia. The Train Unloading Station (TUS) is a 180 ft long, 50 ft wide and 36 ft high U-shaped underground concrete box structure, with 3.3 ft thick base slab and 3.3 ft thick sidewalls supporting a series of transverse rail support girders at 13 ft spacing. The original design of the TUS relied on rail support girders to act as support struts to resist the cantilever bending of the sidewalls and was designed for a +26 ft water table elevation. However, during construction, it was discovered that the actual water table was 23 ft higher. Due to extremely high buoyant and hydrostatic forces, the structure, as originally designed, could potentially float and the sidewalls and base slab were structurally inadequate to resist the hydrostatic pressure. Additionally, for construction flexibility, the structural characteristic of the TUS sidewalls was changed from a propped cantilever to an unsupported cantilever. By the time, these critical design changes were realized, the construction of the Train Unloading Station was 50% complete! To quickly resolve these design issues and retrofit the partially built TUS structure, a simplified design method was developed utilizing materials which were locally available and proposing a solution which can be successfully executed by the local contractors with limited expertise. The retrofit included extending the base slab of the structure to prevent buoyant uplift and stiffening a 33-ft portion of the “unbuilt” TUS to change the load distribution and reduce the design forces in the structure which was already built. The retrofit measures were successfully implemented and the construction of the TUS was completed on time. The Train Unloading Station continues to operate successfully.