Within the presented paper an analysis of possible causes for failure of rail fastening system Delta Lager I is presented. The type of fastening attributed as Delta Lager I is commonly used in underground railway system. Routine safety inspections revealed higher amount of broken high-strength steel bolts that secures interconnection between the rail and a concrete sleeper. Performed computations were carried out using ANSYS 11.0 to help to found out cause of the problem. Spatial computational model of fastening construction including different contact regions was modeled in conformity with drawing documentation. Further were performed non-linear computations in several alternatives of imperfections configuration. On accounts of FEM computations were determined inadequacies in construction of rail fastening system.