One 6-lane wide “Railway over Bridge (ROB)” including its “Approach Viaducts” structure was proposed to be built over “Level Crossing” at Km 284.170 near “Topsi” area on NH-60 along “Ranigang–Suri” road in the state of “West Bengal”. The entire structure having multiple long span PSC and RCC superstructures was planned to be built over “Bored Cast-in-situ RCC Pile Foundation” of 1.00 m diameter. As per the preliminary “Geotechnical Investigation” data, the subsurface profile consists of medium stiff to very stiff/hard sandy clayey silt and/or very dense silty sand as overburden soil which is underlain by highly to moderately/slightly weathered and fractured sandstone of variable strength with or without intermittent band of weak to hard shale and coal. Based on the test results of the successfully casted “Test Pile” of 1.00 m diameter in one side viaduct of ROB, the installation of “Working Pile” was taken up. After being unsuccessful in installations of few “Working Piles” due to the complete loss of concrete through the pile bore having unknown connection to the underlying cavity, a detailed “Geophysical Investigation”, namely “Electrical Resistivity Tomography”, was undertaken along and across the project road which revealed the presence of “low electrical resistivity zones” scattered all along the area at different depths and those identified anomalous zones interpreted as underlying cavity and/or saturated soil at some of the pier locations of one side of viaduct. In later stage, the presence of “water-filled cavity” was established through exploratory boreholes of adequate depth. Due to the presence of underground “cavities” at variable depths in some pier locations along one viaduct side of ROB, the “Open Foundations” of size 8.00 m × 8.00 m at 2.00 m depth from existing ground level supporting the shorter superstructure spans were adopted in place of originally proposed “Pile Foundation” supporting longer spans. It was recommended to adopt “Open Foundation” instead of “Pile Foundation” so that the “base pressure bulb” remains confined within the overlying soil and not get extended in the underlying cavity inside of rock mass. To ascertain safety of the proposed structure, the detailed “Finite Element Analysis (FEM)” was undertaken for evaluating the maximum stress and settlement of ground including any possible deformation of the underlying cavities due to the proposed open foundation at the identified pier locations. This paper presents the detailed methodology adopted for finalization of “Open Foundation” in place of originally proposed “Pile Foundation” for the “Approach Viaduct” of the said ROB structure having underlying “Subsurface Cavity”.