This case study delves into the strategic use of top-down construction techniques in the development of a Road Over Bridge (ROB) spanning a deep cut designed for railway tracks. Situated near Delhi, India, the proposed ROB features a railway crossing at the base of a deep cut, with an approximate total span of 150m and a deep cut depth of 20m. The initial construction methodology proposal involved the conventional sequence of construction which commences with excavation up to the required depth followed by construction of foundation, substructure, and superstructure. Hence, the road traffic is allowed to operate only after all the structural and excavation works are completed. However, this method has some significant drawbacks with regards to the duration of construction, excessive delay in resumption of traffic, unfavourable aspects related to safety and economy of tall and slender substructure components such as piers and abutment. Moreover, owing to the challenges involved in erection of superstructure at considerable heights, the choice of available superstructure types is limited. To overcome these issues, the top-down construction strategy has been adopted. In this method, the structural construction works (construction of foundation, substructure, and superstructure) precede the excavation works and the traffic is resumed on the road immediately after completion of all structural works. Hence, there is no delay on account of the time-consuming excavation work. Also, cost effective and efficient superstructure types like voided slab, PSC box girder can be adopted since the formwork can be supported from existing natural ground level which is at shallow depth. Moreover, provision of slender substructure components is replaced with pile groups which are more efficient and economical.

Deep-cut, ROB, Railway, Top-Down