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The contractor needs to construct a pile cap on the embankment for a six-lane road bridge project across the Hooghly River located near Kolkata, India. The difference in ground level on the land side and riverbed level was more than 11 m. The bottom of the pile cap needs to be constructed 13 m below ground level from the land side. Due to the challenging topography, the contractor has developed a unique system of temporary earth retaining structure using sheet piles as cofferdam with tie-back arrangement and strutting systems as intermediate supports. Analysis of the cofferdam was carried out using WALLAP and PLAXIS, specialized geotechnical software. Since the construction was happening on a perennial riverbank, mitigation of scour, access, equipment placement, navigational channel, and water ingress were the challenges faced by the contractor. This paper will highlight the critical design process of a cofferdam with a tieback system and also bring out the contractor challenges in the construction of a pile cap at a deeper depth on a river embankment.
Kalidoss et al. (Fri,) studied this question.