Promoters of railways in India faced a major challenge in crossing the wide rivers, which changed their course dramatically with seasons. The climatic conditions vary considerably and so does the flow through the rivers.The volume of water register seasonal variations of magnitude unknown in other parts of the world. The varying character of the river-bed soil further aggravates the problem. Most rivers pass through alluvial soil devoid of rocks. To quote Charles Greaves, one of the early engineers visiting India in 1852: "The whole of the Bengal plain is nothing but a sea of mud, there is hardly a stone as big as coconut or a hill as high as a house.It is wonder having regard to the softness or looseness of the soil that Calcutta remained where it was." (Source: http://www.irsme.nic.in/mm.asp)
Quote from the publication http://www.irsme.nic.in/files/mmfiles/BRIDGES_RRB.pdf
James Meadows Rendel, the great consulting engineer, associated with railways in India from its very inception commented in 1854:
"There are engineering difficulties to contend with in India, which people at home cannot possibly conceive. Yet I am bound to say that the works executed by East Indian Railways (EIR) are equal to any of the kind done in this country; several large bridges have been built over river streams and rivers near Hooghly, and on exceedingly treacherous, sinking and shifting ground. Yet no failures have happened nor have any major accidents taken place, although since the planning of railway, heavier flood have risen in Bengal than have been witnessed since the days of Clive."
About 50% of these bridges are more than 100 years old. Though more than 1000 bridges are rebuilt/rehabilitated every year, the backlog is enormous. Old railway bridges are facing following types of problems:
• Aging and fatigue consideration
• Increased loading standards for axle load
• Increased longitudinal loads
• Rebuilding metre gauge bridges for broad gauge work.
• Replacement of Early Steel Girders provided prior to 1905.
• Corrosion problems in coastal areas.
Article Source: http://www.irsme.nic.in/mm.asp