Connecting Adam's Bridge

Adam's Bridge, the collection of limestone shoals between the Mannar Island of Sri Lanka, and the Pamban Island of South India has sparked both the imagination and inventive thinking of many. The closest distance between the two countries-between Dhanushkodi, and Talaimannar is about 30 km, and a bridge connecting the two countries has been a long argued prospect. Such a bridge will be beneficial to both countries in terms of economics and trade. The engineering and environmental challenges of such a construction are overwhelming and a unique Geo-chemical engineering method might hold the answer to this problem.

The Jaffna Peninsula and the surrounding area consists of a Miocene limestone basement and the sea in the area of the Palk Strait is very shallow. This makes it possible to easily construct a permanent causeway between the two countries by connecting the limestone shoals of the Adam's Bridge. Although a simple construction, a permanent separating structure will disrupt the sediment movement through that channel and can be detrimental to fisheries as well. The complete disconnection of the water circulation through the gap can pose significant environmental problems. Building a bridge across the entire span is a possibility that is too costly. Therefore the ideal solution would be to construct a combined, landmass-bridge structure.

http://www.geo.shimane-u.ac.jp/spfs/g_students/mext/08sansfica/Sansfica08_2L.jpg

 To support the construction of a bridge, the existing landmasses or shoals should be elevated. Bridges can be constructed on these elevated landmasses while leaving gaps for the flow of water. Some of these gaps can be dredged deeper to allow for the same volume of water to flow. This could also serve the purpose of a navigable channel for ships as proposed by the Sethusamudram Project. Another prospect is for electricity generation by means of hydro-turbines installed at gaps where the flow of water will be heightened.

It is in elevating these landmasses that the unique geo-chemical engineering method comes into play. Research conducted by Prof. R.D. Schuiling indicates that these landmasses can be elevated in a cost effective manner by injecting Sulphuric acid into the limestone basement. The principle here is that, Sulphuric acid will react with the limestone to produce Gypsum, which has a higher molar volume. Thus, the rock will expand, and this expansion will be accommodated by surface uplift. (R.D.Schuiling, Current Science Vol 86).

This process involves drilling bore holes along the trend of the Adam's bridge and injecting Sulphuric Acid at modest pressures insufficient for hydro-fracturing. The well jointed Miocene limestone is expected to facilitate the migration of the acid through the basement. The acid will be injected to bottom layers of the limestone leaving the top layers unaffected thus avoiding contact with the biosphere and and associated environmental problems.

Prof. Schuiling points out that if industrial waste Sulphuric acid is used for the process it would be an economically viable technology while also solving the disposal problem of such acids. He further addresses possible environmental effects. Since the expansion of the rock takes place at the bottom layers and is separated by a layer of un-reacted limestone, there won't be direct consequence from the reaction. As for the concerns with heavy metals if waste acids are used, it has been experimentally proven that such heavy metals are immobilized during the reaction.

While a social and political consensus regarding the construction of the Adam's Bridge has not yet been reached, and no comprehensive EIA has been conducted in this regard, if these happen in the near future and if the two countries go ahead with the project, this Geo-chemical engineering technology will be a compelling prospect.