Significance of water pumping test in detecting subsurface weak features with reference to projects of Eastern India

A good number of projects have been constructed and several others are under construction/investigation in Eastern India. Experience in working in these projects dictates that the weak features of these sites are of various types and mostly hidden under thick overburden cover. The tropical climatic condition and high rain fall are responsbile for the formation of thick overburden and vegetation cover. In the high altitudes of the Eastern India including the Himalayan terrain, there are the extensive action of ice and water which have formed thick glacial, fluvioglacial and hill wash deposits. In general loose surficial deposit and weathering of rock to various extent are seen in most of the river valleyproject sites of Eastern India. For example, the Umling Dam Site (Fig. 1) of Meghalaya consists of thick riverine material and also thick surficial deposit followed by a mantle of weathered rock of considerable thickness. Sub-surface exploration mainly by drilling followed by water pumping tests is therefore carried out in almost all river valley projects to evaluate the rock condition at depth.