Foundation Investigations in Thick Overburden Matrix Material of a Proposed Dam—A Case Study

There is an acute scarcity of water during peak summer season in Andaman & Nicobar Islands. Most of the rainwater is wasted during rainy season. If storage facility is available by constructing dams, rainwater could be entrapped for further use. Absence of perennial rivers and need for drinking, irrigation and other purposes, it was proposed to construct a dam across a small stream to store water to encounter such problems. This paper presents foundation investigation at various locations such as dam axis, left and right abutments, and upstream and downstream of dam axis. There was thick layer of about 6 m overburden of matrix material including boulders of different sizes mixed with sand silt and clayey soil at the dam axis and exposed rock could be seen at some locations. It was not possible to carry out SPT testing and undisturbed sampling. Drilling of five numbers of drill holes at predetermined locations was carried out. Various field tests such as permeability by Packer method (single and double Packer), open end permeability tests and extracting of core recovery to ascertain RQD value were carried out in all the drill holes to ascertain feasibility of foundation materials for constructing dam. Geotechnical challenges have been discussed in present paper during foundation investigations such as drilling in thick overburden in matrix materials at dam axis, Packer tests in fractured rocks and also extracting of rock core. It was concluded from Field permeability and RQD values that the foundation consisted of fractured rock with semi-pervious nature.