CONSTRUCTION-STAGE GEOTECHNICAL PROBLEMS OF THE KAMTHIKHERI DAM

The 32 m high Kamthikheri Dam, a 2013 m long earthen structure with a central gravity masonry spillway, is located on the penoh river in the eastern part of Maharashtra state of India. The dam was construoted from 1968 to 1977 in an area of extreme geologic complexity, represented by the highly folded and faulted Sausar metasedimentary sequence of the Archaean age. The construction of Kamthikheri Dam came to an abrupt halt during 1970 due to sudden revealation of the presence of an extremely weak and cavernous rock below the foundation of the spillway and also of the earth dam which was already constructed on the either bank. Subsurface exploration carried out at this stage confirmed the occurrence of a 15 m wide fault gouge and a 30 m thick band of crystalline marble on the either aide of an intrusive pegmatite body cutting across the spillway foundations The marble was proved cavernous for a depth of 35 m below the river bed and was occurring below a very thin cover of granulite and pegmatite along the heel of the dam. These features undetected during the earlier geological investigations posed serious problems of stabl1ity and watertightness of the dam and the reservoir at the Pench project Site.

The project engineers had constructed the upstream casing of the earth dam of the graded, pervious sand, on sound engineering principles. But parts of this sand casing was found to have been laid directly on the cavernous rook without making provisions of ay remedial foundation treatment. The cavernous marble, exposed all along the left bank extended below the entire 300 m length of thealready completed saddle dam and pond grave hasards of leakage and failure of the dam by piping and erosion of the sand casing material. These geotechnical prolems encountered at the advanced stage of construction of the Kamthikheri Dam necessitated adequate reappraisal and a radical revision of planning and design of the remedial treatment for the weak and permeable foundations to ensure safety and economic construction of the dam.

EVALUATION OF GEOLOGICAL AND POUNDATION PROBLEMS AT THE PENCH PROJECT

The earlier geological studies at the project site were carried out by fermor and West (Pascoe 1950) and more recently by Straczec and Rao (1970) in connection with the assessment of manganese ore deposite of the Kanhan-Pench Valley. The rooks exposed in the area. comprise a highly folded and metamorphosed sequence of the crystalline schists and gneisses of the basement Tirodi Stage in which the younger Sausar rock like Lohangi granulites marbles and Mansar schists occur as irregular, often lenticular bands. The Smear rocks are associated with several thin bands of manganiferous marble, which has been proved to be extensively cavernous at the Pench Dam Site. The rooks in the area have been repeatedly folded and overturned into complex synformal and antiformal structures and were subjected to severe faulting and thrust movements.

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