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ABSTRACT : Khanpur Dam in Pakistan was constructed on deep alluvial deposits underlain by foundation rock. The dam, since its operation in 1983, has predicament of seepage and in spite of several studies and remedial measures taken in this regard, the problem has not been resolved completely. The present study presents a review of performance of different components of Khanpur Dam in the context of seepage. In this research, Geostudio 2004 package has been used to see the effect of different factors on the quantity of seepage and the results have been validated with the help of field data. The research work concludes that upstream blanket is working efficiently and seepage through the main dam has been stabilized due to the strengthening of the upstream blanket because of sediment deposition. Geostudio analysis as well as field data has indicated that previous grout work at left and right abutments has failed to produce the required results and seepage which is being measured at the downstream toe of the dam is through the abutments instead of through the body or foundations of the dam and recommends that by extending the grout curtain up to a depth of 140' in case of left abutment and to a depth of 160' in case of right abutment, the quantities of seepage can significantly be reduced.
Key words: earthern dam, seepage, upstream blanket, grout curtain, alluvium
INTRODUCTION
Seepage control in earthern dams is very important and a slight negligence can lead to catastrophe. Seepage reducing methods make use of relatively impermeable cutoffs, grout curtain and upstream blankets which consume energy at locations within cross sections where large water pressures and seepage forces can have no detrimental effects. The net result is that water pressures and seepage forces are reduced in the critical exit regions (Cedergren, 1980). Selection of seepage reduction measure depends upon site conditions. Generally in dams located on deep permeable alluvium relatively impervious compacted earth blankets are placed upstream of dams and levees to lengthen the seepage path and thereby reduce the exit gradients and the quantity of seepage. Turnbull and Mansur (1961) observed that along Mississippi river valley upper strata of silt and clay form a relatively impervious blanket over older beds of sand and gravels....