STABILITY ANALYSIS OF CONCRETE FACE ROCKFILL DAMS

Abstract

Concrete face rockfill dams are becoming- more attrac-tive and being constructed in increasing proportions every year throughout the world. The reason is that rolled rock- . fill of higher relative density can be achieved by the use of modern compaction techniques which avoids large post con-struction settlements and thereby the cracking of slab and leakage through the dam. Reduction in cost of quarrying, placing and compaction due to availability of efficient earth moving machinery has led to the economic design of concrete face rockfill dams. The rockfill embankments with slope at angle of repose attain adequate stability and are inherently stable under all operating conditions. Thus only some exercise would be required for the design of safe slopes under seismic conditions. A 100m high concrete face rockfill dam with up stream and down stream side slopes equal to 1.5H:1V has been adopted for the analyses. The dam located in a trapezoidal and wide valley is in a seismic zone of Himalayan ranges. The foundation has been assumed to be rigid. The analyses have been carried out using a two-dimensional finite element program called DLEARN and plain strain conditions were assumed.The transverse section of the dam have been analysed for self weight with seismic, accelerations acting at the base of concrete face rockfill dam.The output time history of acceleration at different heights of the dam on the down stream face were obtained from dynamic analysis using program DLEARN. The analysis were conducted for constant elastic modulus in concrete facing and rockfill zone;and stress proportional elastic moduli in concrete facing and rockfill material. The permanent displacements have been calculated, for different slopes with many combinations of friction angle while applying different peak ground accelerations. An expression relating permanent displacement to peak acceleration and critical acceleration has been derived analytically.