CRITICAL ANALYSIS OF STEEL LINER DESIGN FOR PRESSURE SHAFT WITH SPECIAL REFERENCE TO NATHPA JHAKRI HYDRO ELECTRIC PROJECT

Abstract

in high head under ground power plants, pressure shafts are a general feature. They are normally lined with steel liner and back filled with concrete. Where the water tightness and loss of head are very important factors, steel liners are invariably provided. The surrounding rock is used as a dependable structural material to share the internal pressure resulting in reduced thickness of liner and hence economy. Modern trend in favour of under ground pressure shaft with steel liner has been promoted mostly by the economy involved due to substantial saving in high grade steel. The pressure shaft steel liner thickness is designed by the well known thin cylinder formula considering the maximum internal water pressure causing the hoop stress. -Assessment of maximum water pressure is complicated by the phenomenon of water hammer caused when the rate of-flow in the conduit -is rapidly changed. The thickness designed for internal, pressure is checked for external pressure. If this thickness is insufficient for external pressure then either stiffeners are provided to balance external pressure or drainage arrangements are made to reduce the external pressure....