ABSTRACT
This paper discusses case study of water conveying tunnel that encountered very poor rock mass conditions along its longitudinal profile during the construction of an underground crude oil storage project. This case study deals with a surprise occurrence of hydrothermally altered zones in contact with a 1.5 m thick mafic dyke in five-meter stretch of tunnel during construction of water curtain tunnel. The initial basic design carried out based on the interpretated rock class had to undergo significant changes for ensuring stability of the water curtain tunnel. Numerical analysis of the affected tunnel section was conducted to study stress-deformation behavior of affected tunnel section and evaluate final support requirements. The designed support system included Reinforced Rib Shotcrete (RRS) to arrest long term displacements, along with the use of fiber reinforced shotcrete layers and wire mesh packed in the over-excavated section and loose rock mass areas.
