Stability analysis and evaluation of rock support in headrace tunnel of Khimti-2 Hydroelectric Project

Abstract

The tunnelling activities have been increasing considerably in Nepal with the development of many hydropower projects. During the design phase, tunnel alignment selection and rock mass quality prediction along with rock support requirements have a direct impact on overall cost and time requirements of the project. The major decisions that must be made in planning, designing and constructing a tunnel is mainly influenced by the geology along the tunnel alignment. An assessment on the stability of the Headrace Tunnel (HRT) of Khimti-2 HEP has been done. Ten excavated sections of headrace tunnel have been selected for the study at the critical zones. Squeezing and spalling phenomena have been assessed by empirical and semi-analytical method. The wedge block stability analysis has been done using UNWEDGE software. Further, rock support estimation from Q-method as well as support optimization have been done from numerical method with phase² software developed by Rocscience. From the numerical analysis, the support has been optimized based on the Q values.