Design optimization of support system for swelling and squeezing zone in Gavoshan water conveyance tunnel

摘要

Construction of underground structures through swelling and squeezing rocks exhibit most difficulties which need much more technical knowledge, experience, money and time to overcome. In this paper problems encountered during construction of Govoshan 20 km. length water conveyance tunnel are discussed. About 1 km of this tunnel goes through very fractured serpantinite zone with potential of swelling and squeezing behavior. For this reason a TBM which has been chosen to excavate the tunnel should be passed through this troublesome zone, and excavation continued by drilling and blasting and top heading and bench method. Due to existing stability problems nearly all common design methods such as empirical, observational, numerical and analytical used to evaluate necessary support for stabilization. Finally via Justification and Engineering Judgment 20 cm thickness shotcrete, combined with lattice girder made of 25 mm bars and swellex rock bolts with the pattern of 1.2*1 m accompanied with invert strut, selected as optimum support design, which has showed very successful performance till now.