Challenges in the construction tunnel in BIM rocks: Case Study for Farish tunnels

Summary

Abstract

It is generally recognized that excavation and construction of tunnels in so-called BIM rocks (solid blocks bound by a weaker matrix) is very challenging task. Knowing the fact that all experiences from the practice related to excavations in such rock mass media, are welcomed, and the paper presents the authors’ experience in constructing two parallel tunnels forming part of the Macedonian Prilep – Gradsko Expressway. The tunnels are located in the Farish Gorge, an area characterized by highly complex geological conditions due to the presence of carbonate breccia characterized with stronger core carbonate block in a weaker claylike matrix, at some zones intensely fractured. These specific geotechnical conditions represented a significant challenge for the excavation and stabilization of the tunnel profiles, as well as difficulties in selecting the appropriate blasting excavation methodology. During the construction phase, optimization of both the blasting excavation and the primary support methods was carried out; however, these optimizations led to a reduction in support measures due to the failure to consider the blocky structure of the BIM rocks, which in turn affected the overall tunnel stability. In the present study, an overview of ground improvement measures is presented for this rock mass media, prone to rapid deformation development at the tunnel face. Gathered experiences from this study can contribute to a better understanding of the behavior of BIM rock masses during tunnel excavation and provides practical recommendations for their more effective engineering treatment in similar geological environment.