It is very important that the geological conditions along the route of excavated tunnel are known in advance for the tunneling operation, safety, and for its construction economy. In shielded TBM tunneling, inspection of the ground is almost limited to field observations of excavated chips, tunnel face condition, and monitored operational parameters including the TBM thrust, torque, power, and penetration rate due to restricted access to the ground. The information obtained from this inspection can be used as a feedback for the next excavation stroke for adjusting TBM operational parameters such as machine thrust and penetration to avoid potential problems caused by geological conditions, and for taking precautionary measures especially in adverse geological conditions. The operational monitoring system used in excavation of Ghomroud water conveyance tunnel by Wirth Double Shield TBM (model TB 453 E/TS) along with field observations (investigations of muck pile and tunnel face condition) brought an ample data for evaluation of rock mass quality (in term of rock mass class of RMR classification) using numerical analysis. The purpose of this study is to evaluate the relationships among the chip size, TBM operational parameters, rock type, and rock mass quality. The results constitute a useful tool to examine rock quality during tunnel excavation using a TBM or shielded machine while tunneling is in progress. The descriptions of the methodology and the results of the study are subject of this paper.


Geo-data, including geological, geomechanical, geotechnical and hydrogeological information, is essential for successful tunneling accomplishment. The geo-database involves rock types, structural discontinuities and rock properties in their relation to the designed construction. A proper assessment of quality of rock environment requires precise and adequate input values obtained usually by the engineeringgeological investigation. Common methods of investigation provide data with a certain timedelay, and the data might not be dense enough (regarding as sufficient number of data for the rock mass characterization). During the excavation of eastern part of the Ghomroud Tunnel, by using computer monitoring system, installed on the Wirth TB 453 E/TS tunneling machine, the means for scanning the excavation process parameters including TBM thrust, torque, power, penetration rate have been forgathered. Using the investigation of the rock-machine interaction, quantitative classification of the rock mass could be obtained by determining the penetration indices and investigating about chip analysis. The results of classification have been verified by checking tunnel face condition and common RMR evaluation from ratings (Bieniawski, 1989) [1]. The results of this research proved that this method can be a powerful tool in quantitative assessment of rock mass strength properties while the tunnel is in progress.

Project Description and GeologicSetting

Ghomroud tunnel project includes a 36-Km tunnel with 4.5 m excavation diameter and originates from Dez river catchments area. This transferring system will convey potable water from Zagros range to central Iran. The tunnel construction was started in 2002. Drilling and blasting was used to excavate the first-380 m of tunnel from downstream portal.

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