Abstract
In underground construction, especially tunnel building, a detailed knowledge of the geological conditions ahead of the tunnel face is essential for both safety and efficiency of work. Many tunnel collapses have been reported to occur because of a lack of accurate evaluation of the geological conditions. While conventional horizontal boring conducted from a tunnel face provides good accuracy, it is infrequently conducted due to its high cost and time-consuming nature. In addition, the tunnel seismic reflection method has limited practicality owing to the complexity of data processing. This paper presents a new approach based on the specific energy of the mechanical drilling rig to evaluate the geological conditions ahead of the tunnel face. In order to assess the geological conditions, rock mass quality index, buried depth of the tunnel and tunnel deformation investigation were undertaken, and the obtained data were compared to the specific energy. Results from the comparison reveal the evaluation criterion that if the distribution of specific energy in some areas deviates from the distribution of buried depth, it is considered that abnormal geological conditions exist in this area. This work can greatly contribute to the accurate and effective evaluation of the geological conditions ahead of the tunnel face.
Highlights
Evaluation of geological conditions ahead of a tunnel face is of major importance for safe and economic tunnel building [1,2,3]
To the authors’ knowledge, little research on the relationship between the specific energy of the mechanical drilling rig in the region ahead of the tunnel face derived from MWD data, rock mass quality index, buried depth of the tunnel and tunnel deformation has been reported, if any
A new method was proposed to evaluate the geological conditions ahead of a tunnel face based on the comparative analysis of the relationship among specific energy, rock mass quality score (RQS, an index used in Japan to evaluate the quality of tunnel rock mass), buried depth of the tunnel and tunnel deformation
Summary
Evaluation of geological conditions ahead of a tunnel face is of major importance for safe and economic tunnel building [1,2,3]. Due to the complexity of analyzing and processing the MWD data, the existing methods of utilizing specific energy to evaluate geological conditions ahead of tunnel face have limited practical guidance for onsite applications. To the authors’ knowledge, little research on the relationship between the specific energy of the mechanical drilling rig in the region ahead of the tunnel face derived from MWD data, rock mass quality index, buried depth of the tunnel and tunnel deformation has been reported, if any. A new method was proposed to evaluate the geological conditions ahead of a tunnel face based on the comparative analysis of the relationship among specific energy, rock mass quality score (RQS, an index used in Japan to evaluate the quality of tunnel rock mass), buried depth of the tunnel and tunnel deformation.
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