Tunnel boring is shown to be a suitable technique method in hard rock tunnelling. Performance, disc cutter consumption and therefore cost are strongly influenced when using Tunnel Boring Machines (TBMs) in hard rock conditions. Furthermore, good predictions of TBM performance and cost facilitate the control of risk as well as avoiding delays and budget overruns. Good rock boreability assessments may be decisive for planning and controlling risk when extremely hard rocks are involved. An ongoing TBM project in particularly hard rock has been analyzed in terms of performances and cutter life assessments. Extensive geological back-mapping, complete rock laboratory testing and gathering of TBM data has been carried out in order to analyze and assess performance and cutter life by using the CSM, Gehring and NTNU prediction models for hard rock TBMs.

1 Introduction

Tunnel boring machine (TBM) performance and cutter consumption have a great influence on the successful planning in mechanized tunnelling specially in hard rock conditions. Rock masses containing few or no fractures increases greatly the risk to achieve accurate predictions. In the case of low fracturing rock masses, a detailed fracturing analysis is essential which will enable us to determine if the intact rock or rock mass properties control the boring process.

This study is a brief analysis of performance predictions using the CSM, Gehring and NTNU models for a 7.2 m diameter open gripper TBM on an ongoing hydropower in Norway. In addition, cutter consumption and cutter life assessments by using the NTNU cutter life model were performed. Proper laboratory testing involving strength and drillability methods and field TBM data analysis were carried out in order to achieve the research goal.

Reliable fitting is found using the CSM, Gehring and NTNU model along the section studied at this TBM project in hard rock. The NTNU cutter life model shows suitable cutter life assessments for the sections analyzed.

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