Hard Rock Tunnel Boring: Performance Predictions and Cutter Life Assessments

Abstract

The use of hard rock tunnel boring machines (TBMs) has become widely and generally used with success but in too many cases, due to unanticipated situations and/or inappropriate assessments, with catastrophic consequences. Hard rock tunnel boring involves major investments and high levels of geological risk, which require reliable performance predictions and cutter life assessments. Hard rock tunnel boring leads the interaction between the rock mass and the machine, which is a process of great complexity. The tunnelling system around the excavation process has a great relevance in the final goal of performance predictions for hard rock TBMs, which is the estimation of time and cost. The overall aim of this thesis is to build on the existing knowledge of tunnel boring and wear processes, technology and capacity, thus enhancing performance prediction and cutter life assessments in hard rock tunnel boring projects. The prediction model for hard rock TBMs developed by the Norwegian University of Science and Technology (NTNU) is based on a combination of field performance data, engineering geological back-mapping, and laboratory testing. The development of TBM technology during recent decades, and the possible influence of parameters not considered in previous versions, has made revision of the model to improve prediction accuracy an essential requirement. TBM specifications, the penetration rate and cutter life models have been revised and extended to adapt to the current technology. In addition, it has been incorporated a new definition of the rock mass fracturing, the influence of the cutterhead velocity (rpm) on penetration rate on the in response to the results of in-situ trials 'RPM tests' and cutter thrust on cutter life. The tunnel length effect on time consumption for the tunnelling activities has been introduced for the estimation of the machine utilization and therefore in the advance rate model. A revised and extended version of the current version of the NTNU prediction model for TBM performance and cutter life has been published included in this thesis. Cutter consumption and parameters such as cutter ring wear play a significant role in performance and cost predictions, especially in hard rock conditions. Cutter wear involves a complex tribological system in interaction with the geological properties of the rock mass. Existing laboratory test methods fail to reproduce wear behaviour encountered during tunnel boring. Because of this, and the importance of cutter wear, it was considered of interest to develop a new rock abrasivity test method for tool life assessments in hard rock tunnel boring: The Rolling Indentation Abrasion Test (RIAT). Understanding the processes and failure mechanisms during cutter wear enabled new knowledge to be applied as part of the development of the new rock abrasivity test method for laboratory use. In addition, cutter wear mechanisms affecting cutter rings during tunnel boring might lead to better cutter consumption predictions and future improvements in cutter ring development.