Analysis of performance of tunnel boring machine-based systems

Tunneling using tunnel boring machines (TBMs) in rock offers an attractive alternative to the conventional Drill-and-Blast method in many underground construction projects. However, the performance of TBM-based excavation systems has been less than expected in many tunneling projects. Maximizing the performance of such systems, and predicting such performance a priori, are important to both clients and contractors of underground construction projects. The main contribution of this work has been the systematic use of case history data to provide the construction industry with an evolutionary, predictive tool for prognosis of performance of TBM-based excavation systems. Components of a tunnel boring machine-based excavation system typically used in hard rock are described. Procedures were developed to aid engineers with prognosis of time and cost to complete a given tunnel. A data base from many tunneling projects has been assembled, and construction simulation programs have been developed and validated. Performance of the excavation system is tied to geology, equipment reliability, and duration of activities that comprise the excavation cycle. A new paradigm of analysis has been developed. It aims to understand the variability in time and cost to complete a given tunnel, by considering: (1) reliability and characteristics of machine and its back-up system, (2) geology variation along tunnel, and (3) quality of management. The quality of management includes competence of crew, competence of geotechnical engineers, degree of planning and preparation for contingencies, and maintenance programs adopted by the contractor. Since penetration rate is a critical factor to the performance of TBMs, rock cutting mechanics is therefore important to study of TBM-based excavation systems. The problem of rock cutting using disc cutters is studied. Indentation of rock by rigid indenters is reviewed, and the most important parameters affecting the indentation process are identified. Analytical and numerical modeling of the rock indentation problem is reviewed, and recommendations for future numerical modeling and experimental work are presented.