Interaction of rock mass characteristics with full-faced tunneling machine performance [Key Note]

The industry deals with excavation have shown a major interest in the use of full-faced tunneling machines (TBMs), because of their demonstrated capabilities in attaining high rates of advance in tunnel construction,. Mechanical tunneling may differ from other tunneling methods -drill and blast- due to the high level of machine and rock interaction. Accurate estimates of machine performance are a crucial part of any tunneling project. It is almost impossible for owners or contractors to make realistic evaluations of time and cost required for completing a project, without knowing the machine advancement. The aim of this paper is to overview on interaction of rock mass characteristics with full-faced tunneling machine performance in rocks. For this aim, literatures and some tunnel cases have been reviewed and the findings are shared together with some updated knowledge relevant with rock mass and machine interaction.
Since late 1950s, numerous researches have been conducted for estimating the machine advancement in rock mass. Full-faced tunnelling machine performance is influenced by numerous factors, categorized in general as rock properties and machine specifications. However, influences of intact and mass rock properties on the performance could be various in weight depend on rock mass characteristics and specification of utilized machine as well as site condition. Rock mass characteristics including the orientation, condition and frequency of discontinuities, local geological features such as; folding, metamorphism, faults, foliations and also intact rock properties consisting strength, brittleness, mineralogy, texture, hardness, porosity and abrasiveness are crucial parameters for any project excavated with machines. Those rock features together with utilized machine specifications; thrust, torque, disc dia., power etc., allow estimating machine penetration in accurate.
Various models are introduced to estimate the machine advancement. Some of them are simply developed base on cutter force and intact rock strength including uniaxial compressive and tensile strength of rock. Several formulas have been offered for estimation of the cutting forces from intact rock strengths and cutting geometry. Consequently, numerous researches have been conducted for quantifying rock mass properties affecting on machine performance and then models were introduced base on the combination of quantified intact and mass rock properties together with machine specification. It is worthy that TBM performance prediction models, including Colorado School of Mines (CSM), Modified CSM, NTNU (Norwegian University of Science and Technology) and Qtbm should be mentioned herein since they are the most commonly utilized models for mechanized tunneling in present. Accordingly, numerous efforts have been given to develop the best model for estimating the machine advancement in rock mass since more than fifty years: however, each model has some advantages and disadvantages to be applied for practice. Some of them based on cutting force and intact rock parameters, while others relevant with combination of rock mass characteristics and machine specifications. It could be concluded that, rock mass characteristics and utilized machine have a great effects on both breakthrough of machines and the time to complete projects. Thus, rock characteristics and ground conditions should be examined carefully at the early stage of the project and then updated until project is concluded.