A new hard rock TBM performance prediction model for project planning

► In this paper a simple model is proposed to evaluate rock mass boreability and TBM performance range. ► In the developed model, machine performance has been related to UCS, RQD average cutterhead thrust and RPM. ► This paper also introduces a new boreability classification based on rock masses characteristics to allow for prediction of FPI values. ► Various ground conditions are categorized in six different classes from B-0 as tough boring ground to B-V as easy ground for boring. ► Combining stability conditions and boreability characteristics of rock types allows for development of a new concept for classification of TBM excavatability. Among the models used for performance prediction of hard rock tunnel boring machines two stand out and are often used in the industry. They include the semi theoretical model by Colorado School of Mines and the empirical model by Norwegian University of Science and Technology in Trondheim (NTNU). While each have their strong points and area of applications, more accurate prediction has been sought by modifying one of the existing models or introduction of a new model. To achieve this, a database of actual machine performance from different hard rock TBM tunneling projects has been compiled and analyzed to develop a new TBM performance prediction model. To analyze the available data and offer new equations using statistical methods, relationships between different geological and TBM operational parameters were investigated. Results of analyzes show that there are strong relationships between geological parameters (like UCS, joint spacing and RQD) and TBM performance parameters specially Field Penetration Index (FPI). In this study, a boreability classification system and a new empirical chart, for preliminary estimation of rock mass boreability and TBM performance is suggested.