Rock Joint Rate (RJR); a new method for performance prediction of tunnel boring machines (TBMs) in hard rocks

Abstract

Rock Joint Rate (RJR) is a novel method for predicting the penetration rate (PR) of tunnel boring machines (TBMs) in hard rock environments. This model is devised based on a combination of geological and operational data obtained from a number of tunnels excavated in igneous and sedimentary rocks. The Geological condition, TBM excavation parameters and the tunnel diameter are regarded as the main input parameters in the RJR method. The rock mass uniaxial compressive strength (UCS) and the discontinuities' characteristics along the tunnel excavation axis including the number, frequency, orientation, spacing and aperture of the joints are the principle geological parameters. In addition, the machine thrust force and the cutterhead rotation speed (RPM) have been introduced as the main involved operational parameters of the machine. Easy to use input parameters, the simple investigation procedure, not requiring complicated laboratory tests and the capability to control the overall costs of a project as well as precise estimations of the operation time by dint of accurate determination of penetration rate (PR) are the main advantages of the proposed RJR model. In this method, a number of indices including the machine stress index (MS), strength ratio (SR), raw penetration rate (PRw) and basic penetration rate (PRb), which are derived from the integration of the main input parameters in RJR model are defined for evaluating the penetration rate of the machine. Overall, in this research, around 140,000 performance databases corresponding to 22,300 boring strokes of three different tunnels with a total excavated length of about 19 km were utilized to validate the proposed RJR model. According to the acquired results in this study, the estimated value of PR by the suggested method of RJR (PRRJR) shows a good agreement with the field penetration rates (PRField). Therefore, this model can be employed as a new method for predicting the penetration rate of TBMs in hard rocks.