Using field data and operational constraints to maximize hard rock TBM penetration and advance rates

•The range of optimum cutter spacing is identified for various rock types and UCS values.•Two formulas are developed for the normal force index (NFI) and rolling force index (RFI).•Cutter linear speed is identified as an influential factor for both NFI and RFI.•Fn-p diagram is developed to correlate between TBM operational limits and actual performance.•Optimum layout designs of TBMs are studied in various geological conditions. In this paper, the influence of rock type and uniaxial compressive strength on the cutter penetration is investigated to provide a basic guideline for the optimum field cutter spacing. The successfully utilized cutterhead layout designs are also studied in various rock types and different categories of tunnel sizes for projects with relatively high performance. The results of the conducted analyses show that the maximum cutter penetration in uniaxial compressive strength values below 50 and above 150 MPa is achieved when the cutter spacing is close to 90 and below 80 mm respectively. The study on the layout design characteristics of the cutterhead shows the evenly distributed scheme is more used with success even in softer rocks (when the rock mass condition is good). In softer rocks, the extension of the openings may have to be well over 50% of the cutterhead radius to maximize its performance. It is also found that the linear speed of the cutters has a direct correlation with two major parameters of normal force index (NFI) and rolling force index (RFI). In this regard, two formulas are generated using statistical analysis of the data from around 260 tunnel projects to evaluate both NFI and RFI. The corresponding formulas have coefficients of determination of 77 and 68% respectively. These formulas are used in an optimization process to maximize cutter penetration using various operational constraints (cutter load capacity, cutterhead torque limit, cutter geometry constrains, and cutterhead penetration rate limits). The new findings of this study can provide a foundation to improve the design process of hard rock TBMs and to optimize their performance considering various project setting parameters.