Web-based Tool to Estimate the TBM Penetration Rate - Performance

There are several traditional, widely used empirical methods for estimating TBM performance, all developed from data recorded in real tunnelling projects. As with any empirical approach, these methods must be applied with care—particularly when geological, geotechnical, or machine conditions differ from those on which the models were originally based. Nevertheless, they can still offer a useful indication of the expected performance range for a selected TBM.

In our 2012 paper, we examined the influence of various rock mass and machine parameters on TBM penetration rate (https://link.springer.com/article/10.1007/s10706-012-9594-2). The study showed that applied thrust per disc is the dominant factor controlling penetration in the NTNU and RMi models, whereas the Q-value (from the Q classification system) is the most influential parameter in the QTBM model. Uniaxial compressive strength of intact rock has relatively minor impact in both NTNU and QTBM. Joint spacing plays a significant role in NTNU and RMi, while in QTBM, low induced biaxial stress (<1.7 MPa) and low quartz content (<5%) greatly increase their influence on penetration rate.

Additionally, I created a web-based application that estimates penetration rates using the NTNU method. The tool also enables parameter sensitivity analysis to evaluate how variations in input data affect the estimated penetration rate. For more information on the NTNU method, please refer to Javier Macias’s PhD thesis, available at the following link (https://share.google/Dx1v1lV5b9VhOKAvQ).

After estimating the penetration rate, PR (m/h), the TBM advance rate can be calculated by multiplying PR by the TBM utilisation, U (%). Utilisation is defined as the ratio of boring time (Tb) to the total time, where total time includes Tb plus all downtime components. Boring time is the time required to bore a given tunnel length (e.g., 1 km) and can be expressed as Tb = 1000/PR (h/km). Downtime (h/km) includes TBM breakdowns, back-up breakdowns, cutter inspection/change, support installation, TBM resetting after each excavation stroke, muck transport and unloading, routine maintenance of the cutterhead, TBM, and back-up, surveying, and utility installation (Farrokh, 2018). Farrokh (2018) compiled data from 18 projects and reported that actual utilisation ranged from 18–30% for single-shield TBMs, 29–45% for double-shield TBMs, and 22–45% for open TBMs. As a guide for estimating the TBM advance rate when the tunnel alignment is divided into geotechnical groups, the following utilisation ranges may be used:

• Poor ground conditions leading to difficult TBM operation: 10 to 20%

• Average ground conditions with typical TBM operation: 20 to 35%

• Good-quality ground and efficient operations: 35 to 45%