The effects of using large cutter diameters in hard rock TBM tunneling

Abstract

This thesis is written in cooperation with the Robbins Company to:

- Document the effect of using large diameter cutters (19”) compared to smaller diameters (17”)

- Document the effect of using 20” cutter rings on 19” cutters

- Evaluate Robbins estimation methods to the NTNU-method and the recorded data.

The report starts with a short introduction to cutter wear and the factors influencing on it. Before presenting acalculation of the effects the difference cutter diameters theoretical will have on advance rate and cutter life.The calculations suggest an advance rate of a 10 meter diameter TBM with 17” cutters being 77.3% of the rate of aTBM with 19” cutters. The 20” cutters will have an advance rate of 91.3 % of the 19” cutter machine. The cutter lifein hours is calculated to be 13% lower for a machine with 17” cutters than a machine with 19”. The effect of using20” cutter rings is calculated to extend the cutter life in hours with 16%.The field work on the thesis is done on two 10m diameter double shield TBMs boring in India, the AMR1 projectand the Veligonda Project. Both machines are utilizing 19” with 20” cutter rings. The geological conditions arevarying for both projects.

The field testing and the lab testing is done according to the NTNU model and includes net penetration tests andchip analysis. The processing and calculations are done according to the NTNU-model.The AMR1 project has had an average penetration rate of 1.62 m/h and a cutter life of 1.25 h/c, or 2.02 m/h. TheVeligonda project has an average penetration rate slightly higher 1.90 m/h. The cutter life has been significantly higher with 12.75 h/c in the first period at the project. On the second period it was a change in the geology and thecutter life was reduced to 1.90 h/c. The utilization rates for the projects have been generally low with an averagemachine utilization of around 30%.

When comparing the results to comparable projects it gives the following indications:

- The advance rate is significantly improved when using large cutter diameters.

- The 20” cutter rings have a beneficial effect on weekly advance rates in hard and abrasive rock.

- The 20” cutter rings gives a slight economic saving in hard and abrasive rock compared to 19” cutter rings.

The estimation of the AMR project from NTNU and Robbins has some major differences. This has been looked at indetail and it gives an indication of a systematically overestimation in advance rate and cutter life for the Robbinsestimates. This leads to an underestimation of the cutter costs of the AMR1 project. The biggest differences in theestimates are at the AMR2 where the boring still has not started.