The use of tunnel boring machines (TBMs) for civil and mining engineering applications has been increasing steadily for the last 30 years. The TBM method is the most economical way to excavate long tunnels in suitable rock conditions.' When rock conditions are reasonably good, a TBM may be two or four times faster than drilling and blasting. The factors affecting the performance of TBMs are mainly rock characteristics, rock structure, the design parameters of the machine, and the experience of the operator. In this study, some of the design parameters of the TBMs were statistically investigated using the published data belonging to 325 individual machines used between 1953 and 1994. The following results were found: Significant linear correlations exist between the machine diameter and the design parameters. Cutter head power, thrust, torque, weight, and the number of cutters increase linearly with increasing machine diameter. The slope of the regression lines increases with increasing years. This means that the machines built in recent years are more powerful with more weight than the machines built in former times, for a given diameter. Also, the larger the machine diameter, the greater the difference between the machine groups.
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