Investigation into vibration patterns generated by full-scale linear rock cutting tests

Tunnel boring machines (TBMs) should be operated in accordance with the geological variances to reach favourable excavation rates. Therefore, recognizing the real time geological conditions during the excavation and responding properly in a short time has great importance. In that aspect, field measurements of the vibrations generated during excavation by TBMs have been analysed for ground identification in various studies. However, there are many influencing factors and noise sources affecting vibrations of TBMs in the field, and there is a need for a better understanding of vibrations created during the rock cutting process under a controlled environment. With this aim, laboratory rock cutting tests are realized by a full-scale linear rock cutting machine equipping a full-size (17-inch diameter) disc cutter and accelerometers on three different rock samples with uniaxial compressive strength values ranging from 21 to 82 MPa. Forces acting on the cutting tool and vibrations generated during cutting tests are simultaneously recorded in three orthogonal directions. Peak, root mean square (RMS), and interval RMS accelerations are calculated from the recorded vibration data, and Weibull distributions that are the best fit for this kind of data are generated. The relations between vibrations, cutting performance parameters, cutting geometry, and mechanical properties of rocks are analysed. The results indicate that the vibrations increase with increasing tool forces, penetration, and chip size. There is a moderately strong and positively proportional relation between normal force and vibrations at the optimum cutting configuration. Most notably, peak normal force, average normal force and specific energy at optimum cutting conditions and interval RMS acceleration exhibit moderately strong to strong relationships. A notable correlation is found between maximum acceleration and peak normal force. The preliminary equations for predicting tool forces and rock strength based on the vibration values are provided, which shows the importance of real-time vibration measurements in TBMs. The rock properties and mineralogical composition have a great effect on the vibrations and it is possible to generally conclude that as the rock strength increases, the vibrations increase. It is observed that accelerations above 20 g can occur during the rock cutting process. These results indicate that vibrations generated during rock cutting may be used for the identification of geological conditions ahead of a TBM and knowing the vibration levels could help for determining the real time operational parameters of TBMs and for design of the various components of TBMs. The study can be further improved by additional rock cutting test data.