A model for the prediction of tunnel boring machine performance

A key factor in the successful application of a Tunnel Boring Machine (TBM) in tunnelling is the ability to develop accurate penetration rate estimates for determining project schedule and costs. Rate of penetration (ROP), defined as the distance the machine advances in a given time in rock, is a complex process that not only depends upon intact and rock mass properties (strength, fractures, and texture of rock) but also machine specifications including thrust and torque requirement. The Earth Mechanics Institute (EMI) of the Colorado School of Mines (CSM) has developed a model to predict the performance of TBM in hard rock conditions. The model is primarily based on intact rock properties and machine specification. Although the model has proven reliable in massive rock conditions, its accuracy has been limited in brittle rocks exhibiting a high degree of fracturing. Therefore, this research was conducted to investigate the effect of rock mass fracture and brittleness on TBM performance. In order to accomplish the goal, extensive mapping of the tunnel was conducted to make a record of the joints and fractures along the 16-kilometer long Queens Water Tunnel in New York City. A large number of cores were taken from inside the tunnel where rock exhibited varying degrees of fracturing to conduct geomechanical tests including uniaxial compressive strength, tensile strength, and punch penetration tests. Additionally, the field TBM data from the tunnel was analysed in detail. Consequently, the data collected for the machine, rock properties and geology were then subjected to a multiple regression analysis together with the basic penetration rate derived from the existing model. As a result of this research, a new model was proposed for TBM performance prediction.