Application of rock engineering in mechanical tunneling

Tunnel excavation is one of the main challenging issues for developers, contractors, rock and geo-engineers. Since the behavior of rock mass effects the project from cost, time and scheduling point view, before the construction was began, rock engineers or engineering geologists should perform pre-geotechnical investigation in site area so that the convenient excavation method would be chosen. Currently, there is more than one method to excavate tunnel for both civil and mining. Drill and blast, so-called a conventional method is one of them. Another one is the mechanical excavation method is performed by commonly using either full-face; tunnel boring machines, or partial face machines; roadheader, depend on rock type and condition encountered in the field. Mechanical excavation that means using high technological excavation machines for excavating tunnel is so common in several decades, since they are safe, and faster than conventional method, especially in urban areas. Although these machines are so powerful and safety, to achieve the ultimate production rate, rock mass behavior has to be identified prior the machine was selected; otherwise tunnel could be not only completed later than to be estimated but also more expensive than to be expected. In this paper, influence of rock properties in mechanical tunneling is evaluated and the main rock mass properties -spacing, frequency and orientation of rock fractures-, and intact rock strength parameters –uniaxial compressive and tensile strength- are highlighted.