Technology advancement increased the desire to mechanical excavation in mining and civil industries. This may be due to a large number of benefits as well as small deficits of mechanical excavation. Currently, tunnel boring machines (TBMs) are the most common mechanical equipment for excavation with drilling capability suitable for various geological conditions. Thus, for the purpose of reducing production costs and lost energy, the optimum design of these machines, proper for special conditions, is very important. One of the most important parameters to estimate the consumed energy in drilling projects is the specific energy (SE), which is defined as the required energy to excavate unit volume of rock mass. SE depends on properties of the rock mass, machine, and operation parameters. So far, many studies have been carried out on the relation between these parameters and SE. Teale (1965) introduced the concept of SE in rock mechanics for the first time from drilling in the oil industry which is defined as a function of thrust, torque, penetration rate and excavation face area. The aim of this work is to propose new relations between the SE and the strain energy of rock mass ( W ) using the geological mappings of rock mass and TBM operational parameters from Amir-Kabir Water Transferring Tunnel of Iran. Strain energy is an appropriate criterion to estimate SE because it is a function of different parameters such as rock mass behavior, pre and post failure properties and peak and residual strains. Theoretically, SE should be equal to the area under complete stress-strain curve of rock mass but it is not true in reality because a large amount of energy is wasted due to different reasons such as over breaking, friction, and machine vibration. In this study the lost energy in a mechanized excavation by TBM is estimated applying the strain energy ratio (?).
