Chapter-11 - Rate of tunnelling

Abstract

Excavations of tunnels are affected by many uncertainties. The probable time of completion of tunneling projects is grossly underestimated in many cases. This is because proper evaluation of the factors that affect the rate of tunnel excavation is not made. The factors, which affect tunnel excavation, may be enumerated as: (1) variation in ground/job conditions and geological problems encountered, (2) quality of management and managerial problems, and (3) various types of breakdown or hold ups. The rate of tunneling is affected by the ground conditions. The factors, under the ground condition, affecting the rate of tunneling are as: size and shape of the tunnel and presence of inflammable gas. On the basis of the factors affecting the rate of tunneling, the ground conditions are classified into three categories - good, fair, and poor. It means that for the good ground conditions the rate of tunneling is higher and for the poor ground conditions the rate of tunneling is lower. In addition, the rate of tunneling may vary in the same ground condition depending upon management quality.