Karaj Water Conveyance Tunnel (KWCT) is 30-km long and has been designed for transferring 16 m3 /s of water from Amir-Kabir dam to northwest of Tehran. Lot No. 1 of this long tunnel, with a length of 16 km, is under construction with a double shield TBM and currently about 8.7 km of the tunnel has been excavated/lined. This paper will offer an overview of the project, concentrating on the TBM operation and will review the results of field performance of the machine. In addition to analysis of the available data including geological and geotechnical information and machine operational parameters, actual penetration and advance rates will be compared to the estimated machine performance using prediction models, such as CSM, NTNU and QTBM. Also, results of analysis to correlate TBM performance parameters to rock mass characteristics will be discussed. This involves statistical analysis of the available data to develop new empirical methods. The preliminary results of this study revealed that the available prediction models need some corrections or modifications to produce a more accurate prediction in geological conditions of this particular project.

۱ Introduction

Performance of a TBM in a given project depends on many factors which can be classified in 3 categories: (1) Machine specifications, (2) Ground characteristics and (3) Operating parameters. In tunneling projects, ground characteristics or boreability of the rock mass is an important parameter for selecting machine type and specifications. It is clear that proper evaluation of rock mass boreability can also play a major role in machine operation to achieve the best performance. Boreability is the term commonly used to express the ease or difficulty of rock mass excavation by a tunnel boring machine. There are several methods (prediction models) developed by researchers to determine boreability of rock masses and its relation to machine performance (e.g. Blindheim 1979; Rostami and Ozdemir 1993; Rostami 1997; Bruland 1998; Barton 2000).

On the other hand, growth of TBM manufacturing technology and existence of some shortcomings in the prediction models have made it necessary to perform more research on the adjustment of the models for application in special cases. Recently, many researchers have worked on development of new TBM performance prediction models or modification and adjustment of existing models. Ribacchi and Lembo-Fazio (2005) evaluated the relationship between RMR and performance of a double shield machine in the Varzo tunnel. Also Sapigni et al. (2002) studied the empirical relation between RMR and penetration rate. Cassinelli et al. (1982) used correlation between rock structure rating system (RSR) and actual TBM performance to evaluate the penetration rate.

Sanio (1985) found strong correlations between uniaxial compressive strength (UCS) of rock and the specific energy defined as the amount of energy needed to excavate a unit volume of rock. Bruland (1998) updated and improved the NTNU model (introduced by Blindheim 1979) based on field data mainly collected from Norwegian tunnels. Rostami and Ozdemir (1993) and Rostami (1997) developed the CSM model for cutting force estimation of disc cutters based on the Brazilian tensile strength (BTS) and UCS of rock. Subsequently, Yagiz (2002) modified the CSM model adding rock mass properties as an input parameter into the model. Ramezanzadeh et al. (2008) has also followed up on this work and developed a database of TBM field performance for over 60 km of tunnels. Then, he offered adjustment factors for CSM models to account for joints and discontinuities.