ABSTRACT
The Khayam Main Drain project comprised the construction of a 5.5km of 3.7m ID storm water collection tunnel as part of the Tehran Main Drainage Scheme. The scheme to relieve seasonal flooding in the south of the city was in part funded by the World Bank. The tunnel alignment passes through sand and gravel strata beneath the water table dictating the use of a soft ground tunnel boring machine. The project started in December 1995 and was completed in July 1999.
The World Bank made their loan conditional on the Tehran Municipality allowing only joint ventures of local construction companies and international contractors with proven track records in TBM tunnelling to tender. In addition the World Bank insisted on the appointment of an international consulting firm (ICF) as sub consultant to the local consultant supervising the construction of the tunnel. Foreseeing the need for further sewer and water tunnels in the immediate future the Employer elected to purchase a Lovat EPBM and provide it as a leased item to the successful tenderer.
The construction required a number of firsts in Tehran including, inter alia:
The first ever use of a soft ground tunnel boring machine in Iran
The application of a deep well dewatering system to obviate closed face working
In addition to these technical challenges the contract arrangements created a large number of interfaces each with a potential for disrupting the contract
