Homayoon Orumchi - Project Manager of AHAB Company. Dowlat Abad, Metro Line 6, Tehran, Iran
Mohammad Mojallal - School of Civil Engineering, University of Tehran, Engelab Avenue, Tehran, Iran
Mehdi Hedayati - Site Manager of Line 6 Project. Dowlat Abad, Metro Line 6, Tehran, Iran.

Mechanized tunneling is a multi-dimensional project which includes a huge diversity of techniques, sciences and experiments and all these tools are actually used inside a media which is called ground. An important procedure at the design and manufacturing phases in terms of quality, and production rate in building mechanized tunnel is precast concrete lining. Precast concrete segments are designed based on three type of loading, i.e. primary loads such as vertical and horizontal loads, dead weight and surcharge, secondary loads like internal and construction loads and earthquake load and finally special loads such as effects of two or more shield tunnel construction and ground subsidence. This paper states that how these criticalcomponents were conducted in construction of mechanized, under construction tunnel, of Tehran subway line 6, a 10.5 km tunnel- 5.5 km completed- with 9.16 m excavation diameter. The space between the excavated external diameter and the outside of completed ring made up of segments is filled with grout. Each ring contains 8 segments plus one key segment. Forcuring concrete segments, thermal curing is selected. In this article, the quality of precast concrete lining segments is discussed as the major component of tunnel building construction. Moreover thermal curing of segments in order to increase production rate is explained. An average 10-hour compressive strength of concrete with admixture amount of 0.6%, is more than 15 MPa. This can fulfill the design requirements. Moreover, it can be seen that 28-day compressive strength of concrete with admixture amount of 0.6% and cement amount of 3 350 kg / m is perfect and in average of 55 MPa. Also results of a statistical study about the common damages of installed concrete segments implemented for the completed lining are shown in order to verify the final outcome of the design and selected production methods. It is concluded that the rate of shield segment damage in line 6 is much less than the common standards. The results show that, only 378 of 9000 segments (1000 ring) have construction damages (4.2%). Moreover, in the 1000 ring only 14 rings have steps or lips in the tunnel (other) which is much lower than the numbers mentioned in related standards.

Shield Segment Damage, Lining, Thermal Curing, Metro Line 6