| The Encountered Geotechnical Problems at Tunnel of Otogar – Kirazlı Which Excavating With Tunnel Boring Machine Using
Otogar – Kirazlı Tunnel is the continuation project of the light rail train system line between Aksaray and the Airport, which extends the current railway between Otogar –Esenler to Bağcılar Kirazlı. The project is very significant in its role to help reduce the traffic load. This study evaluates the deformations formed over the acceptable limit during the tunnel excavation especially at the km 2+000 area, their reasons and comparison with acceptable values.
The project is more than 5 km in length and the overburden varies between 15 to 55 m. The engineering characteristics were determined through the 35 boreholes drilled, SPT and pressuremeter experiments conducted and laboratory experiments held with materials taken from these boreholes.
According to data gained from these boreholes, it is evident that an important section of the excavated tunnel soil largely consists of clay, opened at soil condition.
At this project which used a Tunnel Boring Machine, EPB – TBM was chosen due to its suitability for this kind of ground conditions. Although using a Tunnel Boring Machine is faster and safer than conventional tunnel construction methods, foreign objects in ground like undetected wells are increasing the risks, which reduce the safety of the tunnel construction. At Otogar – Kirazlı tunnel project, although BMP measurements taken from the buildings until km 2+000 were lower than 25 mm, the acceptable value for this project, on a building at the 2+000 km where the overburden decreased to nearly 17 m, the deformations increased to 76 mm due to an undetected hole. Similarly, the angle deformations increased to 1/200, which is over the accepted angle deformation value of 1/500.
Following the problems related to deformation, many works were undertaken to detect and fill the existing holes in the area. The probability of encountering such problems is very high at areas with shallow overburden, especially considering the fact that the project was constructed at a very crowded residential area. For this reason, treatment works were undertaken at the km 4+200 area which shows the same conditions with km 2+000, to prevent similar problems.
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