Comparative studies on the performance of a roadheader, impact hammer and drilling and blasting method in the excavation of metro station tunnels in Istanbul
Introduction
The use of TBMs is found unfavourable in short tunnels and in these cases drilling and blasting method is preferred, however, this method is restricted in urban areas. In favourable conditions, roadheader and impact hammer are preferred due to many advantages over conventional methods. These include improved safety, minimal ground disturbances, elimination of blast vibration, reduced ventilation requirements and cost. Therefore, hydraulic impact hammers have been used widely in metro tunnelling projects in Istanbul since 1992. However, roadheaders have been also used in Taksim–Levent and Kadikoy–Kartal metro tunnels in some extend (Bilgin et al., 2002, Ocak et al., 2007).
Although many researchers investigated the factors affecting the performance of roadheaders and impact hammers it is believed that new published data will improve existing performance prediction models. (Bilgin et al., 1996, Bilgin et al., 1997, Bilgin et al., 2002, Bilgin et al., 2005, Bilgin et al., 2007, Copur et al., 1998, Thuro and Plinninger, 1998, Thuro and Plinninger, 1999, Tumac et al., 2007, Ocak et al., 2007, Tuncdemir, 2007, Ocak, 2007, Ocak, 2008). The main objective of this paper is to contribute to accumulated and published data from various tunnelling projects in Istanbul in order to improve predicting the machine performance to schedule and plan the tunnelling projects and determine the excavation efficiency.
The performances of a roadheader (Westfalia WAV 178) and impact hammer (MB 1700) mounted on the carriers, Volvo EC210B, Sumitomo SH200LC, and Caterpillar 3066T, are investigated. The main rock formations of study areas were Trakya and Kartal formations. The first stage of the project is commissioned to Yapi Merkezi–Yuksel–Dogus–Yenigun–Belen consortium. The metro tunnels are being currently excavated by two Herenknecht TBMs of 6.5 m diameter, detailed information about these machines may be found elsewhere (Bilgin et al., 2007). NATM is used only in the excavation of station tunnels which is the subject of this paper.
Section snippets
Description of the metro tunnel project
The population of Istanbul is approximately 14 million and one third of this population lives in Anatolian side. The project of Kartal metro system is planned to meet the enormous transportation demand between East and West of Istanbul. The project will be integrated with Marmaray Project, which is under construction and which will connect European and Anatolian sides at Ibrahimaga station (Fig. 1).
The project of Kadikoy–Kartal metro system starts from Kadikoy square, joins the station of
Site geology
Tunnels between Kozyatagi–Kadikoy are excavated generally in Trakya and Kartal formations (Fig. 2). Trakya formation of carboniferous age consists of sandstone–siltstone–claystone–mudstone–shale in sequences. Limestone and conglomerates layers are also rarely observed. Diabase and andesite dykes having some 10 m thickness are frequently encountered. In the east of tunnel alignment, Kartal formation of Devonian age is found. Kartal formation consists of fine-grained, laminated, fractured and
Comparison of the performance of different excavation methods
The tunnel excavation of the first stage (Kozyatagi–Kadikoy) started in May 2005 with two TBMs and still continues. Impact hammers is used in the excavation of the station tunnels having length of 180 m. Roadheader is only used in Kozyatagi Station due to technical difficulties such as excessive cutter consumption and difficulty in transporting the machine within short length of station tunnels. Excavating machines are seen in Fig. 3 and main characteristics are given in Table 3, Table 4. The
Comparison of recorded machine performances
Field values of NCR for roadheader and NBR for impact hammer are compared with predicted values using some prediction models. Bilgin developed a model based on data collected from different tunnelling projects carried out in Istanbul. Eqs. (1), (2) given by Bilgin are for estimating NBR of impact hammers and Eqs. (2), (3) are for estimating NCR of roadheaders, especially for axial type roadheaders (Bilgin et al., 1996, Bilgin et al., 1997, Bilgin et al., 2002). Copur developed Eqs. (4), (5) for
Conclusions
This study gives a unique opportunity to compare impact hammers and roadheaders with conventional drilling and blasting method. It is emphasized that drilling and blasting method is most efficient method in high strength rocks. Although blasting in urban area is restricted due to vibrations and difficulties in transport of blasting agents, in extreme conditions its use becomes a necessity. Roadheader is proved to be more efficient than impact hammer in terms of machine utilization time and
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